History UsefulNotes / PrehistoricLifeOtherExtinctCreatures

* Sarcopterygians, aka “Lobe-finned fish”. Actually, considering these animals as ''fishes'' may appear rather arbitrary to some paleo-fans. Rather than true fish, they were a sorta middle-way between typical fish and amphibians, and many of them spent part of their life ''outside'' water, thus breaking the "fully-aquatic" criterium. They are traditionally divided in three groups: Actinists, Lungfish and Rhipidists [[hottip:*:The third term it actually in disuse: today the correct one is "basal tetrapodomorphs". But if we use the latter, the pun with "actinists" [[RuleOfCool wouldn't work anymore]]]]. Actinists, better-known as Coelacanths from the common name of their only [[strike:one]] [[ScienceMarchesOn two]] surviving species, are perhaps the most famous, and at the same time, the least amphibian-like: indeed, they ''were'' fully-aquatic, thus "true fish". They appeared in the Devonian Period, and were marine creatures that have remained virtually unmodified since 400 million years: but now they seriously risk to go extinct soon or later, [[HumansAreBastards only because]] [[WhatMeasureIsANonCute they are not so cute]] [[FindingNemo as clownfish are]]. Lungfish were a bit closer to us: they really have [[ExactlyWhatItSaysOnTheTin lungs]] for breathing air other than classic gills, appeared in the Devonian as well and specialized themselves to muddy, marshy environment with very oxygen-poor waters: that's why their lifesaving airsacs evolved. Today are the most successful missing-links between fish and land vertebrates (although less than ten species are still alive today), and yet they are less-often-mentioned than Coelacanths. Finally, "rhipidists" are an artificial assemblage of not-related lobe-finned fish. Among them were ''the ancestors of mankind'', as well as all land-living vertebrates ever existed, from [[{{Digimon}} dinosaurs]] to [[Anime/{{Hamtaro}} hamsters]]. ''Eusthenopteron'' has always been the stock rhipidist, probably because of the look of its tail that recalls ProngsOfPoseidon; recently, the basically identical but far bigger ''Hyneria'' has gained some notoriety thanks to [[WalkingWithDinosaurs Walking With Monsters]], portrayed as a ''Film/{{Jaws}}''-like [[CarnivoreConfusion villain]]. It's the ''only'' lobe-finned fish represented in that show, and [[SomewhereAPaleontologistIsCrying with no mention at all about the role of lobe-finned fish as our-ancestors]].

* Sarcopterygians, aka “Lobe-finned fish”. Actually, considering these animals as ''fishes'' may appear rather arbitrary to some paleo-fans. Rather than true fish, they were a sorta middle-way between typical fish and amphibians, and many of them spent part of their life ''outside'' water, thus breaking the "fully-aquatic" criterium. They are traditionally divided in three groups: Actinists, Lungfish and Rhipidists [[hottip:*:The third term it actually in disuse: today the correct one is "basal tetrapodomorphs". But if we use the latter, the pun with "actinists" [[RuleOfCool wouldn't work anymore]]]]. Actinists, better-known as Coelacanths from the common name of their only [[strike:one]] [[ScienceMarchesOn two]] surviving species, are perhaps the most famous, and at the same time, the least amphibian-like: indeed, they ''were'' fully-aquatic, thus "true fish". They appeared in the Devonian Period, and were marine creatures that have remained virtually unmodified since 400 million years: but now they seriously risk to go extinct soon or later, [[HumansAreBastards only because]] [[WhatMeasureIsANonCute they are not so cute]] [[FindingNemo as clownfish are]]. Lungfish were a bit closer to us: they really have [[ExactlyWhatItSaysOnTheTin lungs]] for breathing air other than classic gills, appeared in the Devonian as well and specialized themselves to muddy, marshy environment with very oxygen-poor waters: that's why their lifesaving airsacs evolved. Today are the most successful missing-links between fish and land vertebrates (although less than ten species are still alive today), and yet they are less-often-mentioned than Coelacanths. Finally, "rhipidists" are an artificial assemblage of not-related lobe-finned fish. Among them were ''the ancestors of mankind'', as well as all land-living vertebrates ever existed, from [[{{Digimon}} dinosaurs]] to [[Anime/{{Hamtaro}} hamsters]]. ''Eusthenopteron'' has always been the stock rhipidist, probably because of the look of its tail that recalls ProngsOfPoseidon; recently, the basically identical but far bigger ''Hyneria'' has gained some notoriety thanks to [[WalkingWithDinosaurs Walking With Monsters]], portrayed as a {{Jaws}}-like [[CarnivoreConfusion villain]]. It's the ''only'' lobe-finned fish represented in that show, and [[SomewhereAPaleontologistIsCrying with no mention at all about the role of lobe-finned fish as our-ancestors]].

* In the Devonian, Elasmobranchs were represented with generic forms such as ''Cladoselache'', already with the familiar exposed gills, but with a ''terminal mouth'', unlike most modern sharks. Actually all the fish-groups seen so far get their success for the first time in this period: Devonian is called with reason "the Fish Age" because it was the age in which fish were more diversified than every else. Many Paleozoic "sharks" are very cool-looking: let's give a look at the "Ironing Board" shark ''Stethacanthus'', the eel-like freshwater sharks of the ''Xenacanthid'' family, and the weirdest of them all, the totally bizarre-toothed ''Helicoprion''. In the Mesozoic, the dominant group was made of more modern-looking animals: among them, the "Switchblade Shark" ''Hybodus'' and the ray-like ''Ptychodus''. However, the first true sharks appeared only in the Cretaceous, along with the first modern-looking bony fish; among them were also the first true rays/skates. Some sharks from that period were similar to {{Jaws}}-things. The "Ginsu Shark" ''Cretoxyrhina'', for example, growed to the size of Spielberg's beast, and preyed upon [[BadAss marine reptiles]]. Despite this, the biggest and most famous prehistoric shark was still alive ''just 1.5 million years ago'', when hominids were already existing: ''Carcharocles'', better known as {{Megalodon}}.

* Sarcopterygians, aka “Lobe-finned fish”. Actually, considering these animals as ''fishes'' may appear rather arbitrary to some paleo-fans. Rather than true fish, they were a sorta middle-way between typical fish and amphibians, and many of them spent part of their life ''outside'' water, thus breaking the "fully-aquatic" criterium. They are traditionally divided in three groups: Actinists, Lungfish and Rhipidists [[hottip:*:The third term it actually in disuse: today the correct one is "basal tetrapodomorphs". But if we use the latter, the pun with "actinists" [[RuleOfCool wouldn't work anymore]]]]. Actinists, better-known as Coelacanths from the common name of their only [[strike:one]] [[ScienceMarchesOn two]] surviving species, are perhaps the most famous, and at the same time, the least amphibian-like: indeed, they ''were'' fully-aquatic, thus "true fish". They appeared in the Devonian Period, and were marine creatures that have remained virtually unmodified since 400 million years: but now they seriously risk to go extinct soon or later, [[HumansAreBastards only because]] [[WhatMeasureIsANonCute they are not so cute]] [[FindingNemo as clownfish are]]. Lungfish were a bit closer to us: they really have [[ExactlyWhatItSaysOnTheTin lungs]] for breathing air other than classic gills, appeared in the Devonian as well and specialized themselves to muddy, marshy environment with very oxygen-poor waters: that's why their lifesaving airsacs evolved. Today are the most successful missing-links between fish and land vertebrates (although less than ten species are still alive today), and yet they are less-often-mentioned than Coelacanths. Finally, "rhipidists" are an artificial assemblage of not-related lobe-finned fish. Among them were ''the ancestors of mankind'', as well as all land-living vertebrates ever existed, from [[{{Digimon}} dinosaurs]] to [[{{Hamtaro}} hamsters]]. ''Eusthenopteron'' has always been the stock rhipidist, probably because of the look of its tail that recalls ProngsOfPoseidon; recently, the basically identical but far bigger ''Hyneria'' has gained some notoriety thanks to [[WalkingWithDinosaurs Walking With Monsters]], portrayed as a {{Jaws}}-like [[CarnivoreConfusion villain]]. It's the ''only'' lobe-finned fish represented in that show, and [[SomewhereAPaleontologistIsCrying with no mention at all about the role of lobe-finned fish as our-ancestors]].

!! Thank you bug!

Insects. The most abundant, diversified, biomechanically efficient, and last but not least, by far the most-studied animals by modern-fauna zoologists. Sadly, in Paleontology this is not the same. Their fossil record is ''extremely'' poor, for understandable reasons: their tiny body isn't precisely the most adapt to turn into stone, and their terrestrial habitat doesn't help either--most fossil animals discovered so far were aquatic indeed, just because water helps a lot the process of fossilization. However, if we know something more about the ancient relatives of modern insects, we have to thank pines, firs, spruces and larchs.

!!Once upon a time…

[[http://en.wikipedia.org/wiki/Triadobatrachus Hopping]] [[http://en.wikipedia.org/wiki/Karaurus crawling]], and [[http://en.wikipedia.org/wiki/Eocaecilia digging]]

[[http://en.wikipedia.org/wiki/Diplocaulus Boomerang-heads,]] [[http://en.wikipedia.org/wiki/Phlegetontia eel-bodies,]] and [[http://en.wikipedia.org/wiki/Urocordylus whip-tails]]

[[http://en.wikipedia.org/wiki/Eryops When amphibians]] [[http://en.wikipedia.org/wiki/Cacops were like]] [[http://en.wikipedia.org/wiki/Platyhystrix crocs 1]]

[[http://en.wikipedia.org/wiki/Mastodonsaurus When amphibians]] [[http://en.wikipedia.org/wiki/Gerrothorax were like]] [[http://en.wikipedia.org/wiki/Koolasuchus crocs 2]]

[[http://en.wikipedia.org/wiki/Proterogyrinus Egg-shells,]] [[http://en.wikipedia.org/wiki/Seymouria what an]] [[http://en.wikipedia.org/wiki/Diadectes invention!]]

[[http://en.wikipedia.org/wiki/Ichthyostega The first]] [[http://en.wikipedia.org/wiki/Tiktaalik pioneers]]

[[http://en.wikipedia.org/wiki/Coelacanthiformes Lungs,]] [[http://en.wikipedia.org/wiki/Eusthenopteron what an]] [[http://en.wikipedia.org/wiki/Lungfish invention!]]

[[http://en.wikipedia.org/wiki/Xiphactinus Bones,]] [[http://en.wikipedia.org/wiki/Lepidotes what an]] [[http://en.wikipedia.org/wiki/Leedsichthys invention!]]

[[http://en.wikipedia.org/wiki/Acanthodii Jaws,]] [[http://en.wikipedia.org/wiki/Palaeoniscus what an]] [[http://en.wikipedia.org/wiki/Cheirolepis invention!]]

[[http://en.wikipedia.org/wiki/Cladoselache Shark]] [[http://en.wikipedia.org/wiki/Stethacanthus tales 1]]

[[http://en.wikipedia.org/wiki/Hybodus Shark]] [[http://en.wikipedia.org/wiki/Cretoxyrhina tales 2]]

[[http://en.wikipedia.org/wiki/Carcharocles_megalodon Shark tales 3]]

[[http://en.wikipedia.org/wiki/Bothriolepis Tough]] [[http://en.wikipedia.org/wiki/Coccosteus guys 1]]

[[http://en.wikipedia.org/wiki/Dunkleosteus Tough guys 2]]

[[http://en.wikipedia.org/wiki/Cephalaspis Tough]] [[http://en.wikipedia.org/wiki/Pteraspis guys 3]]

[[http://en.wikipedia.org/wiki/Cyclostomata Our earliest origins 1]]

[[http://en.wikipedia.org/wiki/Haikouichthys Our earliest origins 2]]

[[http://en.wikipedia.org/wiki/Conodont Our earliest origins 3]]

[[http://en.wikipedia.org/wiki/Trilobite The first eyes]]

[[http://en.wikipedia.org/wiki/Crustacea Crabs]] and [[http://en.wikipedia.org/wiki/Xiphosura pseudo-crabs]]

[[http://en.wikipedia.org/wiki/Pterygotus Our distant enemies?]]

[[http://en.wikipedia.org/wiki/Palaeophonus Out of water, at last!]]

[[http://en.wikipedia.org/wiki/Arthropleura Everything’s better]] [[http://en.wikipedia.org/wiki/Meganeura with Euras]]

[[http://en.wikipedia.org/wiki/Ammonite Ammon’s horns]]

[[http://en.wikipedia.org/wiki/Belemnite Stony arrows]]

[[http://en.wikipedia.org/wiki/Orthoceras Finding Nemo]]

[[http://en.wikipedia.org/wiki/Rudist Clams]] and [[http://en.wikipedia.org/wiki/Lingula pseudo-clams]]

* Among non-cephalopod mollusks, [[http://en.wikipedia.org/wiki/Bivalvia Bivalves]] (clams and their kin), [[http://en.wikipedia.org/wiki/Gastropoda Gastropods]] (water/land snails and slugs), [[http://en.wikipedia.org/wiki/Scaphopoda Scaphopods]] ("tusk-shells"), and [[http://en.wikipedia.org/wiki/Polyplacophora Chitons]], and [[http://en.wikipedia.org/wiki/Monoplacophora "cap-shells"]], have been found in great number in fossil record from almost all ages (despite very few cap-shells are still living today, and since have remained unchanged since the Paleozoic, they deserve the title of "Living Fossils"). Most of these molluscs were similar to ours, but the Cretaceous “Rudists” were odd-shaped bivalves, with one half-shell much larger than the other, resembling an amphor with a lid above. However, the most abundant invertebrate group in Paleozoic deposits are a sort of pseudo-clams, the [[http://en.wikipedia.org/wiki/Brachiopoda Brachiopods]], which actually weren't even molluscs at all. They are still-living today, but are only a minor portion of the invertebrate fauna of the seas, and aren't known much among laymen. Some of them like the Lingula, have remained totally unchanged since 400 million years!

[[http://en.wikipedia.org/wiki/Cystoidea Invertebrates]] [[http://en.wikipedia.org/wiki/Blastoidea love]] [[http://en.wikipedia.org/wiki/Crinoidea geometry]]

[[http://en.wikipedia.org/wiki/Graptolite Odd]] [[http://en.wikipedia.org/wiki/Cothurnocystis relatives]]

[[http://en.wikipedia.org/wiki/Sessile_invertebrate Survival of the toughest]]

[[http://en.wikipedia.org/wiki/Foraminifera A treasure]] [[http://en.wikipedia.org/wiki/Nummulite in the rocks]]

[[http://en.wikipedia.org/wiki/Magnoliophyta A flowery smell from Cretaceous]]

[[http://en.wikipedia.org/wiki/Ginkgophyta Dinosaur-tree]]

[[http://en.wikipedia.org/wiki/Pinophyta A resiny smell from Jurassic]]

[[http://en.wikipedia.org/wiki/Cycadophyta Cycads,]] [[http://en.wikipedia.org/wiki/Bennettitales pseudo-cycads,]] and [[http://en.wikipedia.org/wiki/Pteridospermatophyta seed-ferns]]

[[http://en.wikipedia.org/wiki/Pteridophyta The Mesozoic undergrowth]]

[[http://en.wikipedia.org/wiki/Lycopodiophyta The Paleozoic overgrowth]]

[[http://en.wikipedia.org/wiki/Cooksonia The first shoot]]

[[http://en.wikipedia.org/wiki/Ediacara_biota Animals, or plants?]]

[[http://en.wikipedia.org/wiki/Stromatolite The first Earthlings]]

* [[http://en.wikipedia.org/wiki/Lissamphibia Ancient frogs and salamanders]]: In paleontology, the word "Amphibian" has traditionally had a much broader meaning than that commonly attributed. Amphibians have been all [[http://en.wikipedia.org/wiki/Tetrapoda Tetrapods]] ("four-limbed vertebrates") excluded "reptiles" and the latter's descendants, Birds-Mammals. Today, even scientists tend to restrict the world to indicate only modern frogs and salamanders ([[AndZoidberg and Caecilians]]) and their common ancestors. If you want to use "amphibians" in its former, broader sense, you have to call modern groups "Lissamphibians". We'll use here amphibian in the old, wider meaning because it's far much handier to say this rather than "basal tetrapod" every time we refer to non-frog, non-salamander ([[AndZoidberg and non-caecilian]]) animals. Lissamphibians have a rather mysterious story. Again, like lizards, snakes, birds, rodents and bats, their skeleton is way too fragile to fossilize well, and the reconstruction of their story has many holes within it. Anyway, we're pretty sure that, [[SarcasmMode surprisingly]], both frogs and salamanders originated in the Triassic period. Yes, they too did it. And they already resembled our modern froggies/salamanders (except some details). ''[[http://en.wikipedia.org/wiki/Triadobatrachus Triadobatrachus]]'' is often mentioned as "the first frog", lived in Triassic and was very frog-like except for having shorter hindlimbs, and it wasn't probably capable to leap yet. But Jurassic frogs were already virtually identical to ours. While salamanders haven't changed much from their apparition in the Triassic, with animals like ''[[http://en.wikipedia.org/wiki/Karaurus Karaurus]]'' being already proper salamanders in every detail. Among prehistoric salamanders is also worth to be cited ''[[http://en.wikipedia.org/wiki/Andrias_scheuchzeri Andrias scheuchzeri]]'', a very close relative of modern Giant Japanese Salamander (the largest modern lissamphibian); it has been one of the very first fossil animals ever described, in year 1726, when paleontology ''still'' didn't even exist yet as scientific field; because of its size (and scientific ignorance of those years), its human-sized skeleton was interpreted as belonging to a human dead during the Biblical Deluge! (please note ''Andrias'' [[ExactlyWhatItSaysOnTheTin just means man]] in Greek). [[http://en.wikipedia.org/wiki/Gymnophiona Caecilians]] have the scantier fossil record among all lissamphibians: we don't even know when they appeared. But we're pretty sure the earliest ones still had limbs, just like snakes' ancestors.

* [[http://en.wikipedia.org/wiki/Labyrinthodontia Extinct amphibian groups]]: They are traditionally called "labyrinthodonts" or "stegocephalians", but these terms shouldn't be used today, just like "thecodonts" for basal Archosaurs or "pelycosaurs" for basal Synapsids. This because they don't indicate any natural grouping of animals, but are instead catch-all words with little scientific significance [[ScienceMarchesOn in modern phylogenetic systematics]]. Labyrinthodonts means "labyrinth teeth", because many of these animals had convoluted, labyrinth-like internal patterns inside their teeth, but this doesn't interest us too much. Their importance was much, much greater than this and lies upon another aspect. They were, simply, the links between fish and truly terrestrial vertebrates, a keystone group for mankind's evolution. And yet, just like mammal-like "reptiles" and mesozoic mammals, they have not gained much attention in pop-culture (it seems ''only apes and monkeys'' [[SmallReferencePools were our ancestors]] in pop-consciousness...). Their [[DidNotDoTheResearch apparently]] monotonous, uninteresting appearence may have contributed to this, or rather... just [[WhatMeasureIsANonHuman our mammalian pride]] generates a sort of "denial" towards our deep origins? Anyway, basal tetrapods ''weren't'' boring, uninteresting things: anything but. They were ''very'' diversified in shape, size and ecology; many of them were huge (the record to date is 30 ft of length!), but others were as small as modern lissamphibians; they were generally lizard-like, salamander-like or crocodile-like (sometimes limbless and snake- or eel-like), but others were rather strange-looking: it's enough to mention ''[[http://en.wikipedia.org/wiki/Diplocaulus Diplocaulus]]'' (one of the most depicted paleoamphibians in artworks), with its boomerang-head that ''no other vertebrate'' has ever had; lesser-known but just as peculiar, ''[[http://en.wikipedia.org/wiki/Platyhystrix Platyhystrix]]'', with its Dimetrodon-like crest. Or, still, ''[[http://en.wikipedia.org/wiki/Mastodonsaurus Mastodonsaurus]]'' (sometimes misspelled "Mastodontosaurus"), hippo-sized and with an even huger head, ''as long as a human''. Not to mention ''[[http://en.wikipedia.org/wiki/Gerrothorax Gerrothorax]]'', a neotenic form which conserved gills the-whole-life, just like modern [[http://en.wikipedia.org/wiki/Axolotl Axolotl]]. The most iconic prehistoric amphibian still remains, however, the early Permian, alligator-like ''[[http://en.wikipedia.org/wiki/Eryops Eryops]]''. The latter lived alongside the famous ''Dimetrodon'', and this may explain why is considered the archetypical "giant amphibian". "Giant amphibian" is the term usually utilized in pop-media when referring to it or to other large-size "labyrinthodonts". Actually, some of the aforementioned animals weren't really giants: ''Diplocaulus'' wasn't longer than 3 ft, for example. As a whole, non-lissamphibian amphibians first appeared in the [[http://en.wikipedia.org/wiki/Devonian Devonian]] period (but we'll talk about these earliest forms in another section), and encountered an enormous success, expecially in the Carboniferous, when immense swamps allowed them to spread widely on Earth. One of the most known Carboniferous amphibians is the tiny-limbed, eel-like ''[[http://en.wikipedia.org/wiki/Crassigyrinus Crassigyrinus]]''. But protoamphibians managed to flourish in the successive two periods as well, Permian and Triassic, conviving well with the rapidly-evolving reptiles and mammal-ancestors: ''Eryops'', ''Diplocaulus'' and the reptile-looking ''[[http://en.wikipedia.org/wiki/Cacops Cacops]]'' were all Early Permian, while the huge ''Mastodonsaurus'' was an Early Triassic guy. Most giant amphibians went mysteriously extinct at the end of the Triassic (just like many early reptilian lineages: basal archosaurs, rhynchosaurs, ''Tanystropheus'', gliding lizards, nothosaurs, placodonts and so on)... except one: the recently discovered ''[[http://en.wikipedia.org/wiki/Koolasuchus Koolasuchus]]'' from Australia, which managed to survive until the Cretaceous. This one has recently received some attention in popular media: it was portrayed both in WalkingWithDinosaurs and (unnamed) in Disney's {{Dinosaurs}}.

* [[http://en.wikipedia.org/wiki/Reptiliomorpha The closest reptile relatives]]: These "giant amphibians" deserve their own space here. The animals already mentioned belonged to two groups, the [[http://en.wikipedia.org/wiki/Lepospondyli Lepospondyls]] (''Diplocaulus'') and [[http://en.wikipedia.org/wiki/Temnospondyli Temnospondyls]] (all the others), both groups with uncertain affinities with modern frogs/salamander/caecilians (we still don't know from who the latter originated). This time we're talking about Reptiliomorphs ("reptile-shaped"); that is, tetrapods much closer to ''reptiles'' than to frog or ''Eryops''es. They had the same variety in shape and size as the other paleoamphibians, but were generally more land-living than the others, and progressively gained those traits which allow us humans to remain costantly out of water without dehydratating: waterproof skin, efficient lungs and kidneys for storing water, but above all, amniotic eggs; that is, those oval, shelled things we use to eat for dinner, and that come to our mind when hearing the word "egg". Before that, eggs were just those tiny, soft marbles modern frogs still produce today. Among quasi-reptiles, the most mentioned has long been the Early Permian ''[[http://en.wikipedia.org/wiki/Seymouria Seymouria]]'', because [[ScienceMarchesOn it was once considered the missing-link between amphibians and reptiles]]; now the most portrayed ones are the [[http://en.wikipedia.org/wiki/Embolomeri Anthracosaurs]], which were the dominant "amphibian" group in the Carboniferous, often (but not always) huge-sized. Also worth of mention are: the iguana-like ''[[http://en.wikipedia.org/wiki/Diadectes Diadectes]]'' from Early Permian, maybe one of the first herbivorous vertebrates ever appeared, along with plant-eating Synapsids like ''Edaphosaurus''; and the small, lizard-like ''[[http://en.wikipedia.org/wiki/Westlothiana Westlothiana]]'' from Early Carboniferous, which was for a short time believed the "first reptile", being even more ancient than the modern record-holder ''Hylonomus''.

* ''[[http://en.wikipedia.org/wiki/Ichthyostega Ichthyostega]]'': Along with ''Eryops'', ''Ichthyostega'' is the most famous paleoamphibian, but this time is a bit more justified: it has long had an enormous importance in paleontology indeed. Discovered in Greenland (still not the GrimUpNorth place we know today) and living in the Devonian Period, ''Ichthyostega'' has been the first four-limbed vertebrate known to science for almost a century: one of the icons of evolution thus, just like ''Archaeopteryx'' and horses. Now we know many other "missing links" between fish and tetrapods: the most astonishing is ''[[http://en.wikipedia.org/wiki/Tiktaalik Tiktaalik]]'' which was really a middle-way between a fish and an early "amphibian". ''Ichthyostega'' has often been described as a "fish with limbs", and with reason: its was still more fish-like than amphibian-like. Its 4 ft long body was streamlined like a fish; its head was smooth and very fish-like; its tail still retained a ''fin'' (albeit reduced); and its skin was, arguably, still covered with bony scales, just like fishes. But it had ''limbs'' instead of paired fins; very odd limbs to modern standards, since they had ''seven digits'' (all the other following tetrapods had only no more than five toes, a trait then inherited by reptiles-birds-mammals-humans). Expect to see it still mentioned as "the first land-living vertebrate". This is justified in works created some years ago, ex. Walking With Monsters, [[hottip: *:though the chosen animal in that show was, surprisingly, the much more obscure relative ''[[http://en.wikipedia.org/wiki/Hynerpeton Hynerpeton]]'', but that CGI animal was pratically an ''Ichthyostega'' in shape and size, so it doesn't matter.]] but not in the most recent ones: [[ScienceMarchesOn now we think it was completely aquatic, and its limbs developed to move upon the bottom of swamps, rivers and lakes, since they would be too weak to support its bulk on land]]. And is ''very'' unlikey that it could emit loud screams as shown in ''Monsters'', as well as laying frog-like eggs; [[AllAnimalsAreDogs not all amphibians are frogs]], mind you, and ''Ichthyostega'' and its kin were far more fish-like than frog-like in RealLife.

* [[http://en.wikipedia.org/wiki/Sarcopterygii Lobe-finned fish]]: Let's start with those which [[YourMileageMayVary might]] be considered the most interesting of them all. Considering these animals as ''fishes'' may appear rather arbitrary to some paleo-fans: rather than true fish, they were a sorta middle-way between typical fish and amphibians, and many of them spent part of their life ''outside'' water, thus breaking the "fully-aquatic" criterium. They are traditionally divided in three groups: Actinists, Lungfish and Rhipidists[[hottip: *:The third term it actually in disuse: today the correct one is "basal tetrapodomorphs". But if we use the latter, the pun with "actinists" [[RuleOfCool wouldn't work anymore]]]]. [[http://en.wikipedia.org/wiki/Coelacanthiformes Actinists]], better-known as Coelacanths from the common name of their only [[strike:one]] [[ScienceMarchesOn two]] surviving species, are perhaps the most famous, and at the same time, the least amphibian-like: indeed, they ''were'' fully-aquatic, thus "true fish". They appeared in the Devonian Period, and were marine creatures that have remained virtually unmodified since 400 million years: but now they seriously risk to go extinct soon or later, [[HumansAreBastards only because]] [[WhatMeasureIsANonCute they are not so cute]] [[FindingNemo as clownfish are]]. [[http://en.wikipedia.org/wiki/Lungfish Lungfish]] were a bit closer to us: they really have [[ExactlyWhatItSaysOnTheTin lungs]] for breathing air other than classic gills, appeared in the Devonian as well and specialized themselves to muddy, marshy environment with very oxygen-poor waters: that's why their lifesaving airsacs evolved. Today are the most successful missing-links between fish and land vertebrates (although less than ten species are still alive today), and yet they are less-often-mentioned than Coelacanths. Finally, [[http://en.wikipedia.org/wiki/Tetrapodomorpha "rhipidists"]]. They are the only now-extinct group, but some of them were ''among the ancestors of mankind'', as well as all land-living vertebrates ever existed, from [[{{Digimon}} dinosaurs]] to [[{{Hamtaro}} hamsters]]. ''[[http://en.wikipedia.org/wiki/Eusthenopteron Eusthenopteron]]'' has always been the stock rhipidist, probably because the look of its tail that recalls ProngsOfPoseidon; recently, the pratically identical but far bigger ''[[http://en.wikipedia.org/wiki/Hyneria Hyneria]]'' has gained some notoriety thanks to [[WalkingWithDinosaurs Walking With Monsters]], portrayed as a {{Jaws}}-like [[CarnivoreConfusion villain]]. It's the ''only'' lobe-finned fish represented in that show, and [[SomewhereAPaleontologistIsCrying with no mention at all about the role of these animals as our-ancestors]].

* [[http://en.wikipedia.org/wiki/Actinopterygii Fish]]: Yes, just ''fish''. For the fussiest among us, "ray-finned fish". They are by far the most diversified non-tetrapods today, compounding the 90% of our modern ichthyofauna, but only a small percentage of the pre-dinosaurian one. They appeared in the Devonian, but reached their immense today-success only at the Cretaceous, when they underwent an explosive evolution. From seahorses to puffers, from swordfish to ocean-sunfish, from piranhas to deep-sea anglers; almost all the most today-familiar fishie-kinds appeared only ''after'' the Cretaceous/Tertiary Rock-Falls-[[strike:Everyone]]-Someone-Dies event. Among the few modern ray-finned fish which were already in life during the mosasaur/plesiosaur/ichthyosaur existence, there were herrings, sturgeons, gars and few, few others. There were also now-extinct guys as well in the Cretaceous: the most portrayed is the 15-20ft long, bulldog-faced ''[[http://en.wikipedia.org/wiki/Xiphactinus Xiphactinus]]'', which competed successfully with its neighbouring mosasaurs in the "large predator" role. There was an even more awesome fish in the Jurassic sea: the ''whale-sized'', filter-feeding ''[[http://en.wikipedia.org/wiki/Leedsicthys Leedsicthys]]''. Among other smaller (yet still intriguing) Mesozoic fish, we can mention: the "Saber toothed herring" ''[[http://en.wikipedia.org/wiki/Enchodus Enchodus]]''; the gar-like ''[[http://en.wikipedia.org/wiki/Aspidorhynchus Aspidorhynchus]]''; the stocky ''[[http://en.wikipedia.org/wiki/Dapedium Dapedium]]''; the herring-like ''[[http://en.wikipedia.org/wiki/Leptolepis Leptolepis]]''; and, above all, the carp-like ''[[http://en.wikipedia.org/wiki/Lepidotes Lepidotes]]''. The latter was a very successful genus, with dozens of species described: this was the meal the fishing-dinosaur ''[[StockDinosaurs Baryonyx]]'' might have preferred for lunch, as shown by remains of ''Lepidotes'' within its ribcage. On the contrary, very few ray-finned fishes are known before the Triassic. ''[[http://en.wikipedia.org/wiki/Palaeoniscus Palaeoniscus]]'' and ''[[http://en.wikipedia.org/wiki/Cheirolepis Cheirolepis]]'' are the most cited: their look was a sort of middle between a regular fish and a shark, but we'll understand later why. Some modern ray-finned fish have maintained this mixed look today: sturgeons are the most typical example.

* [[http://en.wikipedia.org/wiki/Acanthodii Acanthodian fish]]: Maybe the least-famous among all prehistoric fish; and yet, possibly among the most important at all times. This because they probably were the very first vertebrates with ''jaws''. This is not a trivial thing at all: thanks to this invention (made in the Silurian Period, just before the already-mentioned Devonian), fish as a whole started to be the most important large-sized animals in marine and inland waters, becoming active predators and outcompeting the so-called "Sea Scorpions" (see in the Invertebrates section) in this role. This role obligated them to become more mobile and faster, thus giving them one day the capability to get out the water and to become human-ancestors (this thing is called "Pre-adaptation" in evolutionary terms). "Acanthode" means "spiky", and they indeed had the same, regular-fish/shark mixed look of the aforementioned early rayfins, plus [[ExactlyWhatItSaysOnTheTin many fin-spikes]]. They hadn't a great success compared to other groups, and became extinct at the end of the Permian, another victim of the most devastating mass-extinction of all times, that wiped out 90% of all living things.

* [[http://en.wikipedia.org/wiki/Chondrichthyes Sharks]]: Not always EverythingsEvenWorseWithSharks, really. For many animal-lovers, they are among the most fascinating living things. And so is among paleo-fans. Prehistoric sharks were as diversified as modern shark are today, or rather, even more. But stop now. Things aren't always so simple as they seem. "Shark" is an ambiguous word: usually refers to ''some'' of the modern cartilaginous fish, expecially the most streamlined ones such as the Great White, but not, to say, the flattened rays and skates. But in paleontology, it usually refers to ''all'' cartilaginous fish, or at least, those belonging to the [[http://en.wikipedia.org/wiki/Elasmobranchii Elasmobranchian]] subgroup. The other main subgroup, the [[http://en.wikipedia.org/wiki/Holocephali Holocephalians]], are usually called [[ChimeraBeast Chimeras]] or, more confidentially, Rabbit-Fish. Cartilaginous fish (both sharks and chimeras) originated in the Devonian period. Chimeras have virtually not changed since then, and still retain today that mixed "shark/typical fish" appearence very common among Paleozoic fish. In the Devonian, Elasmobranchs were represented with generic forms such as ''[[http://en.wikipedia.org/wiki/Cladoselache Cladoselache]]'', already with the familiar exposed gills, but with a ''terminal mouth'', unlike most modern sharks. Actually all the fish-groups seen so far get their success for the first time in this period: Devonian is called with reason "the Fish Age" because it was the age in which fish were more diversified than every else. Sharks are often called "living fossils" because their anatomy has remained virtually unchanged since 400 million years, and yet they managed to survive the strong competiton both from the first Jurassic large sea-reptiles at first, and from the first Cretaceous ray-finned fish then. Many primitive "sharks" are very cool-looking: let's give a look at the "Ironing Board" shark ''[[http://en.wikipedia.org/wiki/Stethacanthus Stethacanthus]]'', the eel-like freshwater sharks of the ''[[http://en.wikipedia.org/wiki/Xenacanthidae Xenacanthid]]'' family, and the "Switchblade Shark" ''[[http://en.wikipedia.org/wiki/Hybodus Hybodus]]''. More modern-looking sharks first appeared in the Cretaceous, along with the first modern-looking bony fish; among them, also the very first flattened kinds (aka rays/skates). Some "sharks" (in modern sense) from that period were similar to {{Jaws}}-things. The "Ginsu Shark" ''[[http://en.wikipedia.org/wiki/Cretoxyrhina Cretoxyrhina]]'', for example, growed to the size of Spielberg's beast, and preyed upon [[BadAss marine reptiles]]. Despite this, the biggest and most famous prehistoric shark was still alive ''just 1.5 million years ago'', when hominids were already existing: ''Carcharocles'', better known as {{Megalodon}}.

** [[http://en.wikipedia.org/wiki/Carcharocles_megalodon "Megalodon"]]: There's already a [[{{Megalodon}} trope]] intentionally dedicated to it, but we'll add some paleontological information here. The "megalodont" is the largest fish known to science which could hunt large prey, but possibly not the largest shark ever; perhaps our modern [[http://en.wikipedia.org/wiki/Rhyncodon_typus Whale-Shark]] may get as large as it was. And we're unsure it really was the largest fish ever as often said: the aforementioned filter-feeder ''Leesdichthys'' might get larger. Many books have exagerrated the megalodont's size, to the point [[UpToEleven measures of 100 ft weren't rarely heard in media]]; if so, it would be as large as a blue whale... Adding material to RuleOfCool, its huge jaws have been sometimes depicted [[FridgeHorror with six or more children inside, just to show how big they are]]. And Megalodon ''is not'' its scientific name, but only the surname: the correct way to call it is either ''Carcharocles megalodon'' or ''Carcharodon megalodon''. It was probably similar in shape to an oversized Great White, but this still remains uncertain. Some scientists think it wasn't so close to the white shark; if so, its correct scientific name is ''Carcharocles megalodon''. On the other hand, other paleontologists note the strong resemblance between the two sharks' jaws, and think the megalodon was a ''very'' close relative of the Great White. If so, they'd belong to the same genus, with the Great White being ''Carcharodon carcharias'', and the Megalodont ''Carcharodon megalodon''. And its teeth were indeed ''very'' similar to a White's, simple triangles with serrated edges but without those secondary points seen in some other modern shark species. These huge teeth have given it the famous-today second term of its scientific name: Megalodon means "big tooth" indeed. It's cool, that one of the largest carnivorous dinosaurs has also a reference to the Great White, because of its similarly serrated edge of its teeth: ''Carcharodontosaurus'' just means "White-Shark lizard". Another word about teeth: shark teeth are perhaps the most abundant vertebrate fossils, just as common as the famous Ammonites; yet ironically, their owners are much, much rarer in fossil record than most other fishes. Their cartilaginous skeletons don't usually fossilize, while their hard, enamel-rich teeth do very well. Indeed, many prehistoric sharks have been described only from one tooth.

* [[http://en.wikipedia.org/wiki/Placoderm Jawed armored fish]]: Called "Placoderms", they were the most numerous and diversified fish group living in the Fish-Golden-Age (the Devonian), but no one seems to have survived in the following period, Carboniferous. Placoderms' fossil abundance in devonian rocks might also be related to their main anatomical feature: a thick [[ExactlyWhatItSaysOnTheTin body armor]] made by large, articulated plates that covered the first half of their body. Placoderms and the so-called "Ostracoderms" (see further) are the only ancient armored fish known. But wait, we've said an inaccuracy. The classic fish scales we commonly know actually ''are'' a kind of body-armor, just as the plates of placoderms: only much lighter. They have the same basic bony structure, but are very diversified among fish groups. Scales of Teleosteans (aka the subgroup including almost all modern ray-finned fish) are thin laminae visible under their skin; those of sharks and some archaic rayfins (like the [[http://en.wikipedia.org/wiki/Gar gar]]) are covered with ''enamel'' like teeth, and the shark's ones look ''just like minute teeth''. This thing is quite interesting, as we'll see later. Placoderms are called "jawed armored fish" to separate them from the apparently similar, jawless Ostracoderms. We know several groups of placoderms, but the most relevant are the [[http://en.wikipedia.org/wiki/Antiarchi Antiarchs]] and the [[http://en.wikipedia.org/wiki/Arthrodira Arthrodires]]. Antiarchs had a singular anatomical feature: their pectoral fins had a very unlikely look among fish, resembling more ''crustacean legs'' than fins; the most well-known among them is ''[[http://en.wikipedia.org/wiki/Bothriolepis Bothriolepis]]'', one of the most common fossil fish in history, with 100 different species found on every continent. Arthrodires hadn't such crab-like legs, but in return they have very peculiar teeth, [[RunningGag as we'll see later]]; ''[[http://en.wikipedia.org/wiki/Coccosteus Coccosteus]]'' it traditionally regarded as the prototypical arthrodiran.

** ''[[http://en.wikipedia.org/wiki/Dunkleosteus Dunkleosteus]]'': ''Bothriolepis'', ''Coccosteus'' and most other placoderms were small predators of invertebrates or smaller fish... but not ''Dunkleosteus''. Its name means "Dunkle's bone", but in older sources it used to be called "Dinicththys" ("fearsome fish"). But today nobody uses this name anymore. Just like the "Brontosaurus -> Apatosaurus" and "Diatryma -> Gastornis" examples, this is a pity for many long-standing paleofans: a really cool name deleted by ScienceMarchesOn and replaced by a really unexpressive one... This Devonian arthrodire was similar to ''Coccosteus'', just overgrown: 30 ft long, the size of a killer-whale, it was the largest vertebrate known so far which lived before dinosaurs. Its size is even more astounding, if you think most other Devonian armoured fishes were salmon-sized. It is one of the most famous prehistoric "leviathans" along with Megalodon, ''Liopleurodon'', ''Mosasaurus'' and ''Basilosaurus'', and was the fiercest-looking among them, thanks to its armour, and also its strange-looking teeth, [[MadnessMantra as we'll see later]]; no surprisingly, it is a staple in those not-so-common paleobooks which show also pre-dinosaurian fauna, always described as a [[PrehistoricMonster "monstrous killing machine"]]. Surprisingly, despite all this, ''Dunkleosteus'' has had ''very'' few apparitions in TV to date, much less than, to say, the not-so-impressive ''Elasmosaurus'' (another egregious case of EverythingsBetterWithDinosaurs: OK, elasmo wasn't a dino, but lived in the same age...) Perhaps the only relevant example in recent media is [[WalkingWithDinosaurs Sea Monsters]], where ''Dunkleosteus'' was portrayed with [[HellishPupils cat eyes to make it even scarier-looking]] (while most drawings show rounded, fish-like pupils), with a non-proved [[IAmAHumanitarian cannibalistic attitude]], and, to put the cherry on the cake, its hide was ''[[ColourCodedForYourConvenience blood red]]''. If you have watched that show, you'll remember those strange, blade-like teeth which cut like scissors (at last, we're talking about them); these are instead TruthInTelevision. Only... they weren't ordinary teeth; they were ''bony plates'', the same kind of those which covered its forebody. And this is not an isolated case in the fish-world; remember we talked about sharks, and their enamel-covered, teeth-like scales? Finally we'll get it. At the start of fish evolution, scales and teeth ''were the same thing''. Then, body scales were lost by land vertebrates, never to return: the so-called reptilian "scales" are a totally different thing, just horny thickening of the skin (usually) without bony core, just like our fingernails. But ''mouth scales'' remained, and how: and they allow us to chew our meals today. Our incisors, canines, premolars and molars are, really, the only remaining fish-scales we still have. Keep this in mind, every time you go to the dentist.

* [[http://en.wikipedia.org/wiki/Ostracoderm Jawless armored fish]]: This is the first fish group we encounter which had appeared about 480 million years ago, during the [[http://en.wikipedia.org/wiki/Ordovician Ordovician Period]], far before the others already seen. They become very successful in the following period, the [[http://en.wikipedia.org/wiki/Silurian Silurian]], and managed to survive well in the Devonian along with the many new, jawed lineages already mentioned above. But stop now. Again, "ostracoderm" is an old, catch-all term which shouldn't be used anymore in a cladistic sense, but since is handy for us, we'll use it. They actually are made by several lineages which arose separately during fish evolution, but shared a similar body-plan. The most relevant are three: [[http://en.wikipedia.org/wiki/Heterostraci Heterostracians]], [[http://en.wikipedia.org/wiki/Anaspida Anaspids]], and [[http://en.wikipedia.org/wiki/Osteostracian Osteostracians]]. The vaguely skate-like osteostracian ''[[http://en.wikipedia.org/wiki/Cephalaspis Cephalaspis]]'' and the tiny, long-snouted heterostracian ''[[http://en.wikipedia.org/wiki/Pteraspis Pteraspis]]'' are the two most popular kinds in books and docus. The main ostracoderm subgroups differed each other mainly by body-shape and anatomical features, but they have a rather similar ecological role, so we don't get in detail about the single kinds. Ostracoderms are called "Jawless armored fish" because... [[ExactlyWhatItSaysOnTheTin guess.]] Their mouth was a simple opening without teeth or any grinding mechanism, making their feeding-style a filter-feeding and/or a food-sucking one, unlike their jawed successors. And they were small. ''Very'' small. If we'll put a modern-day grouper among them, it'll appear to them as a Great White Shark'll appear to us. Several species were not bigger than a human hand, and some were even shorter than a human "pinkie" finger! However, their most evident feature was their armor. This armor covered ''the whole body'', and made a defense tougher than any human-created armor; it was made by the same hard bony material already seen in placoderms and modern fish (in the shape of scales). At this point is worth noting a thing: these fish ''didn't have'' a true skeleton inside yet, at least the meaning we usually intend for "skeleton". Their backbone was still a little more that a simple chord with some cartilage, but no bone: in fact, the first bony tissue even appeared among Vertebrates was ''outside'' the body, making de facto ostracoderms more similar to ''arthropods'' than to most modern backboned animals in this respect. The trend started reversing first with placoderms, which lost their posterior armour to be faster and more manouvrable (as needed by their hunting habits), but still had a cartilaginous skeleton inside. Sharks transformed their armour in a dense mesh of tooth-like bony scales, but still have no bone tissue in their internal skeleton (this means their nickname "cartilaginous fish" is ''not totally'' correct: they ''have'' bone, but only on their skin and within their teeth). Only [[http://en.wikipedia.org/wiki/Teleostomi Teleostomian fish]] (ray-finned + acanthodians + lobe-finned) make this work complete, developing bony ribs, bony vertebrae, bony girdles, and so on. Finally, the first land animals felt useless and heavy their old, scaly, fishy exoskeleton and lost it for good (even though some of their descendants re-built some kinds of body armor: turtles, crocs, ankylosaurs, glyptodonts, knights etc).

* The First Vertebrates: If you get in your hands an old textbook, you'll probably read Ostracoderms were "the first fish ever", thus "the first vertebrates": actually it's untrue. Ostracoderms, indeed, were already ''very'' evolved animals. Practically, their only archaic feature was the jawless mouth that obligated them to eat only little items: all their other traits were as sophisticated as those of the other fishes. Particularly well-preserved fossil finds show us they had complex brains and very kin senses just like modern fish. An they ''had'' a whole-fishy shape, with all the classic fins (though less-developed than those of more recent fish-groups). And they ''weren't'' the ancestors of the other fish (and thus of amphibians, mammals, mankind etc.): rather, jawless armored fish went extinct at the end of the Devonian without leaving offspring. The "most primitive vertebrate" title belongs to even more primitive animals. Sadly, the common ancestors of all vertebrates are extremely poorly-known in paleontology: this because, being so ancient, they hadn't ''any'' sort of bony-covering, and thus they hardly fossilize; despite this, more-basal-than-ostracoderm vertebrates were possibly as abundant as the latter in Ordovician and Silurian seas, and maybe were successful even beyond the Devonian, perhaps until the Triassic (as we'll se at the end). The amazing thing is, unlike armoured fish, some of the basal, unarmored vertebrate groups ''have'' survived until now. We’re talking about [[http://en.wikipedia.org/wiki/Hagfish Hagfish]] [[hottip: *:It has recently been found, however, that hagfish weren't full vertebrates, only their closest relatives: but we trait them in the traditional way because is more convenient for comparison.]] and [[http://en.wikipedia.org/wiki/Lamprey Lampreys]]. They didn't descend from ostracoderms which lost their armour, as said in old texts; they are far more archaic things, which resemble anything but a typical fish in shape (expecially the hagfish). Using the word "fish" for these animals may appear arbitrary to some paleo-fans, having no fins, no fish-shape, and in the case of hagfish, ''not even eyes'' And yet, they are ''very sophisticated'' critters nonetheless: their partially parasitic way-of-life towards the "proper fishes" needs specific adaptations, and also a larger size than ostracoderms: in fact, both hagfish and lamprey may reach 3 ft length or even more. However, their earliest ancestors were very different animals: they were ''really'' tiny creatures, even smaller than ostracoderms, and were almost surely filter-feeders just like the latter. The most known among these critters has been, until few years, the recently discovered ''[[http://en.wikipedia.org/wiki/Haikouichthys Haikouichthys]]'' that lived in the [[http://en.wikipedia.org/wiki/Cambrian Cambrian Period]]: that is, the very first age in which life on Earth began to really diversify. ''Haikouichthys'' was only ''0.5 inches'' long, and its appearence was anything like a fish: a kinda "moving leaflet" without paired fins, maybe similar to the classic [[http://en.wikipedia.org/wiki/Cephalochordata "amphioxus"]] (aka ''lancelet'') so common in biology texts. However, [[ScienceMarchesOn it has recently been proposed]] it was only a vertebrate-relative just like the "lancelet". ''Haikouichthys'' appeared in ''[[WalkingWithDinosaurs Walking With Monsters]]'', described as "the very first vertebrate, forerunner of all backboned animals in the future". That's all very well, since at that time it was considered as such. But... since it is a such non-spectacular character to show in a docu-drama like this... RuleOfCool does remedy all our problems: we see our alleged forerunner portrayed as [[SomeWhereAPaleontologistIsCrying a shoal animal swimming in the open sea, with high-developed swimming capabilities, and above all, with the same parasitic feeding behaviour of hagfishes]]. While in RealLife it was almost certainly a solitary, slow-moving bottom-dweller and an amphioxus-like filter-feeder, just like the living animal which resembles the common vertebrate ancestor more than anything else: the lamprey's larval stage, aka the "Ammocoetes". Still another group of pre-fishian vertebrates is known to science, perhaps even more enigmatic than ''Haikouichthys'': the [[http://en.wikipedia.org/wiki/Conodont Conodonts]]. We known thousands and thousands of microscopic fossil "jaws" discovered everywhere from the Cambrian to Triassic terrains, attributed to them, but since few years ago, nothing from the rest of their body. In the past, scientist didn't even know if conodont remains pertained to vertebrate ancestor at all; recently, thanks to new discoveries, it has been found they were probably elongated, lamprey/hagfish-shaped critters: perhaps the ancestors of the latter? Conodonts are a prime example of the many still unresolved, intriguing mysteries of Paleontology.

When thinking about animal fossils, our mind usually goes on the pietrified bones of dinosaurs. But dinosaurs in paleontology are ''extremely rare finds'' compared to other vertebrate groups, such as sea-reptiles, Cenozoic mammals and fish. And yet, vertebrates as a whole are in turn only a ''very small'' part of the total. Indeed, more than 90 % animal fossils that Earth left to us are from Invertebrates Some invertebrate groups like Ammonites and Trilobites are so common they're object of collection by many paleo-fans; while it's ''unlikely'' dinosaur bones will receive this trade (despite some trade of dinosaur bones do exist as well, but it's highly debated if it's a right thing to do, since dino fossils are such a rarity).

* [[http://en.wikipedia.org/wiki/Trilobite Trilobites]]: There are things which are more important than others. Trilobites are among them. Their [[http://en.wikipedia.org/wiki/List_of_trilobites awesome]] fossil abundance, in fact, makes them "index fossils", that is, a hallmark to date a certain period of Earth's evolution. Trilobites are the hallmark of the [[http://en.wikipedia.org/wiki/Paleozoic Paleozoic Era]], the era which preceeds the famous Mesozoic one. Trilobites lived in ''all'' the Paleozoic periods from Cambrian to Permian, and ''no one'' managed to survive the worst mass-extincion ever to make its way in the Triassic. Thus, fit perfectly the role of index fossils about Paleozoic. But wait. Trilobites are ''not'' crustaceans. There is the tendency in pop-culture to identify ''all'' aquatic arthropods as this; since crustaceans make the quasi-totality of them today, this is justified. But things in Prehistory, as always, are more complicated. There ''were'' many crustaceans in and after the Paleozoic, as we'll se later; but many others armored, spineless Paleozoic critters ''weren't''. Trilobites are the most abundant of these, and lived mainly in the earliest periods of the Paleozoic: then, they'll be joined by crustaceans and chelicerates (see further), and their number began to fall. It's a bit useless to describe them: see the link in this entry to take a look. It's worth noting, however, they were among the very first animals to develope complex eyes, superficially similar to those of modern insects, made by many adjacent facets. Also note that, despite their completeness, we still don't know so much about their way-of-life; their soft tissues rarely have been preserved, making a problem for scientists. Trilobites were very diversified in look and arguably behavior, but most of them were bottom-dwellers and all were microphagous (ate very small items). In short, they were ''very'' similar in ecology to ostracoderms (the jawless armored fish). In fiction they rarely appear, just like all prehistoric invertebrates (authors typically [[TheyJustDidntCare prefer to show modern spineless animals in substitution]]); when this happens, they tend to look like those of the [[http://en.wikipedia.org/wiki/Phacopida Phacopids]] subgroup. Don't expect to se [[http://en.wikipedia.org/wiki/Agnostida Agnostids]] or [[http://en.wikipedia.org/wiki/Proetida Proetids]], despite the former were among the first trilobites ever appeared, while the latter were the only ones which managed to survive until the end of the Permian.

* [[http://en.wikipedia.org/wiki/Crustacea Crustaceans]] and [[http://en.wikipedia.org/wiki/Xiphosura Pseudo-Crustaceans]]: Since Trilobites and Sea Scorpions (see further) are now extinct, we have today only [[strike:two]] three remaining groups of marine arthropods: Crustaceans, Xiphosurans, and [[http://en.wikipedia.org/wiki/Pycnogonida Pantopods]] But since the latter haven't almost left fossil record, we'll talk only about the first two. The only xiphosuran left today is deceptively called "Horseshoe Crab" (its correct name is "Limulus"). this might people think they are just another kind of crab, thus uninteresting guys; it's anything but. They in fact are not crustaceans at all, but rather primitive relatives of spiders and scorpions; but unlike the latter, they are ''always'' remained aquatic creatures. Their appearence quite reminds that of a large-headed, sword-tailed Trilobite: this is not an incidence, because the trilobite-like body-plan is the original one among ''all'' the most basal Arthropods ever (see "Cambrian Life"). And their larval stage is ''even more'' trilobite-looking. Limuluses are, in an extent, the arthropodian equivalents of the famous Coelacanth: classicaly mentioned as a prime example of "living fossils", because their anatomy has remained virtually unchanged since the early Paleozoic. Today there are very few species all very similar each other, but luckily they seem not to share the same, [[HumansAreBastards disheartening]] fate of the coelacanth (at least for now...). One useful note about our modern horse-shoed friend: it is not dangerous to humans at all as sometimes heard, its tail being totally harmless and lacking any venom: instead, it has a mechanical meaning, allowing the animal to move upon certain sandy soils, or overturn itself when upside down. Prehistoric crustaceans are ''far'' less interesting-looking: today they are ''enormously'' diversified per-se, from krill to the Japanese Giant Crab, from woodlice to barnacles (yes, these too are crustaceans). Their extinct equivalents were about the same groups we see nowadays, and ruled the same echological niches. Just like trilobites and xiphosuran, crustaceans' fossil record is huge thanks to their often-calcified exoskeleton. While pantopods have left few fossils just because they have got an unarmored body (a general rule among invertebrates).

* [[http://en.wikipedia.org/wiki/Eurypterida "Sea Scorpions"]]: Probably among the prehistoric critters with the most striking-sounding name: "Sea Scorpions"... just weren't scorpions. Even though scientist think they might be the ancestors of the ''true'' scorpions, those with the stingy thing on the tip of their... what? Tail? [[hottip: *:No, no. The scorpion's "tail" is only the rear-end of its abdomen - nobody'll ever see an arthropod with tail, believe us. The tail is a typical vertebrate feature]]. Eurypterids, the correct name instead of "marine scorpions", lived through most Paleozoic from Ordovician until the Great Permian/Triassic Extinction, nearly as long as the Trilobites. They are often cited as "the largest arthropods of all times", but [[YourMileageMayVary this might depend to who you ask]]: modern [[http://en.wikipedia.org/wiki/Japanese_spider_crab Japanese Giant Crabs]], with their gigantic legs, might be considered even larger, or at least, wider. And most eurypterids were ''much, much smaller'' than the 10 ft long ''[[http://en.wikipedia.org/wiki/Pterygotus Pterygotus]]'' (by far the most portrayed in media, [[RuleOfCool for obvious reasons]]). Anyway, it seems the largest sea scorpions have been the heaviest marine arthropods nonetheless. And yet, if they were alive today, most eurypterids wouldn't really be scary-looking things. They'd look just like slender, paddle-legged, odd-looking lobsters: think a common grouper could gulp most of them with ease; and even ''Pterygotus'' could have even been appreciated as a delicacy by [[ITasteDelicious human gourmets]]. But at the times of their primeness (Ordovician and Silurian Periods) they were the largest predators in the seas (excluding giant cephalopods), while fish (still represented only by ostracoderms and few others) were still ''very'' small things. And they were [[DidNotDoTheResearch Scorpions]]. [[BigCreepyCrawlies Giant Scorpions]]. That's done. Here are the [[DesignatedVillain perfect]] guys for the BigBad role: those cruel, monstrous things which had nothing better in their life than persecute our poor little (literally little) ancestors... But wait! Wait! Let's not forget a thing: [[CarnivoreConfusion Predators Are Not Mean]], they are necessary to ol'Mother Nature's balance of life in our modern world. And so were they in the prehistoric one as well. Not only that: we might even have to ''thank'' sea scorpions for having existed! Preying upon our ancestors, it's possible they have unwillingly ''helped'' them to evolve their best traits we humans still retain, such as complex brains and fastness; going even further, one could say they made fish to get out of the water and become those four-limbed, land-loving animals from which we humans have originated. [[SurrealHumor Thank you Scorpion]]!

* [[http://en.wikipedia.org/wiki/Scorpiones True Scorpions]], [[http://en.wikipedia.org/wiki/Spider Spiders]] and [[http://en.wikipedia.org/wiki/Myriapoda Milli/Centipedes]]: The very first animals which made their first steps onto dryland weren't vertebrates, but Arthropods. It's easy to understand why. At the Silurian, vertebrates still were all fish-like and their fins weren't articulated structures which could make a leverage to substain the body constrasting the force of gravity; while Arthropods have had articulated legs since the Cambrian, 100 million years before. Thus, they were in clear advantage. The very first land arthropods weren't insects though; the latter have been a more recent appearence within Evolution. The first colonizer were the "Myriapods" (millipedes, centipedes and their extinct kin) and the [[http://en.wikipedia.org/wiki/Chelicerata "Chelicerates"]]. The latter include, other than Spiders and Scorpions, the aforementioned "Horseshoe-crabs" and "Sea-Scorpions" which remained aquatic animals. We are not sure how arthropods managed to reach the land, but we know for sure that myriapods and "true" scorpions were already present in the Silurian, while the first known spiders appeared much later, only in the Carboniferous (contemporary to the very first reptiles). All these invertebrates were astonishingly similar to their today-descendants, to the point that the latter may be counted as real "living fossils". Most prehistoric land-living arthropods remained as small as they still are today, but some grew larger: expecially in the Carboniferous, and we'll discover why just in that period. Generally, Paleozoic land arthropods tend to be represented in a very generic way in fiction or documentaries, typically lived-interpreted by actual animals. For example, the series ''[[WalkingWithDinosaurs Walking With Monsters]]'' portrayed a land-scorpion in the Devonian (perhaps ''[[http://en.wikipedia.org/wiki/Palaeophonus Palaeophonus]]''), live-acted by a modern scorpion species. However, the same series has made perhaps the first example in TV of documentary-related arthropods in CGI. Other than trilobites and eurypterids, we can see the large, still semi-aquatic scorpion ''[[http://en.wikipedia.org/wiki/Brontoscorpio Brontoscorpio]]'' in the Silurian (imprecisely described as a "Sea-Scorpion", [[TaxonomicTermConfusion making to believe]] it was a ''Pterygotus'' relative...); in Carboniferous settings, the large, fully-terrestrial scorpion ''[[http://en.wikipedia.org/wiki/Pulmonoscorpius Pulmonoscorpius]]'' appears (unnamed), as well as the giant spider "Megarachne" - considered the largest spider ever at the time, but its fossil has later revealed actually to be an [[ScienceMarchesOn eurypterid]]; thus not a spider, and not even ''land-living''. The latter has been perhaps the most awesome case of RuleOfCool within the entire Walking With series: with its creepy ''[[DarkIsEvil black venom]]'', it destroys a nest full of young protoreptiles ''apparently for mere vengeance'', and if it was not enough, it seems ''laughing sadistically upon its victims'' while the narrator saying THE ARTHROPODS ARE BACK! Not to mention those awe-inspiring "giant ants" in ''Beasts'' - these were discovered in the same Messel Pits in which the first bats have been discovered, but their behaviour as it appears in the docu is ''totally speculative'', mind you. Nonetheless, the absolute stars of the series among CGI land-arthropods were two ''really'' big Carboniferous animals: the proto-millipede ''[[http://en.wikipedia.org/wiki/Arthropleura Arthropleura]]'' and the proto-dragonfly ''[[http://en.wikipedia.org/wiki/Meganeura Meganeura]]''.

** ''[[http://en.wikipedia.org/wiki/Arthropleura Arthropleura]]'' and ''[[http://en.wikipedia.org/wiki/Meganeura Meganeura]]'': Which animal do you prefer, the largest land arthropod ever known to science, or the largest flying insect ever known to science? It almost seems intentional they have similar-sounding names; actually ''Arthropleura'' means "articulated flanks", ''Meganeura'' "large wing-veins", thus being only an incidence. Both from the Carboniferous, they represent well the tendence towards gigantism among Arthropods in this age. They were not the only overgrown land invertebrates in their world (and many other arthropods at that time were normal-sized, let's not forget it). But both made surely the UpToEleven example. And yet, in the following age, the Permian, land insects and millipedes returned as small as we were initially at their Silurian/Devonian origins, and remained such for all Mesozoic and Cenozoic, until today. Why just in the Carboniferous? The most credited theory trots out the almost-universally utilized fuel within the animal kingdom: Oxygen. Thanks to the extraordinary luxury of vegetation typical of that period, the vital gas increased its level more than every other time in Prehistory. And since size of land arthropods is severly limited by the oxygen abundance (because of their particular [[http://en.wikipedia.org/wiki/Invertebrate_trachea tracheal respiratory sistem]]), this was the ''only'' time ever in which insects and their kin managed to make the BigCreepyCrawlies trope a TruthInTelevision one. The 7 ft long ''Arthropleura'' is the most odd-looking of the two: despite being a millipede-relative, it resembled more an elongated, land-living trilobite in shape, with its body dorsally flattened and wide-framed, long antennae and short legs. It was the "cow" of its habitat, the largest herbivore of its fauna, which grazed decomposing plant material, but thanks to its size and armour, it probaby had very few enemies when fully-grown: even giant amphibians (the most powerful predators at that time) rarely attacked it, according to our best guesses. The 3 ft wingspaned ''Meganeura'', on the other hand, had a typical dragonfly-like appearence, and was arguably [[GiantFlyer an astounding flier]] and a skilled aerial predator of smaller insects, just like its modern relatives. And it too had very few enemies: giant amphibians normally couldn't get catching giant dragonflies up to the canopy where they arguably passed most the time. In few words: both are two very, ''very'' cool guys. And yet, just like all prehistoric invertebrates, ''Arthropleura'' and ''Meganeura'' haven't traditionally received much attention by writers, due in part to DidNotDoTheResearch, in part because much, much [[BigCreepyCrawlies Bigger Creepy Crawlies]] already exist in Fictionland for centuries. A curious thing is that ''Meganeura'' has traditionally received more attention than ''Arthropleura'', despite its less-awesome size and look; but now this seems no longer true, in part thanks to the influence of [[WalkingWithDinosaurs "Walking With...]] - expecially "Prehistoric Park", which made ''Arthropleura'' the main animal character in the ''Bug House'' episode. Even though the most awesome scene is seen in ''Monsters'', were an ''Arthropleura'' and an anthracosaur (reptiliomorph "amphibian") [[RuleOfCool fight each other just like a cobra and a mongoose would in RealLife]].

* [[http://en.wikipedia.org/wiki/Insecta Prehistoric Insects]]: Insects. The most abundant, diversified, biomechanically efficient, and last but not least, by far the most-studied animals by modern-fauna zoologists. Sadly, in Paleontology this is not the same. Their fossil record is ''extremely'' poor, for understandable reasons: their tiny body isn't precisely the most adapt to turn into stone, and their terrestrial habitat doesn't help either (most fossil animals discovered so far were aquatic indeed, just because water helps a lot the process of fossilization). However, if we know something more about the ancient relatives of modern insects, we have to thank pines, firs, spruces and larchs. Remember JurassicPark, and those fossilized mosquitoes in amber from which dinosaurian DNA was extracted ? The DNA extraction thing was obviously fictional, but the amber thing itself is TruthInTelevision. Insects preserved in amber are perhaps the most marvelous fossil a palaeontologist could wish in its life. Not only they are perfectly preserved in every detail, included external anatomy and ''even color'' (an almost unique example among fossils); they have ''their original tissues preserved, single cells included''. And they can provide an extraordinary clue to understand the entire ecosystem in which they lived in indirect ways. Unfortunately, most insects fossilized in amber come from the Cenozoic Era (the "mammal" age), a period in which insect were already similar to their modern relatives. But we still know little about their Mesozoic ancestors, still less about the Paleozoic ones - except for those living in the "Coal age", the Carboniferous (such as the aforementioned ''Meganeura'') because many of them did preserve well in coal. Anyway... we know some things with a good grade of certainty. The first insects appeared in the Devonian [[hottip:* :Technically these were the first Hexapods, since springtails are no longer considered proper insects by modern enthomologists: however, we follow the traditional view because it's more convenient.]], later than scorpions and millipedes: they were still wingless as modern [[http://en.wikipedia.org/wiki/Collembola springtails]] and [[http://en.wikipedia.org/wiki/Thysanura silverfish]] still are, but then the Carboniferous saw their success: the ''very first'' flying animals appeared, reaching large size up to ''Meganeura'' and starting their radiation destined to continue even today: not only dragonflies, but also cockroaches, grasshoppers and beetles appeared first in the Carboniferous. Other groups began their history in the Triassic: moths, wasps, flies and true bugs appeared at that time or a bit later. [[http://en.wikipedia.org/wiki/Insect_evolution Insect evolution]] has always been related with that of terrestrial plants, as we'll see better in the "Plants" section. It's worth noting, however, that this relationship has always been ''far more strict'' than one may think: biologists talk about a veritable Co-evolution between insects and seed-producing plants, expecially the flowering ones (Angiosperms). This partnership reached its climax in the Cretaceous, when flowering plants became the new dominant group, just because of the relationship with two new kinds of insects barely appeared: the pollinators and the social ones. The former include butterflies, bees, wasps, flies and even some beetles, while the latter include ants, bees, wasps, and termites. Both ensembles began to affect dramatically their ecosystem, conditioning indirectly the evolution of ''all'' the other terrestrial animals, dinosaurs included. Many paleontologists think if neornithan birds and placental mammals are the most today-diversified land vertebrates, they have to thank the insect-plant mutualism which has created well-suited habitats for their (initial) small size and eating-versatility. Think about those birds and bats who feed only upon nectar, anteaters and pangolins which feed upon nothing but social insects, or the infinite insectivorous/"angiospermivorous" modern animals. And think about all the plant-related products we humans utilize today. [[SoGoodWeMentionedItTwice Thank you, bug]]!

* Cephalopods:

** [[http://en.wikipedia.org/wiki/Ammonite Ammonites]]: Is there anybody who has never seen those pietrified spiraled shells at least once in its life? Ammonites are probably the most iconic fossil invertebrate remains at all, thanks to their elegant shape and their extreme abundance in Mesozoic deposits, to the point they're used as index-fossils to identify Dinosaur-age-related rocks, just like Trilobites for the pre-dinosaurian ones. But wait... ammonites are ''not'' exclusive to Mesozoic! They appeared in the middle Paleozoic, but that's right, achieved their highlights in Mesozoic with kinds which are exclusive of this era: so, it works just the same. Before the first paleontologists were born, ammonites were already well-known to people, who asked themselves what the heck they are: Mother Nature's jokes, Pietrified snakes, the "horn of Ammon" (the meaning of their our-day name), or what? The very first human which understood their real nature was LeonardoDaVinci in XVI century, but wasn't believed: we had to expect the Founder-of-Paleontology, Cuvier, after see the true fossil's nature understood at the end of the XVIII. Sometimes is heard the modern-day [[http://en.wikipedia.org/wiki/Nautilus Nautilus]] is the "modern ammonite": this is not true, as we'll see later: ammonites went ''totally extinct'' at the Cretaceous/Cenozoic extinction ever, the most famous victims (after real and alleged dinosaurs) of the most infamous (though [[DidNotDoTheResearch not the worse]]) mass-extincion ever. Indeed, ammonites are very mysterious things, despite their abundance. We know almost nothing about the shape of their soft parts, since they don't fossilize usually: it seems, though, they were intermediate between the more basal Nautilus and the our more evolved octopusquids. Octopusquids have very complex eyes, almost identical to vertebrates, while Nautilus has one of the simplest eyes one can imagine, nothing but darkrooms without lens. And ammonites? Who knows... And their tentacles? Octopusquids have eight/ten with suckers, Nautilus more but lacking suckers. And ammonites? It seems were more nautilus-like in this respect. In drawings and models, however, expect to see Ammonites [[EverythingsSquishierWithCephalopods with octopusquid eyes, octopusquid tentacles]] and, last but not least, octopusquid ink (while Nautilus hasn't ink at all in RealLife). Despite their fame, Ammonites are very rare things in TV. Don't expect to hear more than a single line about them -if at all. Even WalkingWithDinosaurs has dedicated only a brief cameo to them, in Jurassic "Cruel Seas". Indeed, for an unexplicable reason, ammonites are usually associated with Jurassic seas, despite they were just as common in Triassic and Cretaceous.... In dinosaur books, things are a bit better: ammonites here are frequent, but... don't expect to see single kinds identified, either (unless you've a technical or semi-technical work). And don't expect to see the so-called "heteromorph" ammonites, aka strange-looking species with ''uncoiled'' shells common in Cretaceous.

** [[http://en.wikipedia.org/wiki/Coleoidea Squids]] and [[http://en.wikipedia.org/wiki/Belemnite Pseudo-Squids]]: Ammonites ''were not'' the only tentacled things in the Mesozoic: Belemnites were just as abundant. They have left many remains as the former, but these aren't so iconic as ammonites are. This is easy to understand: they haven't any elegant external shell, just a sort of smooth, sharp internal cuttlebone which made people think about the most awesome things, from pietrified arrows to [[EveryoneIsSatanInHell devil's fingers]]. Despite this, we know a bit more about belemnites than to ammonites: they were close relatives to modern squid and cuttles, and they arguably ''had'' octopusquid eyes and certainly had ten tentacles - or, better, ten ''arms'': the fussy guys tell us that the correct term for tentacles is "arms" while "tentacle" should be used only for those two long, thin things with a club-like end which are exclusive to cuttles/squids but not belemnites. If ammons are a rarity in TV, what about belemns? It they appear at all, they'll be [[SmallTaxonomyPools identified as squids]]. On the other hand. if dealing with true octopusquids (more aptly called "new coleoideans"), they have a ''very scarce fossil'' record; most of them haven't any internal cuttlebone, often their only bodypart that fossilized is the "beaked mouth". And we already know how hard a soft-bodied animal fossilized. Thus, scientists are happy when founding complete remains of them. However, they lived during the whole Mesozoic Era (despite octopussies and argonauts seem a more recent thing), and GiantSquid -like forms already existed in the Cretaceous.

** [[http://en.wikipedia.org/wiki/Nautiloid "Nautiloids"]]: They have nothing to do with [[TwentyThousandLeaguesUnderTheSea Nemo's Nautilus]], still less with [[FindingNemo this Nemo]]... "nautiloid" is a catch-all term including all the most archaic cephalopods, from which ammonites and belemnites and [[IncrediblyLamePun cuttlenites and squidenites]] and octop... ahem... derived in a direct or indirect way. Indeed, nautiloids were not exclusively Paleozoic things as it's easy to think: they too were thriving in the Mesozoic like their relatives. But don't expect to see any nautiloid in media outside pre-dinosaurian Age, nor expect to see them in the Devonian, Carboniferous or Permian periods; more commonly, they are shown in the Ordovician and Silurian seas, aka in the early Paleozoic. It's not necessary to be a genius to understand why: in these periods, Nautiloids were the top-predators of the seas (along with sea-scorpions), [[RuleOfCool while since Devonian they were outcompeted by fish, followed by marine reptiles and cetaceans]]. Basal cephalopods began with long, straight shells but later these became more and more coiled, until their only still-living direct descendant, the aforementioned Nautilus (hence nautiloids, "pseudo-nautiluses"), a triumphant example of "living fossil" just as the iconic Coelacanth. Some of these shells are so well preserved that ''even their original colors'' are partially conserved (for example ''[[http://en.wikipedia.org/wiki/Orthoceras Orthoceras]]'', the kind traditionally most portrayed, which had zigzaging lines on its cone-shaped shell). Indeed, the so-called "orthocones", aka cone-shelled nautiloids, are by far the most portrayed because their strange look of [[BizarreFoods living tentacled-icecreams]]. The Walking With series has chosen the "giant orthocone" ''[[http://en.wikipedia.org/wiki/Cameroceras Cameroceras]]'' as the archetypical nautiloid, [[RuleOfCool for obvious reasons]]. But most nautiloids weren't bigger than a common cuttlefish in RealLife. To compensate, the "giant orthocone" has been represented with its correct anatomy: simple darkroom-like eyes and more than ten sucker-less tentacles (oops... arms), instead of the octopusquid eyes and sucker-filled appendixes often-seen in paleo-art.

* Other Invertebrates: There is not much to say about the portrayal of extinct non-arthropod / non-cephalopod invertebrates in media: they rarely appear even in books/documentaries, much less in Fictionland, and when they do, they are almost never named (except sometimes for the names of each group, but only in popular-science works). As an example, the original Disney's {{Fantasia}} showed several ''modern'' critters to symbolize the early evolution of invertebrates, but few or nothing among the ''really'' prehistoric ones. The WalkingWith series did the same: only modern medusae, sponges and sea-urchins appear, all live-acted. Indeed, many modern invertebrate groups have populated our seas since the Cambrian Period, but many others are extinct today.

** [[http://en.wikipedia.org/wiki/Mollusca Molluscs]] and [[http://en.wikipedia.org/wiki/Brachiopoda Pseudo-Molluscs]]: Among non-cephalopod mollusks, [[http://en.wikipedia.org/wiki/Bivalvia Bivalves]] (clams and their kin), [[http://en.wikipedia.org/wiki/Gastropoda Gastropods]] (water/land snails and slugs), [[http://en.wikipedia.org/wiki/Scaphopoda Scaphopods]] ("tusk-shells"), and [[http://en.wikipedia.org/wiki/Polyplacophora Chitons]], and [[http://en.wikipedia.org/wiki/Monoplacophora "cap-shells"]], have been found in great number in fossil record from almost all ages (despite very few cap-shells are still living today, and since have remained unchanged since the Paleozoic, they deserve the title of "Living Fossils"). Most of these molluscs were similar to ours, but the Cretaceous [[http://en.wikipedia.org/wiki/Rudist Rudists]] were odd-shaped bivalves, with one half-shell much larger than the other, resembling an amphor with a lid above. However, the most abundant invertebrate group in Paleozoic deposits are a sort of pseudo-clams, the Brachiopods, which actually weren't even molluscs at all. They are still-living today, but are only a minor portion of the invertebrate fauna of the seas, and aren't known much among laymen. Some of them like the [[http://en.wikipedia.org/wiki/Lingula Lingula]], have remained totally unchanged since 400 million years!

** [[http://en.wikipedia.org/wiki/Echinodermata Sea-urchins and their relatives]]: Echinoderms are extremely abundant in fossil record from Cambrian to Recent, because their hard internal "skeleton" fossilizes well (with one exception: [[http://en.wikipedia.org/wiki/Holothuroidea holoturoids]] or "sea-cucumbers" which are soft-bodied). Other than our familiar groups, [[http://en.wikipedia.org/wiki/Echinoidea echinoids]] aka sea-urchins, [[http://en.wikipedia.org/wiki/Asteroidea asteroids]] (the starfish, not [[RockFallsEveryoneDies that]] asteroid!) and [[http://en.wikipedia.org/wiki/Ophiuroidea ophiuroids]] (bristle-stars), we have some now-extinct groups such as the [[http://en.wikipedia.org/wiki/Cystoidea cystoids]] and the [[http://en.wikipedia.org/wiki/Blastoidea blastoids]] (please note all these musical-sounding rhymes). But those far more common in Paleozoic fossil record are a now rare but still-living group, the fern-like [[http://en.wikipedia.org/wiki/Crinoidea crinoids]] aka Sea-Lilies.

** [[http://en.wikipedia.org/wiki/Graptolite Graptolites]]: Believe it or not, sea-urchins, sea-lilies and whatnot are among ''the closest relatives of vertebrates''. But there is one now-extinct group that is even more unbelievably closer to us: Graptolites, so common in certain Paleozoic periods that are used like the more famous Trilobites as Index-Fossils. Graptolites were colonial animals more similar to the extremely more archaic cnidarians (jellies, corals etc.) in look, and their shape was awesomely diversified among species. If alive today, they'll resemble floating corals or something similar. Another group that is hard to believe to be close kin to vertebrates are the [[http://en.wikipedia.org/wiki/Homalozoa Homalozoans]]: vaguely resembling a cross between a fish, a crustacean and something else, they were once considered archaic protovertebrate, now they are believed to be closer to Echinoderms (if not echinoderms themselves). The most astonishing among them is the strongly asymmetrical ''[[http://en.wikipedia.org/wiki/Cothurnocystis Cothurnocystis]]''.

** Sessile Invertebrates: There is a general rule in Paleontology that ''no one living thing'' can escape: if you have hard portions within our body (shells, bones, armors etc.), you'll leave the memory of your importance in History of Life; it you have not these, you are probably destined to be forgotten forever. Sad, but true. This explains why so many modern relevant invertebrate groups are almost unknown in paleontology: for example, non-colonial cnidarians (medusae, sea-anemones) and several "worms" (annelids, nematodes, flatworms and so on). Who knows ''how many'' ancient important animal groups have ''actually'' existed in the Paleozoic and further, that we even know the existence... The odds do enhance however, if you are a colonial organism; if so, you probably have an external "skeleton" made of some sort of hard material (calcium carbonate, silicium, or simply horny matter like that of our hair and nails). Fortunately, many colonial groups are well-known in paleontology, and have had an unimaginable relevance not only for the evolution of life, but even for having ''building many portions of our planet''. Their skeletons, fossilized and transformed in hard rock, have accumulated in million years and became our sedimentary rocks, from sandstone to mudstone. Naturally all creatures with something hard inside or outside have contributed to this (molluscs for example have had a great role as well). Among colonial organisms we've already seen the floating Graptolites; among those still-living, the most important have been three group of "sessile invertebrates" (those fixed to the bottom of seas and lakes): [[http://en.wikipedia.org/wiki/Porifera sponges]], [[http://en.wikipedia.org/wiki/Anthozoa corals]] and the less-familiar [[http://en.wikipedia.org/wiki/Bryozoa bryozoans]].

* [[http://en.wikipedia.org/wiki/Protozoa Single-celled "animals"]]: It may seem strange to you, but ''even'' microrganisms have left fossils, and a plenty of it. Of course these fossils do not receive much attention in media, but are of extreme interest among paleontologists. Again, the only-the-tough-ones-preserve rule also counts for single-celled Protozoans: pratically the only group which has left significative fossil record is the [[http://en.wikipedia.org/wiki/Foraminifera Foraminifers]] ("forams" for their friends), only because they have a sort of minute "shell" which covers their softer innerparts. But they have been ''very'' important for scientists in several ways. First, foraminifers have largely contributed to form sedimentary rocks like corals and molluscs: despite their minute size, they were so in high-numbers in ancient seas that their impact has been notable. Then, they have aided scientists to conferm the RockFallsEveryoneDies thesis about non-avian dinosaur extinction. In rocks made ''before'' the mass-extinction forams abound, in those originated ''just after'' the extinction, they are almost missing (except few which managed to survive): a proof that the K/T extinction wasn't a slow journey to death, but a rapid cataclysm (geologically rapid, mind you: it could be last 100.000 years, which is ''nothing'' in geology!). Third, they are inherently cool: some of them were not even ''microrganisms'', would well visible to a naked eye, and reached even 6 cm of width: the latter are called [[http://en.wikipedia.org/wiki/Nummulite Nummulites]] (from "nummus", "coin" in Latin). They were indeed small, round calcareous disks, and being exclusive to the Cenozoic, they are considered the best index-fossils for the Mammal-Age. Nummulites are expecially abundant in Egypt (still underwater at the time), to the point that... [[PyramidPower egyptian pyramids]] are made by the so-called "nummulite limestone", derived from fossilized nummulite shells melted together.

* [[http://en.wikipedia.org/wiki/Cambrian_Explosion Cambrian Fauna]]: Cambrian. The first Paleozoic Period, in which the famous "Cambrian Explosion" of life happened. The less-known thing is, we humans are ''unbelievably lucky'' if we know that remote event. At that time, animals just were starting to achieve hard parts in their body, and we already know that, usually, soft-bodied organisms do not preserve at all. The astounding luck is, one of the greatest exceptions of this ruthless rule are ''just some deposits from the Cambrian Period.'' : it almost seem Ol'Mother Nature [[BecauseDestinySaysSo has done this deliberately for ourselves...]]. The most famous and historically relevant is the [[http://en.wikipedia.org/wiki/Burgess_Shale Burgess Shale]] in British Columbia, but still others are also known (for example in China). For obvious reason, our curiosity now reaches the top: which were the first animals (not counting protozoans) that thrived in our oceans? Well, the answer is not simple: we can divide them in two ensembles. One is made from those groups either still alive today or extinct several ages after the Cambrian: among the former, most non-arthropod / non-cephalopod invertebrate groups already seen; among the latter, the Trilobites. We'll talk here about the second ensemble: many Cambrian invertebrates were indeed ''exclusive of the Cambrian'' and didn't survive long enough, not even to reach the following period, Ordovician (in which the most famous Paleozoic critters, sea-scorpions, nautiloids, armored fish etc. appeared). Thus, is easy to imagine many of them were ''really'' [[OurMonstersAreWeird bizarre-looking]] to our limited point of view. We still know very very few things about their lifestyle, but their appearence is extraordinarily well-known, because these Cambrian deposits ''have preserved soft-bodies''; not only that, they have preserved them very well! It would be too long to mention [[http://en.wikipedia.org/wiki/Burgess_Shale_type_fauna all the members]] of the Cambrian Fauna: see [[http://www.google.it/imgres?imgurl=http://www.trilobites.info/burgess_community_sm.jpg&imgrefurl=http://www.trilobites.info/triloclass.htm&usg=__s0Eofooa0oLw4onLe4Slh3sbJ6g=&h=479&w=720&sz=125&hl=it&start=10&zoom=1&um=1&itbs=1&tbnid=3LpTQO2S2iy5RM:&tbnh=93&tbnw=140&prev=/images%3Fq%3Dcambrian%2Bfauna%26um%3D1%26hl%3Dit%26rls%3Dcom.microsoft:en-US%26rlz%3D1I7ADBF_it%26tbs%3Disch:1&ei=lyRVTZfKAcTrOYLpxYAF the image here]] for having an idea. It's immediately recognizable the bizarre shrimp-like animal in the center, by far the biggest creature in this fauna, and arguably the top predator. It is called ''[[http://en.wikipedia.org/wiki/Anomalocaris Anomalocaris]]'' (meaning "[[ExactlyWhatItSaysOnTheTin bizarre shrimp]]" indeed), and was a distant relative of arthropods with no articulated legs but with the same composed eyes of the Trilobites. Of course it is the most portrayed Cambrian animal in documentaries and illustrations, classicaly mentioned as "[[PrehistoricMonster the first prehistoric monster ever appeared on Earth]]"; actually, if alive today, the "terrible" anomalocarid would appear as a really [[{{Narm}} narmy thing]], a sort of 3 ft long, shell-less, pincer-less lobster, nothing dangerous for a tough-boned, tough-muscled, tough-skinned mammal we are in comparison. Actually, anomalocarids were highly specialized predators, with a mouth build for prey around 1/12 to 1/6 of their own size. But at its time, all the other organism were ''very small'': The other creatures you see in the linked image are not longer than your hand, all possible prey for anomalocarids - except those which were so small that a full grown ''Anomalocaris canadensis'' (the largest know species) whould have ignored them. Creatures like ''Hallucigenia'' and ''Pikaia'' were hunted by smaller predators, such as ''Opabinia'' and ''Anomalocaris saron''. The later was the species shown in ''WalkingWithMonsters'', though ridiculously oversized (6 ft.!?) and prone to attack it's own kind, despite the fact that neither its mouth nor grasps could injur an equally sized specimen in the way it was depicted, let alone possibly eating it. Apart from Anomalocaris, we can mention at least other three invertebrates which are stock in drawings: ''[[http://en.wikipedia.org/wiki/Hallucigenia Hallucigenia]]'', ''[[http://en.wikipedia.org/wiki/Opabinia Opabinia]]'', and ''[[http://en.wikipedia.org/wiki/Pikaia Pikaia]]''. The first has a so strange look that its name means "hallucination-generator": it was a sort of "worm" with long paired spikes for uncertain purpose, and long softed paired legs: the reconstruction of ''Hallucigenia'' has had an astounding ScienceMarchesOn tangle for many years, and it still remains one of the most enigmatic Cambrian animal: nobody knowns exactly in which phylum it has to be placed. ''Opabinia'' was related with ''Anomalocaris'', but had an even weirder look: maybe no other fossil animal resembles a fiction-related extraterrestrial thing more than ''Opabinia''. It had ''five eyes'' put in circular fashion on its head, and a pincer-like grasp at the end of a long, flexible proboscis, often mistaken for the creatures mouth which was actually located behind the proboscis. But the most important find is the third guy, ''Pikaia'': despite its rather insignificant appearence, it is the most well-known among ''vertebrate ancestor'', a sort of prehistoric relative of our [[http://en.wikipedia.org/wiki/Lancelet Lancelet]] (the closest vertebrate relative still-living today). This relevance has made ''Pikaia'' one of the unofficial symbols of Evolution, just like the ur-amphibian ''Ichthyostega'', the ur-bird ''Archaeopteryx'' and the ur-horse ''Eohippus''. But wait....have you see these critters in TV at least once? A hard thing, even if you watched [[WalkingWithDinosaurs Walking With Monsters]]. In this RuleOfCool-filled show, the ''only real'' Cambrian invertebrate to appear is....Guess what? Well, the superpredator ''Anomalocaris'' of course! The other two invertebrate guys shown up are... [[TheyJustDidntCare a modern jellyfish]] and an [[AnachronismStew anachronistical phacopid trilobite]] (remember that phacopids first evolved in the Ordovician, while Cambrian trilobites were very different-looking to the classic image we have when thinking about these animals). The absence of such awesome animals like ''Opabinia'' and ''Hallucigenia'' makes another egregious example of a missed opportunity, like the missing of the giant bird ''Argentavis''. Talking about ''Pikaia'', this time its missing is no problem for us: the aforementioned proto-vertebrate ''Haikouichthys'' did perform its role. Still another thing: if you watch the list of creatures from the Burgess Shale, you'll note almost all animals (the main exception being ''Anomalocaris'') have uncommonly short scientific names, most of them ending in '''-a'''. A rather amusing thing to read, and - let's face it - a ''true'' oasis of happiness among so many other unutterable, absurdely-difficult names.

* [[http://en.wikipedia.org/wiki/Magnoliophyta Flowering plants]]: Dinosaur-Age-related vegetation wasn't so different to ours as commonly believed. Right, non-flowering plants were dominant at the time, but still today there are ''great'' extensions of dryland dominated by conifers - the siberian Taiga, not the Amazon, is the largest forest in our days, mind you. But not only because of that. If we have the chance to really WalkingWithDinosaurs in the Cretaceous, we'll encounter many familiar critters. Most main groups of Angiosperms aka Flowering plants had already evolved: it has recently found that ''even grass'' populated the landscapes in which Triceratopses used to roam - though this doesn't justify at all the still-not-present ''grasslands'' so-common in Mesozoic {{Prehistoria}}. Most Cretaceous flowering plants were still trees then; most herbs have evolved later, despite they seem simpler-built. Some of the Cretaceous flowering trees have virtually unchanged since; the [[http://en.wikipedia.org/wiki/Magnolia Magnolia tree]] it the prototypical example. Another plant often cited to be already living alongside dinosaurs is the [[http://en.wikipedia.org/wiki/Nymphaeaceae Water Lily]]. But most trees we see in today-temperate settings, from oaks to apple-trees, from figs to vines were starting to evolve (though they became really widespread only after the mass-extinction). While grasslands ''only'' appeared in the Middle of the Mammal Age. The spread of [[http://en.wikipedia.org/wiki/Poaceae grass]] is probably related with the global cooling/drying of Earth at the time, since grass is particularly well-adapted to cold, dry environment. Its success has been ''awesomely'' important for many of the today-most popular animals to evolve: if there had never been grass, elephants, lions and whatnot, simply, would not be here now. The evolution of large grazing herds of grass-eaters and their following predators would be not possible without this kind of vegetation, which to our limited knowledge, seems often the simplest, humblest thing one could imagine... We humans ourselves have to be grateful to grass for existing: remember that mankind evolution deveoloped ''just'' thanks to the existence of grassy savannahs in Africa, while our closest relatives, chimps and gorillas, still are non-human "great apes" ''just'' for having been remained forest critters. Not to mention the matchless relevance grasses have in a more direct way for us: cereals, forage, hay, straw, bamboo, bread, pizza, hay fever... two-thirds of mankind food is still made of few kinds of cultivated grasses. [[RuleOfThree Thank you grass]]!

* [[http://en.wikipedia.org/wiki/Ginkgo Ginkgo]] and [[http://en.wikipedia.org/wiki/Ginkgophyta its ancestors]]: When hearing the StockPhrase "Living Fossil", our mind goes automatically to moving guys: the Coelacanth, the Tuatara, the Horseshoe Crab... It's easy to forget that living fossils exist even in the a-bit-disregarded plant word. The ''Ginkgo biloba'' is the most-often cited example, and with reason: it's the ''only'' species of its whole group to have survived until today: it's hard to believe its ancient kin was one of the dominant group of landplant during the whole Mesozoic era. But wait... isn't ginkgo a normal-looking flowering plant? Indeed it looks like one of these... but hey, Not Broadleaf Plants are Angiosperms, as we'll see soon. Once, Ginkgo and its ancestors were put together with pines, firs and sequoias in the catch-all group called Gymnosperms (aka all non-flowering seedplants). But ScienceMarchesOn, and if you'll still use this term, expect somebody deleting your sentence.

* [[http://en.wikipedia.org/wiki/Pinophyta Ancient conifers]]: Really? Pines, firs and spruces lived alongside Jurassic Brontosaurs and Camptosaurs? And were they ''even'' their ''main food''? About the latter we're not sure; but about the former, yes, they did. At least, pine and fir ancestors, still non-adapted to cold climates. {{Prehistoria}} is ''always'' a warm place to pass some vacation, and pine-looking trees seem a bit out-of-place there for us folks... but [[RealLife Real Life Is Always Different]] [[SomewhereAPaleontologistIsCrying When Talking About Paleontology]]. But wait, we've not finished. Since in common thought conifer = [[http://en.wikipedia.org/wiki/Pinaceae pine/fir]], some paleoartists tend to ''litterally'' feed brontosaurs and camptosaurs with modern conifers; expect thus to see ''Camarasaurus'' with a mouthful of spruce-needles, or ''Albertosaurus'' knocking down some poor pinetrees during its hunt-rush for a tasty hypacrosaur. This may be [[TruthInTelevision Truth In Art]], right, but the most widespread conifer in Mesozoic pertained, rather, to other conifer kinds, many of them still-living today: [[http://en.wikipedia.org/wiki/Taxaceae yews]], [[http://en.wikipedia.org/wiki/Cephalotaxaceae plum-yews]], [[http://en.wikipedia.org/wiki/Podocarpaceae yellow-woods]], [[http://en.wikipedia.org/wiki/Araucariaceae monkey-puzzles]], and, the more striking of all, [[http://en.wikipedia.org/wiki/Sequoioideae Sequoia trees]]. If you think brachiosaurs and titanosaurs were the real giants of their world, think again: a fully-grown ''Giraffatitan'', next to an ancient redwood, would be as tall as a beer can would be next to a fully-grown man.

* [[http://en.wikipedia.org/wiki/Cycadophyta Cycads]], [[http://en.wikipedia.org/wiki/Bennettitales pseudo-cycads]] and [[http://en.wikipedia.org/wiki/Pteridospermatophyta Seed-ferns]]: These are the plants we usually associate with the idea of Prehistory (along with true ferns and lycopods, see later). They were very palm-looking, and the still-living Cycads are often confused with the latter in RealLife: however, true palms started to appear only at the end of the Cretaceous, thus ''Diplodocus'' whip-tail would never become twisted on palm-branches. On the other hand, cycads were perhaps the most abundant seed-producing plant in the Mesozoic, along with their close (and often confused with them) relatives, the Cycadeoids or Bennettitals. However, an ever more ancient group of seed plants was still more archaic-looking. These are called Pteridosperms, aka "seed ferns": they resembled ferns in shape, only they [[ExactlyWhatItSaysOnTheTin produced seeds for spreading their kind]] unlike the latter. One seed fern, the Triassic ''[[http://en.wikipedia.org/wiki/Glossopteris Glossopteris]]'', has ben often mentioned in textbooks because it has been an historical proof for the Pangea theory. Remains of it have been discovered in Permian rocks both in Africa and in South America, India, Australia and even Antarctica: only the supercontinent thesis could explain why ''Glossopteris'' took roots in all these landmasses without swimming. Another famous Permian critter, the near-reptile ''Mesosaurus'', has been the subject of the same matter, since it too was discovered in all these continents (easier to understand if we think it was a small freshwater swimmer, thus too weak to navigate in open oceans). Both seed ferns and pseudo-cycads went extinct before the Cenozoic, while cycads have managed to reach our day and embellish our cities.

* [[http://en.wikipedia.org/wiki/Pteridophyta Horsetails and True Ferns]]: These are the today-most common archaic-looking plants. Watch one of them and your mind could travel back in time down to the ''Edaphosaurus'' days and even further. You'll note at this point that most archaic plants are either fern-looking, or palm-looking. This is not mere case: this "bodyplan" is the most ancient among terrestrial plants, and ''all'' the others - from the pine-like to grass-like - are simple evolutions of the latter. These spore-reproducing critters were already thriving in the Carboniferus, the Golden Age of Plants, but they have never been dominant compared to other groups: they have, rather, played the undergrowth role, and still play this today: but today they suffer the concurrence of modern herb-shaped floweringplants. This doens't mean, however, that ferns and horsetails have always been ''small things'': take a look to the aptly named [[http://en.wikipedia.org/wiki/Tree_fern tree ferns]], arguably one of the favourite food of large veggiesaurs, and still widespread in the original vegetation of New Zealand and part of Australia - it seems the LandDownUnder and its little sister ''really'' are an endless source of living fossils: not only the platypus or the tuatara. Even [[http://en.wikipedia.org/wiki/Equisetopsida equisetuses]] (the horsetails) have had some 30 ft tall members in their family, and some overgrown guys are still-living today: [[http://en.wikipedia.org/wiki/Equisetum_giganteum this]], for example.

* [[http://en.wikipedia.org/wiki/Lycopodiophyta Carboniferous vegetation]]: However, the most striking-looking among prehistoric plants are maybe those which dominated the Carboniferous world. 100 ft tall or more, these plants, if alive today, would resemble odd-looking trees, but were actually archaic spore-reproducing critters. But wait, they ''were not ferns'', nor were they even close fern relatives. They were even more primitive plants: the Giant Lycopods. Lycopods are still-living today, but now they are nothing but tiny herb-like greens; in the Coal-Age, though, lycopods thrived in the widespread swamps with several species very different-looking among each other. ''[[http://en.wikipedia.org/wiki/Lepidodendron Lepidodendron]]'' and ''[[http://en.wikipedia.org/wiki/Sigillaria Sigillaria]]'' are the iconic members of the group. Dinosaur-related vegetation was not such a strange-looking world, after all: while yes, Carboniferus was ''really'' a different world than ours. Imagine a wet landscape full of scaly-trunked "trees" with no more than one or two big branches on which ''Meganeura'' dragonflies used to perch like birds; a world in which every storm was enough to make those tough-looking plants to fall down with extreme ease, creating a dense undergrowth in which man-sized yet inoffensive ''Arthropleura''s crawled in the undergrowth eating the abundant dead plant matter like armored cattle. [[WalkingWithDinosaurs Prehistoric Park]] has recreated in TV that weird and wonderful world to our pleasure - and the other sequel ''Monsters'' as well, but the ''Prehistoric Park'' one is far more fascinating and also more [[RealLife realistic]]. Sadly, this world has disappeared in the Permian, when Earth became to be [[DarkerAndEdgier cooler and drier]], but has left to us one legacy: tons and tons of fossil coal we burn today. No other age has gifted to us so much coal, just because no other age has had a similar lush of green. But there is another reason: since giant lycopods were not only fragile things but also grew much faster than our seed-trees, they produced an enormous quantity of decaying plant matter during the about 50 million years of the Carboniferous. In short, if we managed to begin the Industrial Revolution, we have to thank Carboniferous vegetation. [[MadnessMantra Thank you!]]

* The most primitive plants / pseudo-plants: Carboniferous forests were not the very first ones in Earth's history: some tree-like plants had already existed in the preceeding period, the Devonian, and most were already shaped like their descendants (lycopods, tree-ferns etc.), for example ''[[http://en.wikipedia.org/wiki/Archaeopteris Archaeopteris]]'' (''not [[StockDinosaurs Archaeopteryx]]''!!!). But the deepest origin of land vegetations go even before that. in the Silurian Period, when fish started to get their jaws, and scorpions get their first airbreath, the very first aquatic plants began to colonize dryland: ''[[http://en.wikipedia.org/wiki/Cooksonia Cooksonia]]'' is the most known. They were small, fragile-looking greens still partially submerged in water, but they did already have the same basic structure of Jurassic redwood trees or modern beeches: they had internal fiber which made their body more resistent, with erect "branches"; a thin covering of cere which prevented their dry-exposed parts to dry under the sun: and they were the first [[http://en.wikipedia.org/wiki/Vascular_plant vascular plants]], that is, plants with inner conducts in which lymph flows, making their metabolism faster and more efficient. Sadly, we still know very few things about plant groups even more primitive than these (many of them ''are not even plant'' in modern taxonomy): their non-vascular body was usually soft and didn't fossilize well - yes, not even plants manage to escape to the fatal rule of only-the-tough-ones-preserve. Thus, natural history of [[http://en.wikipedia.org/wiki/Bryophyta mosses]], [[http://en.wikipedia.org/wiki/Marchantiophyta liverworts]] and [[http://en.wikipedia.org/wiki/Anthocerotophyta hornworts]] still remains an enigma, as well as that of [[http://en.wikipedia.org/wiki/Chlorophyta Green algae]] and several other kinds of organisms collectively called "Algae" in [[ScienceMarchesOn traditional biology]] that are not classified as true plants since many years. Not even [[http://en.wikipedia.org/wiki/Fungus fungi]] and [[http://en.wikipedia.org/wiki/Lichen lichens]] escaped this fate: they are virtually unknown in fossil record, but we know at least they were already present alongside the first terrestrial plant in the Devonian Period. It's the logic which tell us fungi were already there at the time: they have always played a crucial role in land ecosystems as the main decomposing organisms. Thus it's easy to think if there weren't fungi at the Devonian, dead plant matter from that age would have been accumulated in huge quantities without decomposing, literally stuffing dry lands with tons and tons of trunks, leaves and so on: maybe...some of the latter will be still-present today!

* Pre-Cambrian life: It is sometimes said that multicellular organisms appeared at the "Cambrian Explosion": actually, multicellular ''animals'' appeared then, but this doesn't mean all Pre-Cambrian forms of life were one-celled like modern "protozoans" and bacterians. We have the improperly-called [[http://en.wikipedia.org/wiki/Ediacara_biota Ediacaran fauna]], which lived just before the beginning of the Paleozoic Era. Several macroscopic organisms lived then, but they are so different than even those of the Cambrian that we don't know for sure if they are plant or animal: more probably, they were neither. The distinction bewteen animals and plants is so fixed in our common sense that it's difficult to imagine a world were eterotrophic and autotrophic beings were still not distinguished each other. The fate of the Ediacar critters at the end of the Archeozoic (aka Pre-Cambrian) Era is just as mysterious as that of many Cambrian creatures: they really disappeared, or were the common ancestor of all Paleozoic --> Mesozoic --> Cenozoic --> Neozoic forms of life, ''ourselves'' included? It'll remain for long one of the greatest mystery in Paleontology. However, many unicellular creatures have left their track in Archeozoic rocks: obviously they are micro-fossils, thus not visible to a naked eye, but they are of immense importance, because they are the most ancient forms of life known to science. The most relevant are the so-called [[http://en.wikipedia.org/wiki/Blue_algae blue-green algae]] (actually a kind of bacterians), which since 2.700 million years ago have created (and still do create today) the so-called [[http://en.wikipedia.org/wiki/Stromatolite Stromatolites]], rocky concretions made from the accumulation of huge numbers of microrganisms along with inorganic matter, all cemented together. Cyanobacterians (the true name of blue-green algae) have had a keystone role for the whole life: they were the very first organisms to produce oxygen as a waste-prodoct of their photosyntesis, and widespread it in waters and the air. Before that, organisms made only fermentation (like modern yeast) and were anaerobical, they didn't consume oxygen for their vital necessities: its only after the apparition of photosyntetical beings that aerobical organism could appear and become the ancestor of the future multi-cellular organisms (remember that ''plants'' do make respiration as well, just like animals). Today, bacteria still have a keystone role in our ecosystems: they regulate the whole thing, still producing most oxygen today, recycling nutrients in the soil, making associations with other organisms (humans included) often allowing them to live, "eating" the petroleum we reverse on the sea, fermenting bread and beer, making antibiotics and so on. Yes, there aren't only disease-bearers, among bacteria: if you and me are here, we have to thank bacteria more than every other living beings! But how the first cells appeared? Talking about this issue, we completely get out the field of Paleontology: this still remains mainly speculation and phylosophy, even though biologists are making great effort to find the answer.

[[folder:Mammals]]
As said in StockDinosaurs, only ''few'' kinds of prehistoric mammals will appear in Fictionland, generally those from the Ice Ages. EverythingsBetterWithDinosaurs, useless to say it. But if there weren't dinos, extinct mammals as a whole would be much, ''much'' more popular than they are today: a lot of them were in RealLife as large and powerful as many stock dinosaurs. Not to mention the fact a consistent part of them were the ancestors of modern hairy, milk-producing vertebrates. In short, they would be ''very'' interesting guys to show in fiction. And yet most of them still remain docu-related animals - if they're lucky enough. Programs from the 2000s like ''[[WalkingWithDinosaurs Walking With Beasts]]'' and the ''IceAge'' film series tried to partially avert the trope, but even these shows didn't escape the EverythingsBetterWithDinosaurs fate: not only the well-known case of "Dawn of Dinosaurs". Though it's little-known, Walking With was initially intended to show ''prehistoric mammals'', but producers received money "only for a show about dinosaurs" - only after the dinosaurs' success they could start with ''Beasts'', changed to a simple sequel at that point. Here is a '''very''' partial list of extinct mammals. If you want to see more about the stock ones (Mammoths and sabertooth Cats) see StockDinosaurs.

* The most classic extinct mammalian groups:

** [[http://en.wikipedia.org/wiki/Mammuthus Giant mammoths]]: It is often heard the mammoth was bigger than a modern elephant. This is not true if we consider the stock guy, the hairy, curly-tusked tundra-dweller called [[StockDinosaurs Woolly mammoth]] all people know: but this ''is'' true talking about other mammoth species. There were indeed ''many'' species of mammothes in RealLife, and as a group they lived across most of the Ice-Ages world. The largest ones did challenge the "indricothere" (see later) as the "Biggest land mammal ever" title, but only if you count their weight (the indricothere would ever be taller than every mammoth, thanks to its giraffe-like body frame). The most famous are two American species, the [[http://en.wikipedia.org/wiki/Mammuthus_imperator Imperial mammoth]] and the southerner [[http://en.wikipedia.org/wiki/Mammuthus_columbi Columbian Mammoth]]; giant mammothes have been discovered in the famous US tar-pits like [[http://en.wikipedia.org/wiki/La_Brea_Tar_Pits La Brea]] along with sabertoothed ''Smilodon fatalis'' and many other mammals (prehistoric camels, mastodons, giant ground sloths, giant wolves, pronghorns, American lions ans so on), some of them still-living today and other extinct after the Ice Ages. Other mammothes as large as the latter were the Asian [[http://en.wikipedia.org/wiki/Mammuthus_trogontherii Steppe Mammoth]] and the less-known but possibly the largest of them all, ''[[http://en.wikipedia.org/wiki/Mammuthus_sungari Mammuthus sungari]]''. The lower popularity of the giant mammothes (despite their size) compared to the woolly one is probably due to their more normal, less-spectacular appearence. They were more similar-looking to modern elephants than to the popular image of "the mammoth" because they were mostly hairless and with classic-shaped tusks (though longer than modern bush elephants); this because they inhabited relatively warmer climates, and their greater size was enough to preserve heat without the woolly covering.

** [[http://en.wikipedia.org/wiki/Machairodontinae Whatever-toothed cats]]: There were dozens kinds of [[http://en.wikipedia.org/wiki/Saber-toothed_cat sabertoothed cats]] in RealLife other than the stock American ''[[StockDinosaurs Smilodon]]'' from the Ice Ages. Some of them are nicknamed according to the form of their fangs: ''[[http://en.wikipedia.org/wiki/Homotherium Homotherium]]'' was the "Scimitar-tooth", ''[[http://en.wikipedia.org/wiki/Megantereon Megantereon]]'' the "dirktooth". While ''[[http://en.wikipedia.org/wiki/Machairodus Machairodus]]'' was the Euro-Afro-Asian sabertoothed equivalent of ''Smilodon'', not to mention the actual prototype of the group; many European paleoartists have considered ''Machairodus'' as the ''real'' stock sabretooth instead of ''Smilodon''. But there were also more familiar-looking cats in the past: these ones are mentioned later in another section. However, ''[[http://en.wikipedia.org/wiki/Dinofelis Dinofelis]]'', despite resembling more a leopard, was actually a short-fanged saber-toothed cat. The habits of all these whatever-toothed cats is still a mystery; certsinly, they were not identical among each other, and it's arguable they had different hunting styles according to the shape of their fangs; maybe some were solitary while others were pack-hunters, just like the difference between modern tigers/leopards/whatnot and lions. A curious thing is, some prehistoric meat-eating mammals which were not cats at all, developed a bewildering "sabre-toothed" look ''before'' true cats appeared: two main examples are the pseudo-cat ''[[http://en.wikipedia.org/wiki/Eusmilus Eusmilus]]'' (mentioned later) and the marsupial ''[[http://en.wikipedia.org/wiki/Thylacosmilus Thylacosmilus]]'', in particular the latter, being closer to ''kangaroos'' than to cats. Imagine a [[MixAndMatchCritter sabretooth with a kangaroo pouch]] and you'll have the idea.

** ''[[http://en.wikipedia.org/wiki/Megatherium Megatherium]]'': One of the largest land mammals that ever lived, ''Megatherium'' had the same size of an elephant or a ''T. rex'': reached 5 m when fully erect, and its name means...well... [[ExactlyWhatItSaysOnTheTin big beast]]. Lived just few thousands years ago in South America, and ancient humans knew it, to the point that they actually might have used it and other relatives as a... living pantry! Megathere's remains have been discovered in ancient caves, and it is said that some human hunters enclosed some of these animals in those caves. In old portraits, ''Megatherium'' was classically shown with a horse-like head and sometimes a giraffe-like tongue to reach foliage on the tree-tops; the horsehead and giraffe-tongue are probably mere fantasies, but the high-browsing habits aren't; indeed, the robustness of its body allowed it to stay only on its hindfeet (which, curiously, had only one claw each), while the three-clawed forefeet were used to pull down branches. Actually, our "big-beast" was not a horse o a giraffe relative... was a ''sloth''. More precisely, the stock animal within the group called [[http://en.wikipedia.org/wiki/Ground_Sloth Giant Ground Slothes]], related with anteaters and armadillos, not to ungulates. Megatherium represent the UpToEleven example, but many other "giant slothes" weren't so giant-things (even though still large by human standards). Very strongly-built and weaponed with enormous claws, they were actually capable to walk around with their body upright, a bit like giant bears. Being members of the [[http://en.wikipedia.org/wiki/Xenarthra Xenarthran]] group, they were prevalently South American (some of them migrated to the North however) and had primitive teeth: nonetheless, they were so well-adapted to their environments that they flourished for almost the entire length of the Mammal-Ages: they got mysteriously extinct only few thousand years ago. It's also worth noting that modern slothes are just members of the same group, but specialized to the familiar tree-living style. Their slowness is arguably an evolved trait to mimetize them within the canopy; giant ground slothes were arguably faster-moving, like a modern giant anteater.

** [[http://en.wikipedia.org/wiki/Glyptodont Glyptodonts]]: After Ankylosaurs went extinct, evolution decided to create their mammalian equivalents: the glyptodonts. They were Xenarthrans as well, but related to armadillos rather than to sloths. Lived in South America for dozen million years, before going extinct only few thousands years ago: in short, they had the same identical history of their cousins, the giant sloths. Both groups were veggie-eaters (despite giant sloth might be at least partially scavengers), and when adult, they feared no predators except humans. There is a secret behind giant sloth's and glyptodonts' success: their backbone. It was far, far stronger that every other mammal, thus permitting them carrying such heavy bodies around withouth suffering back pain. ''[[http://en.wikipedia.org/wiki/Glyptodon Glyptodon]]'' is the most well-known glyptodont, but it's also worth of mention ''[[http://en.wikipedia.org/wiki/Doedicurus Doedicurus]]'': with its mace-like tail, it was the most ''Ankylosaurus''-like of them all. These were among the biggest glyptos, and thus [[RuleOfCool the most depicted]]. Talking about glyptodonts' armor, it was the most powerful among every land-vertebrate (tortoises excluded). It was made by a ''single piece'' made by several ossicles fused together, smooth and usually round-shaped, unlike ankylosaurs whose armor was more flexible and spiky. With their compact frame and rigid armor, Glyptodonts were probably slower-moving than ankylosaurs, but still faster than a Galapagos' tortoise. Despite these differences, the glyptodont's armor was astonishingly similar to an ankylosaur's; only the upper parts of the body were covered, the underbelly was unarmored like ankylosaurs and hairy like modern armadillos; the head had a "shield" again like ankylos, and their tail was also covered by bone. Like ''Megatherium'', also ''Glyptodon'' was known by ancient humans; but we are not sure what was the real thing that made these amazing animals extinct: climatic changes? Human hunting? Or what? Now, only far smaller xenarthrans survive; armadillos, tree-slothes and true anteaters (sadly, the natural history of anteaters is poorly-understood).

* Prehistoric hoofed mammals:

** [[http://en.wikipedia.org/wiki/Evolution_of_the_horse Horse ancestors]]: The eternal symbol of Evolution. Almost the same level the Dodo is the icon of extinction. And yet, horse ancestors weren't so cool-looking compared to most other extinct [[http://en.wikipedia.org/wiki/Ungulate hoofed mammals]], really. The most famous of these is, obviously, the [[RuleOfCool less horse-like]] of them all: ''Eohippus'' --> ''Hyracotherium'' --> ''Eohippus'' --> ''Protorohippus''. An almost-unbelievable ScienceMarchesOn affair has encircled horse's evolution, despite its iconic role in popular science. Anyway, all this doesn't involve us so much. Expect to see this (whatever name is to be used) small, basal ungulate called ''horse'' anyway, despite it, actually, having nothing more in common with horses than with tapirs or rhinoceri: the "Hyracotheohippus stew" includes several different early ungulates, some of theme ''were'' horse-ancestors and some weren't. Systematics of primitive ungulates (many of them called [[http://en.wikipedia.org/wiki/Condylarthra Condylarths]]) is a total mess. Among sure horse ancestors, they make a [[AWorldwidePunomenon sort of pun if read together]]: ''Mesohippus'', ''Merychippus'', ''Pliohippus'' and dozens other ''hippus''... all North American. Also worth of note is ''Hipparion'' which, sadly, breaks the pun having ''hippus'' as prefix: it also breaks the geographic rule, being an Old World critter, an offshot of the horse tree which didn't leave any descendents. Remember that ''all'' modern equines did descend from North American ancestors. And oh: the latter were not only horse's ancestors: also donkey's and zebra's, never forget this. Modern equids are so closely related each others, they could well be considered variations of a single kind of animal; indeed, they are all put in a single genus, ''Equus''.

** ''[[http://en.wikipedia.org/wiki/Uintatherium Uintatherium]]'': As we'll say later, not all rhinoceros-looking fossil mammals were real rhinos; but they'll probably get [[DidNotDoTheResearch identified as such in popular media]]. The most well-known are ''Uintatherium'' and ''Brontotherium'', both found in huge numbers in several fossil deposits of Western Usa. The poor uintathere is perhaps [[TheWoobie the most mistreated]] extinct mammal of them all: expect somebody describing its appearence as "[[PrehistoricMonster monstrous/scary]]". Right, it had six giraffe-like horns and two upper protruding tusks: but, honestly, if ''Uintatherium'' was alive today, it would appear not more scary than an elephant, rhino, hippo or giraffe... Also expect a crack about its "tiny" brain (just what happens to its Woobiesaurian equivalent, ''[[StockDinosaurs Stegosaurus]]''), and just like the stegosaur, expect the writer saying [[TooDumbToLive its dumbness being the real reason of its extinction!]] In RealLife, uintatheres were among the very first mammals to reach large size (up to a modern-day rhino), and their body-plan was ''very successful'' at the time, to the point they roamed northern continents in huge numbers for million years in Early Cenozoic, before being substituted by the even larger brontotheres (see below).

** ''[[http://en.wikipedia.org/wiki/Brontotherium Brontotherium]]'': This is the prototype of its group of mammals, the [[ExactlyWhatItSaysOnTheTin brontotheres]]. While ''Uintatherium'' was not related with any modern hoofed mammals, brontotheres were distant relatives of [[http://en.wikipedia.org/wiki/Perissodactyla horses, tapirs and rhinos]]. The biggest brontotheres were almost Triceratops-sized or Elephant-sized, and their cool-name indeed means "thunder beasts". They had a more rhino-like look than uintathere, having one single "horn" on their nose: ''Brontotherium'' 's prominence was forked and slingshot-like, while that of ''[[http://en.wikipedia.org/wiki/Embolotherium Embolotherium]]'' (the brontothere portrayed in [[WalkingWithDinosaurs Walking With Beasts]]) was shovel-like and not forked. Like uintathere, brontotheres too roamed plains of the northern continents in huge numbers in Early Cenozoic: then they eventually gone extinct, perhaps because they weren't capable to adapt to the diffusion of the very first grasslands which replaced their former food (made of scrub and non-grass herbs).

** ''[[http://en.wikipedia.org/wiki/Arsinoitherium Arsinoitherium]]'': Sometimes misspelled "Arsinotherium", it was the most peculiar-looking among "pseudo-rhinos", with its huge, yet light-weighed, hollow "quadruple-horn" (sometimes even asymmetrical). The same size as modern rhinos, this animal is often described as a "cross between a rhino and a hippo" because of its short legs and amphibious habits: it lived along the coasts bordering the shallow seas which covered modern-day Egypt, together with the ur-elephant ''Moeritherium''. It's worth noting that, unlike ''Moeritherium'', ''Arsinoitherium'' was ''not'' an elephant predecessor as said in [[WalkingWithDinosaurs Sea Monsters]], and maybe didn't have that tapir-like nose seen in the program: this mammal is so strange that it is put in its own mammalian order, the Embrithopods, only distantly related to elephants.


** [[http://en.wikipedia.org/wiki/Rhinoceros True prehistoric rhinos]]: Modern rhinos are often referred as "prehistoric-looking" in media (and the genus now housing the White Rhino (''Ceratotherium'') dates back 7 million years). Many classic prehistoric mammals were indeed rhino-looking though with different horn-shapes (the aforementioned six-horned ''Uintatherium'' and the fork-horned ''Brontotherium'' are the most well-known examples), but only some of the extinct "rhinoceroses" were ''really'' such. Among them, the most spectacular were the [[http://en.wikipedia.org/wiki/Coelodonta_antiquitatis Woolly Rhino]], the [[http://en.wikipedia.org/wiki/Elasmotherium_sibiricum Unicorn Rhino]], and above all, the Indricothere (ironically, this one wasn't so rhino-looking). The Unicorn (''Elasmotherium sibiricum'') is often confused with the Woolly (''Coelodonta antiquitatis'') because of their similar appearence: however, the latter was not larger than modern white-rhinos and had ''two'' horns as well; the former was much larger (5 tons, like a modern bush elephant) and with one single horn... perhaps as long as a grown man, and put on the front rather than upon the nose: hence [[ExactlyWhatItSaysOnTheTin unicorn rhinoceros]]. Both lived in the Ice Age in cold climates, alongside mammothes in northern Asia, but the elasmothere was southerner than the coelodont; the latter lived alongside the other, more popular woolly, ([[RhetoricalQuestionBlunder guess what]]). Interesting that both woollies have left soft part of their bodies other than bones, hair included. While the "unicorn rhinoceros" is often said to have been the inspiration of [[DeadUnicornTrope that other unicorn]] when still alive, but this is probably a legend. About Indricotheres (or Paraceratheres, depend on who you ask), they deserve their own entry below.

** [[http://en.wikipedia.org/wiki/Paraceratherium Paracerathere]]: Here is Our Majesty, the biggest land mammal ever lived - though some [[ScienceMarchesOn recent research]] seems to indicate that some mammoths were heavier, but certainly not as tall. Despite its really gigantic size - it was as tall as an apatosaur up to the shoulders, and weighed as ''three'' elephants or, better, as three ''T. rex''es - it still had a quite slender, elegant frame: a sort of muscular giraffe with long neck, small hornless head, and long, slender limbs. Its behavior itself was probably more giraffe-like than rhinoceros-like, browsing the tree tops. In short, it was the new mammalian brachiosaur. Lived at the middle of the Cenozoic (the Age of Mammals), and was only the biggest member of a whole group of extinct "rhinoceri" (better, rhino-relatives): the Hyracodontids, most of them were horse-sized and more similar to horses than to rhinoceros. Our record-holder is also a prime example of IHaveManyNames among prehistoric critters: now called ''Paraceratherium'', its traditional names are ''Indricotherium'' and ''Baluchitherium''.

** [[http://en.wikipedia.org/wiki/Chalicotheriidae Chalicotheres]]: The best example of MixAndMatchCritter among prehistoric mammals: they had the head of an horse, the body-shape of a gorilla, and sloth-like forelimbs with hooked claws for pulling down branches or excavating the soil in search of roots: some nickname them [[MixAndMatchCritter sloth-horses]]. A very successful group of hoofed mammals, distantly related to horses and rhinos (like the aforementioned brontotheres); chalicotheres roamed for a long time in most continents, and some [[WildMassGuessing think]] the famous "Nandi Bear" that could live in modern African rainforests is just a surviving chalicothere. The two most well-known family-members are the north-american ''[[http://en.wikipedia.org/wiki/Moropus Moropus]]'' and the Asian namesake ''[[http://en.wikipedia.org/wiki/Chalicotherium Chalicotherium]]'' - the latter was even stranger since literally ''knuckle-walked'' like a gorilla. The latter was portrayed in [[WalkingWithDinosaurs Walking With Beasts]], along with another species, african ''Ancylotherium'' - maybe the last chalicothere, unless the Nandi Bear....

** ''[[http://en.wikipedia.org/wiki/Irish_elk Megaloceros]]'': Or more precisely, ''Megaloceros giganteus''. Now we enter the world of the most successful ungulates today, Artiodactyls (even-toed ungulates), and how could make this without starting with the most spectacular extinct deer (and one of the most astonishing mammals ever)? But wait: even though it is commonly referred as the "Irish elk", ''Megaloceros'' (also called "Megaceros" in older sources) was more related with European fallow-deer. Maybe it was not the largest deer ever (being moose-sized), but its antlers were another stuff: they could make the modern mooses' ones appear insignificant in comparison. Each one was ''as long as the entire animal's body'', and each one weighed more than 100 kg. Obviously, only males had such a thing above, as most modern deer. Some scientists said that ''just this headgear'' was the cause of its extinction, having grown too much, and making the animal too clumsy... but this is unlikely; if they actually were too big, evolution would have made it smaller at one point, simply. ''Megaloceros'' lived in Europe in the Ice Ages alongside woolly mammoths and other large mammals, and was possibly prey for ancient human-ancestors; its nickname "irish elk" is due to its remains are very common in {{Oireland}}.

** Prehistoric pseudo-deer: Many prehistoric ungulates resembled deers in body-shape and head-shape, but again, not all were members of the [[http://en.wikipedia.org/wiki/Cervidae deer family]] like ''Megaloceros''. Many of them had very unfamiliar-looking horns/antlers above their heads. Among pseudo-deers, the most portrayed are ''[[http://en.wikipedia.org/wiki/Synthetoceras Synthetoceras]]'' and ''[[http://en.wikipedia.org/wiki/Sivatherium Sivatherium]]''. The former was a distant camel-relative, but was antelope-shaped and also with a bit of rhino inside: it had three horns, two of them were antelope-looking, but the third one was on its ''nose'' and was forked just like that of ''Brontotherium'', though longer and more slender. ''Sivatherium'' was moose-like and very large (2.5 m tall at the shoulder), and had deceptively moose-like pseudo-antlers: it actually was a giraffe relative, a sort of short-necked giraffe. Just about this detail: remember the classic Lamarckian "lenghtening of the giraffe's neck" we have learned at school? Indeed, no other extinct mammal has has such a long neck other than our giraffe: modern animals often are not so overshadowed by their prehistoric relatives, really.

** [[http://en.wikipedia.org/wiki/Bovidae Prehistoric Bovids]]: Bovids (the group containing buffalo, sheeps, goats and antelope; that is, all ruminants with ''true'' horns) are the most successful ungulate group today, and are very diversified: their prehistoric relatives were not much different in their appearence. We can mention however the [[http://en.wikipedia.org/wiki/Bison giant bisons]] which lived in Ice Age North America. There were many species of them, some were larger than their present-day relatives and often with more developed horns as well; these traits were perhaps to defend themselves against prehistoric lions (see further). Only one specie of bison still remains in today-America.

** [[http://en.wikipedia.org/wiki/Camelidae Prehistoric camels]]: In prehistory, extinct relatives of camels and llamas were very diversified: the great majority of them were North American, where they started their evolution. Some were even taller than our modern dromedaries: ''[[http://en.wikipedia.org/wiki/Aepycamelus Aepycamelus]]'' was a sort of giraffe-like animal with very elongated neck and limbs. Other "camels" were more antelope-like and runned the ancient North American plains. The well-known specializations for desert-life has appeared very recently in camel story, and regard only modern Old World species: their ancient North American relatives lived mainly in grasslands, thus is unlikely they would have fat-storing humps and resistence against thirst.

** Prehistoric [[http://en.wikipedia.org/wiki/Suidae pigs]]/pseudo-pigs: Many hoofed mammals of the distant past were pig-like in shape: indeed, the pig-frame was the most primitive among "ungulates", still retained by some modern hoofed mammals, the best example being boars, peccaries and also the tapir (which is a perissodactyl). Most prehistoric pseudo-boars were small, but some were not: [[http://en.wikipedia.org/wiki/Entelodontidae Entelodonts]] are the most striking ones. They were bison-sized at the most, and had several bony knobs on their head and jaws, resembling giant warthogs, but their tusks were much smaller than a warthog's or a babyrousa's, and didn't protrude out of the mouth. Their food habits are still unclear: they might be scavengers that drove away small predator from their kill, but also ate vegetation and might even be active hunters sometimes. North American ''[[http://en.wikipedia.org/wiki/Daeodon Daeodon]]'' (also called ''Dinohyus'') is the largest and one of the most depicted entelodont. [[WalkingWithDinosaurs Walking With Beasts]] has shown an unnamed Asian relative, and affected its appearence [[CarnivoreConfusion to make it scarier]], exaggerating the opening of its mouth.

** ''[[http://en.wikipedia.org/wiki/Andrewsarchus Andrewsarchus]]'': One of the most enigmatic mammals, from the first part of the Cenozoic (the Eocene period). Only a skull is known, about 3 ft long and vaguely wolf-like. Some argue it was the largest carnivorous land mammal ever, but we haven't any proof about that; it might be omnivorous instead. It was traditionally considered to be closely related to the much smaller [[http://en.wikipedia.org/wiki/Mesonychia mesonychids]], the first meat-eating mammals which obtained a size larger than a house cat; however, [[http://scienceblogs.com/tetrapodzoology/2009/08/mesonychians_part_iii_andrewsa.php later]] [[http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0007062 phylogenetic studies]] indicate that it might have actually been a close relative of the aforementioned entelodonts (though obviously any phylogenetic placement is only tentative at this point). The mesonychids were once considered the ancestors of whales (see below) because their skull (specifically their teeth and earbones) resembles that of the most primitive cetacean known, ''[[http://en.wikipedia.org/wiki/Pakicetus Pakicetus]]''; now we know that the [[ScienceMarchesOn hippopotamus]] is the closest relative of whales and dolphins. The fossil record of prehistoric hippos is poorly known; on the other hand, the similar-looking [[http://en.wikipedia.org/wiki/Anthracotheriidae anthracotheres]] have a rich number of species described, they were probably the closest hippopotamus relatives, or even their ancestors.

** [[http://en.wikipedia.org/wiki/Evolution_of_cetaceans Early whales]]: ''All'' mammals were small and rodent-shaped in their evolutionary beginnings. Some became larger and more derived after the extinction of the dinosaurs, but none to the same level as whales. The first whale ancestors appeared only 10 million years or so after the non-avian dinosaurs' extinction. Once thought to have descended from doglike mesonychids (see above), whales [[ScienceMarchesOn are now thought to be]] [[http://en.wikipedia.org/wiki/Even-toed_ungulate artiodactyls]] (even-toed ungulates), such as camels, pigs, cattle, deer and particularly hippopotami. The first whales may have descended from the aforementioned anthracotheres, or possibly ''[[http://en.wikipedia.org/wiki/Indohyus Indohyus]]'', which was only discovered in 2007. They probably spent much of their time on land, feeding on dead fish and drowned animals. ''[[http://en.wikipedia.org/wiki/Ambulocetus Ambulocetus]]'' (the "walking whale") is a good example of this: still four-limbed, it was already a good swimmer, but still resembled anything but a whale. Among the first fish-shaped cetaceans, ''[[http://en.wikipedia.org/wiki/Basilosaurus Basilosaurus]]'' reached the length of a modern baleen whale, but was much more slender, sometimes mentioned "[[UpToEleven eel-like]]" (by the way, it was still a whale!). When first discovered, its elongated shape was misidentified for a mosasaur-like marine reptile: hence its strange, dinosaurian-sounding name ("king lizard"). At that time, all whales still were active hunters, like modern orcas and sperm whales, but still with differentiated teeth: pointed the anterior ones, serrated the posterior, an old legacy which betrays their origins from land mammals. The first filter-feeders appeared much more recently, when our planet turned colder and immense shoals of krill began to float in polar waters. Other cetaceans, however, remained small and active predators, originating our dolphins.

** [[http://en.wikipedia.org/wiki/Meridiungulata South American Ungulates]]: South America was isolated from other continents for most of the Mammal Age, and thus its fauna developed in its own direction. There were not only elephant-size sloths and tank-like glyptodonts: there were also less-armoured but still odd-looking "ungulates", not related with any modern animal today, but similar in shape/size to camels, horses, hippos, buffalos, elephants, rhinos, hyraxes, and even chalicotheres (a great example of Convergent Evolution). The two most represented are ''[[http://en.wikipedia.org/wiki/Macrauchenia Macrauchenia]]'' and ''[[http://en.wikipedia.org/wiki/Toxodon Toxodon]]''. ''Macrauchenia'' was a bit camel-like; often depicted with a floppy, elephantine nose because of the shape of its skull, but we don't know if it really had this thing. ''Toxodon'' was more like a stock-built, no-horned buffalo, but it has also been compared with a rhino or a hippo. These two guys lived during the Ice Ages in South American grasslands ("pampas"), and were among the latest members of their groups; but other relatives lived much earlier, always in South America.

** The most primitive Ungulates: Once, "ungulates" (hoofed mammals) were believed a natural group of mammals; now we know that several mammalian lineages reached the ungulate body-plan independently, and they do not make a real ensemble. Those which lived at the beginning of the Cenozoic were rather undifferentiated each other, and did not resemble most modern hoofed mammals. The two most famous are the small "ur-horse" Eohippus/Hyracotherium/Protorohippus and the large ''Uintatherium'', both from the Eocene epoch: among the other eocenic "ungulates", ''[[http://en.wikipedia.org/wiki/Coryphodon Coryphodon]]'' and ''[[http://en.wikipedia.org/wiki/Phenacodus Phenacodus]]'' are frequently portrayed in books. ''Coryphodon'' was perhaps the first land mammal to exceed 1 ton in weight, and was rather similar to an hippo in shape. ''Phenacodus'' was not larger than a dog: with its several small hoofed digits, it was similar to ''Eohippus'' with a very long tail, and it is often mentioned as the prototypical "basal ungulate". Just like Eo/Hyraco/Protorohippus, ''Phenacodus'' could have been a possible prey of the famous giant bird ''Gastornis''; while the massive ''Coryphodon'' and ''Uintatherium'' were too powerful to be threatened by any predator when adults, like modern rhinos and elephants.

* Prehistoric carnivorous mammals:

** Extinct relatives of [[http://en.wikipedia.org/wiki/Felinae modern cats]]: There were not only sabre/scimitar/dirk/whatevertooths in Prehistory. There were also more normal-looking cats, which together make the subfamily Felinae - while sabretooths make the Machairodontinae. The former are known as "biting cats" the latter "stabbing cats", [[CaptainObvious guess why]]. The most well-known "biting" cats were the [[http://en.wikipedia.org/wiki/Panthera_leo_atrox American Lion]] and its European cousin, the [[http://en.wikipedia.org/wiki/Panthera_leo_spelaea Cave Lion]], both simply larger, Ice Ages-related subspecies of the modern lion, well adapted to live in colder climates along with the mammoths. Some think they were the main predators of ancient humans, but this is not certain. Anyway, it seems males haven't any mane, at least according to some prehistoric paintings. Another interesting biting cat was the [[http://en.wikipedia.org/wiki/Miracinonyx American Cheetah]], actually more related with cougar than to cheetah, possibly a specialized hunter of modern pronghorns (which developed their fastness just to escape these "cheetahs"). Not all prehistoric cats were large, though: most were as small as many modern felines, and one of them was the ancestor of our domestic friend.

** [[http://en.wikipedia.org/wiki/Ursidae Prehistoric bears]]: Bears are a very recent group. They have roamed our planet for only 5 to 10 million years. Many prehistoric bears were rather different than our grizzlies: for example, the North American [[http://en.wikipedia.org/wiki/Arctodus short-faced bear]] had long limbs and a [[ExactlyWhatItSaysOnTheTin bulldog-like snout]] and was probably an agile runner and specialized hunter. The most famous extinct bear is, however, the [[http://en.wikipedia.org/wiki/Ursus_spelaeus cave bear]], whose remains are extremely abundant in European caves. Quite similar to a modern kodiak in shape and size, but with a bigger hump on its shoulder and a more prominent skull, Cave Bear is often portrayed as [[EverythingsWorseWithBears the archenemy of Neanderthals]], because both lived in the same places (Pleistocene Europe) and were forced to share the same caves to repair themselves from the rigid Ice Age winters. But it's more probable that Neanderthals were actually the worst enemies of cave bears, and some think they could even have contributed to their extinction.

** Prehistoric [[http://en.wikipedia.org/wiki/Canidae canids]] and [[http://en.wikipedia.org/wiki/Hyaenidae hyenas]]: Prehistoric wolves and hyenas were not so different-looking than ours, but sometimes were larger. The [[http://en.wikipedia.org/wiki/Canis_dirus dire wolf]] was a sort of wolf bigger than ours, possibly a hunter of giant bisons in competition with lions. It has been often found in the same tarpits in which ''Smilodon'' remains have been discovered, along with several other American mammals (elephant relatives, ground sloths, but modern-living mammals as well); the most famous is [[http://en.wikipedia.org/wiki/La_Brea_Tar_Pits Rancho la Brea]], in Los Angeles. Of course, not all extinct dogs were large, don't forget there were fox-ancestors as well. Among extinct hyenas (which by the way, are more closely related to cats than dogs) we can mention the [[http://en.wikipedia.org/wiki/Cave_hyena cave hyena]], similar to modern spotted hyenas but living in northern territories during the Ice Ages. Other hyena species were very different: some were as large as bears, others resembled more cheetah or even weasels! On the other hand, some extinct canid were deceptively hyena-like: ''[[http://en.wikipedia.org/wiki/Borophagus Borophagus]]'' from the Middle Cenozoic is one example, while the archaic ''[[http://en.wikipedia.org/wiki/Hesperocyon Hesperocyon]]'' was more weasel-like. As a side-note: all modern domestic dogs from Chihuahuas to Great Danes descend from the grey wolf, no matter how big they are or how they look; an amazingly rapid evolution, really, lasted only few thousands years.

** [[http://en.wikipedia.org/wiki/Amphicyonidae Bear-dogs]] and [[http://en.wikipedia.org/wiki/Nimravidae Pseudo-cats]]: Before cats, bears, dogs and hyenas appeared on Earth, there were their pseudo-looking relatives, whose appearence was similar to their successors or a mix of these animals. Bear-dogs are more correctly called Amphicyonids: some were very fox- or wolf-like, while others were more similar to bears. A [[AllAnimalsAreDogs very dog-like]] "bear-dog" appears in [[WalkingWithDinosaurs Walking With Beasts]]. Nimravids (the pseudo-cats) were also very diversified: the aforementioned ''Eusmilus'' was indeed a sabretoothed member of the pseudo-cat family, while the namesake ''[[http://en.wikipedia.org/wiki/Nimravus Nimravus]]'' was more similar to modern big cats. The latter has left a perforated skull which could reveal an astonishing story; maybe it was stabbed in its head... just by its relative ''Eusmilus''. Sadly, in some sources, Nimravid are wrongly treated as [[TaxonomicTermConfusion actual cats]].

** The most primitive [[http://en.wikipedia.org/wiki/Carnivora Carnivores in general]]: True carnivore (members of the order Carnivora) appeared soon after the start of the Mammal Age, but remained small and unspecialized for a long amount of time. In the Eocene most of them were still weasel- or genet-like like ''[[http://en.wikipedia.org/wiki/Miacis Miacis]]'' , but they already showed the separation in the two main branches still-living today: the [[http://en.wikipedia.org/wiki/Caniformia dog branch]] (dogs, bears, raccoons, weasels and ''seals'') and the [[http://en.wikipedia.org/wiki/Feliformia cat branch]] (cats, genets, mongooses and ''hyenas''). All modern large-sized carnivores, from bears to lions, wolves to walruses, descend from weasel-shaped critters. However, many small carnivores retain still today their ancient shape/size: because of their small size, they are much rarer in the fossil record and their evolution is less understood.

** [[http://en.wikipedia.org/wiki/Creodontia Creodonts]]: In the Early Cenozoic, at the time "true" carnivores were still weasel-like, creodonts occupied the ecological niche ruled by modern large carnivores. Very diversified in shape and size, their appearence included that of all modern carnivores (hyena-like, dog-like, bear-like, weasel-like, tiger-like, or a mix of all these). However, creodonts were more primitive and arguably slower-moving than our meat-eating mammals: this has been often cited as the cause of their extinction, but scientists aren't sure of that. ''[[http://en.wikipedia.org/wiki/Hyaenodon Hyaenodon]]'' is regarded as the stock creodont. There were several species, from dog-sized to cow-sized: the largest hyaenodont species appears in Walking With as a formidable predator, but some hypothize it was mostly a scavenger. But even bigger creodonts are known to science, some of them could have even been the biggest land meat-eating mammals ever, rivalling the alleged "Biggest carnivore" ''Andrewsarchus''.

* Other extinct mammals:

** [[http://en.wikipedia.org/wiki/Proboscidea Other elephant relatives]]: There were A LOT of them in prehistory: not so in {{Prehistoria}}. Don't expect to see any proboscideans in TV outside docus unless it's a woolly mammoth or an [[StockDinosaurs American mastodon]], even though many of them were far cooler-looking than the latter two. If you don't believe us, take a look at these: the shovel-jawed ''[[http://en.wikipedia.org/wiki/Platybelodon Platybelodon]]'' resembled a cross between an elephant and a hippo. The huge ''[[http://en.wikipedia.org/wiki/Deinotherium Deinotherium]]'' (appropriately named "terrible beast") had two tusks ''growing out of the lower jaw'', and some species were almost as big as the "indricothere". The ancestral ''[[http://en.wikipedia.org/wiki/Moeritherium Moeritherium]]'' (classicaly mentioned as "the first elephant") didn't resemble even an elephant: not bigger than a tapir, with its short trunk and short limbs it was also very tapir-looking rather than elephant-looking. But even more normally-looking proboscideans would appear cool-looking by our standards: other than the aforementioned giant mammoths, see the [[http://en.wikipedia.org/wiki/Anancus European mastodon]] and its sword-like tusks, just as as example. And oh, don't forget some island-dwellers which lived in the Ice Ages and almost managed to survive until human history: the oxymoronic [[http://en.wikipedia.org/wiki/Dwarf_elephant dwarf elephants]]. Yes, they were real, and some ''sheep-sized''. Many of the larger elephant and elephant relative bones (and the smaller ones, too) which were found in the Mediterranean were identified by the ancient Greeks as the remaining bones of monsters, heroes and animals from the [[ClassicalMythology Age of Heroes.]] Some of these bones were identified as cyclopes, but no elephant skulls were. The fossils of Anceint Greece are way too fragmentary due to geological forces (earthquakes and volcanoes) to allow something as fragile as a skull to survive intact.

** Non-cetacean marine mammals: While cetaceans' natural history is now well-known, that of [[http://en.wikipedia.org/wiki/Pinnipedia Pinnipeds]] (seals, sea-lions, walruses, etc.) is still poorly-known: however, we are sure that they descended from bear-like or otter-like ancestors, and are a more recent group than whales. On the other hand, the third group of sea mammals, [[http://en.wikipedia.org/wiki/Sirenia Sirenians]] (manatees and dugongs), are as ancient as cetaceans, and descended from hippo-like ancestors. There was a fourth group of sea mammals in the Cenozoic, the little-known [[http://en.wikipedia.org/wiki/Desmostylia desmostylians]], a sort of "herbivorous seals" which looked a bit like walruses, but ate weeds like manatees and were related to manatees. Together, Desmostylians and Sirenians were/are also distant elephant relatives, while seals/walruses/otaries were Csrnivores (another example of Convergent Evolution).

** Prehistoric [[http://en.wikipedia.org/wiki/Rodentia rodents]]: The rodents' fossil record is very scant: no surprise, since they are so small, and small animals usually hardly fossilize unlike the large ones. Even though most ancient rodents were similar-looking to ours, there were also some striking guys in the past: for example, ''[[http://en.wikipedia.org/wiki/Castoroides Castoroides]]'' was a land-living beaver-relative as large as a black bear; [[http://en.wikipedia.org/wiki/Ceratogaulidae ceratogaulids]] had a couple of hornlet on their nose; while several South American capybara-like forms, such as ''[[http://en.wikipedia.org/wiki/Phoberomys Phoberomys]]'', were ''cow-sized'' and the largest rodents ever. It's not a casual connection, that modern-day capybara (South-American as well) is the biggest modern rodent: as already said, South American mammals were, and still are, ''very unfamiliar'' to a North American or European observer.

** Prehistoric "insectivores": Traditionally we have put in this group all those mammals whose anatomy is comparable to that of most Mesozoic mammals: small size, generic mouse-like look and non-specialized teeth. Actually modern insectivores (bug-eaters) are very different among each other; while the most commonly known (hedgehog, mole, shrew) ''are'' closely related, many other less-familiar insectivores are not. Their resemblance is just due to the fact they still preserve a body-plan similar to the most common one in the Mesozoic, while non-insectivoran mammals modified it becoming more recognizable. Several "insectivores" are known from the Cenozoic's fossil record, but they, being usually small, are rather uncommon like rodents. Maybe the most famous and specialized is ''[[http://en.wikipedia.org/wiki/Leptictidium Leptictidium]]'', a hopping animal similar to a miniaturized kangaroo with a shrew-like head and teeth; not related with any modern mammal, ''Leptictidium'' appears the main character in the first [[WalkingWithDinosaurs Walking With Beasts]] episode, and was also the inspiration for Scrat in the IceAge films.

** Mammals of prehistoric Australia: Australian mammalofauna hasn't changed much since the non-avian dinosaur extinction (not counting human influence of course): there have always been [[http://en.wikipedia.org/wiki/Marsupialia marsupials]] and [[http://en.wikipedia.org/wiki/Monotremata monotremes]] in the LandDownunder. Since modern Australian mammals are already so bizarre-looking, how would their predecessors have looked? Not unlike their descendants, really; but some were a bit larger. [[http://en.wikipedia.org/wiki/Procoptodon Giant kangaroos]] were 10 ft tall, with a short tail and a flat snout; while [[http://en.wikipedia.org/wiki/Diprotodon diprotodonts]] were even larger, ''rhino-sized'', but were wombat relatives, and thus vegetarian. Monotremes, too, were amazing: the [[http://en.wikipedia.org/wiki/Zaglossus giant echidna]] was as large as a sheep. Nevertheless, there was also a unique animal which has no modern relatives: the [[http://en.wikipedia.org/wiki/Thylacoleo marsupial lion]], so-called because of its body shape and sharp claws, but with ''rodent-like incisors'' instead of the classic fangs. Scientists once thought it was indeed vegetarian; now they know it was predatory, just like another unusual marsupial from South America: the aforementioned "marsupial sabretooth", ''[[http://en.wikipedia.org/wiki/Thylacosmilus Thylacosmilus]]''. Yes, there weren't only possums, once, in South America.

** [[http://en.wikipedia.org/wiki/Bat Prehistoric bats]]: Just like birds, bats are a very poorly-known group in fossil record, both for the same reason: their skeleton is way too fragile to fossilize well. Despite this, awesomely well-preserved bat remains have been discovered in the most famous fossil deposit from Early Cenozoic: [[http://en.wikipedia.org/wiki/Messel_pit Messel Pit]], in Germany. This deposit has also many, many other early mammals: among them, the aforementioned hopping bug-eater ''Leptictidium'' and the basal ungulate ''[[http://en.wikipedia.org/wiki/Propalaeotherium Propalaeotherium]]'' have been recently made famous by Walking With (even though the propalaeothere ''wasn't'' an early "horse" as said in the program). These and other mammals from this deposit (among them, several primates and the first pangolins) are so well preserved that ''even their fur and stomach contents are known''. In short, we know'em almost like they were still-living animals. The very first bats have been discovered here, and show us all the traits associated with their modern relatives: fingered wings, large ears, and even structure for echolocating are known from these finds. This has lead scientists to make an intriguing hypothesis: perhaps some sort of gliding proto-bats were already living on Earth ''before'' pterosaurs and non-avian dinosaurs disappeared? This would also mean bat-winged critters ''did'' exist at the Age of Dinosaurs, thus making the "Mesozoic bat-winged fliers" thing partially TruthInTelevision.

* Primate evolution:

** [[http://en.wikipedia.org/wiki/Primate#Evolution Prehistoric non-hominid primates]]: [[StockPhrase Man-Descended-From-Apes]]. ''[[RunningGag Man-Descended-From-Apes]]''. '''[[OverlyLongGag Man-Descended-From-Apes]]'''. '''''[[ThisIsSparta NO!!!]]''''' Man '''didn't descend''' from other modern apes (that is, chimps, gorillas, orangutans, gibbons): we humans '''and''' chimps/gorillas/orangutans/gibbons all descend from a common ancestor, often called "ape" in popular media but no more closely related to chimps as it was to ourselves. Primate evolution is of particular interest for obvious reasons, but it'd be a too long argumentation here, and would go much beyond the aim of this trope: talking about the most interesting extinct critters. Indeed, most ancient non-hominid primates ''weren't'' particularly interesting compared to their modern descendents: their look was a lot monotonous, some resembled more a lemur, other a tarsier, other a monkey, and other modern apes. However, the primitive ''[[http://en.wikipedia.org/wiki/Plesiadapis Plesiadapis]]'' is worth of note: living at the very start of the Mammal Era, it was a sort of middle way between a squirrel and a monkey, with a lemur-body but gnawing teeth like a rodent. Indeed, it has recently been discovered ''rodents'' are the closest relatives of monkeys and apes. Most prehistoric primates were small like ''Plesiadapis'', although oversized baboons and overgrown lemurs are known in fossil record. But the main exception is ''Gigantopithecus'' (see further).

** Prehistoric hominids: [[{{Gandhi}} Until he extends the circle of compassion to all living things, man will not himself find peace]]. That's why this paragraph is at the bottom of the Mammal section. Technically [[PunyHumans a subset of Primates]], hominids is a group of animals somewhat controversial to talk about, for obvious ethical reasons: so we'll talk only about those which were not clearly human, and let's end our TimeTravel with australopithecines. The hominid group itself fluctuates in definition, going from all beings closer to us that to chimps, to all things closer to us that to baboons; the most widely accepted use includes the great apes; that's is, all beings closer to us that to gibbons, and that's the one to be used here. Anyway, this family split off from gibbons about 15 million years ago, and not long after, it split off in two main branches: The Asian branch, nowadays made up of the 2 species of orangutan; and the African branch, which includes gorillas, chimps and us. Focusing in that latter branch, the branch gorillas belong to splits off from the main branch 7 million years ago, and the chimp branch splits from the branch that would lead to us shortly after. That latter branch was subject to selective pressure due to having to adapt to the harshed savannah environment: The 2 modern chimp species split from each other at roughly the same time our branch split from Lucy (see below).

*** Extinct Apes: Due to jungles not being good places for fossilization, not many species of extinct apes are known. The most notable one is ''[[http://en.wikipedia.org/wiki/Gigantopithecus Gigantopithecus]]'', a relative of the orangutan (that also exhibited gorilla-like characters). Its name means "giant ape", and with reason. It measured up to 10 feet when standing upright, ''two times'' bigger than a modern silverback gorilla: a sort of middle-way between a Real-life gorilla and KingKong. Not only that, it was discovered near the Himalayas: could it be the mythical [[BigfootSasquatchAndYeti Yeti]]? If so, this would mean it could be ''still alive'' (don't be too excited: experts say it's ''highly improbable'' that such a large animal has remained unobserved for such a long amount of time...). Sadly, the only certain thing we know about it is just a lower fossil jaw; the shape of the teeth show us it was a plant-eater, possibly specialized to a bamboo-based diet, to the point that some experts think competition with ''the giant panda'' actually drove it to extinction. Other extinct apes were once considered true human ancestors, or at least the common ancestors of apes and humans, but now are believed only distant relatives which shared some apparently human-like traits. ''[[http://en.wikipedia.org/wiki/Proconsul Proconsul]]'', ''[[http://en.wikipedia.org/wiki/Dryopithecus Dryopithecus]]'', and "Ramapithecus" (now ''[[http://en.wikipedia.org/wiki/Sivapithecus Sivapithecus]]'') are often mentioned in old textbook for this, but now their relevance is drastically fallen down.

*** ''[[http://en.wikipedia.org/wiki/Australopithecus Australopithecus]]'' and its kin: In the past, all the closest relatives of the genus ''Homo'' were put in this genus: now this is not such anymore. The beings included in this evolutionary grade are generally ape-like, being to the rest of apes what baboons are to other old-world monkeys: savannah-adapted relatives of a mostly forest-living group. As we get torwards modern times, the species of australopithecines become steadily more bipedal, adapt their feet to ground locomotion, and generally become more human-like. Recent taxonomical revisions have split off 2 other significant genera from ''Australopithecus'': the earlier ''[[http://en.wikipedia.org/wiki/Ardipithecus Ardipithecus]]'', and the robust, man sized ''[[http://en.wikipedia.org/wiki/Paranthropus Paranthropus]]''. Significant species of Australopithecus are ''A. afarensis'', best known for the specimen known as [[TheBeatles Lucy]]; and ''A. africanus'' (the first discovered, in 1925), likely an ancestor of the genus ''Homo''. But this is another story.

[[folder:Amphibians]]
* [[http://en.wikipedia.org/wiki/Lissamphibia Ancient frogs and salamanders]]: In paleontology, the word "Amphibian" has traditionally had a much broader meaning than that commonly attributed. Amphibians have been all [[http://en.wikipedia.org/wiki/Tetrapoda Tetrapods]] ("four-limbed vertebrates") excluded "reptiles" and the latter's descendants, Birds-Mammals. Today, even scientists tend to restrict the world to indicate only modern frogs and salamanders ([[AndZoidberg and Caecilians]]) and their common ancestors. If you want to use "amphibians" in its former, broader sense, you have to call modern groups "Lissamphibians". We'll use here amphibian in the old, wider meaning because it's far much handier to say this rather than "basal tetrapod" every time we refer to non-frog, non-salamander ([[AndZoidberg and non-caecilian]]) animals. Lissamphibians have a rather mysterious story. Again, like lizards, snakes, birds, rodents and bats, their skeleton is way too fragile to fossilize well, and the reconstruction of their story has many holes within it. Anyway, we're pretty sure that, [[SarcasmMode surprisingly]], both frogs and salamanders originated in the Triassic period. Yes, they too did it. And they already resembled our modern froggies/salamanders (except some details). ''[[http://en.wikipedia.org/wiki/Triadobatrachus Triadobatrachus]]'' is often mentioned as "the first frog", lived in Triassic and was very frog-like except for having shorter hindlimbs, and it wasn't probably capable to leap yet. But Jurassic frogs were already virtually identical to ours. While salamanders haven't changed much from their apparition in the Triassic, with animals like ''[[http://en.wikipedia.org/wiki/Karaurus Karaurus]]'' being already proper salamanders in every detail. Among prehistoric salamanders is also worth to be cited ''[[http://en.wikipedia.org/wiki/Andrias_scheuchzeri Andrias scheuchzeri]]'', a very close relative of modern Giant Japanese Salamander (the largest modern lissamphibian); it has been one of the very first fossil animals ever described, in year 1726, when paleontology ''still'' didn't even exist yet as scientific field; because of its size (and scientific ignorance of those years), its human-sized skeleton was interpreted as belonging to a human dead during the Biblical Deluge! (please note ''Andrias'' [[ExactlyWhatItSaysOnTheTin just means man]] in Greek). [[http://en.wikipedia.org/wiki/Gymnophiona Caecilians]] have the scantier fossil record among all lissamphibians: we don't even know when they appeared. But we're pretty sure the earliest ones still had limbs, just like snakes' ancestors.

* [[http://en.wikipedia.org/wiki/Labyrinthodontia Extinct amphibian groups]]: They are traditionally called "labyrinthodonts" or "stegocephalians", but these terms shouldn't be used today, just like "thecodonts" for basal Archosaurs or "pelycosaurs" for basal Synapsids. This because they don't indicate any natural grouping of animals, but are instead catch-all words with little scientific significance [[ScienceMarchesOn in modern phylogenetic systematics]]. Labyrinthodonts means "labyrinth teeth", because many of these animals had convoluted, labyrinth-like internal patterns inside their teeth, but this doesn't interest us too much. Their importance was much, much greater than this and lies upon another aspect. They were, simply, the links between fish and truly terrestrial vertebrates, a keystone group for mankind's evolution. And yet, just like mammal-like "reptiles" and mesozoic mammals, they have not gained much attention in pop-culture (it seems ''only apes and monkeys'' [[SmallReferencePools were our ancestors]] in pop-consciousness...). Their [[DidNotDoTheResearch apparently]] monotonous, uninteresting appearence may have contributed to this, or rather... just [[WhatMeasureIsANonHuman our mammalian pride]] generates a sort of "denial" towards our deep origins? Anyway, basal tetrapods ''weren't'' boring, uninteresting things: anything but. They were ''very'' diversified in shape, size and ecology; many of them were huge (the record to date is 30 ft of length!), but others were as small as modern lissamphibians; they were generally lizard-like, salamander-like or crocodile-like (sometimes limbless and snake- or eel-like), but others were rather strange-looking: it's enough to mention ''[[http://en.wikipedia.org/wiki/Diplocaulus Diplocaulus]]'' (one of the most depicted paleoamphibians in artworks), with its boomerang-head that ''no other vertebrate'' has ever had; lesser-known but just as peculiar, ''[[http://en.wikipedia.org/wiki/Platyhystrix Platyhystrix]]'', with its Dimetrodon-like crest. Or, still, ''[[http://en.wikipedia.org/wiki/Mastodonsaurus Mastodonsaurus]]'' (sometimes misspelled "Mastodontosaurus"), hippo-sized and with an even huger head, ''as long as a human''. Not to mention ''[[http://en.wikipedia.org/wiki/Gerrothorax Gerrothorax]]'', a neotenic form which conserved gills the-whole-life, just like modern [[http://en.wikipedia.org/wiki/Axolotl Axolotl]]. The most iconic prehistoric amphibian still remains, however, the early Permian, alligator-like ''[[http://en.wikipedia.org/wiki/Eryops Eryops]]''. The latter lived alongside the famous ''Dimetrodon'', and this may explain why is considered the archetypical "giant amphibian". "Giant amphibian" is the term usually utilized in pop-media when referring to it or to other large-size "labyrinthodonts". Actually, some of the aforementioned animals weren't really giants: ''Diplocaulus'' wasn't longer than 3 ft, for example. As a whole, non-lissamphibian amphibians first appeared in the [[http://en.wikipedia.org/wiki/Devonian Devonian]] period (but we'll talk about these earliest forms in another section), and encountered an enormous success, expecially in the Carboniferous, when immense swamps allowed them to spread widely on Earth. One of the most known Carboniferous amphibians is the tiny-limbed, eel-like ''[[http://en.wikipedia.org/wiki/Crassigyrinus Crassigyrinus]]''. But protoamphibians managed to flourish in the successive two periods as well, Permian and Triassic, conviving well with the rapidly-evolving reptiles and mammal-ancestors: ''Eryops'', ''Diplocaulus'' and the reptile-looking ''[[http://en.wikipedia.org/wiki/Cacops Cacops]]'' were all Early Permian, while the huge ''Mastodonsaurus'' was an Early Triassic guy. Most giant amphibians went mysteriously extinct at the end of the Triassic (just like many early reptilian lineages: basal archosaurs, rhynchosaurs, ''Tanystropheus'', gliding lizards, nothosaurs, placodonts and so on)... except one: the recently discovered ''[[http://en.wikipedia.org/wiki/Koolasuchus Koolasuchus]]'' from Australia, which managed to survive until the Cretaceous. This one has recently received some attention in popular media: it was portrayed both in WalkingWithDinosaurs and (unnamed) in Disney's {{Dinosaurs}}.

* [[http://en.wikipedia.org/wiki/Reptiliomorpha The closest reptile relatives]]: These "giant amphibians" deserve their own space here. The animals already mentioned belonged to two groups, the [[http://en.wikipedia.org/wiki/Lepospondyli Lepospondyls]] (''Diplocaulus'') and [[http://en.wikipedia.org/wiki/Temnospondyli Temnospondyls]] (all the others), both groups with uncertain affinities with modern frogs/salamander/caecilians (we still don't know from who the latter originated). This time we're talking about Reptiliomorphs ("reptile-shaped"); that is, tetrapods much closer to ''reptiles'' than to frog or ''Eryops''es. They had the same variety in shape and size as the other paleoamphibians, but were generally more land-living than the others, and progressively gained those traits which allow us humans to remain costantly out of water without dehydratating: waterproof skin, efficient lungs and kidneys for storing water, but above all, amniotic eggs; that is, those oval, shelled things we use to eat for dinner, and that come to our mind when hearing the word "egg". Before that, eggs were just those tiny, soft marbles modern frogs still produce today. Among quasi-reptiles, the most mentioned has long been the Early Permian ''[[http://en.wikipedia.org/wiki/Seymouria Seymouria]]'', because [[ScienceMarchesOn it was once considered the missing-link between amphibians and reptiles]]; now the most portrayed ones are the [[http://en.wikipedia.org/wiki/Embolomeri Anthracosaurs]], which were the dominant "amphibian" group in the Carboniferous, often (but not always) huge-sized. Also worth of mention are: the iguana-like ''[[http://en.wikipedia.org/wiki/Diadectes Diadectes]]'' from Early Permian, maybe one of the first herbivorous vertebrates ever appeared, along with plant-eating Synapsids like ''Edaphosaurus''; and the small, lizard-like ''[[http://en.wikipedia.org/wiki/Westlothiana Westlothiana]]'' from Early Carboniferous, which was for a short time believed the "first reptile", being even more ancient than the modern record-holder ''Hylonomus''.

* ''[[http://en.wikipedia.org/wiki/Ichthyostega Ichthyostega]]'': Along with ''Eryops'', ''Ichthyostega'' is the most famous paleoamphibian, but this time is a bit more justified: it has long had an enormous importance in paleontology indeed. Discovered in Greenland (still not the GrimUpNorth place we know today) and living in the Devonian Period, ''Ichthyostega'' has been the first four-limbed vertebrate known to science for almost a century: one of the icons of evolution thus, just like ''Archaeopteryx'' and horses. Now we know many other "missing links" between fish and tetrapods: the most astonishing is ''[[http://en.wikipedia.org/wiki/Tiktaalik Tiktaalik]]'' which was really a middle-way between a fish and an early "amphibian". ''Ichthyostega'' has often been described as a "fish with limbs", and with reason: its was still more fish-like than amphibian-like. Its 4 ft long body was streamlined like a fish; its head was smooth and very fish-like; its tail still retained a ''fin'' (albeit reduced); and its skin was, arguably, still covered with bony scales, just like fishes. But it had ''limbs'' instead of paired fins; very odd limbs to modern standards, since they had ''seven digits'' (all the other following tetrapods had only no more than five toes, a trait then inherited by reptiles-birds-mammals-humans). Expect to see it still mentioned as "the first land-living vertebrate". This is justified in works created some years ago, ex. Walking With Monsters, [[hottip: *:though the chosen animal in that show was, surprisingly, the much more obscure relative ''[[http://en.wikipedia.org/wiki/Hynerpeton Hynerpeton]]'', but that CGI animal was pratically an ''Ichthyostega'' in shape and size, so it doesn't matter.]] but not in the most recent ones: [[ScienceMarchesOn now we think it was completely aquatic, and its limbs developed to move upon the bottom of swamps, rivers and lakes, since they would be too weak to support its bulk on land]]. And is ''very'' unlikey that it could emit loud screams as shown in ''Monsters'', as well as laying frog-like eggs; [[AllAnimalsAreDogs not all amphibians are frogs]], mind you, and ''Ichthyostega'' and its kin were far more fish-like than frog-like in RealLife.

[[folder:Fish]]
"Fish" is a catch-all word containing all non-tetrapod vertebrates; that is, all backboned animals which are ''not only'' fully-aquatic, but descend from fully-aquatic ancestors as well. Ichthyosaurs, Plesiosaurs, Mosasaurs and Dolphins aren't fish, just because they ''did'' descend from land-living creatures. There are only two groups of fish which are still successful today: sharks and ray-finned fish. Not so in Prehistory, as you'll get soon.

* [[http://en.wikipedia.org/wiki/Sarcopterygii Lobe-finned fish]]: Let's start with those which [[YourMileageMayVary might]] be considered the most interesting of them all. Considering these animals as ''fishes'' may appear rather arbitrary to some paleo-fans: rather than true fish, they were a sorta middle-way between typical fish and amphibians, and many of them spent part of their life ''outside'' water, thus breaking the "fully-aquatic" criterium. They are traditionally divided in three groups: Actinists, Lungfish and Rhipidists[[hottip: *:The third term it actually in disuse: today the correct one is "basal tetrapodomorphs". But if we use the latter, the pun with "actinists" [[RuleOfCool wouldn't work anymore]]]]. [[http://en.wikipedia.org/wiki/Coelacanthiformes Actinists]], better-known as Coelacanths from the common name of their only [[strike:one]] [[ScienceMarchesOn two]] surviving species, are perhaps the most famous, and at the same time, the least amphibian-like: indeed, they ''were'' fully-aquatic, thus "true fish". They appeared in the Devonian Period, and were marine creatures that have remained virtually unmodified since 400 million years: but now they seriously risk to go extinct soon or later, [[HumansAreBastards only because]] [[WhatMeasureIsANonCute they are not so cute]] [[FindingNemo as clownfish are]]. [[http://en.wikipedia.org/wiki/Lungfish Lungfish]] were a bit closer to us: they really have [[ExactlyWhatItSaysOnTheTin lungs]] for breathing air other than classic gills, appeared in the Devonian as well and specialized themselves to muddy, marshy environment with very oxygen-poor waters: that's why their lifesaving airsacs evolved. Today are the most successful missing-links between fish and land vertebrates (although less than ten species are still alive today), and yet they are less-often-mentioned than Coelacanths. Finally, [[http://en.wikipedia.org/wiki/Tetrapodomorpha "rhipidists"]]. They are the only now-extinct group, but some of them were ''among the ancestors of mankind'', as well as all land-living vertebrates ever existed, from [[{{Digimon}} dinosaurs]] to [[{{Hamtaro}} hamsters]]. ''[[http://en.wikipedia.org/wiki/Eusthenopteron Eusthenopteron]]'' has always been the stock rhipidist, probably because the look of its tail that recalls ProngsOfPoseidon; recently, the pratically identical but far bigger ''[[http://en.wikipedia.org/wiki/Hyneria Hyneria]]'' has gained some notoriety thanks to [[WalkingWithDinosaurs Walking With Monsters]], portrayed as a {{Jaws}}-like [[CarnivoreConfusion villain]]. It's the ''only'' lobe-finned fish represented in that show, and [[SomewhereAPaleontologistIsCrying with no mention at all about the role of these animals as our-ancestors]].

* [[http://en.wikipedia.org/wiki/Actinopterygii Fish]]: Yes, just ''fish''. For the fussiest among us, "ray-finned fish". They are by far the most diversified non-tetrapods today, compounding the 90% of our modern ichthyofauna, but only a small percentage of the pre-dinosaurian one. They appeared in the Devonian, but reached their immense today-success only at the Cretaceous, when they underwent an explosive evolution. From seahorses to puffers, from swordfish to ocean-sunfish, from piranhas to deep-sea anglers; almost all the most today-familiar fishie-kinds appeared only ''after'' the Cretaceous/Tertiary Rock-Falls-[[strike:Everyone]]-Someone-Dies event. Among the few modern ray-finned fish which were already in life during the mosasaur/plesiosaur/ichthyosaur existence, there were herrings, sturgeons, gars and few, few others. There were also now-extinct guys as well in the Cretaceous: the most portrayed is the 15-20ft long, bulldog-faced ''[[http://en.wikipedia.org/wiki/Xiphactinus Xiphactinus]]'', which competed successfully with its neighbouring mosasaurs in the "large predator" role. There was an even more awesome fish in the Jurassic sea: the ''whale-sized'', filter-feeding ''[[http://en.wikipedia.org/wiki/Leedsicthys Leedsicthys]]''. Among other smaller (yet still intriguing) Mesozoic fish, we can mention: the "Saber toothed herring" ''[[http://en.wikipedia.org/wiki/Enchodus Enchodus]]''; the gar-like ''[[http://en.wikipedia.org/wiki/Aspidorhynchus Aspidorhynchus]]''; the stocky ''[[http://en.wikipedia.org/wiki/Dapedium Dapedium]]''; the herring-like ''[[http://en.wikipedia.org/wiki/Leptolepis Leptolepis]]''; and, above all, the carp-like ''[[http://en.wikipedia.org/wiki/Lepidotes Lepidotes]]''. The latter was a very successful genus, with dozens of species described: this was the meal the fishing-dinosaur ''[[StockDinosaurs Baryonyx]]'' might have preferred for lunch, as shown by remains of ''Lepidotes'' within its ribcage. On the contrary, very few ray-finned fishes are known before the Triassic. ''[[http://en.wikipedia.org/wiki/Palaeoniscus Palaeoniscus]]'' and ''[[http://en.wikipedia.org/wiki/Cheirolepis Cheirolepis]]'' are the most cited: their look was a sort of middle between a regular fish and a shark, but we'll understand later why. Some modern ray-finned fish have maintained this mixed look today: sturgeons are the most typical example.

* [[http://en.wikipedia.org/wiki/Acanthodii Acanthodian fish]]: Maybe the least-famous among all prehistoric fish; and yet, possibly among the most important at all times. This because they probably were the very first vertebrates with ''jaws''. This is not a trivial thing at all: thanks to this invention (made in the Silurian Period, just before the already-mentioned Devonian), fish as a whole started to be the most important large-sized animals in marine and inland waters, becoming active predators and outcompeting the so-called "Sea Scorpions" (see in the Invertebrates section) in this role. This role obligated them to become more mobile and faster, thus giving them one day the capability to get out the water and to become human-ancestors (this thing is called "Pre-adaptation" in evolutionary terms). "Acanthode" means "spiky", and they indeed had the same, regular-fish/shark mixed look of the aforementioned early rayfins, plus [[ExactlyWhatItSaysOnTheTin many fin-spikes]]. They hadn't a great success compared to other groups, and became extinct at the end of the Permian, another victim of the most devastating mass-extinction of all times, that wiped out 90% of all living things.

* [[http://en.wikipedia.org/wiki/Chondrichthyes Sharks]]: Not always EverythingsEvenWorseWithSharks, really. For many animal-lovers, they are among the most fascinating living things. And so is among paleo-fans. Prehistoric sharks were as diversified as modern shark are today, or rather, even more. But stop now. Things aren't always so simple as they seem. "Shark" is an ambiguous word: usually refers to ''some'' of the modern cartilaginous fish, expecially the most streamlined ones such as the Great White, but not, to say, the flattened rays and skates. But in paleontology, it usually refers to ''all'' cartilaginous fish, or at least, those belonging to the [[http://en.wikipedia.org/wiki/Elasmobranchii Elasmobranchian]] subgroup. The other main subgroup, the [[http://en.wikipedia.org/wiki/Holocephali Holocephalians]], are usually called [[ChimeraBeast Chimeras]] or, more confidentially, Rabbit-Fish. Cartilaginous fish (both sharks and chimeras) originated in the Devonian period. Chimeras have virtually not changed since then, and still retain today that mixed "shark/typical fish" appearence very common among Paleozoic fish. In the Devonian, Elasmobranchs were represented with generic forms such as ''[[http://en.wikipedia.org/wiki/Cladoselache Cladoselache]]'', already with the familiar exposed gills, but with a ''terminal mouth'', unlike most modern sharks. Actually all the fish-groups seen so far get their success for the first time in this period: Devonian is called with reason "the Fish Age" because it was the age in which fish were more diversified than every else. Sharks are often called "living fossils" because their anatomy has remained virtually unchanged since 400 million years, and yet they managed to survive the strong competiton both from the first Jurassic large sea-reptiles at first, and from the first Cretaceous ray-finned fish then. Many primitive "sharks" are very cool-looking: let's give a look at the "Ironing Board" shark ''[[http://en.wikipedia.org/wiki/Stethacanthus Stethacanthus]]'', the eel-like freshwater sharks of the ''[[http://en.wikipedia.org/wiki/Xenacanthidae Xenacanthid]]'' family, and the "Switchblade Shark" ''[[http://en.wikipedia.org/wiki/Hybodus Hybodus]]''. More modern-looking sharks first appeared in the Cretaceous, along with the first modern-looking bony fish; among them, also the very first flattened kinds (aka rays/skates). Some "sharks" (in modern sense) from that period were similar to {{Jaws}}-things. The "Ginsu Shark" ''[[http://en.wikipedia.org/wiki/Cretoxyrhina Cretoxyrhina]]'', for example, growed to the size of Spielberg's beast, and preyed upon [[BadAss marine reptiles]]. Despite this, the biggest and most famous prehistoric shark was still alive ''just 1.5 million years ago'', when hominids were already existing: ''Carcharocles'', better known as {{Megalodon}}.

** [[http://en.wikipedia.org/wiki/Carcharocles_megalodon "Megalodon"]]: There's already a [[{{Megalodon}} trope]] intentionally dedicated to it, but we'll add some paleontological information here. The "megalodont" is the largest fish known to science which could hunt large prey, but possibly not the largest shark ever; perhaps our modern [[http://en.wikipedia.org/wiki/Rhyncodon_typus Whale-Shark]] may get as large as it was. And we're unsure it really was the largest fish ever as often said: the aforementioned filter-feeder ''Leesdichthys'' might get larger. Many books have exagerrated the megalodont's size, to the point [[UpToEleven measures of 100 ft weren't rarely heard in media]]; if so, it would be as large as a blue whale... Adding material to RuleOfCool, its huge jaws have been sometimes depicted [[FridgeHorror with six or more children inside, just to show how big they are]]. And Megalodon ''is not'' its scientific name, but only the surname: the correct way to call it is either ''Carcharocles megalodon'' or ''Carcharodon megalodon''. It was probably similar in shape to an oversized Great White, but this still remains uncertain. Some scientists think it wasn't so close to the white shark; if so, its correct scientific name is ''Carcharocles megalodon''. On the other hand, other paleontologists note the strong resemblance between the two sharks' jaws, and think the megalodon was a ''very'' close relative of the Great White. If so, they'd belong to the same genus, with the Great White being ''Carcharodon carcharias'', and the Megalodont ''Carcharodon megalodon''. And its teeth were indeed ''very'' similar to a White's, simple triangles with serrated edges but without those secondary points seen in some other modern shark species. These huge teeth have given it the famous-today second term of its scientific name: Megalodon means "big tooth" indeed. It's cool, that one of the largest carnivorous dinosaurs has also a reference to the Great White, because of its similarly serrated edge of its teeth: ''Carcharodontosaurus'' just means "White-Shark lizard". Another word about teeth: shark teeth are perhaps the most abundant vertebrate fossils, just as common as the famous Ammonites; yet ironically, their owners are much, much rarer in fossil record than most other fishes. Their cartilaginous skeletons don't usually fossilize, while their hard, enamel-rich teeth do very well. Indeed, many prehistoric sharks have been described only from one tooth.

* [[http://en.wikipedia.org/wiki/Placoderm Jawed armored fish]]: Called "Placoderms", they were the most numerous and diversified fish group living in the Fish-Golden-Age (the Devonian), but no one seems to have survived in the following period, Carboniferous. Placoderms' fossil abundance in devonian rocks might also be related to their main anatomical feature: a thick [[ExactlyWhatItSaysOnTheTin body armor]] made by large, articulated plates that covered the first half of their body. Placoderms and the so-called "Ostracoderms" (see further) are the only ancient armored fish known. But wait, we've said an inaccuracy. The classic fish scales we commonly know actually ''are'' a kind of body-armor, just as the plates of placoderms: only much lighter. They have the same basic bony structure, but are very diversified among fish groups. Scales of Teleosteans (aka the subgroup including almost all modern ray-finned fish) are thin laminae visible under their skin; those of sharks and some archaic rayfins (like the [[http://en.wikipedia.org/wiki/Gar gar]]) are covered with ''enamel'' like teeth, and the shark's ones look ''just like minute teeth''. This thing is quite interesting, as we'll see later. Placoderms are called "jawed armored fish" to separate them from the apparently similar, jawless Ostracoderms. We know several groups of placoderms, but the most relevant are the [[http://en.wikipedia.org/wiki/Antiarchi Antiarchs]] and the [[http://en.wikipedia.org/wiki/Arthrodira Arthrodires]]. Antiarchs had a singular anatomical feature: their pectoral fins had a very unlikely look among fish, resembling more ''crustacean legs'' than fins; the most well-known among them is ''[[http://en.wikipedia.org/wiki/Bothriolepis Bothriolepis]]'', one of the most common fossil fish in history, with 100 different species found on every continent. Arthrodires hadn't such crab-like legs, but in return they have very peculiar teeth, [[RunningGag as we'll see later]]; ''[[http://en.wikipedia.org/wiki/Coccosteus Coccosteus]]'' it traditionally regarded as the prototypical arthrodiran.

** ''[[http://en.wikipedia.org/wiki/Dunkleosteus Dunkleosteus]]'': ''Bothriolepis'', ''Coccosteus'' and most other placoderms were small predators of invertebrates or smaller fish... but not ''Dunkleosteus''. Its name means "Dunkle's bone", but in older sources it used to be called "Dinicththys" ("fearsome fish"). But today nobody uses this name anymore. Just like the "Brontosaurus -> Apatosaurus" and "Diatryma -> Gastornis" examples, this is a pity for many long-standing paleofans: a really cool name deleted by ScienceMarchesOn and replaced by a really unexpressive one... This Devonian arthrodire was similar to ''Coccosteus'', just overgrown: 30 ft long, the size of a killer-whale, it was the largest vertebrate known so far which lived before dinosaurs. Its size is even more astounding, if you think most other Devonian armoured fishes were salmon-sized. It is one of the most famous prehistoric "leviathans" along with Megalodon, ''Liopleurodon'', ''Mosasaurus'' and ''Basilosaurus'', and was the fiercest-looking among them, thanks to its armour, and also its strange-looking teeth, [[MadnessMantra as we'll see later]]; no surprisingly, it is a staple in those not-so-common paleobooks which show also pre-dinosaurian fauna, always described as a [[PrehistoricMonster "monstrous killing machine"]]. Surprisingly, despite all this, ''Dunkleosteus'' has had ''very'' few apparitions in TV to date, much less than, to say, the not-so-impressive ''Elasmosaurus'' (another egregious case of EverythingsBetterWithDinosaurs: OK, elasmo wasn't a dino, but lived in the same age...) Perhaps the only relevant example in recent media is [[WalkingWithDinosaurs Sea Monsters]], where ''Dunkleosteus'' was portrayed with [[HellishPupils cat eyes to make it even scarier-looking]] (while most drawings show rounded, fish-like pupils), with a non-proved [[IAmAHumanitarian cannibalistic attitude]], and, to put the cherry on the cake, its hide was ''[[ColourCodedForYourConvenience blood red]]''. If you have watched that show, you'll remember those strange, blade-like teeth which cut like scissors (at last, we're talking about them); these are instead TruthInTelevision. Only... they weren't ordinary teeth; they were ''bony plates'', the same kind of those which covered its forebody. And this is not an isolated case in the fish-world; remember we talked about sharks, and their enamel-covered, teeth-like scales? Finally we'll get it. At the start of fish evolution, scales and teeth ''were the same thing''. Then, body scales were lost by land vertebrates, never to return: the so-called reptilian "scales" are a totally different thing, just horny thickening of the skin (usually) without bony core, just like our fingernails. But ''mouth scales'' remained, and how: and they allow us to chew our meals today. Our incisors, canines, premolars and molars are, really, the only remaining fish-scales we still have. Keep this in mind, every time you go to the dentist.

* [[http://en.wikipedia.org/wiki/Ostracoderm Jawless armored fish]]: This is the first fish group we encounter which had appeared about 480 million years ago, during the [[http://en.wikipedia.org/wiki/Ordovician Ordovician Period]], far before the others already seen. They become very successful in the following period, the [[http://en.wikipedia.org/wiki/Silurian Silurian]], and managed to survive well in the Devonian along with the many new, jawed lineages already mentioned above. But stop now. Again, "ostracoderm" is an old, catch-all term which shouldn't be used anymore in a cladistic sense, but since is handy for us, we'll use it. They actually are made by several lineages which arose separately during fish evolution, but shared a similar body-plan. The most relevant are three: [[http://en.wikipedia.org/wiki/Heterostraci Heterostracians]], [[http://en.wikipedia.org/wiki/Anaspida Anaspids]], and [[http://en.wikipedia.org/wiki/Osteostracian Osteostracians]]. The vaguely skate-like osteostracian ''[[http://en.wikipedia.org/wiki/Cephalaspis Cephalaspis]]'' and the tiny, long-snouted heterostracian ''[[http://en.wikipedia.org/wiki/Pteraspis Pteraspis]]'' are the two most popular kinds in books and docus. The main ostracoderm subgroups differed each other mainly by body-shape and anatomical features, but they have a rather similar ecological role, so we don't get in detail about the single kinds. Ostracoderms are called "Jawless armored fish" because... [[ExactlyWhatItSaysOnTheTin guess.]] Their mouth was a simple opening without teeth or any grinding mechanism, making their feeding-style a filter-feeding and/or a food-sucking one, unlike their jawed successors. And they were small. ''Very'' small. If we'll put a modern-day grouper among them, it'll appear to them as a Great White Shark'll appear to us. Several species were not bigger than a human hand, and some were even shorter than a human "pinkie" finger! However, their most evident feature was their armor. This armor covered ''the whole body'', and made a defense tougher than any human-created armor; it was made by the same hard bony material already seen in placoderms and modern fish (in the shape of scales). At this point is worth noting a thing: these fish ''didn't have'' a true skeleton inside yet, at least the meaning we usually intend for "skeleton". Their backbone was still a little more that a simple chord with some cartilage, but no bone: in fact, the first bony tissue even appeared among Vertebrates was ''outside'' the body, making de facto ostracoderms more similar to ''arthropods'' than to most modern backboned animals in this respect. The trend started reversing first with placoderms, which lost their posterior armour to be faster and more manouvrable (as needed by their hunting habits), but still had a cartilaginous skeleton inside. Sharks transformed their armour in a dense mesh of tooth-like bony scales, but still have no bone tissue in their internal skeleton (this means their nickname "cartilaginous fish" is ''not totally'' correct: they ''have'' bone, but only on their skin and within their teeth). Only [[http://en.wikipedia.org/wiki/Teleostomi Teleostomian fish]] (ray-finned + acanthodians + lobe-finned) make this work complete, developing bony ribs, bony vertebrae, bony girdles, and so on. Finally, the first land animals felt useless and heavy their old, scaly, fishy exoskeleton and lost it for good (even though some of their descendants re-built some kinds of body armor: turtles, crocs, ankylosaurs, glyptodonts, knights etc).

* The First Vertebrates: If you get in your hands an old textbook, you'll probably read Ostracoderms were "the first fish ever", thus "the first vertebrates": actually it's untrue. Ostracoderms, indeed, were already ''very'' evolved animals. Practically, their only archaic feature was the jawless mouth that obligated them to eat only little items: all their other traits were as sophisticated as those of the other fishes. Particularly well-preserved fossil finds show us they had complex brains and very kin senses just like modern fish. An they ''had'' a whole-fishy shape, with all the classic fins (though less-developed than those of more recent fish-groups). And they ''weren't'' the ancestors of the other fish (and thus of amphibians, mammals, mankind etc.): rather, jawless armored fish went extinct at the end of the Devonian without leaving offspring. The "most primitive vertebrate" title belongs to even more primitive animals. Sadly, the common ancestors of all vertebrates are extremely poorly-known in paleontology: this because, being so ancient, they hadn't ''any'' sort of bony-covering, and thus they hardly fossilize; despite this, more-basal-than-ostracoderm vertebrates were possibly as abundant as the latter in Ordovician and Silurian seas, and maybe were successful even beyond the Devonian, perhaps until the Triassic (as we'll se at the end). The amazing thing is, unlike armoured fish, some of the basal, unarmored vertebrate groups ''have'' survived until now. We’re talking about [[http://en.wikipedia.org/wiki/Hagfish Hagfish]] [[hottip: *:It has recently been found, however, that hagfish weren't full vertebrates, only their closest relatives: but we trait them in the traditional way because is more convenient for comparison.]] and [[http://en.wikipedia.org/wiki/Lamprey Lampreys]]. They didn't descend from ostracoderms which lost their armour, as said in old texts; they are far more archaic things, which resemble anything but a typical fish in shape (expecially the hagfish). Using the word "fish" for these animals may appear arbitrary to some paleo-fans, having no fins, no fish-shape, and in the case of hagfish, ''not even eyes'' And yet, they are ''very sophisticated'' critters nonetheless: their partially parasitic way-of-life towards the "proper fishes" needs specific adaptations, and also a larger size than ostracoderms: in fact, both hagfish and lamprey may reach 3 ft length or even more. However, their earliest ancestors were very different animals: they were ''really'' tiny creatures, even smaller than ostracoderms, and were almost surely filter-feeders just like the latter. The most known among these critters has been, until few years, the recently discovered ''[[http://en.wikipedia.org/wiki/Haikouichthys Haikouichthys]]'' that lived in the [[http://en.wikipedia.org/wiki/Cambrian Cambrian Period]]: that is, the very first age in which life on Earth began to really diversify. ''Haikouichthys'' was only ''0.5 inches'' long, and its appearence was anything like a fish: a kinda "moving leaflet" without paired fins, maybe similar to the classic [[http://en.wikipedia.org/wiki/Cephalochordata "amphioxus"]] (aka ''lancelet'') so common in biology texts. However, [[ScienceMarchesOn it has recently been proposed]] it was only a vertebrate-relative just like the "lancelet". ''Haikouichthys'' appeared in ''[[WalkingWithDinosaurs Walking With Monsters]]'', described as "the very first vertebrate, forerunner of all backboned animals in the future". That's all very well, since at that time it was considered as such. But... since it is a such non-spectacular character to show in a docu-drama like this... RuleOfCool does remedy all our problems: we see our alleged forerunner portrayed as [[SomeWhereAPaleontologistIsCrying a shoal animal swimming in the open sea, with high-developed swimming capabilities, and above all, with the same parasitic feeding behaviour of hagfishes]]. While in RealLife it was almost certainly a solitary, slow-moving bottom-dweller and an amphioxus-like filter-feeder, just like the living animal which resembles the common vertebrate ancestor more than anything else: the lamprey's larval stage, aka the "Ammocoetes". Still another group of pre-fishian vertebrates is known to science, perhaps even more enigmatic than ''Haikouichthys'': the [[http://en.wikipedia.org/wiki/Conodont Conodonts]]. We known thousands and thousands of microscopic fossil "jaws" discovered everywhere from the Cambrian to Triassic terrains, attributed to them, but since few years ago, nothing from the rest of their body. In the past, scientist didn't even know if conodont remains pertained to vertebrate ancestor at all; recently, thanks to new discoveries, it has been found they were probably elongated, lamprey/hagfish-shaped critters: perhaps the ancestors of the latter? Conodonts are a prime example of the many still unresolved, intriguing mysteries of Paleontology.

[[folder:Arthropods]]

When thinking about animal fossils, our mind usually goes on the pietrified bones of dinosaurs. But dinosaurs in paleontology are ''extremely rare finds'' compared to other vertebrate groups, such as sea-reptiles, Cenozoic mammals and fish. And yet, vertebrates as a whole are in turn only a ''very small'' part of the total. Indeed, more than 90 % animal fossils that Earth left to us are from Invertebrates Some invertebrate groups like Ammonites and Trilobites are so common they're object of collection by many paleo-fans; while it's ''unlikely'' dinosaur bones will receive this trade (despite some trade of dinosaur bones do exist as well, but it's highly debated if it's a right thing to do, since dino fossils are such a rarity).

* [[http://en.wikipedia.org/wiki/Trilobite Trilobites]]: There are things which are more important than others. Trilobites are among them. Their [[http://en.wikipedia.org/wiki/List_of_trilobites awesome]] fossil abundance, in fact, makes them "index fossils", that is, a hallmark to date a certain period of Earth's evolution. Trilobites are the hallmark of the [[http://en.wikipedia.org/wiki/Paleozoic Paleozoic Era]], the era which preceeds the famous Mesozoic one. Trilobites lived in ''all'' the Paleozoic periods from Cambrian to Permian, and ''no one'' managed to survive the worst mass-extincion ever to make its way in the Triassic. Thus, fit perfectly the role of index fossils about Paleozoic. But wait. Trilobites are ''not'' crustaceans. There is the tendency in pop-culture to identify ''all'' aquatic arthropods as this; since crustaceans make the quasi-totality of them today, this is justified. But things in Prehistory, as always, are more complicated. There ''were'' many crustaceans in and after the Paleozoic, as we'll se later; but many others armored, spineless Paleozoic critters ''weren't''. Trilobites are the most abundant of these, and lived mainly in the earliest periods of the Paleozoic: then, they'll be joined by crustaceans and chelicerates (see further), and their number began to fall. It's a bit useless to describe them: see the link in this entry to take a look. It's worth noting, however, they were among the very first animals to develope complex eyes, superficially similar to those of modern insects, made by many adjacent facets. Also note that, despite their completeness, we still don't know so much about their way-of-life; their soft tissues rarely have been preserved, making a problem for scientists. Trilobites were very diversified in look and arguably behavior, but most of them were bottom-dwellers and all were microphagous (ate very small items). In short, they were ''very'' similar in ecology to ostracoderms (the jawless armored fish). In fiction they rarely appear, just like all prehistoric invertebrates (authors typically [[TheyJustDidntCare prefer to show modern spineless animals in substitution]]); when this happens, they tend to look like those of the [[http://en.wikipedia.org/wiki/Phacopida Phacopids]] subgroup. Don't expect to se [[http://en.wikipedia.org/wiki/Agnostida Agnostids]] or [[http://en.wikipedia.org/wiki/Proetida Proetids]], despite the former were among the first trilobites ever appeared, while the latter were the only ones which managed to survive until the end of the Permian.

* [[http://en.wikipedia.org/wiki/Crustacea Crustaceans]] and [[http://en.wikipedia.org/wiki/Xiphosura Pseudo-Crustaceans]]: Since Trilobites and Sea Scorpions (see further) are now extinct, we have today only [[strike:two]] three remaining groups of marine arthropods: Crustaceans, Xiphosurans, and [[http://en.wikipedia.org/wiki/Pycnogonida Pantopods]] But since the latter haven't almost left fossil record, we'll talk only about the first two. The only xiphosuran left today is deceptively called "Horseshoe Crab" (its correct name is "Limulus"). this might people think they are just another kind of crab, thus uninteresting guys; it's anything but. They in fact are not crustaceans at all, but rather primitive relatives of spiders and scorpions; but unlike the latter, they are ''always'' remained aquatic creatures. Their appearence quite reminds that of a large-headed, sword-tailed Trilobite: this is not an incidence, because the trilobite-like body-plan is the original one among ''all'' the most basal Arthropods ever (see "Cambrian Life"). And their larval stage is ''even more'' trilobite-looking. Limuluses are, in an extent, the arthropodian equivalents of the famous Coelacanth: classicaly mentioned as a prime example of "living fossils", because their anatomy has remained virtually unchanged since the early Paleozoic. Today there are very few species all very similar each other, but luckily they seem not to share the same, [[HumansAreBastards disheartening]] fate of the coelacanth (at least for now...). One useful note about our modern horse-shoed friend: it is not dangerous to humans at all as sometimes heard, its tail being totally harmless and lacking any venom: instead, it has a mechanical meaning, allowing the animal to move upon certain sandy soils, or overturn itself when upside down. Prehistoric crustaceans are ''far'' less interesting-looking: today they are ''enormously'' diversified per-se, from krill to the Japanese Giant Crab, from woodlice to barnacles (yes, these too are crustaceans). Their extinct equivalents were about the same groups we see nowadays, and ruled the same echological niches. Just like trilobites and xiphosuran, crustaceans' fossil record is huge thanks to their often-calcified exoskeleton. While pantopods have left few fossils just because they have got an unarmored body (a general rule among invertebrates).

* [[http://en.wikipedia.org/wiki/Eurypterida "Sea Scorpions"]]: Probably among the prehistoric critters with the most striking-sounding name: "Sea Scorpions"... just weren't scorpions. Even though scientist think they might be the ancestors of the ''true'' scorpions, those with the stingy thing on the tip of their... what? Tail? [[hottip: *:No, no. The scorpion's "tail" is only the rear-end of its abdomen - nobody'll ever see an arthropod with tail, believe us. The tail is a typical vertebrate feature]]. Eurypterids, the correct name instead of "marine scorpions", lived through most Paleozoic from Ordovician until the Great Permian/Triassic Extinction, nearly as long as the Trilobites. They are often cited as "the largest arthropods of all times", but [[YourMileageMayVary this might depend to who you ask]]: modern [[http://en.wikipedia.org/wiki/Japanese_spider_crab Japanese Giant Crabs]], with their gigantic legs, might be considered even larger, or at least, wider. And most eurypterids were ''much, much smaller'' than the 10 ft long ''[[http://en.wikipedia.org/wiki/Pterygotus Pterygotus]]'' (by far the most portrayed in media, [[RuleOfCool for obvious reasons]]). Anyway, it seems the largest sea scorpions have been the heaviest marine arthropods nonetheless. And yet, if they were alive today, most eurypterids wouldn't really be scary-looking things. They'd look just like slender, paddle-legged, odd-looking lobsters: think a common grouper could gulp most of them with ease; and even ''Pterygotus'' could have even been appreciated as a delicacy by [[ITasteDelicious human gourmets]]. But at the times of their primeness (Ordovician and Silurian Periods) they were the largest predators in the seas (excluding giant cephalopods), while fish (still represented only by ostracoderms and few others) were still ''very'' small things. And they were [[DidNotDoTheResearch Scorpions]]. [[BigCreepyCrawlies Giant Scorpions]]. That's done. Here are the [[DesignatedVillain perfect]] guys for the BigBad role: those cruel, monstrous things which had nothing better in their life than persecute our poor little (literally little) ancestors... But wait! Wait! Let's not forget a thing: [[CarnivoreConfusion Predators Are Not Mean]], they are necessary to ol'Mother Nature's balance of life in our modern world. And so were they in the prehistoric one as well. Not only that: we might even have to ''thank'' sea scorpions for having existed! Preying upon our ancestors, it's possible they have unwillingly ''helped'' them to evolve their best traits we humans still retain, such as complex brains and fastness; going even further, one could say they made fish to get out of the water and become those four-limbed, land-loving animals from which we humans have originated. [[SurrealHumor Thank you Scorpion]]!

* [[http://en.wikipedia.org/wiki/Scorpiones True Scorpions]], [[http://en.wikipedia.org/wiki/Spider Spiders]] and [[http://en.wikipedia.org/wiki/Myriapoda Milli/Centipedes]]: The very first animals which made their first steps onto dryland weren't vertebrates, but Arthropods. It's easy to understand why. At the Silurian, vertebrates still were all fish-like and their fins weren't articulated structures which could make a leverage to substain the body constrasting the force of gravity; while Arthropods have had articulated legs since the Cambrian, 100 million years before. Thus, they were in clear advantage. The very first land arthropods weren't insects though; the latter have been a more recent appearence within Evolution. The first colonizer were the "Myriapods" (millipedes, centipedes and their extinct kin) and the [[http://en.wikipedia.org/wiki/Chelicerata "Chelicerates"]]. The latter include, other than Spiders and Scorpions, the aforementioned "Horseshoe-crabs" and "Sea-Scorpions" which remained aquatic animals. We are not sure how arthropods managed to reach the land, but we know for sure that myriapods and "true" scorpions were already present in the Silurian, while the first known spiders appeared much later, only in the Carboniferous (contemporary to the very first reptiles). All these invertebrates were astonishingly similar to their today-descendants, to the point that the latter may be counted as real "living fossils". Most prehistoric land-living arthropods remained as small as they still are today, but some grew larger: expecially in the Carboniferous, and we'll discover why just in that period. Generally, Paleozoic land arthropods tend to be represented in a very generic way in fiction or documentaries, typically lived-interpreted by actual animals. For example, the series ''[[WalkingWithDinosaurs Walking With Monsters]]'' portrayed a land-scorpion in the Devonian (perhaps ''[[http://en.wikipedia.org/wiki/Palaeophonus Palaeophonus]]''), live-acted by a modern scorpion species. However, the same series has made perhaps the first example in TV of documentary-related arthropods in CGI. Other than trilobites and eurypterids, we can see the large, still semi-aquatic scorpion ''[[http://en.wikipedia.org/wiki/Brontoscorpio Brontoscorpio]]'' in the Silurian (imprecisely described as a "Sea-Scorpion", [[TaxonomicTermConfusion making to believe]] it was a ''Pterygotus'' relative...); in Carboniferous settings, the large, fully-terrestrial scorpion ''[[http://en.wikipedia.org/wiki/Pulmonoscorpius Pulmonoscorpius]]'' appears (unnamed), as well as the giant spider "Megarachne" - considered the largest spider ever at the time, but its fossil has later revealed actually to be an [[ScienceMarchesOn eurypterid]]; thus not a spider, and not even ''land-living''. The latter has been perhaps the most awesome case of RuleOfCool within the entire Walking With series: with its creepy ''[[DarkIsEvil black venom]]'', it destroys a nest full of young protoreptiles ''apparently for mere vengeance'', and if it was not enough, it seems ''laughing sadistically upon its victims'' while the narrator saying THE ARTHROPODS ARE BACK! Not to mention those awe-inspiring "giant ants" in ''Beasts'' - these were discovered in the same Messel Pits in which the first bats have been discovered, but their behaviour as it appears in the docu is ''totally speculative'', mind you. Nonetheless, the absolute stars of the series among CGI land-arthropods were two ''really'' big Carboniferous animals: the proto-millipede ''[[http://en.wikipedia.org/wiki/Arthropleura Arthropleura]]'' and the proto-dragonfly ''[[http://en.wikipedia.org/wiki/Meganeura Meganeura]]''.

** ''[[http://en.wikipedia.org/wiki/Arthropleura Arthropleura]]'' and ''[[http://en.wikipedia.org/wiki/Meganeura Meganeura]]'': Which animal do you prefer, the largest land arthropod ever known to science, or the largest flying insect ever known to science? It almost seems intentional they have similar-sounding names; actually ''Arthropleura'' means "articulated flanks", ''Meganeura'' "large wing-veins", thus being only an incidence. Both from the Carboniferous, they represent well the tendence towards gigantism among Arthropods in this age. They were not the only overgrown land invertebrates in their world (and many other arthropods at that time were normal-sized, let's not forget it). But both made surely the UpToEleven example. And yet, in the following age, the Permian, land insects and millipedes returned as small as we were initially at their Silurian/Devonian origins, and remained such for all Mesozoic and Cenozoic, until today. Why just in the Carboniferous? The most credited theory trots out the almost-universally utilized fuel within the animal kingdom: Oxygen. Thanks to the extraordinary luxury of vegetation typical of that period, the vital gas increased its level more than every other time in Prehistory. And since size of land arthropods is severly limited by the oxygen abundance (because of their particular [[http://en.wikipedia.org/wiki/Invertebrate_trachea tracheal respiratory sistem]]), this was the ''only'' time ever in which insects and their kin managed to make the BigCreepyCrawlies trope a TruthInTelevision one. The 7 ft long ''Arthropleura'' is the most odd-looking of the two: despite being a millipede-relative, it resembled more an elongated, land-living trilobite in shape, with its body dorsally flattened and wide-framed, long antennae and short legs. It was the "cow" of its habitat, the largest herbivore of its fauna, which grazed decomposing plant material, but thanks to its size and armour, it probaby had very few enemies when fully-grown: even giant amphibians (the most powerful predators at that time) rarely attacked it, according to our best guesses. The 3 ft wingspaned ''Meganeura'', on the other hand, had a typical dragonfly-like appearence, and was arguably [[GiantFlyer an astounding flier]] and a skilled aerial predator of smaller insects, just like its modern relatives. And it too had very few enemies: giant amphibians normally couldn't get catching giant dragonflies up to the canopy where they arguably passed most the time. In few words: both are two very, ''very'' cool guys. And yet, just like all prehistoric invertebrates, ''Arthropleura'' and ''Meganeura'' haven't traditionally received much attention by writers, due in part to DidNotDoTheResearch, in part because much, much [[BigCreepyCrawlies Bigger Creepy Crawlies]] already exist in Fictionland for centuries. A curious thing is that ''Meganeura'' has traditionally received more attention than ''Arthropleura'', despite its less-awesome size and look; but now this seems no longer true, in part thanks to the influence of [[WalkingWithDinosaurs "Walking With...]] - expecially "Prehistoric Park", which made ''Arthropleura'' the main animal character in the ''Bug House'' episode. Even though the most awesome scene is seen in ''Monsters'', were an ''Arthropleura'' and an anthracosaur (reptiliomorph "amphibian") [[RuleOfCool fight each other just like a cobra and a mongoose would in RealLife]].

* [[http://en.wikipedia.org/wiki/Insecta Prehistoric Insects]]: Insects. The most abundant, diversified, biomechanically efficient, and last but not least, by far the most-studied animals by modern-fauna zoologists. Sadly, in Paleontology this is not the same. Their fossil record is ''extremely'' poor, for understandable reasons: their tiny body isn't precisely the most adapt to turn into stone, and their terrestrial habitat doesn't help either (most fossil animals discovered so far were aquatic indeed, just because water helps a lot the process of fossilization). However, if we know something more about the ancient relatives of modern insects, we have to thank pines, firs, spruces and larchs. Remember JurassicPark, and those fossilized mosquitoes in amber from which dinosaurian DNA was extracted ? The DNA extraction thing was obviously fictional, but the amber thing itself is TruthInTelevision. Insects preserved in amber are perhaps the most marvelous fossil a palaeontologist could wish in its life. Not only they are perfectly preserved in every detail, included external anatomy and ''even color'' (an almost unique example among fossils); they have ''their original tissues preserved, single cells included''. And they can provide an extraordinary clue to understand the entire ecosystem in which they lived in indirect ways. Unfortunately, most insects fossilized in amber come from the Cenozoic Era (the "mammal" age), a period in which insect were already similar to their modern relatives. But we still know little about their Mesozoic ancestors, still less about the Paleozoic ones - except for those living in the "Coal age", the Carboniferous (such as the aforementioned ''Meganeura'') because many of them did preserve well in coal. Anyway... we know some things with a good grade of certainty. The first insects appeared in the Devonian [[hottip:* :Technically these were the first Hexapods, since springtails are no longer considered proper insects by modern enthomologists: however, we follow the traditional view because it's more convenient.]], later than scorpions and millipedes: they were still wingless as modern [[http://en.wikipedia.org/wiki/Collembola springtails]] and [[http://en.wikipedia.org/wiki/Thysanura silverfish]] still are, but then the Carboniferous saw their success: the ''very first'' flying animals appeared, reaching large size up to ''Meganeura'' and starting their radiation destined to continue even today: not only dragonflies, but also cockroaches, grasshoppers and beetles appeared first in the Carboniferous. Other groups began their history in the Triassic: moths, wasps, flies and true bugs appeared at that time or a bit later. [[http://en.wikipedia.org/wiki/Insect_evolution Insect evolution]] has always been related with that of terrestrial plants, as we'll see better in the "Plants" section. It's worth noting, however, that this relationship has always been ''far more strict'' than one may think: biologists talk about a veritable Co-evolution between insects and seed-producing plants, expecially the flowering ones (Angiosperms). This partnership reached its climax in the Cretaceous, when flowering plants became the new dominant group, just because of the relationship with two new kinds of insects barely appeared: the pollinators and the social ones. The former include butterflies, bees, wasps, flies and even some beetles, while the latter include ants, bees, wasps, and termites. Both ensembles began to affect dramatically their ecosystem, conditioning indirectly the evolution of ''all'' the other terrestrial animals, dinosaurs included. Many paleontologists think if neornithan birds and placental mammals are the most today-diversified land vertebrates, they have to thank the insect-plant mutualism which has created well-suited habitats for their (initial) small size and eating-versatility. Think about those birds and bats who feed only upon nectar, anteaters and pangolins which feed upon nothing but social insects, or the infinite insectivorous/"angiospermivorous" modern animals. And think about all the plant-related products we humans utilize today. [[SoGoodWeMentionedItTwice Thank you, bug]]!
[[/folder]]

[[folder:Other Invertebrates]]

* Cephalopods:

** [[http://en.wikipedia.org/wiki/Ammonite Ammonites]]: Is there anybody who has never seen those pietrified spiraled shells at least once in its life? Ammonites are probably the most iconic fossil invertebrate remains at all, thanks to their elegant shape and their extreme abundance in Mesozoic deposits, to the point they're used as index-fossils to identify Dinosaur-age-related rocks, just like Trilobites for the pre-dinosaurian ones. But wait... ammonites are ''not'' exclusive to Mesozoic! They appeared in the middle Paleozoic, but that's right, achieved their highlights in Mesozoic with kinds which are exclusive of this era: so, it works just the same. Before the first paleontologists were born, ammonites were already well-known to people, who asked themselves what the heck they are: Mother Nature's jokes, Pietrified snakes, the "horn of Ammon" (the meaning of their our-day name), or what? The very first human which understood their real nature was LeonardoDaVinci in XVI century, but wasn't believed: we had to expect the Founder-of-Paleontology, Cuvier, after see the true fossil's nature understood at the end of the XVIII. Sometimes is heard the modern-day [[http://en.wikipedia.org/wiki/Nautilus Nautilus]] is the "modern ammonite": this is not true, as we'll see later: ammonites went ''totally extinct'' at the Cretaceous/Cenozoic extinction ever, the most famous victims (after real and alleged dinosaurs) of the most infamous (though [[DidNotDoTheResearch not the worse]]) mass-extincion ever. Indeed, ammonites are very mysterious things, despite their abundance. We know almost nothing about the shape of their soft parts, since they don't fossilize usually: it seems, though, they were intermediate between the more basal Nautilus and the our more evolved octopusquids. Octopusquids have very complex eyes, almost identical to vertebrates, while Nautilus has one of the simplest eyes one can imagine, nothing but darkrooms without lens. And ammonites? Who knows... And their tentacles? Octopusquids have eight/ten with suckers, Nautilus more but lacking suckers. And ammonites? It seems were more nautilus-like in this respect. In drawings and models, however, expect to see Ammonites [[EverythingsSquishierWithCephalopods with octopusquid eyes, octopusquid tentacles]] and, last but not least, octopusquid ink (while Nautilus hasn't ink at all in RealLife). Despite their fame, Ammonites are very rare things in TV. Don't expect to hear more than a single line about them -if at all. Even WalkingWithDinosaurs has dedicated only a brief cameo to them, in Jurassic "Cruel Seas". Indeed, for an unexplicable reason, ammonites are usually associated with Jurassic seas, despite they were just as common in Triassic and Cretaceous.... In dinosaur books, things are a bit better: ammonites here are frequent, but... don't expect to see single kinds identified, either (unless you've a technical or semi-technical work). And don't expect to see the so-called "heteromorph" ammonites, aka strange-looking species with ''uncoiled'' shells common in Cretaceous.

** [[http://en.wikipedia.org/wiki/Coleoidea Squids]] and [[http://en.wikipedia.org/wiki/Belemnite Pseudo-Squids]]: Ammonites ''were not'' the only tentacled things in the Mesozoic: Belemnites were just as abundant. They have left many remains as the former, but these aren't so iconic as ammonites are. This is easy to understand: they haven't any elegant external shell, just a sort of smooth, sharp internal cuttlebone which made people think about the most awesome things, from pietrified arrows to [[EveryoneIsSatanInHell devil's fingers]]. Despite this, we know a bit more about belemnites than to ammonites: they were close relatives to modern squid and cuttles, and they arguably ''had'' octopusquid eyes and certainly had ten tentacles - or, better, ten ''arms'': the fussy guys tell us that the correct term for tentacles is "arms" while "tentacle" should be used only for those two long, thin things with a club-like end which are exclusive to cuttles/squids but not belemnites. If ammons are a rarity in TV, what about belemns? It they appear at all, they'll be [[SmallTaxonomyPools identified as squids]]. On the other hand. if dealing with true octopusquids (more aptly called "new coleoideans"), they have a ''very scarce fossil'' record; most of them haven't any internal cuttlebone, often their only bodypart that fossilized is the "beaked mouth". And we already know how hard a soft-bodied animal fossilized. Thus, scientists are happy when founding complete remains of them. However, they lived during the whole Mesozoic Era (despite octopussies and argonauts seem a more recent thing), and GiantSquid -like forms already existed in the Cretaceous.

** [[http://en.wikipedia.org/wiki/Nautiloid "Nautiloids"]]: They have nothing to do with [[TwentyThousandLeaguesUnderTheSea Nemo's Nautilus]], still less with [[FindingNemo this Nemo]]... "nautiloid" is a catch-all term including all the most archaic cephalopods, from which ammonites and belemnites and [[IncrediblyLamePun cuttlenites and squidenites]] and octop... ahem... derived in a direct or indirect way. Indeed, nautiloids were not exclusively Paleozoic things as it's easy to think: they too were thriving in the Mesozoic like their relatives. But don't expect to see any nautiloid in media outside pre-dinosaurian Age, nor expect to see them in the Devonian, Carboniferous or Permian periods; more commonly, they are shown in the Ordovician and Silurian seas, aka in the early Paleozoic. It's not necessary to be a genius to understand why: in these periods, Nautiloids were the top-predators of the seas (along with sea-scorpions), [[RuleOfCool while since Devonian they were outcompeted by fish, followed by marine reptiles and cetaceans]]. Basal cephalopods began with long, straight shells but later these became more and more coiled, until their only still-living direct descendant, the aforementioned Nautilus (hence nautiloids, "pseudo-nautiluses"), a triumphant example of "living fossil" just as the iconic Coelacanth. Some of these shells are so well preserved that ''even their original colors'' are partially conserved (for example ''[[http://en.wikipedia.org/wiki/Orthoceras Orthoceras]]'', the kind traditionally most portrayed, which had zigzaging lines on its cone-shaped shell). Indeed, the so-called "orthocones", aka cone-shelled nautiloids, are by far the most portrayed because their strange look of [[BizarreFoods living tentacled-icecreams]]. The Walking With series has chosen the "giant orthocone" ''[[http://en.wikipedia.org/wiki/Cameroceras Cameroceras]]'' as the archetypical nautiloid, [[RuleOfCool for obvious reasons]]. But most nautiloids weren't bigger than a common cuttlefish in RealLife. To compensate, the "giant orthocone" has been represented with its correct anatomy: simple darkroom-like eyes and more than ten sucker-less tentacles (oops... arms), instead of the octopusquid eyes and sucker-filled appendixes often-seen in paleo-art.

* Other Invertebrates: There is not much to say about the portrayal of extinct non-arthropod / non-cephalopod invertebrates in media: they rarely appear even in books/documentaries, much less in Fictionland, and when they do, they are almost never named (except sometimes for the names of each group, but only in popular-science works). As an example, the original Disney's {{Fantasia}} showed several ''modern'' critters to symbolize the early evolution of invertebrates, but few or nothing among the ''really'' prehistoric ones. The WalkingWith series did the same: only modern medusae, sponges and sea-urchins appear, all live-acted. Indeed, many modern invertebrate groups have populated our seas since the Cambrian Period, but many others are extinct today.

** [[http://en.wikipedia.org/wiki/Mollusca Molluscs]] and [[http://en.wikipedia.org/wiki/Brachiopoda Pseudo-Molluscs]]: Among non-cephalopod mollusks, [[http://en.wikipedia.org/wiki/Bivalvia Bivalves]] (clams and their kin), [[http://en.wikipedia.org/wiki/Gastropoda Gastropods]] (water/land snails and slugs), [[http://en.wikipedia.org/wiki/Scaphopoda Scaphopods]] ("tusk-shells"), and [[http://en.wikipedia.org/wiki/Polyplacophora Chitons]], and [[http://en.wikipedia.org/wiki/Monoplacophora "cap-shells"]], have been found in great number in fossil record from almost all ages (despite very few cap-shells are still living today, and since have remained unchanged since the Paleozoic, they deserve the title of "Living Fossils"). Most of these molluscs were similar to ours, but the Cretaceous [[http://en.wikipedia.org/wiki/Rudist Rudists]] were odd-shaped bivalves, with one half-shell much larger than the other, resembling an amphor with a lid above. However, the most abundant invertebrate group in Paleozoic deposits are a sort of pseudo-clams, the Brachiopods, which actually weren't even molluscs at all. They are still-living today, but are only a minor portion of the invertebrate fauna of the seas, and aren't known much among laymen. Some of them like the [[http://en.wikipedia.org/wiki/Lingula Lingula]], have remained totally unchanged since 400 million years!

** [[http://en.wikipedia.org/wiki/Echinodermata Sea-urchins and their relatives]]: Echinoderms are extremely abundant in fossil record from Cambrian to Recent, because their hard internal "skeleton" fossilizes well (with one exception: [[http://en.wikipedia.org/wiki/Holothuroidea holoturoids]] or "sea-cucumbers" which are soft-bodied). Other than our familiar groups, [[http://en.wikipedia.org/wiki/Echinoidea echinoids]] aka sea-urchins, [[http://en.wikipedia.org/wiki/Asteroidea asteroids]] (the starfish, not [[RockFallsEveryoneDies that]] asteroid!) and [[http://en.wikipedia.org/wiki/Ophiuroidea ophiuroids]] (bristle-stars), we have some now-extinct groups such as the [[http://en.wikipedia.org/wiki/Cystoidea cystoids]] and the [[http://en.wikipedia.org/wiki/Blastoidea blastoids]] (please note all these musical-sounding rhymes). But those far more common in Paleozoic fossil record are a now rare but still-living group, the fern-like [[http://en.wikipedia.org/wiki/Crinoidea crinoids]] aka Sea-Lilies.

** [[http://en.wikipedia.org/wiki/Graptolite Graptolites]]: Believe it or not, sea-urchins, sea-lilies and whatnot are among ''the closest relatives of vertebrates''. But there is one now-extinct group that is even more unbelievably closer to us: Graptolites, so common in certain Paleozoic periods that are used like the more famous Trilobites as Index-Fossils. Graptolites were colonial animals more similar to the extremely more archaic cnidarians (jellies, corals etc.) in look, and their shape was awesomely diversified among species. If alive today, they'll resemble floating corals or something similar. Another group that is hard to believe to be close kin to vertebrates are the [[http://en.wikipedia.org/wiki/Homalozoa Homalozoans]]: vaguely resembling a cross between a fish, a crustacean and something else, they were once considered archaic protovertebrate, now they are believed to be closer to Echinoderms (if not echinoderms themselves). The most astonishing among them is the strongly asymmetrical ''[[http://en.wikipedia.org/wiki/Cothurnocystis Cothurnocystis]]''.

** Sessile Invertebrates: There is a general rule in Paleontology that ''no one living thing'' can escape: if you have hard portions within our body (shells, bones, armors etc.), you'll leave the memory of your importance in History of Life; it you have not these, you are probably destined to be forgotten forever. Sad, but true. This explains why so many modern relevant invertebrate groups are almost unknown in paleontology: for example, non-colonial cnidarians (medusae, sea-anemones) and several "worms" (annelids, nematodes, flatworms and so on). Who knows ''how many'' ancient important animal groups have ''actually'' existed in the Paleozoic and further, that we even know the existence... The odds do enhance however, if you are a colonial organism; if so, you probably have an external "skeleton" made of some sort of hard material (calcium carbonate, silicium, or simply horny matter like that of our hair and nails). Fortunately, many colonial groups are well-known in paleontology, and have had an unimaginable relevance not only for the evolution of life, but even for having ''building many portions of our planet''. Their skeletons, fossilized and transformed in hard rock, have accumulated in million years and became our sedimentary rocks, from sandstone to mudstone. Naturally all creatures with something hard inside or outside have contributed to this (molluscs for example have had a great role as well). Among colonial organisms we've already seen the floating Graptolites; among those still-living, the most important have been three group of "sessile invertebrates" (those fixed to the bottom of seas and lakes): [[http://en.wikipedia.org/wiki/Porifera sponges]], [[http://en.wikipedia.org/wiki/Anthozoa corals]] and the less-familiar [[http://en.wikipedia.org/wiki/Bryozoa bryozoans]].

* [[http://en.wikipedia.org/wiki/Protozoa Single-celled "animals"]]: It may seem strange to you, but ''even'' microrganisms have left fossils, and a plenty of it. Of course these fossils do not receive much attention in media, but are of extreme interest among paleontologists. Again, the only-the-tough-ones-preserve rule also counts for single-celled Protozoans: pratically the only group which has left significative fossil record is the [[http://en.wikipedia.org/wiki/Foraminifera Foraminifers]] ("forams" for their friends), only because they have a sort of minute "shell" which covers their softer innerparts. But they have been ''very'' important for scientists in several ways. First, foraminifers have largely contributed to form sedimentary rocks like corals and molluscs: despite their minute size, they were so in high-numbers in ancient seas that their impact has been notable. Then, they have aided scientists to conferm the RockFallsEveryoneDies thesis about non-avian dinosaur extinction. In rocks made ''before'' the mass-extinction forams abound, in those originated ''just after'' the extinction, they are almost missing (except few which managed to survive): a proof that the K/T extinction wasn't a slow journey to death, but a rapid cataclysm (geologically rapid, mind you: it could be last 100.000 years, which is ''nothing'' in geology!). Third, they are inherently cool: some of them were not even ''microrganisms'', would well visible to a naked eye, and reached even 6 cm of width: the latter are called [[http://en.wikipedia.org/wiki/Nummulite Nummulites]] (from "nummus", "coin" in Latin). They were indeed small, round calcareous disks, and being exclusive to the Cenozoic, they are considered the best index-fossils for the Mammal-Age. Nummulites are expecially abundant in Egypt (still underwater at the time), to the point that... [[PyramidPower egyptian pyramids]] are made by the so-called "nummulite limestone", derived from fossilized nummulite shells melted together.

* [[http://en.wikipedia.org/wiki/Cambrian_Explosion Cambrian Fauna]]: Cambrian. The first Paleozoic Period, in which the famous "Cambrian Explosion" of life happened. The less-known thing is, we humans are ''unbelievably lucky'' if we know that remote event. At that time, animals just were starting to achieve hard parts in their body, and we already know that, usually, soft-bodied organisms do not preserve at all. The astounding luck is, one of the greatest exceptions of this ruthless rule are ''just some deposits from the Cambrian Period.'' : it almost seem Ol'Mother Nature [[BecauseDestinySaysSo has done this deliberately for ourselves...]]. The most famous and historically relevant is the [[http://en.wikipedia.org/wiki/Burgess_Shale Burgess Shale]] in British Columbia, but still others are also known (for example in China). For obvious reason, our curiosity now reaches the top: which were the first animals (not counting protozoans) that thrived in our oceans? Well, the answer is not simple: we can divide them in two ensembles. One is made from those groups either still alive today or extinct several ages after the Cambrian: among the former, most non-arthropod / non-cephalopod invertebrate groups already seen; among the latter, the Trilobites. We'll talk here about the second ensemble: many Cambrian invertebrates were indeed ''exclusive of the Cambrian'' and didn't survive long enough, not even to reach the following period, Ordovician (in which the most famous Paleozoic critters, sea-scorpions, nautiloids, armored fish etc. appeared). Thus, is easy to imagine many of them were ''really'' [[OurMonstersAreWeird bizarre-looking]] to our limited point of view. We still know very very few things about their lifestyle, but their appearence is extraordinarily well-known, because these Cambrian deposits ''have preserved soft-bodies''; not only that, they have preserved them very well! It would be too long to mention [[http://en.wikipedia.org/wiki/Burgess_Shale_type_fauna all the members]] of the Cambrian Fauna: see [[http://www.google.it/imgres?imgurl=http://www.trilobites.info/burgess_community_sm.jpg&imgrefurl=http://www.trilobites.info/triloclass.htm&usg=__s0Eofooa0oLw4onLe4Slh3sbJ6g=&h=479&w=720&sz=125&hl=it&start=10&zoom=1&um=1&itbs=1&tbnid=3LpTQO2S2iy5RM:&tbnh=93&tbnw=140&prev=/images%3Fq%3Dcambrian%2Bfauna%26um%3D1%26hl%3Dit%26rls%3Dcom.microsoft:en-US%26rlz%3D1I7ADBF_it%26tbs%3Disch:1&ei=lyRVTZfKAcTrOYLpxYAF the image here]] for having an idea. It's immediately recognizable the bizarre shrimp-like animal in the center, by far the biggest creature in this fauna, and arguably the top predator. It is called ''[[http://en.wikipedia.org/wiki/Anomalocaris Anomalocaris]]'' (meaning "[[ExactlyWhatItSaysOnTheTin bizarre shrimp]]" indeed), and was a distant relative of arthropods with no articulated legs but with the same composed eyes of the Trilobites. Of course it is the most portrayed Cambrian animal in documentaries and illustrations, classicaly mentioned as "[[PrehistoricMonster the first prehistoric monster ever appeared on Earth]]"; actually, if alive today, the "terrible" anomalocarid would appear as a really [[{{Narm}} narmy thing]], a sort of 3 ft long, shell-less, pincer-less lobster, nothing dangerous for a tough-boned, tough-muscled, tough-skinned mammal we are in comparison. Actually, anomalocarids were highly specialized predators, with a mouth build for prey around 1/12 to 1/6 of their own size. But at its time, all the other organism were ''very small'': The other creatures you see in the linked image are not longer than your hand, all possible prey for anomalocarids - except those which were so small that a full grown ''Anomalocaris canadensis'' (the largest know species) whould have ignored them. Creatures like ''Hallucigenia'' and ''Pikaia'' were hunted by smaller predators, such as ''Opabinia'' and ''Anomalocaris saron''. The later was the species shown in ''WalkingWithMonsters'', though ridiculously oversized (6 ft.!?) and prone to attack it's own kind, despite the fact that neither its mouth nor grasps could injur an equally sized specimen in the way it was depicted, let alone possibly eating it. Apart from Anomalocaris, we can mention at least other three invertebrates which are stock in drawings: ''[[http://en.wikipedia.org/wiki/Hallucigenia Hallucigenia]]'', ''[[http://en.wikipedia.org/wiki/Opabinia Opabinia]]'', and ''[[http://en.wikipedia.org/wiki/Pikaia Pikaia]]''. The first has a so strange look that its name means "hallucination-generator": it was a sort of "worm" with long paired spikes for uncertain purpose, and long softed paired legs: the reconstruction of ''Hallucigenia'' has had an astounding ScienceMarchesOn tangle for many years, and it still remains one of the most enigmatic Cambrian animal: nobody knowns exactly in which phylum it has to be placed. ''Opabinia'' was related with ''Anomalocaris'', but had an even weirder look: maybe no other fossil animal resembles a fiction-related extraterrestrial thing more than ''Opabinia''. It had ''five eyes'' put in circular fashion on its head, and a pincer-like grasp at the end of a long, flexible proboscis, often mistaken for the creatures mouth which was actually located behind the proboscis. But the most important find is the third guy, ''Pikaia'': despite its rather insignificant appearence, it is the most well-known among ''vertebrate ancestor'', a sort of prehistoric relative of our [[http://en.wikipedia.org/wiki/Lancelet Lancelet]] (the closest vertebrate relative still-living today). This relevance has made ''Pikaia'' one of the unofficial symbols of Evolution, just like the ur-amphibian ''Ichthyostega'', the ur-bird ''Archaeopteryx'' and the ur-horse ''Eohippus''. But wait....have you see these critters in TV at least once? A hard thing, even if you watched [[WalkingWithDinosaurs Walking With Monsters]]. In this RuleOfCool-filled show, the ''only real'' Cambrian invertebrate to appear is....Guess what? Well, the superpredator ''Anomalocaris'' of course! The other two invertebrate guys shown up are... [[TheyJustDidntCare a modern jellyfish]] and an [[AnachronismStew anachronistical phacopid trilobite]] (remember that phacopids first evolved in the Ordovician, while Cambrian trilobites were very different-looking to the classic image we have when thinking about these animals). The absence of such awesome animals like ''Opabinia'' and ''Hallucigenia'' makes another egregious example of a missed opportunity, like the missing of the giant bird ''Argentavis''. Talking about ''Pikaia'', this time its missing is no problem for us: the aforementioned proto-vertebrate ''Haikouichthys'' did perform its role. Still another thing: if you watch the list of creatures from the Burgess Shale, you'll note almost all animals (the main exception being ''Anomalocaris'') have uncommonly short scientific names, most of them ending in '''-a'''. A rather amusing thing to read, and - let's face it - a ''true'' oasis of happiness among so many other unutterable, absurdely-difficult names.
[[/folder]]

[[folder:Plants]]
When thinking about fossils, we automatically think about ''animals''. But also plants have left many remains, some of them just as spectacular than the animal ones (think about the [[http://en.wikipedia.org/wiki/Petrified_wood Petrified Woods]], the most famous being that in Arizona), other less-striking but even more significative, such as prints of leafs (very common in some deposits) and even the fossilized ''pollen'' which has allowed us to understand not only the composition of ancient floras, but even the climate they lived in. And, naturally, the aforementioned [[JurassicPark amber]] which has often caught insects inside, of course.

* [[http://en.wikipedia.org/wiki/Magnoliophyta Flowering plants]]: Dinosaur-Age-related vegetation wasn't so different to ours as commonly believed. Right, non-flowering plants were dominant at the time, but still today there are ''great'' extensions of dryland dominated by conifers - the siberian Taiga, not the Amazon, is the largest forest in our days, mind you. But not only because of that. If we have the chance to really WalkingWithDinosaurs in the Cretaceous, we'll encounter many familiar critters. Most main groups of Angiosperms aka Flowering plants had already evolved: it has recently found that ''even grass'' populated the landscapes in which Triceratopses used to roam - though this doesn't justify at all the still-not-present ''grasslands'' so-common in Mesozoic {{Prehistoria}}. Most Cretaceous flowering plants were still trees then; most herbs have evolved later, despite they seem simpler-built. Some of the Cretaceous flowering trees have virtually unchanged since; the [[http://en.wikipedia.org/wiki/Magnolia Magnolia tree]] it the prototypical example. Another plant often cited to be already living alongside dinosaurs is the [[http://en.wikipedia.org/wiki/Nymphaeaceae Water Lily]]. But most trees we see in today-temperate settings, from oaks to apple-trees, from figs to vines were starting to evolve (though they became really widespread only after the mass-extinction). While grasslands ''only'' appeared in the Middle of the Mammal Age. The spread of [[http://en.wikipedia.org/wiki/Poaceae grass]] is probably related with the global cooling/drying of Earth at the time, since grass is particularly well-adapted to cold, dry environment. Its success has been ''awesomely'' important for many of the today-most popular animals to evolve: if there had never been grass, elephants, lions and whatnot, simply, would not be here now. The evolution of large grazing herds of grass-eaters and their following predators would be not possible without this kind of vegetation, which to our limited knowledge, seems often the simplest, humblest thing one could imagine... We humans ourselves have to be grateful to grass for existing: remember that mankind evolution deveoloped ''just'' thanks to the existence of grassy savannahs in Africa, while our closest relatives, chimps and gorillas, still are non-human "great apes" ''just'' for having been remained forest critters. Not to mention the matchless relevance grasses have in a more direct way for us: cereals, forage, hay, straw, bamboo, bread, pizza, hay fever... two-thirds of mankind food is still made of few kinds of cultivated grasses. [[RuleOfThree Thank you grass]]!

* [[http://en.wikipedia.org/wiki/Ginkgo Ginkgo]] and [[http://en.wikipedia.org/wiki/Ginkgophyta its ancestors]]: When hearing the StockPhrase "Living Fossil", our mind goes automatically to moving guys: the Coelacanth, the Tuatara, the Horseshoe Crab... It's easy to forget that living fossils exist even in the a-bit-disregarded plant word. The ''Ginkgo biloba'' is the most-often cited example, and with reason: it's the ''only'' species of its whole group to have survived until today: it's hard to believe its ancient kin was one of the dominant group of landplant during the whole Mesozoic era. But wait... isn't ginkgo a normal-looking flowering plant? Indeed it looks like one of these... but hey, Not Broadleaf Plants are Angiosperms, as we'll see soon. Once, Ginkgo and its ancestors were put together with pines, firs and sequoias in the catch-all group called Gymnosperms (aka all non-flowering seedplants). But ScienceMarchesOn, and if you'll still use this term, expect somebody deleting your sentence.

* [[http://en.wikipedia.org/wiki/Pinophyta Ancient conifers]]: Really? Pines, firs and spruces lived alongside Jurassic Brontosaurs and Camptosaurs? And were they ''even'' their ''main food''? About the latter we're not sure; but about the former, yes, they did. At least, pine and fir ancestors, still non-adapted to cold climates. {{Prehistoria}} is ''always'' a warm place to pass some vacation, and pine-looking trees seem a bit out-of-place there for us folks... but [[RealLife Real Life Is Always Different]] [[SomewhereAPaleontologistIsCrying When Talking About Paleontology]]. But wait, we've not finished. Since in common thought conifer = [[http://en.wikipedia.org/wiki/Pinaceae pine/fir]], some paleoartists tend to ''litterally'' feed brontosaurs and camptosaurs with modern conifers; expect thus to see ''Camarasaurus'' with a mouthful of spruce-needles, or ''Albertosaurus'' knocking down some poor pinetrees during its hunt-rush for a tasty hypacrosaur. This may be [[TruthInTelevision Truth In Art]], right, but the most widespread conifer in Mesozoic pertained, rather, to other conifer kinds, many of them still-living today: [[http://en.wikipedia.org/wiki/Taxaceae yews]], [[http://en.wikipedia.org/wiki/Cephalotaxaceae plum-yews]], [[http://en.wikipedia.org/wiki/Podocarpaceae yellow-woods]], [[http://en.wikipedia.org/wiki/Araucariaceae monkey-puzzles]], and, the more striking of all, [[http://en.wikipedia.org/wiki/Sequoioideae Sequoia trees]]. If you think brachiosaurs and titanosaurs were the real giants of their world, think again: a fully-grown ''Giraffatitan'', next to an ancient redwood, would be as tall as a beer can would be next to a fully-grown man.

* [[http://en.wikipedia.org/wiki/Cycadophyta Cycads]], [[http://en.wikipedia.org/wiki/Bennettitales pseudo-cycads]] and [[http://en.wikipedia.org/wiki/Pteridospermatophyta Seed-ferns]]: These are the plants we usually associate with the idea of Prehistory (along with true ferns and lycopods, see later). They were very palm-looking, and the still-living Cycads are often confused with the latter in RealLife: however, true palms started to appear only at the end of the Cretaceous, thus ''Diplodocus'' whip-tail would never become twisted on palm-branches. On the other hand, cycads were perhaps the most abundant seed-producing plant in the Mesozoic, along with their close (and often confused with them) relatives, the Cycadeoids or Bennettitals. However, an ever more ancient group of seed plants was still more archaic-looking. These are called Pteridosperms, aka "seed ferns": they resembled ferns in shape, only they [[ExactlyWhatItSaysOnTheTin produced seeds for spreading their kind]] unlike the latter. One seed fern, the Triassic ''[[http://en.wikipedia.org/wiki/Glossopteris Glossopteris]]'', has ben often mentioned in textbooks because it has been an historical proof for the Pangea theory. Remains of it have been discovered in Permian rocks both in Africa and in South America, India, Australia and even Antarctica: only the supercontinent thesis could explain why ''Glossopteris'' took roots in all these landmasses without swimming. Another famous Permian critter, the near-reptile ''Mesosaurus'', has been the subject of the same matter, since it too was discovered in all these continents (easier to understand if we think it was a small freshwater swimmer, thus too weak to navigate in open oceans). Both seed ferns and pseudo-cycads went extinct before the Cenozoic, while cycads have managed to reach our day and embellish our cities.

* [[http://en.wikipedia.org/wiki/Pteridophyta Horsetails and True Ferns]]: These are the today-most common archaic-looking plants. Watch one of them and your mind could travel back in time down to the ''Edaphosaurus'' days and even further. You'll note at this point that most archaic plants are either fern-looking, or palm-looking. This is not mere case: this "bodyplan" is the most ancient among terrestrial plants, and ''all'' the others - from the pine-like to grass-like - are simple evolutions of the latter. These spore-reproducing critters were already thriving in the Carboniferus, the Golden Age of Plants, but they have never been dominant compared to other groups: they have, rather, played the undergrowth role, and still play this today: but today they suffer the concurrence of modern herb-shaped floweringplants. This doens't mean, however, that ferns and horsetails have always been ''small things'': take a look to the aptly named [[http://en.wikipedia.org/wiki/Tree_fern tree ferns]], arguably one of the favourite food of large veggiesaurs, and still widespread in the original vegetation of New Zealand and part of Australia - it seems the LandDownUnder and its little sister ''really'' are an endless source of living fossils: not only the platypus or the tuatara. Even [[http://en.wikipedia.org/wiki/Equisetopsida equisetuses]] (the horsetails) have had some 30 ft tall members in their family, and some overgrown guys are still-living today: [[http://en.wikipedia.org/wiki/Equisetum_giganteum this]], for example.

* [[http://en.wikipedia.org/wiki/Lycopodiophyta Carboniferous vegetation]]: However, the most striking-looking among prehistoric plants are maybe those which dominated the Carboniferous world. 100 ft tall or more, these plants, if alive today, would resemble odd-looking trees, but were actually archaic spore-reproducing critters. But wait, they ''were not ferns'', nor were they even close fern relatives. They were even more primitive plants: the Giant Lycopods. Lycopods are still-living today, but now they are nothing but tiny herb-like greens; in the Coal-Age, though, lycopods thrived in the widespread swamps with several species very different-looking among each other. ''[[http://en.wikipedia.org/wiki/Lepidodendron Lepidodendron]]'' and ''[[http://en.wikipedia.org/wiki/Sigillaria Sigillaria]]'' are the iconic members of the group. Dinosaur-related vegetation was not such a strange-looking world, after all: while yes, Carboniferus was ''really'' a different world than ours. Imagine a wet landscape full of scaly-trunked "trees" with no more than one or two big branches on which ''Meganeura'' dragonflies used to perch like birds; a world in which every storm was enough to make those tough-looking plants to fall down with extreme ease, creating a dense undergrowth in which man-sized yet inoffensive ''Arthropleura''s crawled in the undergrowth eating the abundant dead plant matter like armored cattle. [[WalkingWithDinosaurs Prehistoric Park]] has recreated in TV that weird and wonderful world to our pleasure - and the other sequel ''Monsters'' as well, but the ''Prehistoric Park'' one is far more fascinating and also more [[RealLife realistic]]. Sadly, this world has disappeared in the Permian, when Earth became to be [[DarkerAndEdgier cooler and drier]], but has left to us one legacy: tons and tons of fossil coal we burn today. No other age has gifted to us so much coal, just because no other age has had a similar lush of green. But there is another reason: since giant lycopods were not only fragile things but also grew much faster than our seed-trees, they produced an enormous quantity of decaying plant matter during the about 50 million years of the Carboniferous. In short, if we managed to begin the Industrial Revolution, we have to thank Carboniferous vegetation. [[MadnessMantra Thank you!]]

* The most primitive plants / pseudo-plants: Carboniferous forests were not the very first ones in Earth's history: some tree-like plants had already existed in the preceeding period, the Devonian, and most were already shaped like their descendants (lycopods, tree-ferns etc.), for example ''[[http://en.wikipedia.org/wiki/Archaeopteris Archaeopteris]]'' (''not [[StockDinosaurs Archaeopteryx]]''!!!). But the deepest origin of land vegetations go even before that. in the Silurian Period, when fish started to get their jaws, and scorpions get their first airbreath, the very first aquatic plants began to colonize dryland: ''[[http://en.wikipedia.org/wiki/Cooksonia Cooksonia]]'' is the most known. They were small, fragile-looking greens still partially submerged in water, but they did already have the same basic structure of Jurassic redwood trees or modern beeches: they had internal fiber which made their body more resistent, with erect "branches"; a thin covering of cere which prevented their dry-exposed parts to dry under the sun: and they were the first [[http://en.wikipedia.org/wiki/Vascular_plant vascular plants]], that is, plants with inner conducts in which lymph flows, making their metabolism faster and more efficient. Sadly, we still know very few things about plant groups even more primitive than these (many of them ''are not even plant'' in modern taxonomy): their non-vascular body was usually soft and didn't fossilize well - yes, not even plants manage to escape to the fatal rule of only-the-tough-ones-preserve. Thus, natural history of [[http://en.wikipedia.org/wiki/Bryophyta mosses]], [[http://en.wikipedia.org/wiki/Marchantiophyta liverworts]] and [[http://en.wikipedia.org/wiki/Anthocerotophyta hornworts]] still remains an enigma, as well as that of [[http://en.wikipedia.org/wiki/Chlorophyta Green algae]] and several other kinds of organisms collectively called "Algae" in [[ScienceMarchesOn traditional biology]] that are not classified as true plants since many years. Not even [[http://en.wikipedia.org/wiki/Fungus fungi]] and [[http://en.wikipedia.org/wiki/Lichen lichens]] escaped this fate: they are virtually unknown in fossil record, but we know at least they were already present alongside the first terrestrial plant in the Devonian Period. It's the logic which tell us fungi were already there at the time: they have always played a crucial role in land ecosystems as the main decomposing organisms. Thus it's easy to think if there weren't fungi at the Devonian, dead plant matter from that age would have been accumulated in huge quantities without decomposing, literally stuffing dry lands with tons and tons of trunks, leaves and so on: maybe...some of the latter will be still-present today!

* Pre-Cambrian life: It is sometimes said that multicellular organisms appeared at the "Cambrian Explosion": actually, multicellular ''animals'' appeared then, but this doesn't mean all Pre-Cambrian forms of life were one-celled like modern "protozoans" and bacterians. We have the improperly-called [[http://en.wikipedia.org/wiki/Ediacara_biota Ediacaran fauna]], which lived just before the beginning of the Paleozoic Era. Several macroscopic organisms lived then, but they are so different than even those of the Cambrian that we don't know for sure if they are plant or animal: more probably, they were neither. The distinction bewteen animals and plants is so fixed in our common sense that it's difficult to imagine a world were eterotrophic and autotrophic beings were still not distinguished each other. The fate of the Ediacar critters at the end of the Archeozoic (aka Pre-Cambrian) Era is just as mysterious as that of many Cambrian creatures: they really disappeared, or were the common ancestor of all Paleozoic --> Mesozoic --> Cenozoic --> Neozoic forms of life, ''ourselves'' included? It'll remain for long one of the greatest mystery in Paleontology. However, many unicellular creatures have left their track in Archeozoic rocks: obviously they are micro-fossils, thus not visible to a naked eye, but they are of immense importance, because they are the most ancient forms of life known to science. The most relevant are the so-called [[http://en.wikipedia.org/wiki/Blue_algae blue-green algae]] (actually a kind of bacterians), which since 2.700 million years ago have created (and still do create today) the so-called [[http://en.wikipedia.org/wiki/Stromatolite Stromatolites]], rocky concretions made from the accumulation of huge numbers of microrganisms along with inorganic matter, all cemented together. Cyanobacterians (the true name of blue-green algae) have had a keystone role for the whole life: they were the very first organisms to produce oxygen as a waste-prodoct of their photosyntesis, and widespread it in waters and the air. Before that, organisms made only fermentation (like modern yeast) and were anaerobical, they didn't consume oxygen for their vital necessities: its only after the apparition of photosyntetical beings that aerobical organism could appear and become the ancestor of the future multi-cellular organisms (remember that ''plants'' do make respiration as well, just like animals). Today, bacteria still have a keystone role in our ecosystems: they regulate the whole thing, still producing most oxygen today, recycling nutrients in the soil, making associations with other organisms (humans included) often allowing them to live, "eating" the petroleum we reverse on the sea, fermenting bread and beer, making antibiotics and so on. Yes, there aren't only disease-bearers, among bacteria: if you and me are here, we have to thank bacteria more than every other living beings! But how the first cells appeared? Talking about this issue, we completely get out the field of Paleontology: this still remains mainly speculation and phylosophy, even though biologists are making great effort to find the answer.
[[/folder]]

[[folder:Modern Reptilian groups]]

Contrary to what many shows make to believe, Dinosaurs, Pterosaurs, Dimetrodonts and Sea-Reptiles ''were not'' the ancestors of any modern reptile; instead, some of them were at the origin of ''bird and mammal groups'', as already seen above. However, there were ''true'' relatives of modern reptilian species in the past as well, and they have existed since the beginning of the Age of Dinosaurs or even before that time (except snakes, which are a rather young group evolutionarily speaking). Some of these animals were rather similar to their modern-days relatives, while other were quite different (remember that ''every'' animal group does evolve during the time). In general, most media and even documentaries will go with the larger species of each group. The smaller relatives are almost never mentioned because [[RuleOfCool they are not spectacular enough]], even though they were more abundant that their gigantic versions, just like what happens to modern animals in general.

* [[http://en.wikipedia.org/wiki/Crocodylomorpha Ancient Crocodilians]]: The only still-living reptiles that it wouldn't be too wrong confounding them with dinosaurs. OK, they aren't dinos in a strict sense, but they were their closest non-avian relatives, and shared with dinosaurs ''much more'' traits it may seem at first glance. Both dinosaurs and crocs have/had alveolate teeth with a bit of heterodonty: to make things clear, their teeth were more similar in their structure to the ''mammalian'' ones than, to say, those of lizards. Both dinos and crocs show/showed complex parental care, again ''just'' like mammals and unlike lizards/turtles. And both dinos and crocs did descend from ''bipedal'' ancestors. Quite so. The first common ancestors of both dinos and crocs, the aforementioned Triassic Archosaurs, were a sorta mixup of dinosaurian and crocodilian features, and some ancient croc relatives were deceptively dinosaur-like - the most striking case is the Struthiomimus-like ''[[http://en.wikipedia.org/wiki/Effigia Effigia]]''. But at the Jurassic, their evolution diverged more, and since then, separating crocs from dinos becomes an easier task. However, don't think ancient crocs were boring things: it's anything but. Within their enduring success, they were almost as diversified as dinosaurs, and their size and body plan was ''very'' variable. Some were as small as a chameleon, others larger than ''T. rex''. Some were powerful predators of large land animals; other became fish-lovers or insect-hunters; and some were even aquatic ''filter-feeders''. As a group, they roamed all the three main Earth environments: land, oceans and freshwater - even though the latter was their favourite, because here they didn't suffer any competition, unlike dinosaur-ruled inlands and Sea Reptile-ruled seas. Some examples of ancient crocodilians are following.

** Giant freshwater crocodilians: Let's start with them, [[RuleOfCool for obvious reasons]]. Many people have already heard the names ''[[http://en.wikipedia.org/wiki/Deinosuchus Deinosuchus]]'' and ''[[http://en.wikipedia.org/wiki/Sarcosuchus Sarcosuchus]]'' in media: both were portrayed in popular documentaries, in particular the Walking With Series. But there were ''other'' "supercrocs" as well in the ancient past. ''Deinosuchus'' and ''Sarcosuchus'' make those living during the Dinosaur Age; thus, they arguably [[BadAss preyed occasionally upon giant dinosaurs]]. Few of us know, however, that two enormous crocs lived just ''few million years ago'', in full Mammal Age, when the first hominids just started their evolutive journey: the gharial-like ''[[http://en.wikipedia.org/wiki/Rhamphosuchus Rhamphosuchus]]'' from India and the cayman-like ''[[http://en.wikipedia.org/wiki/Purussaurus Purussaurus]]'' from South America. And they were the same size of the two dinosaur-eating docu-stars.

** Small terrestrial crocodilians: And now, let's discover the opposite end: the smallest crocodilomorphs ever lived were land-loving, long-legged, graceful things with a bit of dinosaur inside. Early Jurassic ''[[http://en.wikipedia.org/wiki/Protosuchus Protosuchus]]'' has been perhaps the most portrayed. Land crocodilians were not related each other however: several croc lines reached this body-plan independently. It's simple to undestand why they remained small: competition from dinosaurs was too strong in dry land, and they could survive only occuping the niche of small, fast-reproducing hunters, just like proto-mammals which shared the same niche. Some scientists hypotize that the nocturnal adaptments mammals underwent during the Mesozoic (herited by all modern mammals, even the daylight-living ones like humans) were not determined by dinosaurs' predation, but rather by the competiton of the (arguably) diurnal land-crocs. Some of the latter were even partially bipedal: for example Jurassic [[http://en.wikipedia.org/wiki/Sphenosuchia Sphenosuchians]] (the most primitive crocodilomorphs known so far), which were smaller than ''Compsognathus'' and could become their prey. Some land-crocs became larger however, expecially in Cretaceous South America and Australia, and were powerful predators in competition with theropod dinosaurs. The most extreme example known of a running croc appeared just after the mass-extinction (that wiped out many crocodilomorphs as well): the large, ''hoofed'' ''[[http://en.wikipedia.org/wiki/Pristichampsus Pristichampsus]]''. The most astonishing thing is, however, that some small-sized land crocodiles managed to survive almost until ''the start of human history'': the Australasian [[http://en.wikipedia.org/wiki/Mekosuchinae Mekosuchians]].

** [[http://en.wikipedia.org/wiki/Thalattosuchia Marine crocodilians]]: Initially, crocodiles were land animals. Then, many of them became amphibian and fresh-water living, as they still are today. But some of them went even further, trying to colonize open seas. Here, they have always had trouble, because of the strong competition with the classic Sea-Reptiles (ichthyosaurs, plesiosaurs, mosasaurs). But a group of them did manage to coexist with the latter: the mainly Jurassic Thalattosuchians (literally "sea crocodiles"). The most archaic ones were still gharial-like, the most known being ''[[http://en.wikipedia.org/wiki/Teleosaurus Teleosaurus]]''; the most evolved didn't even resemble crocs. Rather, they looked like slender ichthyosaurs, because they developed the same ''caudal fins'' of the latter, lost their armor altogether, and transformed their limbs in paddles. They were probably the only fully-marine archosaurs ever, maybe they didn't even lay eggs and gave to birth alive newborn, just like ichthyosaurs, mosasaurs and (perhaps) plesiosaurs. ''[[http://en.wikipedia.org/wiki/Metriorhynchus Metriorhynchus]]'' and the ironically-named ''[[http://en.wikipedia.org/wiki/Geosaurus Geosaurus]]'' ("''land'' lizard") are the two most-portrayed examples.

* [[http://en.wikipedia.org/wiki/Turtle Ancient turtles]]: TurtlePower is TruthInTelevision. Turtles have ''literally'' been among the longest-lived reptiles ever, since appeared 230 million years ago and are still-living today. But their origin is really mysterious. The very first turtles ever discovered, among them ''[[http://en.wikipedia.org/wiki/Proganochelys Proganochelys]]'' from Triassic, had already the classic turtle-shape, shell and toothless beak included; since then, they have not changed their body-plan at all for 250 million years. Mesozoic turtles were ''very'' similar to ours. They have had a great success, colonizing all three main habitat just like crocs: terrestrial, marine, freshwater. And just like crocs, freshwater has been the favourite one, while terrestrial species have always been a minority. Marine turtles reached gigantic sizes in the Cretaceous (the aforementioned ''[[http://en.wikipedia.org/wiki/Archelon Archelon]]'' was 20 ft long and weighed ''several tons''), and were the ''only'' group of Mesozoic sea reptiles which managed to survive the mass-extinction: modern marine turtles do descend from some ancestors already present before the cataclysm happened (though not from ''Archelon'': it went eventually extinct without leaving descendants). Fossil record of Chelonians is extremely abundant (like that of Crocodilians) since freshwater aid the fossilization, and hard-boned shells / bony armors do preserve very well. Most non-marine turtles were small, just like today: but there were two large land-living species just 1 million years before modern history: the [[http://en.wikipedia.org/wiki/Colossochelys Atlas Tortoise]] from India was very Galapagos Tortoise-like but ''as large as a small car''; the Australian [[http://en.wikipedia.org/wiki/Meiolania Horned Tortoise]] was smaller but with a cooler look: it had [[ExactlyWhatItSaysOnTheTin small bovine-like hornlets]] on its head. Extra-note: [[ScienceMarchesOn recent research]] seems to show turtles ''were not'' the most ancient still-living reptiles as traditionally said. Lizards and Tuataras were perhaps more basal, and turtles might even be Archosaur relatives: that is, closer to ''birds'' than to lizards, just like crocodiles. But this is an age-old discussion among paleontologists. [[TurtlePower Everything Is Long-Living With Turtles]], literally.

* Ancient ''true'' [[http://en.wikipedia.org/wiki/Squamata lizards]]: The reptiles we're going to talk about are the '''only''' extinct lizards. Contrary to turtles and croc, lizard's fossil record is extremely poor: their gracile skeletons do not usually fossilize. Ironically, the best-preserved lizard-rests known so far were discovered... into other creatures' ribcages. It's particularly famous the case of ''[[http://en.wikipedia.org/wiki/Bavarisaurus Bavarisaurus]]'', a small Jurassic lizard found into the first discovered ''Compsognathus'' skeleton. We don't know exactly which kind of modern lizards lived already in the Age of Dinosaurs: we're sure there were at least geckos, monitors, and proto-iguanas; while chameleons seem to be a recent evolution, after the non-avian dinosaur extinction, derived from iguana-like ancestors. Lizards occupied the same niche ruled by mammals and the apparently similar land-crocs, as small insectivores or omnivores. Many modern-days lizards are still compared with dinosaurs, or even passed off as "mini-dinosaurs", in documentaries and pop-books; ironically, just because they were used in the past as a model for the early dinosaur paintings and models. This spread the popular notion that ''all'' prehistoric reptiles were nothing but "giant lizards": a notion then adopted by films, comics and whatnot, which has given to us the {{Slurpasaur}} trope. But lizards actually pertain to a ''very different'' group of reptiles than dinosaurs and even crocodiles (both Archosaurs); this group is called the [[http://en.wikipedia.org/wiki/Lepidosauria Lepidosaurs]]. One may even hear the largest modern-day lizards ''literally'' passed off as dinosaurs in documentaries or other non-fictional works; the predestined victim is, obviously, the large-sized monitor-lizard nicknamed [[http://en.wikipedia.org/wiki/Varanus_komodoensis Komodo dragon]]. The astonishing thing is, our Indonesian "dragon" did have in the recent past a close Australian relative much, much larger than itself: ''[[http://en.wikipedia.org/wiki/Megalania Megalania]]'' was 15 ft long, ''twice its Komodan kin''; and lived ''just 1 million years ago''. It was, arguably, one of the most powerful predators of its habitat (but don't forget the contemporary "marsupial lion": though not larger than a lion, some scientists think it was the most efficient mammalian predator ever, maybe even capable to [[BadAss kill a fully-grown Megalania!]]). ''Megalania'' is by far the largest lizard that ever lived. But wait... have we forgotten something? Yeah, the Mosasaurs. It's so easy to forget this, but they ''were'' true lizards; with more than 30 ft in total length, the ultimate size-record belongs definitively to them. Along with ''Megalania'' and the Komodo dragon, Mosasaurs are the only "giant lizards" which are TruthInTelevision.

* [[http://en.wikipedia.org/wiki/Serpentes Ancient snakes]]: The great exception among still-living reptiles: snakes are a ''very'' recent thing, appeared only in the Late Cretaceous, just before the mass-extinction. Their success was obtained only since the beginning of the Mammal-age 65 million years ago, and venomous species appeared even later, 30-20 million years ago. The most ancient still-living snakes are probably boas and pythons, or at least their closest relatives: the most common kind of snakes, the Colubrids (the Garden-Snake and relatives), appeared in fully Cenozoic settings. As bird are nothing but winged dinosaurs, snakes are nothing but legless lizards. They descend from a still unknown kind of Cretaceous lizard which did elongate its body loosing the limbs at the same time. Curiously, the lizard-group closer to snakes in phylogeny is not to be searched among the small slithering ones, like [[http://en.wikipedia.org/wiki/Anguis_fragilis slow-worms]] or [[http://en.wikipedia.org/wiki/Amphisbaenia amphisbaenians]]: they were the gigantic Mosasaurs instead. The latter's reptutation as the Cretaceous "sea-serpents" seems thus [[JustifiedTrope justified]]. Prehistoric snakes are not much portrayed in books or paleo-art: this is probably due to the fact that their remains are very, very scant, ''even more'' than those of their lizardy ancestors: all that we often have are few isolated vertebrae, which don't allow to understand even how long they were. Hence, speculation and exaggerations tend to be common. ''[[http://en.wikipedia.org/wiki/Gigantophis Gigantophis]]'' (which lived just after the dinosaur extinction) is a prime example: only known for fragmentary remains, it may get described as [[RuleOfCool twice the length of an anaconda]] despite it more probably was only a bit longer than the latter, if it was. If dealing with Cretaceous species, it'll probably be a ''[[http://en.wikipedia.org/wiki/Dinilysia Dinilysia]]''.

* [[http://en.wikipedia.org/wiki/Sphenodontia Tuatara and its ancestors]]: The [[http://en.wikipedia.org/wiki/Tuatara Tuatara]] is the modern reptile more often cited for being a "living fossil", and with reason. It is the most ancient and primitive still-living Amniote (amniotes = reptiles + birds + mammals), a survivor which has miracolously managed to be alive today, while ''all'' its relatives went extinct before the end of the Mesozoic. The natural history of the Tuatara group (the Sphenodonts, once called "Rhynchocephalians") is completely distinct to lizards and so on. Sphenodonts are Lepidosaurs just like lizards, but have retained more primitive traits still present in our tuataras; they appeared in the Triassic, like ''almost all'' the main reptilian lineages. Dinosaurs (both Ornithischian and Saurischians), Pterosaurs, Ichthyosaurs, Plesiosaurs, Crocodilians, Turtles, Lizards, even Mammals: all these appeared in the Triassic Period. And tuataras as well. Like turtles, they didn't change much since then; fossils show that prehistoric tuataras were almost ''identical'' to their modern relative; and lived around the world, while they are limited only to New Zealand today. Like komodo dragons, tuataras are often cites as "living dinosaurs" in pop-books. Once the "Rhynchosaurs" (already mentioned in another section) were considered early tuatara-relatives (they are now considered closer to archosaurs): this explains why tuataras used to be called Rhynchocephalians in the past. The latter means "beaked head", and yet nobody'll ''ever'' see a tuatara with a beak! This term was actually referred to the parrot-billed rhynchosaurs, which were once considered Rhynchocephalians as well. And this explains why the term rhynchocephalian has fallen in disuse for indicating the tuatara lineage. While "sphenodont" has always been referred ''only'' to tuataras, ''never'' to rhynchosaurs: thus, scientists now use only this more correct term when referring to our spiky New Zealander.
[[/folder]]

[[folder:Birds]]
The our-days dinosaurs, and the most biomechanically efficient still-living vertebrates, capable to fly at 120 mph and to go round the world with amazing ease. In short, the worthy dinosaur descendants. Here we'll talk about those which lived after ''Archaeopteryx'' and before house sparrows. On the other hand, we'll not talk about historically extinct birds such as the Dodo or the Elephant-Bird: they have nothing to do with only-prehistoric beasts, and they'll deserve a UsefulNotes Page on their own.

* ''[[http://en.wikipedia.org/wiki/Confuciusornis Confuciusornis]]'': ''[[{{Confucius}} Confuciusornis]]'' was from the same famous Chinese Liaoning site in which the popular feathered dinosaur fossils come from. This animal had some evolved traits, for example had already lost its teeth (convergently from modern birds) and shortened its tail, but still retained an old legacy: three-clawed wings. As is easy to think from a Liaoning animal, the Confucius-bird has also preserved prints of feathers, which show two very elongated tail-feathers rather peacock-like. Another basal bird, ''[[http://en.wikipedia.org/wiki/Jeholornis Jeholornis]]'' from the same habitat, is also known as "Shenzhouraptor".

* The MirrorUniverse birds: The most successful Late Cretaceous birds were the [[http://en.wikipedia.org/wiki/Enantiorns Enantiorns]], whose name means "mirror birds". Why? Because of some skeletal features which appear specular compared to modern fliers. They were a sort of middle-ways between the aforementioned Early Cretaceous birds and modern feathered guys, and were very diversified among each other. The ZergRush birds in the WalkingWithDinosaurs episode about pterosaurs were enantiorns, as well as, arguably, those mentioned in the last episode which made the "omnipresent chorus" from the trees. The MirrorUniverse birds went extinct along with non-avian dinos only after the comet/asteroid.

* ''[[http://en.wikipedia.org/wiki/Hesperornis Hesperornis]]'' and ''[[http://en.wikipedia.org/wiki/Ichthyornis Ichthyornis]]'': The two most famous Dinosaur Age-related birds (not counting ''Archaeopteryx''), both from Late Cretaceous North America. Since hespero is [[RuleOfCool far cooler]], here we'll mention it first. ''Hesperornis'' lived in the same habitat in which Pteranodonts, Mosasaurs, Elasmosaurs and ''Archelon''s roamed: the shallow inland sea which used to cover US Midwest at that time, dividing North America in two parallel stripes of land running from Arctic down to the south. Despite its earliness, ''Hesperornis'' was already a ''very'' derived bird: 6 ft long, it was flightless, with vestigial wings, and spent most of its life in water: a sort of proto-penguin, but [[ToothyBird with teeth]]. The much smaller, far less striking ''Ichthyornis'' lived in the same habitat, and was a sorta [[ToothyBird toothed]], long-billed proto-seagull. Both these animals were full birds at that point, and if alive today, they'll be taken for components of modern avifauna.

* The [[http://en.wikipedia.org/wiki/Neornithes "new birds"]]: Neornithes (meaning new birds)or colloquially "Neorns", is the name indicating the last common ancestor of all modern birds and all its descendents. In a narrow sense, they might be considered the ''only real'' birds: if right, this would allow hesperorns, enantiorns, confuciusorns and whatnot to be unequivocally called "dinosaurs". Broadly speaking, Neornithes were the ''only'' Cretaceous birds which managed to overcome the mass-extinction and to make their way in the Cenozoic, the Mammal Age. It's worth noting that their descendants, our modern birdies, have much, much more species today than mammals: thus, one can comfortably say dinosaurs ''still'' rule the world. Some ornithologists could even say "the Mammal Era" should be renamed "Bird Era" and considered a simple extension of the "Dinosaur Era"... But we humans will always be [[WhatMeasureIsANonHuman too proud to be mammals]] to accept this alternative view. Most Cenozoic "new birds" were very similar to their descendants: some were rather generic-looking, while others were more specialized, but still not too different to modern avians. Furthermore, their fossil record is ''extremely'' scant, maybe the scantiest of all Vertebrates; thus, evolution of the single modern-bird lineages is mostly unknown even today, and their phylogenetic tree is full of question marks. But don't worry...there were also many exceptions to this rule: we're going to talk about these.

** ''[[http://en.wikipedia.org/wiki/Gastornis Gastornis]]'': Long-standing paleo-fans will remember for sure the name "Diatryma": that large, flightless, large-headed predatory bird who used to hunt the small "horse" ''Eohippus'' in so many paleo-artistic depictions. Well, now poor Diatryma seems having definitively disappeared... but luckily, it's not such: it has simply changed identity. Now we have to call it ''Gastornis'' (a far less awesome name, we've to admit, but...never mind.) Whatever name should be used, this is actually one of the most enigmatic extinct birds. It might not even be ''carnivorous'' at all: its strong beak wasn't hooked like an eagle's, and its body frame was stocky, seemingly slow-moving. Maybe it only was an omnivore who used its bill to crack nuts, cut vegetation, and sometimes, tear flesh from its prey (but it was more probable it swallowed its eohipps whole, like most modern non-raptorian birds). Anyway, it was a real giant in its forestal world, 40 million years ago: while mammals were still small, some birds grew to large size, creating a sort of BizarroUniverse in which mammals could be lower-ranking in the food pyramid.

** ''[[http://en.wikipedia.org/wiki/Phorusrhacidae Phorusrhacos]]'' and its kin: With these grassland-dwelling non-fliers, we have no doubts this time: thanks to their light weight and slender running legs, Phorusrhacids ''were'' active hunter of small mammals. Not only that, with their strongly hooked, very eagle-like bill, they did not swallow their prey whole. It has recently been discovered they had even ''one clawed finger'' protruding from each of their tiny wings [[hottip: *:This is not so strange as one may think: there are also living birds with this feature, the most notable being the ''two-fingered'' young [[http://en.wikipedia.org/wiki/Hoatzin Hoatzin]]]], for uncertain purpose. Perhaps the most amazing-looking among all prehistoric birds, they have recently nicknamed [[CarnivoreConfusion terror-birds]] in pop- documentaries (for example, [[WalkingWithDinosaurs Prehistoric Park]].) They have left a legacy in our modern world as well: the closely-related [[http://en.wikipedia.org/wiki/Seriema Seriema]] is a medium-sized South American bird whose shape and habits resemble a miniaturized "terrorbird". It's worth noting ''Gastornis''/''Diatryma'' was not related to Phorusrhachids: it has left any descendant since 40 million years. The prototypical South American ''[[http://en.wikipedia.org/wiki/Phorusrhacos Phorusrhacos]]'' (often misspelled "Phororhacos") and the recently-discovered North American ''[[http://en.wikipedia.org/wiki/Titanis Titanis]]'' are the two stock species.

** ''[[http://en.wikipedia.org/wiki/Dromornithidae Dromornis]]'' and its kin: Among the largest birds that ever lived (perhaps ''the largest''): and yet, they've not gained much consideration in popular media, unlike their American contemporary counterparts, the phorusrhachids. This may be due to ScienceMarchesOn. Once, these Australian flightless birds used to be depicted as ostrich-like, thus not-so-impressive animals. Only recently, more fossil founds showed us they were very ''Phorusrhacos''-like, with uncinate bill and large heads. ''[[http://en.wikipedia.org/wiki/Dromornis Dromornis]]'' and ''[[http://en.wikipedia.org/wiki/Genyornis Genyornis]]'' are the two most-often cited species.

** ''[[http://en.wikipedia.org/wiki/Teratornithidae Teratornis]]'' and its kin: We leave (almost) definitively the flighless bird's world and start to watch more traditional fliers. Among prehistoric flying birds, the most depicted ([[RuleOfCool and most striking]]) are the Teratorns. They were very vulture-like animals, but were actually more related to storks than to bird-of-prey: just like modern [[ScienceMarchesOn condors and North-american vultures]]. The namesake ''[[http://en.wikipedia.org/wiki/Teratornis Teratornis]]'' is one of the most abundant birds in fossil record, and has been found in huge numbers in the famous Californian tar-pits in which mammalian sabretooths, giant wolves, mastodons and ground sloths have also been found. Arguably, they went to feed on the carcasses of these mammals, and remained stuck in tar just the same.

** ''[[http://en.wikipedia.org/wiki/Argentavis Argentavis]]'': The aforementioned ''Teratornis'' had an earlier relative, which lived in South America 8 million years before: ''Argentavis'' (its name means "argentinian bird"). Why should we mention it separately? Well... simply because it deserves the GiantFlyer title more than every other prehistoric creature (beside pteranodonts and quetzalcoatls, obviously). Its wingspan was 25 ft (''as much as [[StockDinosaurs Pteranodon]]''); its weight 80 kg (as much as the two-times-wider-winged ''[[StockDinosaurs Quetzalcoatlus]]'', not to mention ''three times the weight of the Pteranodont''). Imagine a "flying ostrich" thing with [[ArabianNights huge roc-like wings]], a sharp beak and a love for carrion. With no doubt, the largest flying bird ever discovered. And yet, despite its coolness, ''Argentavis'' has yet to appear in fiction. And **heck**, it has actually had one single apparition in documentaries to date: "Paleoworld", as a ''side-note'' of Phorusrhacids! Since [[WalkingWithDinosaurs Walking With Beasts]] producers did recreate ''Argentavis'' world (the Sabretooth episode, in which "terrorbirds" did appear)... they wasted a perfectly good opportunity.

** Giant flying seabirds: ''Argentavis'' wasn't the only GiantFlyer in the Cenozoic: we have to add the [[http://en.wikipedia.org/wiki/Pelagornithidae Pelagorns]]. These were rather albatross-like or pelican-like marine birds, but they had two cool traits: their wingspan reached 20 ft (a bit less than ''Argentavis'') and their beak was ''toothed'', seemingly revealing the trope ToothyBird being a RealLife thing in the past. Sadly, this is not true: these "teeth" weren't real teeth, but their bill had an ondulating, pseudo-toothed edge, just like one modern bird, the duck-like [[http://en.wikipedia.org/wiki/Merganser Merganser]]. The only RealLife toothy-birds were those living alongside non-avian dinosaurs, such as ''Archaeopteryx'', ''Hesperornis'', and ''Ichthyornis'' (which weren't even typical "birds"). Pelagorns were the new feathered version of ''Pteranodon'', almost as large as it, and went extinct only 1 million years ago. ''[[http://en.wikipedia.org/wiki/Osteodontornis Osteodontornis]]'' is the typical member of the group.

** Giant non-flying seabirds: When ''Hesperornis'' went eventually extinct at the end of the Mesozoic, a new kind of birds took soon its niche: but this time we're talking about much, ''much'' familiar-looking creatures: penguins. ''Giant'' penguins. The largest of them, ''[[http://en.wikipedia.org/wiki/Anthropornis Anthropornis]]'', was nearly as tall as a fully-grown human and weighed 200 kg, more than a modern ostrich; but it probably was as nice-looking as modern penguins are. Giant penguins swum in the southern seas for million years, until they were outcompeted 20 million years ago by a new group of large marine animals, their mammalian equivalents: seals and sea-lions.


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** ''[[http://en.wikipedia.org/wiki/Dunkleosteus Dunkleosteus]]'': ''Bothriolepis'', ''Coccosteus'' and most other placoderms were small predators of invertebrates or smaller fish... but not ''Dunkleosteus''. Its name means "Dunkle's bone", but in older sources it used to be called "Dinicththys" ("fearsome fish"). But today nobody uses this name anymore. Just like the "Brontosaurus -> Apatosaurus" and "Diatryma -> Gastornis" examples, this is a pity for many long-standing paleofans: a really cool name deleted by ScienceMarchesOn and replaced by a really unexpressive one... This Devonian arthrodire was similar to ''Coccosteus'', just [[{{Understatement}} a bit]] overgrown: 30 ft long, the size of a killer-whale, it was the largest vertebrate known so far which lived before dinosaurs. Its size is even more astounding, if you think most other Devonian armoured fishes were salmon-sized. It is one of the most famous prehistoric "leviathans" along with Megalodon, ''Liopleurodon'', ''Mosasaurus'' and ''Basilosaurus'', and was the fiercest-looking among them, thanks to its armour, and also its strange-looking teeth, [[MadnessMantra as we'll see later]]; no surprisingly, it is a staple in those not-so-common paleobooks which show also pre-dinosaurian fauna, always described as a [[PrehistoricMonster "monstrous killing machine"]]. Surprisingly, despite all this, ''Dunkleosteus'' has had ''very'' few apparitions in TV to date, much less than, to say, the not-so-impressive ''Elasmosaurus'' (another egregious case of EverythingsBetterWithDinosaurs: OK, elasmo wasn't a dino, but lived in the same age...) Perhaps the only relevant example in recent media is [[WalkingWithDinosaurs Sea Monsters]], where ''Dunkleosteus'' was portrayed with [[HellishPupils cat eyes to make it even scarier-looking]] (while most drawings show rounded, fish-like pupils), with a non-proved [[IAmAHumanitarian cannibalistic attitude]], and, to put the cherry on the cake, its hide was ''[[ColourCodedForYourConvenience blood red]]''. If you have watched that show, you'll remember those strange, blade-like teeth which cut like scissors (at last, we're talking about them); these are instead TruthInTelevision. Only... they weren't ordinary teeth; they were ''bony plates'', the same kind of those which covered its forebody. And this is not an isolated case in the fish-world; remember we talked about sharks, and their enamel-covered, teeth-like scales? Finally we'll get it. At the start of fish evolution, scales and teeth ''were the same thing''. Then, body scales were lost by land vertebrates, never to return: the so-called reptilian "scales" are a totally different thing, just horny thickening of the skin (usually) without bony core, just like our fingernails. But ''mouth scales'' remained, and how: and they allow us to chew our meals today. Our incisors, canines, premolars and molars are, really, the only remaining fish-scales we still have. Keep this in mind, every time you go to the dentist.

* [[http://en.wikipedia.org/wiki/Trilobite Trilobites]]: There are things which are more important than others. Trilobites are among them. Their [[http://en.wikipedia.org/wiki/List_of_trilobites awesome]] fossil abundance, in fact, makes them "index fossils", that is, a hallmark to date a certain period of Earth's evolution. Trilobites are the hallmark of the [[http://en.wikipedia.org/wiki/Paleozoic Paleozoic Era]], the era which preceeds the famous Mesozoic one. Trilobites lived in ''all'' the Paleozoic periods from Cambrian to Permian, and ''no one'' managed to survive the worst mass-extincion ever to make its way in the Triassic. Thus, fit perfectly the role of index fossils about Paleozoic. But wait. Trilobites are ''not'' crustaceans. There is the tendency in pop-culture to identify ''all'' aquatic arthropods as this; since crustaceans make the quasi-totality of them today, this is justified. But things in Prehistory, as always, are [[{{Understatement}} a bit]] more complicated. There ''were'' many crustaceans in and after the Paleozoic, as we'll se later; but many others armored, spineless Paleozoic critters ''weren't''. Trilobites are the most abundant of these, and lived mainly in the earliest periods of the Paleozoic: then, they'll be joined by crustaceans and chelicerates (see further), and their number began to fall. It's a bit useless to describe them: see the link in this entry to take a look. It's worth noting, however, they were among the very first animals to develope complex eyes, superficially similar to those of modern insects, made by many adjacent facets. Also note that, despite their completeness, we still don't know so much about their way-of-life; their soft tissues rarely have been preserved, making a problem for scientists. Trilobites were very diversified in look and arguably behavior, but most of them were bottom-dwellers and all were microphagous (ate very small items). In short, they were ''very'' similar in ecology to ostracoderms (the jawless armored fish). In fiction they rarely appear, just like all prehistoric invertebrates (authors typically [[TheyJustDidntCare prefer to show modern spineless animals in substitution]]); when this happens, they tend to look like those of the [[http://en.wikipedia.org/wiki/Phacopida Phacopids]] subgroup. Don't expect to se [[http://en.wikipedia.org/wiki/Agnostida Agnostids]] or [[http://en.wikipedia.org/wiki/Proetida Proetids]], despite the former were among the first trilobites ever appeared, while the latter were the only ones which managed to survive until the end of the Permian.

** [[http://en.wikipedia.org/wiki/Ammonite Ammonites]]: Is there anybody who has never seen those pietrified spiraled shells at least once in its life? Ammonites are probably the most iconic fossil invertebrate remains at all, thanks to their elegant shape and their extreme abundance in Mesozoic deposits, to the point they're used as index-fossils to identify Dinosaur-age-related rocks, just like Trilobites for the pre-dinosaurian ones. But wait... ammonites are ''not'' exclusive to Mesozoic! They appeared in the middle Paleozoic, but that's right, achieved their highlights in Mesozoic with kinds which are exclusive of this era: so, it works just the same. Before the first paleontologists were born, ammonites were already well-known to people, who asked themselves what the heck they are: Mother Nature's jokes, Pietrified snakes, the "horn of Ammon" (the meaning of their our-day name), or what? The very first human which understood their real nature was LeonardoDaVinci in XVI century, but wasn't believed: we had to expect the Founder-of-Paleontology, Cuvier, after see the true fossil's nature understood at the end of the XVIII. Sometimes is heard the modern-day [[http://en.wikipedia.org/wiki/Nautilus Nautilus]] is the "modern ammonite": this is not true, as we'll see later: ammonites went ''totally extinct'' at the Cretaceous/Cenozoic extinction ever, the most famous victims (after real and alleged dinosaurs) of the most infamous (though [[DidNotDoTheResearch not the worse]]) mass-extincion ever. Indeed, ammonites are very mysterious things, despite their abundance. We know almost nothing about the shape of their soft parts, since they don't fossilize usually: it seems, though, they were intermediate between the more basal Nautilus and the our more evolved octopusquids. Octopusquids have very complex eyes, almost identical to vertebrates, while Nautilus has one of the simplest eyes one can imagine, nothing but darkrooms without lens. And ammonites? Who knows... And their tentacles? Octopusquids have eight/ten with suckers, Nautilus [[{{Understatement}} a bit more]] but lacking suckers. And ammonites? It seems were more nautilus-like in this respect. In drawings and models, however, expect to see Ammonites [[EverythingsSquishierWithCephalopods with octopusquid eyes, octopusquid tentacles]] and, last but not least, octopusquid ink (while Nautilus hasn't ink at all in RealLife). Despite their fame, Ammonites are very rare things in TV. Don't expect to hear more than a single line about them -if at all. Even WalkingWithDinosaurs has dedicated only a brief cameo to them, in Jurassic "Cruel Seas". Indeed, for an unexplicable reason, ammonites are usually associated with Jurassic seas, despite they were just as common in Triassic and Cretaceous.... In dinosaur books, things are a bit better: ammonites here are frequent, but... don't expect to see single kinds identified, either (unless you've a technical or semi-technical work). And don't expect to see the so-called "heteromorph" ammonites, aka strange-looking species with ''uncoiled'' shells common in Cretaceous.

** [[http://en.wikipedia.org/wiki/Rhinoceros True prehistoric rhinos]]: Modern rhinos are often referred as "prehistoric-looking" in media. Many classic prehistoric mammals were indeed rhino-looking though with different horn-shapes (the aforementioned six-horned ''Uintatherium'' and the fork-horned ''Brontotherium'' are the most well-known examples), but only some of the extinct "rhinoceroses" were ''really'' such. Among them, the most spectacular were the [[http://en.wikipedia.org/wiki/Coelodonta_antiquitatis Woolly Rhino]], the [[http://en.wikipedia.org/wiki/Elasmotherium_sibiricum Unicorn Rhino]], and above all, the Indricothere (ironically, this one wasn't so rhino-looking). The Unicorn (''Elasmotherium sibiricum'') is often confused with the Woolly (''Coelodonta antiquitatis'') because of their similar appearence: however, the latter was not larger than modern white-rhinos and had ''two'' horns as well; the former was much larger (5 tons, like a modern bush elephant) and with one single horn... perhaps as long as a grown man, and put on the front rather than upon the nose: hence [[ExactlyWhatItSaysOnTheTin unicorn rhinoceros]]. Both lived in the Ice Age in cold climates, alongside mammothes in northern Asia, but the elasmothere was southerner than the coelodont; the latter lived alongside the other, more popular woolly, ([[RhetoricalQuestionBlunder guess what]]). Interesting that both woollies have left soft part of their bodies other than bones, hair included. While the "unicorn rhinoceros" is often said to have been the inspiration of [[DeadUnicornTrope that other unicorn]] when still alive, but this is probably a legend. About Indricotheres (or Paraceratheres, depend on who you ask), they deserve their own entry below.

** [[http://en.wikipedia.org/wiki/Glyptodont Glyptodonts]]: After Ankylosaurs went extinct, evolution decided to create their mammalian equivalents: the glyptodonts. They were Xenarthrans as well, but related to armadillos rather than to sloths. Lived in South America for dozen million years, before going extinct only few thousands years ago: in short, they had the same identical history of their cousins, the giant sloths. Both groups were veggie-eaters (despite giant sloth might be at least partially scavengers), and when adult, they feared no predators except humans. There is a secret behind giant sloth's and glyptodonts' success: their backbone. It was far, far stronger that every other mammal, thus permitting them carrying such heavy bodies around withouth suffering back pain. ''[[http://en.wikipedia.org/wiki/Glyptodon Glyptodon]]'' is the most well-known glyptodont, but it's also worth of mention ''[[http://en.wikipedia.org/wiki/Doedicurus Doedicurus]]'': with its mace-like tail, it was the most ''Ankylosaurus''-like of them all. These were among the biggest glyptos, and thus [[RuleOfCool the most depicted]]. Talking about glyptodonts' armor, it was the most powerful among every land-vertebrate (tortoises excluded). It was made by a ''single piece'' made by several ossicles fused together, smooth and usually round-shaped, unlike ankylosaurs whose armor was more flexible and spiky. With their compact frame and rigid armor, Glyptodonts were probably slower-moving than ankylosaurs, but still faster than a Galapagos' tortoise. Despite these differences, the glyptodont's armor was astonishingly similar to an ankylosaur's; only the upper parts of the body were covered, the underbelly was unarmored and hairy like ankylosaurs and modern armadillos; the head had a "shield" again like ankylos, and their tail was also covered by bone. Like ''Megatherium'', also ''Glyptodon'' was known by ancient humans; but we are not sure what was the real thing that made these amazing animals extinct: climatic changes? Human hunting? Or what? Now, only far smaller xenarthrans survive; armadillos, tree-slothes and true anteaters (sadly, the natural history of anteaters is poorly-understood).

** [[http://en.wikipedia.org/wiki/Chalicotheriidae Chalicotheres]]: The best example of MixAndMatchCritter among prehistoric mammals: they had the head of an horse, the body-shape of a gorilla, and sloth-like forelimbs with hooked claws for pulling down branches or excavating the soil in search of roots: some nickname them [[FunnyName sloth-horses]]. A very successful group of hoofed mammals, distantly related to horses and rhinos (like the aforementioned brontotheres); chalicotheres roamed for a long time in most continents, and some [[WildMassGuessing think]] the famous "Nandi Bear" that could live in modern African rainforests is just a surviving chalicothere. The two most well-known family-members are the north-american ''[[http://en.wikipedia.org/wiki/Moropus Moropus]]'' and the Asian namesake ''[[http://en.wikipedia.org/wiki/Chalicotherium Chalicotherium]]'' - the latter was even stranger since literally ''knuckle-walked'' like a gorilla. The latter was portrayed in [[WalkingWithDinosaurs Walking With Beasts]], along with another species, african ''Ancylotherium'' - maybe the last chalicothere, unless the Nandi Bear....

** ''[[http://en.wikipedia.org/wiki/Irish_elk Megaloceros]]''. Or more precisely, ''Megaloceros giganteus''. Now we enter the world of the most successful ungulates today, Artiodactyls (even-toed ungulates), and how could make this without starting with the most spectacular extinct deer (and one of the most astonishing mammals ever). But wait: even though it is commonly referred as the "Irish elk", ''Megaloceros'' (also called "Megaceros" in older sources) was more related with European fallow-deer. Maybe it was not the largest deer ever (being moose-sized), but its antlers were another stuff: they could make the modern mooses' ones appear insignificant in comparison. Each one was ''as long as the entire animal's body'', and each one weighed more than 100 kg. Obviously, only males had such a thing above, as most modern deer. Some scientists said that ''just this headgear'' was the cause of its extinction, having grown too much, and making the animal too clumsy... but this is unlikely; if they actually were too big, evolution would have made it smaller at one point, simply. ''Megaloceros'' lived in Europe in the Ice Ages alongside woolly mammoths and other large mammals, and was possibly prey for ancient human-ancestors; its nickname "irish elk" is due to its remains are very common in {{Oireland}}.

** Prehistoric pigs/pseudo-pigs: Many hoofed mammals of the distant past were pig-like in shape: indeed, the pig-frame was the most primitive among "ungulates", still retained by some modern hoofed mammals, the best example being boars, peccaries and also the tapir (which is a perissodactyl). Most prehistoric pseudo-boars were small, but some were not: [[http://en.wikipedia.org/wiki/Entelodontidae Entelodonts]] are the most striking ones. They were bison-sized at the most, and had several bony knobs on their head and jaws, resembling giant warthogs, but their tusks were much smaller than a warthog's or a babyrousa's, and didn't protrude out of the mouth. Their food habits are still unclear: they might be scavengers that drove away small predator from their kill, but also ate vegetation and might even be active hunters sometimes. North American ''[[http://en.wikipedia.org/wiki/Daeodon Daeodon]]'' (also called ''Dinohyus'') is the largest and one of the most depicted entelodont. [[WalkingWithDinosaurs Walking With Beasts]] has shown an unnamed Asian relative, and affected its appearence [[CarnivoreConfusion to make it scarier]], exaggerating the opening of its mouth.

** [[http://en.wikipedia.org/wiki/Evolution_of_cetaceans Early whales]]: ''All'' mammals were small and rodent-shaped in their evolutionary beginnings. Some became larger and more derived after the extinction of the dinosaurs, but none to the same level as whales. The first whale ancestors appeared only 10 million years or so after the non-avian dinosaurs' extinction. Once thought to have descended from doglike mesonychids (see above), whales [[ScienceMarchesOn are now thought to be]] [[http://en.wikipedia.org/wiki/Even-toed_ungulate artiodactyls]] (even-toed ungulates), such as camels, pigs, cattle, deer and particularly hippopotami. The first whales may have descended from the aforementioned anthracotheres, or possibly ''[[http://en.wikipedia.org/wiki/Indohyus Indohyus]]'', which was only discovered in 2007. They probably spent much of their time on land, feeding on dead fish and drowned animals. ''[[http://en.wikipedia.org/wiki/Ambulocetus Ambulocetus]]'' (the "walking whale") is a good example of this: still four-limbed, it was already a good swimmer, but still resembled anything but a whale. Among the first fish-shaped cetaceans, ''[[http://en.wikipedia.org/wiki/Basilosaurus Basilosaurus]]'' reached the length of a modern baleen whale, but was much more slender, almost eel-like. When first discovered, its elongated shape was misidentified for a mosasaur-like marine reptile: hence its strange, dinosaurian-sounding name ("king lizard"). At that time, all whales still were active hunters, like modern orcas and sperm whales; the first filter-feeders appeared much more recently, when our planet turned colder and immense shoals of krill began to float in polar waters. Other cetaceans, however, remained small and active predators, originating our dolphins.

** Extinct relatives of modern cats: There were not only sabre/scimitar/dirk/whatevertooths in Prehistory. There were also more normal-looking cats, which together make the subfamily Felinae - while sabretooths make the Machairodontinae. The former are known as "biting cats" the latter "stabbing cats", [[CaptainObvious guess why]]. The most well-known "biting" things were the [[http://en.wikipedia.org/wiki/Panthera_leo_atrox American Lion]] and its European cousin, the [[http://en.wikipedia.org/wiki/Panthera_leo_spelaea Cave Lion]], both simply larger, Ice Ages-related subspecies of the modern lion, well adapted to live in colder climates along with the mammoths. SOme think they were the main predators of ancient humans, but this is not certains. Anyway, it seems males haven't any mane, at least according to some prehistoric paintings. Another interesting biting cat was the [[http://en.wikipedia.org/wiki/Miracinonyx American Cheetah]], actually more related with cougar than to cheetah, possibly a specialized hunter of modern pronghorns (which developed their fastness just to escape these "cheetahs"). Not all prehistoric cats were large, though: most were as small as many modern felines, and one of them was the ancestor of our domestic friend.

** [[http://en.wikipedia.org/wiki/Creodontia Creodonts]]: In the Early Cenozoic, at the time "true" carnivores were still weasel-like, creodonts occupied the ecological niche ruled by modern large carnivores. Very diversified in shape and size, their appearence included that of all modern carnivores (hyena-like, bear-like, weasel-like, tiger-like, or a mix of all these). However, creodonts were more primitive and arguably slower-moving than our meat-eating mammals: this has been often cited as the cause of their extincion, but scientists aren't sure of that. ''[[http://en.wikipedia.org/wiki/Hyaenodon Hyaenodon]]'' is regarded as the stock creodont. There were several species, from dog-sized to cow-sized: the largest hyaenodont species appears in Walking With as a formidable predator, but some hypothize it was mostly a scavenger. But even bigger creodonts are known to science, some of them could have even been the biggest land meat-eating mammals ever, rivalling the alleged "Biggest carnivore" ''Andrewsarchus''.

** [[http://en.wikipedia.org/wiki/Proboscidea Other elephant relatives]]: There were A LOT of them in prehistory: not so in {{Prehistoria}}. Don't expect to see any proboscideans in TV outside docus unless it's a woolly mammoth or an [[StockDinosaurs American mastodon]], even though many of them were far cooler-looking than the latter two. If you don't believe us, take a look at these: the shovel-jawed ''[[http://en.wikipedia.org/wiki/Platybelodon Platybelodon]]'' resembled a cross between an elephant and a hippo. The huge ''[[http://en.wikipedia.org/wiki/Deinotherium Deinotherium]]'' (appropriately named "terrible beast") had two tusks ''growing out of the lower jaw'', and some species were almost as big as the "indricothere". The ancestral ''[[http://en.wikipedia.org/wiki/Moeritherium Moeritherium]]'' (classicaly mentioned as "the first elephant") didn't resemble even an elephant: with its short trunk and short limbs, it was more similar to a modern tapir. But even more normally-looking proboscideans would appear cool-looking by our standards: other than the aforementioned giant mammoths, see the [[http://en.wikipedia.org/wiki/Anancus European mastodon]] and its sword-like tusks, just as as example. And oh, don't forget some island-dwellers which lived in the Ice Ages and almost managed to survive until human history: the oxymoronic [[http://en.wikipedia.org/wiki/Dwarf_elephant dwarf elephants]]. Yes, they were real, and some ''sheep-sized''. Many of the larger elephant and elephant relative bones (and the smaller ones, too) which were found in the Mediterranean were identified by the ancient Greeks as the remaining bones of monsters, heroes and animals from the [[ClassicalMythology Age of Heroes.]] Some of these bones were identified as cyclopes, but no elephant skulls were. The fossils of Anceint Greece are way too fragmentary due to geological forces (earthquakes and volcanoes) to allow something as fragile as a skull to survive intact.

** Non-cetacean marine mammals: While cetaceans' natural history is now well-known, that of [[http://en.wikipedia.org/wiki/Pinnipedia Pinnipeds]] (seals, sea-lions, walruses, etc.) is still poorly-known: however, we are sure that they descended from bear-like or otter-like ancestors, and are a more recent group than whales. On the other hand, the third group of sea mammals, [[http://en.wikipedia.org/wiki/Sirenia Sirenians]] (manatees and dugongs), are as ancient as cetaceans, and descended from hippo-like ancestors. There was a fourth group of sea mammals in the Cenozoic, the little-known [[http://en.wikipedia.org/wiki/Desmostylia desmostylians]], a sort of "herbivorous seals" which looked a bit like walruses, but ate weeds like manatees and were related to manatees.

* [[http://en.wikipedia.org/wiki/Chondrichthyes Sharks]]: Not always EverythingsEvenWorseWithSharks, really. For many animal-lovers, they are among the most fascinating living things. And so is among paleo-fans. Prehistoric sharks were as diversified as modern shark are today, or rather, even more. But stop now. Things aren't always so simple as they seem. "Shark" is an ambiguous word: usually refers to ''some'' of the modern cartilaginous fish, expecially the most streamlined ones such as the Great White. But in paleontology, it usually refers to ''all'' cartilaginous fish, or at least, those belonging to the [[http://en.wikipedia.org/wiki/Elasmobranchii Elasmobranchian]] subgroup. Cartilaginous fish originated in the Devonian period with generic form such as ''[[http://en.wikipedia.org/wiki/Cladoselache Cladoselache]]''; actually all the fish-groups seen so far get their success for the first time in this period: Devonian is called with reason "the Fish Age" because it was the age in which fish were more diversified than every else. Sharks are often called "living fossils" because their anatomy has remained virtually unchanged since 400 million years, and yet they managed to survive the strong competiton both from the first Jurassic large sea-reptiles at first, and from the first Cretaceous ray-finned fish then. Many primitive "sharks" are very cool-looking: let's give a look at the "Ironing Board" shark ''[[http://en.wikipedia.org/wiki/Stethacanthus Stethacanthus]]'', the eel-like freshwater sharks of the ''[[http://en.wikipedia.org/wiki/Xenacanthidae Xenacanthid]]'' family, and the "Switchblade Shark" ''[[http://en.wikipedia.org/wiki/Hybodus Hybodus]]''. More modern-looking sharks first appeared in the Cretaceous, along with the first modern-looking bony fish; and some of them were similar to {{Jaws}}-things. The "Ginsu Shark" ''[[http://en.wikipedia.org/wiki/Cretoxyrhina Cretoxyrhina]]'', for example, growed to the size of Spielberg's beast, and preyed upon [[BadAss marine reptiles]]. Despite this, the biggest and most famous prehistoric shark was still alive ''just 1.5 million years ago'', when hominids were already existing: ''Carcharocles'', better known as {{Megalodon}}.

* [[http://en.wikipedia.org/wiki/Cambrian_Explosion Cambrian Fauna]]: Cambrian. The first Paleozoic Period, in which the famous "Cambrian Explosion" of life happened. The less-known thing is, we humans are ''unbelievably lucky'' if we know that remote event. At that time, animals just were starting to achieve hard parts in their body, and we already know that, usually, soft-bodied organisms do not preserve at all. The astounding luck is, one of the greatest exceptions of this ruthless rule are ''just some deposits from the Cambrian Period.'' : it almost seem Ol'Mother Nature [[BecauseDestinySaysSo has done this deliberately for ourselves...]]. The most famous and historically relevant is the [[http://en.wikipedia.org/wiki/Burgess_Shale]] in British Columbia, but still others are also known (for example in China). For obvious reason, our curiosity now reaches the top: which were the first animals (not counting protozoans) that thrived in our oceans? Well, the answer is not simple: we can divide them in two ensembles. One is made from those groups either still alive today or extinct several ages after the Cambrian: among the former, most non-arthropod / non-cephalopod invertebrate groups already seen; among the latter, the Trilobites. We'll talk here about the second ensemble: many Cambrian invertebrates were indeed ''exclusive of the Cambrian'' and didn't survive long enough, not even to reach the following period, Ordovician (in which the most famous Paleozoic critters, sea-scorpions, nautiloids, armored fish etc. appeared). Thus, is easy to imagine many of them were ''really'' [[OurMonstersAreWeird bizarre-looking]] to our limited point of view. We still know very very few things about their lifestyle, but their appearence is extraordinarily well-known, because these Cambrian deposits ''have preserved soft-bodies''; not only that, they have preserved them very well! It would be too long to mention [[http://en.wikipedia.org/wiki/Burgess_Shale_type_fauna all the members]] of the Cambrian Fauna: see [[http://www.google.it/imgres?imgurl=http://www.trilobites.info/burgess_community_sm.jpg&imgrefurl=http://www.trilobites.info/triloclass.htm&usg=__s0Eofooa0oLw4onLe4Slh3sbJ6g=&h=479&w=720&sz=125&hl=it&start=10&zoom=1&um=1&itbs=1&tbnid=3LpTQO2S2iy5RM:&tbnh=93&tbnw=140&prev=/images%3Fq%3Dcambrian%2Bfauna%26um%3D1%26hl%3Dit%26rls%3Dcom.microsoft:en-US%26rlz%3D1I7ADBF_it%26tbs%3Disch:1&ei=lyRVTZfKAcTrOYLpxYAF the image here]] for having an idea. It's immediately recognizable the bizarre shrimp-like animal in the center, by far the biggest creature in this fauna, and arguably the top predator. It is called ''[[http://en.wikipedia.org/wiki/Anomalocaris Anomalocaris]]'' (meaning "[[ExactlyWhatItSaysOnTheTin bizarre shrimp]]" indeed), and was a distant relative of arthropods with no articulated legs but with the same composed eyes of the Trilobites. Of course it is the most portrayed Cambrian animal in documentaries and illustrations, classicaly mentioned as "[[PrehistoricMonster the first prehistoric monster ever appeared on Earth]]"; actually, if alive today, the "terrible" anomalocarid would appear as a really [[{{Narm}} narmy thing]], a sort of 3 ft long, shell-less, pincer-less lobster, nothing dangerous for a tough-boned, tough-muscled, tough-skinned mammal we are in comparison. Actually, anomalocarids were highly specialized predators, with a mouth build for prey around 1/12 to 1/6 of their own size. But at its time, all the other organism were ''very small'': The other creatures you see in the linked image are not longer than your hand, all possible prey for anomalocarids - except those which were so small that a full grown ''Anomalocaris canadensis'' (the largest know species) whould have ignored them. Creatures like ''Hallucigenia'' and ''Pikaia'' were hunted by smaller predators, such as ''Opabinia'' and ''Anomalocaris saron''. The later was the species shown in ''WalkingWithMonsters'', though ridiculously oversized (6 ft.!?) and prone to attack it's own kind, despite the fact that neither its mouth nor grasps could injur an equally sized specimen in the way it was depicted, let alone possibly eating it. Apart from Anomalocaris, we can mention at least other three invertebrates which are stock in drawings: ''[[http://en.wikipedia.org/wiki/Hallucigenia Hallucigenia]]'', ''[[http://en.wikipedia.org/wiki/Opabinia Opabinia]]'', and ''[[http://en.wikipedia.org/wiki/Pikaia Pikaia]]''. The first has a so strange look that its name means "hallucination-generator": it was a sort of "worm" with long paired spikes for uncertain purpose, and long softed paired legs: the reconstruction of ''Hallucigenia'' has had an astounding ScienceMarchesOn tangle for many years, and it still remains one of the most enigmatic Cambrian animal: nobody knowns exactly in which phylum it has to be placed. ''Opabinia'' was related with ''Anomalocaris'', but had an even weirder look: maybe no other fossil animal resembles a fiction-related extraterrestrial thing more than ''Opabinia''. It had ''five eyes'' put in circular fashion on its head, and a pincer-like grasp at the end of a long, flexible proboscis, often mistaken for the creatures mouth which was actually located behind the proboscis. But the most important find is the third guy, ''Pikaia'': despite its rather insignificant appearence, it is the most well-known among ''vertebrate ancestor'', a sort of prehistoric relative of our [[http://en.wikipedia.org/wiki/Lancelet Lancelet]] (the closest vertebrate relative still-living today). This relevance has made ''Pikaia'' one of the unofficial symbols of Evolution, just like the ur-amphibian ''Ichthyostega'', the ur-bird ''Archaeopteryx'' and the ur-horse ''Eohippus''. But wait....have you see these critters in TV at least once? A hard thing, even if you watched [[WalkingWithDinosaurs Walking With Monsters]]. In this RuleOfCool-filled show, the ''only real'' Cambrian invertebrate to appear is....Guess what? Well, the superpredator ''Anomalocaris'' of course! The other two invertebrate guys shown up are... [[TheyJustDidntCare a modern jellyfish]] and an [[AnachronismStew anachronistical phacopid trilobite]] (remember that phacopids first evolved in the Ordovician, while Cambrian trilobites were very different-looking to the classic image we have when thinking about these animals). The absence of such awesome animals like ''Opabinia'' and ''Hallucigenia'' makes another egregious example of a missed opportunity, like the missing of the giant bird ''Argentavis''. Talking about ''Pikaia'', this time its missing is no problem for us: the aforementioned proto-vertebrate ''Haikouichthys'' did perform its role. Still another thing: if you watch the list of creatures from the Burgess Shale, you'll note almost all animals (the main exception being ''Anomalocaris'') have uncommonly short scientific names, most of them ending in '''-a'''. A rather amusing thing to read, and - let's face it - a ''true'' oasis of happiness among so many other unutterable, absurdely-difficult names.

** Non-cetacean marine mammals: While cetaceans' natural history is now well-known, that of [[http://en.wikipedia.org/wiki/Pinnipedia Pinnipeds]] (seals, sea-lions, walruses, etc.) is still poorly-known: however, we are sure that they descended from bear-like or otter-like ancestors, and are a more recent group than whales. On the other hand, the third group of sea mammals, [[http://en.wikipedia.org/wiki/Sirenia Sirenians]] (manatees and dugongs), are as ancient as cetaceans, and descended from hippo-like ancestors. There was a fourth group of sea mammals in the Cenozoic, the little-known [[http://en.wikipedia.org/wiki/Desmostylia desmostylians]], a sort of "herbivorous seals" which looked a bit like walruses, but ate weeds like hippos and were related to manatees.

** Mammals of prehistoric Australia: Australian mammalofauna hasn't changed much since the non-avian dinosaur extinction (not counting human influence of course): there have always been [[http://en.wikipedia.org/wiki/Marsupialia marsupials]] and [[http://en.wikipedia.org/wiki/Monotremata monotremes]] in the LandDownunder. Since modern Australian mammals are already so bizarre-looking, how would their predecessors have looked? Not unlike their descendants, really; but some were a bit larger. [[http://en.wikipedia.org/wiki/Procoptodon giant kangaroos]] were 10 ft tall, with a short tail and a flat snout; while [[http://en.wikipedia.org/wiki/Diprotodon diprotodonts]] were even larger, ''rhino-sized'', but were wombat relatives, and thus vegetarian. Monotremes, too, were amazing: the [[http://en.wikipedia.org/wiki/Zaglossus giant echidna]] was as large as a sheep. Nevertheless, there was also a unique animal which has no modern relatives: the [[http://en.wikipedia.org/wiki/Thylacoleo marsupial lion]], so-called because of its body shape and sharp claws, but with ''rodent-like incisors'' instead of the classic fangs. Scientists once thought it was indeed vegetarian; now they know it was predatory, just like another unusual marsupial from South America: the aforementioned "marsupial sabretooth", ''[[http://en.wikipedia.org/wiki/Thylacosmilus Thylacosmilus]]''. Yes, there weren't only possums, once, in South America.

* ''[[http://en.wikipedia.org/wiki/Confuciusornis Confuciusornis]]'': ''[[{{Confucius}} Confuciusornis]]'' was from same the famous Chinese Liaoning site in which the popular feathered dinosaur fossils come from. This animal had some evolved traits, for example had already lost its teeth (convergently from modern birds) and shortened its tail, but still retained an old legacy: three-clawed wings. Another basal bird, ''[[http://en.wikipedia.org/wiki/Jeholornis Jeholornis]]'' from the same habitat, is also known as "Shenzhouraptor".

The most well-known are the [[http://en.wikipedia.org/wiki/Panthera_leo_atrox American Lion]] and its European cousin, the [[http://en.wikipedia.org/wiki/Panthera_leo_spelaea Cave Lion]], both simply larger, Ice Ages-related subspecies of the modern lion, well adapted to live in colder climates along with the mammoths.
** [[http://en.wikipedia.org/wiki/Ursidae Prehistoric bears]]: Bears are a very recent group. They have roamed our planet for only 5 to 10 million years. Many prehistoric bears were rather different than our grizzlies: for example, the North American [[http://en.wikipedia.org/wiki/Arctodus short-faced bear]] had long limbs and a[[ExactlyWhatItSaysOnTheTin bulldog-like snout]] and was probably an agile runner and specialized hunter. The most famous extinct bear is, however, the [[http://en.wikipedia.org/wiki/Ursus_spelaeus cave bear]], quite similar to a modern kodiak in shape and size. It is often portrayed as [[EverythingsWorseWithBears the archenemy of Neanderthals]], because both lived in the same places (Pleistocene Europe) and were forced to share the same caves to repair themselves from the rigid Ice Age winters. Its fossil record is very abundant in European caves.

** Prehistoric [[http://en.wikipedia.org/wiki/Canidae canids]] and [[http://en.wikipedia.org/wiki/Hyaenidae hyenas]]: Prehistoric wolves and hyenas were not so different-looking than ours, but sometimes were larger. The [[http://en.wikipedia.org/wiki/Canis_dirus dire wolf]] has been often found in the same tarpits in which ''Smilodon'' remains have been discovered, along with several other American mammals (elephant relatives, ground sloths, but modern-living mammals as well); the most famous is [[http://en.wikipedia.org/wiki/La_Brea_Tar_Pits Rancho la Brea]], in Los Angeles. Among extinct hyenas (which by the way, are more closely related to cats than dogs) we can mention the [[http://en.wikipedia.org/wiki/Cave_hyena cave hyena]], similar to modern spotted hyenas but living in northern territories during the Ice Ages. Some extinct canid were deceptively hyena-like: ''[[http://en.wikipedia.org/wiki/Borophagus Borophagus]]'' from the Middle Cenozoic is one example. As a side-note: all modern domestic dogs from Chihuahuas to Great Danes descend from the grey wolf, no matter how big they are or how they look; an amazingly rapid evolution, really, lasted only few thousands years.

** [[http://en.wikipedia.org/wiki/Amphicyonidae Bear-dogs]] and [[http://en.wikipedia.org/wiki/Nimravidae Pseudo-cats]]: Before cats, bears, dogs and hyenas appeared on Earth, there were their pseudo-looking relatives, whose appearence was similar to their successors or a mix of these animals. Bear-dogs are more correctly called Amphicyonids: some were very fox- or wolf-like, while others were more similar to bears. A [[AllAnimalsAreDogs very dog-like]] "bear-dog" appears in [[WalkingWithDinosaurs Walking With Beasts]]. Nimravids (the pseudo-cats) were also very diversified: the aforementioned ''Eusmilus'' was indeed a sabretoothed member of the pseudo-cat family, while the namesake ''[[http://en.wikipedia.org/wiki/Nimravus Nimravus]]'' was more similar to modern big cats. The latter has left a perforated skull which could reveal an astonishing story; maybe it was stabbed in its head... just by its relative ''Eusmilus''.

** [[http://en.wikipedia.org/wiki/Creodontia Creodonts]]: In the Early Cenozoic, at the time "true" carnivores were still weasel-like, creodonts occupied the ecological niche ruled by modern large carnivores. Very diversified in shape and size, their appearence included that of all modern carnivores (hyena-like, bear-like, tiger-like, or a mix of all these). However, creodonts were more primitive and arguably slower-moving than our meat-eating mammals: this has been often cited as the cause of their extincion, but scientists aren't sure of that. ''[[http://en.wikipedia.org/wiki/Hyaenodon Hyaenodon]]'' is regarded as the stock creodont. The largest hyaenodont species appears in Walking With as a formidable predator, but some hypothize it was mostly a scavenger. But even bigger creodonts are known to science, some of them could have even been the biggest land meat-eating mammals ever, rivalling ''Andrewsarchus'' (see later).

** Prehistoric deer/pseudo-deer: Many prehistoric ungulates resembled deers in body-shape and head-shape, but again, not all were members of the [[http://en.wikipedia.org/wiki/Cervidae deer family]]. Many of them had very unfamiliar-looking horns/antlers above their heads. The most spectacular extinct cervid (and one of the most astonishing mammals ever) was ''[[http://en.wikipedia.org/wiki/Irish_elk Megaloceros giganteus]]'', commonly referred as the "Irish elk", though it was more related with European fallow-deer. This guy was moose-sized and with antlers which could make the mooses' ones appear insignificant in comparison: each one was ''as long as the entire animal's body'', and each one weighed more than 100 kg. Obviously, only males had such a thing above, as most modern deer. Among pseudo-deers, the most portrayed are ''[[http://en.wikipedia.org/wiki/Synthetoceras Synthetoceras]]'' and ''[[http://en.wikipedia.org/wiki/Sivatherium Sivatherium]]''. The former was antelope-shaped but with a bit of rhino inside: it had three horns, two of them were traditional-looking, but the third one was on its ''nose'' and was forked just like that of ''Brontotherium'', though longer and more slender. ''Sivatherium'' was moose-like and very large (2.5 m tall at the shoulder), and had deceptively moose-like pseudo-antlers: it actually was a giraffe relative, a sort of short-necked giraffe. Just about this detail: remember the classic Lamarckian "lenghtening of the giraffe's neck" we have learned at school? Indeed, no other extinct mammal has has such a long neck: modern animals often are not so overshadowed by their prehistoric relatives, really.

** [[http://en.wikipedia.org/wiki/Bovidae Prehistoric Bovids]]: Bovids (the group containing buffalo, sheeps, goats and antelope; that is, all ruminants with ''true'' horns) are the most successful ungulate group today, and are very diversified: their prehistoric relatives were not much different in their appearence. We can mention however the [[http://en.wikipedia.org/wiki/Bison giant bisons]] which lived in Ice Age North America. There were many species of them, some were larger than their present-day relatives and often with more developed horns as well. Only one specie of bison still remains in today-America.

** [[http://en.wikipedia.org/wiki/Entelodontidae Entelodonts]]: Many hoofed mammals of the distant past were pig-like in shape: indeed, the pig-frame was the most primitive among "ungulates", still retained by some modern hoofed mammals, the best example being the tapir. Most prehistoric pseudo-boars were small, but some were not: Entelodonts are the most striking ones. They were bison-sized at the most, and had several bony knobs on their head and jaws, resembling giant warthogs, but their tusks were much smaller than a warthog's or a babyrousa's, and didn't protrude out of the mouth. Their food habits are still unclear: they might be scavengers that drove away small predator from their kill, but also ate vegetation and might even be active hunters sometimes. North American ''[[http://en.wikipedia.org/wiki/Daeodon Daeodon]]'' (also called ''Dinohyus'') is the largest and one of the most depicted entelodont. [[WalkingWithDinosaurs Walking With Beasts]] has shown an unnamed Asian relative, and affected its appearence [[CarnivoreConfusion to make it scarier]], exaggerating the opening of its mouth.

** [[http://en.wikipedia.org/wiki/Meridiungulata South American Ungulates]]: South America was isolated from other continents for most of the Mammal Age, and thus its fauna developed in its own direction. There were not only elephant-size sloths and tank-like glyptodonts: there were also less-armoured but still odd-looking "ungulates", not related with any modern animal today, but similar in shape to camels, horses, hippos, buffalos, elephants, rhinos, hyraxes, and even chalicotheres (a great example of Convergent Evolution). The two most represented are ''[[http://en.wikipedia.org/wiki/Macrauchenia Macrauchenia]]'' and ''[[http://en.wikipedia.org/wiki/Toxodon Toxodon]]''. ''Macrauchenia'' was a bit camel-like; often depicted with a floppy, elephantine nose because of the shape of its skull, but we don't know if it really had this thing. ''Toxodon'' was more like a stock-built, no-horned buffalo, but it has also been compared with a rhino or a hippo. These two guys lived during the Ice Ages in South American grasslands ("pampas"), but other relatives lived much earlier, always in South America.

** [[http://en.wikipedia.org/wiki/Evolution_of_the_horse Horse ancestors]]: The eternal symbol of Evolution. Almost the same level the Dodo is the icon of extinction. And yet, horse ancestors weren't so cool-looking compared to most other extinct [[http://en.wikipedia.org/wiki/Ungulate hoofed mammals]], really. The most famous of these is, obviously, the [[RuleOfCool less horse-like]] of them all: ''Eohippus'' --> ''Hyracotherium'' --> ''[[http://en.wikipedia.org/wiki/Eohippus Eohippus]]'' --> ''Protorohippus''. An almost-unbelievable ScienceMarchesOn affair has encircled horse's evolution, despite its iconic role in popular science. Anyway, all this doesn't involve us so much. Expect to see this (whatever name is to be used) small, basal ungulate called ''horse'' anyway, despite it, actually, having nothing more in common with horses than with tapirs or rhinoceri: the "Hyracotheohippus stew" includes several different early ungulates, some of theme ''were'' horse-ancestors and some weren't. Systematics of primitive ungulates (many of them called [[http://en.wikipedia.org/wiki/Condylarthra Condylarths]]) is a total mess. Among sure horse ancestors, they make a [[AWorldwidePunomenon sort of pun if read together]]: ''Mesohippus'', ''Merychippus'', ''Pliohippus'' and dozens other "hippus"... all North American. Also worth of note is ''Hipparion'' which, sadly, breaks the pun having "hipp" as prefix: it also breaks the geographic rule, being an Old World critter, an offshot of the horse tree which didn't leave any descendents. Remember that ''all'' modern equines did descend from North American ancestors. And oh: the latter were not only horse's ancestors: also donkey's and zebra's, never forget this. Modern equids are so closely related each others, they could well be considered variations of a single kind of animal.

** [[http://en.wikipedia.org/wiki/Rhinoceros True prehistoric rhinos]]: Modern rhinos are often referred as "prehistoric-looking" in media. Many classic prehistoric mammals were indeed rhino-looking though with different horn-shapes (the aforementioned six-horned ''Uintatherium'' and the fork-horned ''Brontotherium'' are the most well-known examples), but only some of the extinct "rhinoceroses" were ''really'' such. Among them, the most spectacular were the [[http://en.wikipedia.org/wiki/Coelodonta_antiquitatis Woolly Rhino]], the [[http://en.wikipedia.org/wiki/Elasmotherium_sibiricum Unicorn Rhino]], and above all, the Indricothere (ironically, this one wasn't so rhino-looking). The Unicorn (''Elasmotherium sibiricum'') is often confused with the Woolly (''Coelodonta antiquitatis'') because of their similar appearence: however, the latter was not larger than modern white-rhinos and had ''two'' horns as well; the former was much larger (5 tons, like a modern bush elephant) and with one single horn... as long as a grown man, and put on the front rather than upon the nose: hence [[ExactlyWhatItSaysOnTheTin unicorn rhinoceros]]. Both lived in the Ice Age in cold climates, alongside mammothes in northern Asia, but the elasmothere was southerner than the coelodont; the latter lived alongside the other, more popular woolly ([[RhetoricalQuestionBlonder guess what]]). About Indricotheres (or Paraceratheres, depend on who you ask), they deserve their own entry below.

** [[http://en.wikipedia.org/wiki/Paraceratherium Paracerathere]]: Here is Our Majesty, the biggest land mammal ever lived - though some [[ScienceMarchesOn recent research]] seems to indicate that some mammoths were heavier, but certainly not as tall. Despite its really gigantic size - it was as tall as an apatosaur up to the shoulders, and weighed as ''three'' elephants or, better, as three ''T. rex''es - it still had a quite slender, elegant frame: a sort of muscular giraffe with long neck, small head, and long, slender limbs. Its behavior itself was probably more giraffe-like than rhinoceros-like, browsing the tree tops. In short, it was the new mammalian brachiosaur. Lived at the middle of the Cenozoic (the Age of Mammals). It's also a prime example of IHaveManyNames among prehistoric critters: now called ''Paraceratherium'', its traditional names are ''Indricotherium'' and ''Baluchitherium''.

** [[http://en.wikipedia.org/wiki/Chalicotheriidae Chalicotheres]]: The best example of MixAndMatchCritter among prehistoric mammals: they had the head of an horse, the body-shape of a gorilla, and sloth-like forelimbs with hooked claws for pulling down branches: some nickname them "sloth-horses". A very successful group of hoofed mammals, distantly related to horses and rhinos (like the aforementioned brontotheres); they roamed for a long time in most continents, and some [[WildMassGuessing think]] the famous "Nandi Bear" that could live in modern African rainforests is just a surviving chalicothere. The two most well-known family-members are the north-american ''[[http://en.wikipedia.org/wiki/Moropus Moropus]]'' and the Asian namesake ''[[http://en.wikipedia.org/wiki/Chalicotherium Chalicotherium]]'' - the latter was even stranger since literally ''knuckle-walked'' like a gorilla.

** ''[[http://en.wikipedia.org/wiki/Arsinoitherium Arsinoitherium]]'': Sometimes misspelled "Arsinotherium", it was the most peculiar-looking among the aforementioned "pseudo-rhinos", with its huge, yet light-weighed, hollow "quadruple-horn". The same size as modern rhinos, this animal is often described as a "cross between a rhino and a hippo" because of its short legs and amphibious habits: it lived along the coasts bordering the shallow seas which covered modern-day Egypt, together with the ur-elephant ''Moeritherium''. It's worth noting that, unlike ''Moeritherium'', ''Arsinoitherium'' was ''not'' an elephant predecessor as said in [[WalkingWithDinosaurs Sea Monsters]], and maybe didn't have that tapir-like nose seen in the program: this mammal is so strange that it is put in its own mammalian order, the Embrithopods, only distantly related to elephants.

** [[http://en.wikipedia.org/wiki/Glyptodont Glyptodonts]]: After Ankylosaurs went extinct, evolution decided to create their mammalian equivalents: the glyptodonts. They were Xenarthrans as well, but related to armadillos rather than to sloths. Lived in South America for dozen million years, before going extinct only few thousands years ago: in short, they had the same identical history of their cousins, the giant sloths. Both groups were veggie-eaters (despite giant sloth might be at least partially scavengers), and when adult, they feared no predators except humans. Their armor, indeed, was the most powerful among every land-vertebrate (tortoises excluded), being made by a ''single piece'' made by several ossicles fused together, smooth and usually round-shaped, unlike ankylosaurs whose armor was more flexible and spiky. With their compact frame and rigid armor, Glyptodonts were probably slower-moving than ankylosaurs, but still faster than a Galapagos' tortoise. Despite these differences, the glyptodont's armor was astonishingly similar to an ankylosaur's; only the upper parts of the body were covered, the underbelly was unarmored and hairy like modern armadillos; the head had a "shield" just like ankylos, and the tail was also covered by bone.

There is a secret behind giant sloth's and glyptodonts' success: their backbone. It was far, far stronger that every other mammal, thus permitting them carrying such heavy bodies around withouth suffering back pain. ''[[http://en.wikipedia.org/wiki/Glyptodon Glyptodon]]'' is the most well-known glyptodont, but it's also worth of mention ''[[http://en.wikipedia.org/wiki/Doedicurus Doedicurus]]'': with its mace-like tail, it was the most ''Ankylosaurus''-like of them all.

** [[http://en.wikipedia.org/wiki/Mammuthus Giant mammoths]]: It is often heard the mammoth was bigger than a modern elephant. This is not true if we consider the stock guy, the hairy, curly-tusked tundra-dweller called [[StockDinosaurs Woolly mammoth]] all people know: but this ''is'' true talking about other mammoth species. There were indeed ''many'' species of mammothes in RealLife, and as a group they lived across most of the Ice-Ages world. The largest ones did challenge the "indricothere" (see later) as the "Biggest land mammal ever" title, but only if you count their weight (the indricothere would ever be taller than every mammoth, thanks to its giraffe-like body frame). The most famous are two American species, the [[http://en.wikipedia.org/wiki/Mammuthus_imperator Imperial mammoth]] and the southerner [[http://en.wikipedia.org/wiki/Mammuthus_columbi Columbian Mammoth]]; giant mammothes have been discovered in the famous US tar-pits like [[http://en.wikipedia.org/wiki/La_Brea_Tar_Pits La Brea]] along with sabertooths and many other animals, some of them still-living today and other extinct after the Ice Ages. Other mammothes as large as the latter were the Asian [[http://en.wikipedia.org/wiki/Mammuthus_trogontherii Steppe Mammoth]] and the less-known but possibly the largest of them all, ''[[http://en.wikipedia.org/wiki/Mammuthus_sungari Mammuthus sungari]]''. The lower popularity of the giant mammothes (despite their size) compared to the woolly one is probably due to their more normal, less-spectacular appearence. They were more similar-looking to modern elephants than to the popular image of "the mammoth" because they were mostly hairless and with classic-shaped tusks (though longer than modern bush elephants); this because they inhabited relatively warmer climates, and their greater size was enough to preserve heat without the woolly covering.

** [[http://en.wikipedia.org/wiki/Felidae Extinct cats]]: There were dozens kinds of [[http://en.wikipedia.org/wiki/Saber-toothed_cat sabertoothed cats]] in RealLife other than the stock American ''[[StockDinosaurs Smilodon]]'' from the Ice Ages. Some of them are nicknamed according to the form of their fangs: ''[[http://en.wikipedia.org/wiki/Homotherium Homotherium]]'' was the "Scimitar-tooth", ''[[http://en.wikipedia.org/wiki/Megantereon Megantereon]]'' the "dirktooth". While ''[[http://en.wikipedia.org/wiki/Machairodus Machairodus]]'' was the Euro-Afro-Asian sabertoothed equivalent of ''Smilodon'', not to mention [[http://en.wikipedia.org/wiki/Machairodontinae the actual prototype of the group]]; many European paleoartists have considered ''Machairodus'' as the ''real'' stock sabretooth instead of ''Smilodon''. But there were also more familiar-looking cats in the past. The most well-known are the [[http://en.wikipedia.org/wiki/Panthera_leo_atrox American Lion]] and its European cousin, the [[http://en.wikipedia.org/wiki/Panthera_leo_spelaea Cave Lion]], both simply larger, Ice Ages-related subspecies of the modern lion, well adapted to live in colder climates along with the mammoths. While ''[[http://en.wikipedia.org/wiki/Dinofelis Dinofelis]]'', despite resembling more a leopard, was actually a short-fanged saber-toothed cat. Don't think however that all extinct felines were large: most were around a house cat in size, and some of them were the ancestor of modern small cats like our domestic friend. A curious thing is, some prehistoric meat-eating mammals which were not cats at all, developed a bewildering "sabre-toothed" look ''before'' true cats appeared: two main examples are the pseudo-cat ''[[http://en.wikipedia.org/wiki/Eusmilus Eusmilus]]'' and the marsupial ''[[http://en.wikipedia.org/wiki/Thylacosmilus Thylacosmilus]]'', in particular the latter, being closer to ''kangaroos'' than to cats.

** ''[[http://en.wikipedia.org/wiki/Megatherium Megatherium]]'': One of the largest land mammals that ever lived, ''Megatherium'' had the same size of an elephant or a ''T. rex'': reached 5 m when fully erect, and its name means...well... [[ExactlyWhatItSaysOnTheTin big beast]]. This is the stock animal within the group called [[http://en.wikipedia.org/wiki/Ground_Sloth Giant Ground Sloths]]. Some of them were among the hugest land mammals ever lived, but many others weren't so giant-things (even though still large by human standards). Very strongly-built and weaponed with enormous claws, they were capable to walk around with their body upright, a bit like giant bears. Being members of the [[http://en.wikipedia.org/wiki/Xenarthra Xenarthran]] group, they were prevalently South American (some of them migrated to the North however) and had primitive teeth: nonetheless, they were so well-adapted to their environments that they flourished for almost the entire length of the Mammal-Ages: they got mysteriously extinct only few thousand years ago.

** [[http://en.wikipedia.org/wiki/Glyptodont Glyptodonts]]: After Ankylosaurs went extinct, evolution decided to create their mammalian equivalents: the glyptodonts. They were Xenarthrans as well, but related to armadillos rather than to sloths. Lived in South America for dozen million years, before going extinct only few thousands years ago: in short, they had the same identical history of their cousins, the giant sloths. Both groups were veggie-eaters (despite giant sloth might be at least partially scavengers), and when adult, they feared no predators except humans. There is a secret behind giant sloth's and glyptodonts' success: their backbone. It was far, far stronger that every other mammal, thus permitting them carrying such heavy bodies around withouth suffering back pain. ''[[http://en.wikipedia.org/wiki/Glyptodon Glyptodon]]'' is the most well-known glyptodont, but it's also worth of mention ''[[http://en.wikipedia.org/wiki/Doedicurus Doedicurus]]'': with its mace-like tail, it was the most ''Ankylosaurus''-like of them all.

* ''[[http://en.wikipedia.org/wiki/Confuciusornis Confuciusornis]]'': Early Cretaceous birds were still very dinosaur-looking. For example, the [[{{Confucius}} phylosophical]] ''Confuciusornis'' which was from same the famous Chinese Liaoning site in which the popular bird-dinos come from. This animal had some evolved traits, for example had already lost its teeth (convergently from modern birds) and shortened its tail, but still retained an old legacy: three-clawed wings. Its similar-looking cousin, ''[[http://en.wikipedia.org/wiki/Jeholornis Jeholornis]]'' from the same habitat, is also, not surprisingly, called ''Shenzhouraptor''.

* ''[[http://en.wikipedia.org/wiki/Hesperornis Hesperornis]]'' and ''[[http://en.wikipedia.org/wiki/Ichthyornis Ichthyornis]]'': The two most famous Dinosaur Age-related birds (not counting ''Archaeopteryx''), both from Late Cretaceous North America. But wait... isn't "''Ichthyornis'' and ''Hesperornis''" the right way to utter them? Since hespero is [[RuleOfCool far cooler]], here we'll mention it first. ''Hesperornis'' lived in the same habitat in which Pteranodonts, Mosasaurs, Elasmosaurs and ''Archelon''s roamed: the shallow inland sea which used to cover US Midwest at that time, dividing North America in two parallel stripes of land running from Arctic down to the south. Despite its earliness, ''Hesperornis'' was already a ''very'' derived bird: 6 ft long, it was flightless, with vestigial wings, and spent most of its life in water: a sort of proto-penguin, but [[ToothyBird with teeth]]. The much smaller, far less striking ''Ichthyornis'' lived in the same habitat, and was a sorta [[ToothyBird toothed]], long-billed proto-seagull. Both these animals were full birds at that point, and if alive today, they'll be taken for components of modern avifauna.

** [[http://en.wikipedia.org/wiki/Ursidae Prehistoric bears]]: Bears are a very recent group. They have roamed our planet for only 5 to 10 million years. Many prehistoric bears were rather different than our grizzlies: for example, the North American [[http://en.wikipedia.org/wiki/Arctodus short-faced bear]] had long limbs and a[[ExactlyWhatItSaysOnTheTin bulldog-like snout]] and was probably an agile runner and specialized hunter. The most famous extinct bear is, however, the [[http://en.wikipedia.org/wiki/Ursus_spelaeus cave bear]], quite similar to a modern kodiak in shape and size. It is often portrayed as the archenemy of Neanderthals, because both lived in the same places (Pleistocene Europe) and were forced to share the same caves to repair themselves from the rigid Ice Age winters. Its fossil record is very abundant in European caves.

** Prehistoric [[http://en.wikipedia.org/wiki/Canidae canids]] and [[http://en.wikipedia.org/wiki/Hyaenidae hyenas]]: Prehistoric wolves and hyenas were not so different-looking than ours, but sometimes were larger. The [[http://en.wikipedia.org/wiki/Canis_dirus dire wolf]] has been often found in the same tarpits in which ''Smilodon'' remains have been discovered, along with several other American mammals (elephant relatives, ground sloths, but modern-living mammals as well); the most famous is [[http://en.wikipedia.org/wiki/La_Brea_Tar_Pits Rancho la Brea]], in Los Angeles. Among extinct hyenas (which by the way, are more closely related to cats than dogs) we can mention the [[http://en.wikipedia.org/wiki/Cave_hyena cave hyena]], similar to modern spotted hyenas but living in northern territories during the Ice Ages. Some extinct canid were deceptively hyena-like: ''[[http://en.wikipedia.org/wiki/Borophagus Osteoborus]]'' from the Middle Cenozoic is one example.

** [[http://en.wikipedia.org/wiki/Amphicyonidae Bear-dogs]] and [[http://en.wikipedia.org/wiki/Nimravidae Pseudo-cats]]: Before cats, bears, dogs and hyenas appeared on Earth, there were their pseudo-looking relatives, whose appearence was similar to their successors or a mix of these animals. The aforementioned ''Eusmilus'' was indeed a sabretoothed member of the pseudo-cat family. A [[AllAnimalsAreDogs very dog-like]] "bear-dog" appears in [[WalkingWithDinosaurs Walking With Beasts]].

** [[http://en.wikipedia.org/wiki/Creodontia Creodonts]]: In the Early Cenozoic, at the time "true" carnivores were still weasel-like, creodonts occupied the ecological niche ruled by modern large carnivores. Very diversified in shape and size, they were more primitive and arguably slower-moving than our meat-eating mammals: this has been often cited as the cause of their extincion, but scientists aren't sure of that. ''[[http://en.wikipedia.org/wiki/Hyaenodon Hyaenodon]]'' is regarded as the stock creodont. The largest hyaenodont species appears in Walking With as a formidable predator, but some hypothize it was mostly a scavenger.

** [[http://en.wikipedia.org/wiki/Proboscidea Other elephant relatives]]: There were A LOT of them in prehistory: not so in {{Prehistoria}}. Don't expect to see any proboscideans in TV outside docus unless it's a woolly mammoth or an [[StockDinosaurs American mastodon]], even though many of them were far cooler-looking than the latter two. If you don't believe us, take a look at these: the shovel-jawed ''[[http://en.wikipedia.org/wiki/Platybelodon Platybelodon]]'' resembled a cross between an elephant and a hippo. The huge ''[[http://en.wikipedia.org/wiki/Deinotherium Deinotherium]]'' (appropriately named "terrible beast") had two tusks ''growing out of the lower jaw''. The ancestral ''[[http://en.wikipedia.org/wiki/Moeritherium Moeritherium]]'' (classicaly mentioned as "the first elephant") didn't resemble even an elephant: with its short trunk and short limbs, it was more similar to a modern tapir. But even more normally-looking proboscideans would appear cool-looking by our standards: other than the aforementioned giant mammoths, see the [[http://en.wikipedia.org/wiki/Anancus European mastodon]] and its sword-like tusks, just as as example. And oh, don't forget some island-dwellers which lived in the Ice Ages and almost managed to survive until human history: the oxymoronic [[http://en.wikipedia.org/wiki/Dwarf_elephant dwarf elephants]]. Yes, they were real, and some ''sheep-sized''. Many of the larger elephant and elephant relative bones (and the smaller ones, too) which were found in the Mediterranean were identified by the ancient Greeks as the remaining bones of monsters, heroes and animals from the [[ClassicalMythology Age of Heroes.]] Some of these bones were identified as cyclopes, but no elephant skulls were. The fossils of Anceint Greece are way too fragmentary due to geological forces (earthquakes and volcanoes) to allow something as fragile as a skull to survive intact.

** Prehistoric [[http://en.wikipedia.org/wiki/Rodentia rodents]]: The rodents' fossil record is very scant: no surprise, since they are so small, and small animals usually hardly fossilize unlike the large ones. There were however some striking rodent in the past: for example, ''[[http://en.wikipedia.org/wiki/Castoroides Castoroides]]'' was a beaver-relative as large as a black bear; [[http://en.wikipedia.org/wiki/Ceratogaulidae ceratogaulids]] had a couple of hornlet on their nose; while several South American capybara-like forms, such as ''[[http://en.wikipedia.org/wiki/Phoberomys Phoberomys]]'', were ''cow-sized'' and the largest rodents ever. It's not a casual connection, that modern-day capybara (South-American as well) is the biggest modern rodent: as already said, South American mammals were, and still are, ''very unfamiliar'' to a North American or European observer.

** [[http://en.wikipedia.org/wiki/Bat Prehistoric bats]]: Just like birds, bats are a very poorly-known group in fossil record, both for the same reason: their skeleton is way too fragile to fossilize well. Despite this, awesomely well-preserved bat remains have been discovered in the most famous fossil deposit from Early Cenozoic: [[http://en.wikipedia.org/wiki/Messel_pit Messel Pit]], in Germany. This deposit has also many, many other early mammals: among them, the aforementioned hopping bug-eater ''Leptictidium'' and the basal ungulate ''[[http://en.wikipedia.org/wiki/Propalaeotherium Propalaeotherium]]'' have been recently made famous by Walking With (even though the propalaeothere ''wasn't'' an early "horse" as said in the program). These and other mammals from this deposit are so well preserved that ''even their fur and stomach contents are known''. In short, we know'em almost like they were still-living animals. The very first bats have been discovered here, and show us all the traits associated with their modern relatives: fingered wings, large ears, and even structure for echolocating are known from these finds. This has lead scientists to make an intriguing hypothesis: perhaps some sort of gliding proto-bats were already living on Earth ''before'' pterosaurs and non-avian dinosaurs disappeared? This would also mean bat-winged critters ''did'' exist at the Age of Dinosaurs, thus making the "Mesozoic bat-winged fliers" thing partially TruthInTelevision.

* ''[[http://en.wikipedia.org/wiki/Confuciusornis Confuciusornis]]'' from Early Cretaceous China had lost its teeth (convergently from modern birds) and shortened its tail, but still retained an old legacy: three-clawed wings. Its similar-looking cousin, ''[[http://en.wikipedia.org/wiki/Jeholornis Jeholornis]]'' from the same habitat, is also, not surprisingly, called ''[[http://en.wikipedia.org/wiki/Shenzhouraptor Shenzhouraptor]]''.

** [[http://en.wikipedia.org/wiki/Glyptodont Glyptodonts]]: After Ankylosaurs went extinct, evolution decided to create their mammalian equivalents: the glyptodonts. They were Xenarthrans as well, but related to armadillos rather than to sloths. Lived in South America for dozen million years, before going extinct only few thousands years ago: in short, they had the same identical history of their cousins, the giant sloths. Both groups were veggie-eaters (despite giant sloth might be at least partially scavengers), and when adult, they feared no predators except humans. There is a secret behind their success: their backbone. It was far, far stronger that every other mammal, thus permitting them carrying such heavy bodies around withouth suffering back pain. ''[[http://en.wikipedia.org/wiki/Glyptodon Glyptodon]]'' is the most well-known glyptodont, but it's also worth of mention ''[[http://en.wikipedia.org/wiki/Doedicurus Doedicurus]]'': with its mace-like tail, it was the most ''Ankylosaurus''-like of them all.

** [[http://en.wikipedia.org/wiki/Evolution_of_the_horse Horse ancestors]]: The eternal symbol of Evolution. Almost the same level the Dodo is the icon of extinction. And yet, horse ancestors weren't so cool-looking compared to most other extinct [[http://en.wikipedia.org/wiki/Ungulate hoofed mammals]], really. The most famous of these is, obviously, the [[RuleOfCool less horse-like]] of them all: ''Eohippus'' --> ''Hyracotherium'' --> ''[[http://en.wikipedia.org/wiki/Eohippus Eohippus]]'' --> ''Protorohippus''. An almost-unbelievable ScienceMarchesOn affair has encircled horse's evolution, despite its iconic role in popular science. Anyway, all this doesn't involve us so much. Expect to see this (whatever name is to be used) small, basal ungulate called ''horse'' anyway, despite it, actually, having nothing more in common with horses than with tapirs or rhinoceri: the "Hyracotheohippus stew" includes several different early ungulates, some of theme ''were'' horse-ancestors and some weren't. Systematics of primitive ungulates (many of them called [[http://en.wikipedia.org/wiki/Condylarthra Condylarths]]) is a total mess.

** ''[[http://en.wikipedia.org/wiki/Brontotherium Brontotherium]]'': This is the prototype of its group of mammals, the [[ExactlyWhatItSaysOnTheTin brontotheres]], whose cool name means "thunder beasts". While ''Uintatherium'' was not related with any modern hoofed mammals, brontotheres were distant relatives of [[http://en.wikipedia.org/wiki/Perissodactyla horses, tapirs and rhinos]]. They had a more rhino-like look than uintathere, having one single "horn" on their nose: ''Brontotherium'' 's prominence was forked and slingshot-like, while that of ''[[http://en.wikipedia.org/wiki/Embolotherium Embolotherium]]'' (the brontothere portrayed in [[WalkingWithDinosaurs Walking With Beasts]]) was shovel-like and not forked. Like uintathere, brontotheres too roamed plains of the northern continents in huge numbers in Early Cenozoic: then they eventually gone extinct, perhaps because they weren't capable to adapt to the diffusion of the very first grasslands which replaced their former food (made of scrub and non-grass herbs).

** [[http://en.wikipedia.org/wiki/Rhinoceros True prehistoric rhinos]]: Modern rhinos are often referred as "prehistoric-looking" in media. Many classic prehistoric mammals were indeed rhino-looking though with different horn-shapes (the aforementioned six-horned ''Uintatherium'' and the fork-horned ''Brontotherium'' are the most well-known examples), but only some of the extinct "rhinoceroses" were ''really'' such. Among them, the most spectacular were the [[http://en.wikipedia.org/wiki/Coelodonta_antiquitatis Woolly Rhino]], the [[http://en.wikipedia.org/wiki/Elasmotherium_sibiricum Unicorn Rhino]], and above all, the Indricothere (ironically, this one wasn't so rhino-looking). The Unicorn (''Elasmotherium sibiricum'') is often confused with the Woolly (''Coelodonta antiquitatis'') because of their similar appearence: however, the latter was not larger than modern white-rhinos and had ''two'' horns as well; the former was much larger (5 tons, like a modern bush elephant) and with one single horn... as long as a grown man, and put on the front rather than upon the nose: hence [[ExactlyWhatItSaysOnTheTin unicorn rhinoceros]]. About Paraceratheres, they deserve their own entry below.

** [[http://en.wikipedia.org/wiki/Paraceratherium Paracerathere]]: Here is Our Majesty, the largest land mammal ever lived (though some [[ScienceMarchesOn recent research]] seems to indicate that some mammoths were even larger). Despite its really gigantic size - it was as tall as an apatosaur up to the shoulders, and weighed as ''three'' elephants or, better, as three ''T. rex''es - it still had a quite slender, elegant frame: a sort of muscular giraffe with long neck, small head, and long, slender limbs. Its behavior itself was probably more giraffe-like than elephant-like, browsing the tree tops. In short, it was the new mammalian brachiosaur. Lived at the middle of the Cenozoic (the Age of Mammals). It's also a prime example of IHaveManyNames among prehistoric critters: now called ''Paraceratherium'', its traditional names are ''Indricotherium'' and ''Baluchitherium''.

** Prehistoric deer/pseudo-deer: Many prehistoric ungulates resembled deers in body-shape and head-shape, but again, not all were members of the [[http://en.wikipedia.org/wiki/Cervidae deer family]]. Many of them had very unfamiliar-looking horns/antlers above their heads. The most spectacular extinct cervid (and one of the most astonishing mammals ever) was ''[[http://en.wikipedia.org/wiki/Irish_elk Megaloceros giganteus]]'', commonly referred as the "Irish elk", though it was more related with European fallow-deer. This guy was moose-sized and with antlers which could make the mooses' ones appear insignificant in comparison: each one was ''as long as the entire animal's body'', and each one weighed more than 100 kg. Obviously, only males had such a thing above, as most modern deer. Among pseudo-deers, the most portrayed are ''[[http://en.wikipedia.org/wiki/Synthetoceras Synthetoceras]]'' and ''[[http://en.wikipedia.org/wiki/Sivatherium Sivatherium]]''. The former was antelope-shaped but with a bit of rhino inside: it had three horns, two of them were traditional-looking, but the third one was on its ''nose'' and was forked just like that of ''Brontotherium'', though longer and more slender. ''Sivatherium'' was moose-like and very large (2,5 m tall at the shoulder), and had deceptively moose-like pseudo-antlers: it actually was a giraffe relative, a sort of short-necked giraffe.

** [[http://en.wikipedia.org/wiki/Camelidae Prehistoric camels]]: In prehistory, extinct relatives of camels and llamas were very diversified: the great majority of them were North American. Some were even taller than our modern dromedaries: ''[[http://en.wikipedia.org/wiki/Aepycamelus Alticamelus]]'' was a sort of giraffe-like animal with very elongated neck and limbs. The well-known specializations for desert-life has appeared very recently in camel story, and regard only modern Old World species: their ancient North American relatives lived mainly in grasslands, thus is unlikely they would have fat-storing humps and resistence against thirst.

** [[http://en.wikipedia.org/wiki/Entelodontidae Entelodonts]]: Many hoofed mammals of the distant past were pig-like in shape: indeed, the pig-frame was the most primitive among "ungulates", still retained by some modern hoofed mammals, the best example being the tapir. Most prehistoric pseudo-boars were small, except Entelodonts: they were bison-sized at the most, and had several bony knobs on their head and jaws, resembling giant warthogs, but their tusks were much smaller than a warthog's or a babyrousa's, and didn't protrude out of the mouth. Their food habits are still unclear: they might be scavengers that drove away small predator from their kill, but also ate vegetation and might even be active hunters sometimes. North American ''[[http://en.wikipedia.org/wiki/Daeodon Daeodon]]'' (also called ''Dinohyus'') is the largest and one of the most depicted entelodont. [[WalkingWithDinosaurs Walking With Beasts]] has shown an unnamed Asian relative, and affected its appearence [[CarnivoreConfusion to make it scarier]], exaggerating the opening of its mouth.

** [[http://en.wikipedia.org/wiki/Meridiungulata South American Ungulates]]: South America was isolated from other continents for most of the Mammal Age, and thus its fauna developed in its own direction. There were not only elephant-size sloths and tank-like glyptodonts: there were also less-armoured but still odd-looking "ungulates", not related with any modern animal today, but similar in shape to camels, horses, hippos, buffalos, rhinos and even chalicotheres (a great example of Convergent Evolution). The two most represented are ''[[http://en.wikipedia.org/wiki/Macrauchenia Macrauchenia]]'' and ''[[http://en.wikipedia.org/wiki/Toxodon Toxodon]]''. ''Macrauchenia'' was a bit camel-like; often depicted with a floppy, elephantine nose because of the shape of its skull, but we don't know if it really had this thing. ''Toxodon'' was more like a stock-built, no-horned buffalo, but it has also been compared with a rhino or a hippo. These two guys lived during the Ice Ages in South American grasslands ("pampas").

** [[http://en.wikipedia.org/wiki/Evolution_of_cetaceans Early whales]]: ''All'' mammals were small and rodent-shaped in their evolutionary beginnings. Some became larger and more derived after the extinction of the dinosaurs, but none to the same level as whales. The first whale ancestors appeared only 10 million years or so after the non-avian dinosaurs' extinction. Once thought to have descended from doglike mesonychids (see above), whales [[ScienceMarchesOn are now thought to be]] [[http://en.wikipedia.org/wiki/Even-toed_ungulate artiodactyls]] (even-toed ungulates), such as camels, pigs, cattle, deer and particularly hippopotami. The first whales may have descended from the aforementioned antharcotheres, or possibly ''[[http://en.wikipedia.org/wiki/Indohyus Indohyus]]'', which was only discovered in 2007. They probably spent much of their time on land, feeding on dead fish and drowned animals. ''[[http://en.wikipedia.org/wiki/Ambulocetus Ambulocetus]]'' (the "walking whale") is a good example of this: still four-limbed, it was already a good swimmer, but still resembled anything but a whale. Among the first fish-shaped cetaceans, ''[[http://en.wikipedia.org/wiki/Basilosaurus Basilosaurus]]'' reached the length of a modern baleen whale, but was much more slender, almost eel-like. When first discovered, its elongated shape was misidentified for a mosasaur-like marine reptile: hence its strange, dinosaurian-sounding name ("king lizard"). At that time, all whales still were active hunters, like modern orcas and sperm whales; the first filter-feeders appeared much more recently, when our planet turned colder and immense shoals of krill began to float in polar waters. Other cetaceans, however, remained small and active predators, originating our dolphins.

** The most primitive Ungulates: Once, "ungulates" (hoofed mammals) were believed a natural group of mammals; now we know that several mammalian lineages reached the ungulate body-plan independently, and they do not make a real ensemble. Those which lived at the beginning of the Cenozoic were rather undifferentiated each other, and did not resemble most modern hoofed mammals. The two most famous are the small "ur-horse" ''Protorohippus'' and the large ''Uintatherium'', both from the Eocene epoch: among the other eocenic "ungulates", ''[[http://en.wikipedia.org/wiki/Coryphodon Coryphodon]]'' and ''[[http://en.wikipedia.org/wiki/Phenacodus Phenacodus]]'' are frequently portrayed in books. ''Coryphodon'' was perhaps the first land mammal to exceed 1 ton in weight, and was rather similar to an hippo in shape. ''Phenacodus'' was not larger than a dog: with its several small hoofed digits, it was similar to ''Eohippus'' with a very long tail, and it is often mentioned as the prototypical "basal ungulate". Just like ''Protorohippus'', ''Phenacodus'' could have been a possible prey of the famous giant bird ''Gastornis''; while the massive ''Coryphodon'' and ''Uintatherium'' were too powerful to be threatened by any predator when adults, like modern rhinos and elephants.

* [[http://en.wikipedia.org/wiki/Reptiliomorpha The closest reptile relatives]]: These "giant amphibians" deserve their own space here. The animals already mentioned belonged to two groups, the [[http://en.wikipedia.org/wiki/Lepospondyli Lepospondyls]] (''Diplocaulus'') and [[http://en.wikipedia.org/wiki/Temnospondyli Temnospondyls]] (all the others), both groups with uncertain affinities with modern frogs/salamander/caecilians (we still don't know from who the latter originated). This time we're talking about Reptiliomorphs ("reptile-shaped"); that is, tetrapods much closer to ''reptiles'' than to frog or ''Eryops''es. They had the same variety in shape and size as the other paleoamphibians, but were generally more land-living than the others, and progressively gained those traits which allow us humans to remain costantly out of water without dehydratating: waterproof skin, efficient lungs and kidneys for storing water, but above all, amniotic eggs; that is, those oval, shelled things we use to eat for dinner, and that come to our mind when hearing the word "egg". Before that, eggs were just those tiny, soft marbles modern frogs still produce today. Among quasi-reptiles, the most mentioned has long been the Early Permian ''[[http://en.wikipedia.org/wiki/Seymouria Seymouria]]'', because [[ScienceMarchesOn it was once considered the missing-link between amphibians and reptiles]]; now the most portrayed ones are the [[http://en.wikipedia.org/wiki/Embolomeri Anthracosaurs]], which were the dominant "amphibian" group in the Carboniferous, often (but not always) huge-sized. Also worth of mention are: the iguana-like ''[[http://en.wikipedia.org/wiki/Diadectes Diadectes]]'' from Early Permian, maybe one of the first herbivorous vertebrates ever appeared, along with plant-eating Synapsids like ''Edaphosaurus''; and the small, lizard-like ''[[http://en.wikipedia.org/wiki/Westlothiana Westlothiana]]'' from Early Carboniferous, which was for a short time believed the "first reptile", being even more ancient than the modern record-holder ''[[UsefulNotesPrehistoricLifeNonDinosaurianReptiles Hylonomus]]''.

* [[http://en.wikipedia.org/wiki/Reptiliomorpha The closest reptile relatives]]: These "giant amphibians" deserve their own space here. The animals already mentioned belonged to two groups, the [[http://en.wikipedia.org/wiki/Lepospondyli Lepospondyls]] (''Diplocaulus'') and [[http://en.wikipedia.org/wiki/Temnospondyli Temnospondyls]] (all the others), both groups with uncertain affinities with modern frogs/salamander/caecilians (we still don't know from who the latter originated). This time we're talking about Reptiliomorphs ("reptile-shaped"); that is, tetrapods much closer to ''reptiles'' than to frog or ''Eryops''es. They had the same variety in shape and size as the other paleoamphibians, but were generally more land-living than the others, and progressively gained those traits which allow us humans to remain costantly out of water without dehydratating: waterproof skin, efficient lungs and kidneys for storing water, but above all, amniotic eggs; that is, those oval, shelled things we use to eat for dinner, and that come to our mind when hearing the word "egg". Before that, eggs were just those tiny, soft marbles modern frogs still produce today. Among quasi-reptiles, the most mentioned has long been the Early Permian ''[[http://en.wikipedia.org/wiki/Seymouria Seymouria]]'', because [[ScienceMarchesOn it was once considered the missing-link between amphibians and reptiles]]; now the most portrayed ones are the [[http://en.wikipedia.org/wiki/Embolomeri Anthracosaurs]], which were the dominant "amphibian" group in the Carboniferous, often (but not always) huge-sized. Also worth of mention is the iguana-like ''[[http://en.wikipedia.org/wiki/Diadectes Diadectes]]'' from Early Permian, maybe one of the first herbivorous vertebrates ever appeared, along with plant-eating Synapsids like ''Edaphosaurus''.

* [[http://en.wikipedia.org/wiki/Cambrian_Explosion Cambrian Fauna]]: Cambrian. The first Paleozoic Period, in which the famous "Cambrian Explosion" of life happened. The less-known thing is, we humans are ''unbelievably lucky'' if we know that remote event. At that time, animals just were starting to achieve hard parts in their body, and we already know that, usually, soft-bodied organisms do not preserve at all. The astounding luck is, one of the greatest exceptions of this ruthless rule are ''just some deposits from the Cambrian Period.'' : it almost seem Ol'Mother Nature [[BecauseDestinySaysSo has done this deliberately for ourselves...]]. The most famous and historically relevant is the [[http://en.wikipedia.org/wiki/Burgess_Shale]] in British Columbia, but still others are also known (for example in China). For obvious reason, our curiosity now reaches the top: which were the first animals (not counting protozoans) that thrived in our oceans? Well, the answer is not simple: we can divide them in two ensembles. One is made from those groups either still alive today or extinct several ages after the Cambrian: among the former, most non-arthropod / non-cephalopod invertebrate groups already seen; among the latter, the Trilobites. We'll talk here about the second ensemble: many Cambrian invertebrates were indeed ''exclusive of the Cambrian'' and didn't survive long enough, not even to reach the following period, Ordovician (in which the most famous Paleozoic critters, sea-scorpions, nautiloids, armored fish etc. appeared). Thus, is easy to imagine many of them were ''really'' [[OurMonstersAreWeird bizarre-looking]] to our limited point of view. We still know very very few things about their lifestyle, but their appearence is extraordinarily well-known, because these Cambrian deposits ''have preserved soft-bodies''; not only that, they have preserved them very well! It would be too long to mention [[http://en.wikipedia.org/wiki/Burgess_Shale_type_fauna all the members]] of the Cambrian Fauna: see [[http://www.google.it/imgres?imgurl=http://www.trilobites.info/burgess_community_sm.jpg&imgrefurl=http://www.trilobites.info/triloclass.htm&usg=__s0Eofooa0oLw4onLe4Slh3sbJ6g=&h=479&w=720&sz=125&hl=it&start=10&zoom=1&um=1&itbs=1&tbnid=3LpTQO2S2iy5RM:&tbnh=93&tbnw=140&prev=/images%3Fq%3Dcambrian%2Bfauna%26um%3D1%26hl%3Dit%26rls%3Dcom.microsoft:en-US%26rlz%3D1I7ADBF_it%26tbs%3Disch:1&ei=lyRVTZfKAcTrOYLpxYAF the image here]] for having an idea. It's immediately recognizable the bizarre shrimp-like animal in the center, by far the biggest creature in this fauna, and arguably the top predator. It is called ''[[http://en.wikipedia.org/wiki/Anomalocaris Anomalocaris]]'' (meaning "[[ExactlyWhatItSaysOnTheTin bizarre shrimp]]" indeed), and was a distant relative of arthropods with no articulated legs but with the same composed eyes of the Trilobites. Of course it is the most portrayed Cambrian animal in documentaries and illustrations, classicaly mentioned as "[[PrehistoricMonster the first prehistoric monster ever appeared on Earth]]"; actually, if alive today, the "terrible" anomalocarid would appear as a really [[{{Narm}} narmy thing]], a sort of 3 ft long, shell-less, poncer-less lobster, nothing dangerous for a tough-boned, tough-muscled, tough-skinned mammal we are in comparison. Actually, anomalocarids were highly specialized predators, with a mouth build for prey around 1/12 of their own size. But at its time, all the other organism were ''very small'': The other creatures you see in the linked image are not longer than your hand, all possible prey for ''Anomalocaris''. Apart from the latter, we can mention at least other three invertebrates which are stock in drawings: ''[[http://en.wikipedia.org/wiki/Hallucigenia Hallucigenia]]'', ''[[http://en.wikipedia.org/wiki/Opabinia Opabinia]]'', and ''[[http://en.wikipedia.org/wiki/Pikaia Pikaia]]''. The first has a so strange look that its name means "hallucination-generator": it was a sort of "worm" with long paired spikes for uncertain purpose, and long softed paired legs: the reconstruction of ''Hallucigenia'' has had an astounding ScienceMarchesOn tangle for many years, and it still remains one of the most enigmatic Cambrian animal: nobody knowns exactly in which phylum it has to be placed. ''Opabinia'' was related with ''Anomalocaris'', but had an even weirder look: maybe no other fossil animal resembles a fiction-related extraterrestrial thing more than ''Opabinia''. It had ''five eyes'' put in circular fashion on its head, and a pincer-like grasp at the end of a long, flexible proboscis, often mistaken for the creatures mouth which was actually located behind the proboscis. But the most important find is the third guy, ''Pikaia'': despite its rather insignificant appearence, it is the most well-known among ''vertebrate ancestor'', a sort of prehistoric relative of our [[http://en.wikipedia.org/wiki/Lancelet Lancelet]] (the closest vertebrate relative still-living today). This relevance has made ''Pikaia'' one of the unofficial symbols of Evolution, just like the ur-amphibian ''Ichthyostega'', the ur-bird ''Archaeopteryx'' and the ur-horse ''Eohippus''. But wait....have you see these critters in TV at least once? A hard thing, even if you watched [[WalkingWithDinosaurs Walking With Monsters]]. In this RuleOfCool-filled show, the ''only real'' Cambrian invertebrate to appear is....Guess what? Well, the superpredator ''Anomalocaris'' of course! The other two invertebrate guys shown up are... [[TheyJustDidntCare a modern jellyfish]] and an [[AnachronismStew anachronistical phacopid trilobite]] (remember that phacopids first evolved in the Ordovician, while Cambrian trilobites were very different-looking to the classic image we have when thinking about these animals). The absence of such awesome animals like ''Opabinia'' and ''Hallucigenia'' makes another egregious example of a missed opportunity, like the missing of the giant bird ''Argentavis''. Talking about ''Pikaia'', this time its missing is no problem for us: the aforementioned proto-vertebrate ''Haikouichthys'' did perform its role. Still another thing: if you watch the list of creatures from the Burgess Shale, you'll note almost all animals (the main exception being ''Anomalocaris'') have uncommonly short scientific names, most of them ending in '''-a'''. A rather amusing thing to read, and - let's face it - a ''true'' oasis of happiness among so many other unutterable, absurdely-difficult names.

* [[http://en.wikipedia.org/wiki/Cambrian_Explosion Cambrian Fauna]]: Cambrian. The first Paleozoic Period, in which the famous "Cambrian Explosion" of life happened. The less-known thing is, we humans are ''unbelievably lucky'' if we know that remote event. At that time, animals just were starting to achieve hard parts in their body, and we already know that, usually, soft-bodied organisms do not preserve at all. The astounding luck is, one of the greatest exceptions of this ruthless rule are ''just some deposits from the Cambrian Period.'' : it almost seem Ol'Mother Nature [[BecauseDestinySaysSo has done this deliberately for ourselves...]]. The most famous and historically relevant is the [[http://en.wikipedia.org/wiki/Burgess_Shale]] in British Columbia, but still others are also known (for example in China). For obvious reason, our curiosity now reaches the top: which were the first animals (not counting protozoans) that thrived in our oceans? Well, the answer is not simple: we can divide them in two ensembles. One is made from those groups either still alive today or extinct several ages after the Cambrian: among the former, most non-arthropod / non-cephalopod invertebrate groups already seen; among the latter, the Trilobites. We'll talk here about the second ensemble: many Cambrian invertebrates were indeed ''exclusive of the Cambrian'' and didn't survive long enough, not even to reach the following period, Ordovician (in which the most famous Paleozoic critters, sea-scorpions, nautiloids, armored fish etc. appeared). Thus, is easy to imagine many of them were ''really'' [[OurMonstersAreWeird bizarre-looking]] to our limited point of view. We still know very very few things about their lifestyle, but their appearence is extraordinarily well-known, because these Cambrian deposits ''have preserved soft-bodies''; not only that, they have preserved them very well! It would be too long to mention [[http://en.wikipedia.org/wiki/Burgess_Shale_type_fauna all the members]] of the Cambrian Fauna: see [[http://www.google.it/imgres?imgurl=http://www.trilobites.info/burgess_community_sm.jpg&imgrefurl=http://www.trilobites.info/triloclass.htm&usg=__s0Eofooa0oLw4onLe4Slh3sbJ6g=&h=479&w=720&sz=125&hl=it&start=10&zoom=1&um=1&itbs=1&tbnid=3LpTQO2S2iy5RM:&tbnh=93&tbnw=140&prev=/images%3Fq%3Dcambrian%2Bfauna%26um%3D1%26hl%3Dit%26rls%3Dcom.microsoft:en-US%26rlz%3D1I7ADBF_it%26tbs%3Disch:1&ei=lyRVTZfKAcTrOYLpxYAF the image here]] for having an idea. It's immediately recognizable the bizarre shrimp-like animal in the center, by far the biggest creature in this fauna, and arguably the top predator. It is called ''[[http://en.wikipedia.org/wiki/Anomalocaris Anomalocaris]]'' (meaning "[[ExactlyWhatItSaysOnTheTin bizarre shrimp]]" indeed), and was a distant relative of arthropods with no articulated legs but with the same composed eyes of the Trilobites. Of course it is the most portrayed Cambrian animal in documentaries and illustrations, classicaly mentioned as "[[PrehistoricMonster the first prehistoric monster ever appeared on Earth]]"; actually, if alive today, the "terrible" anomalocarian would appear as a really [[{{Narm}} narmy thing]], a sort of 3 ft long lobster with a bit of jellyfish inside, nothing so dangerous for a tough-boned, tough-muscled, tough-skinned mammal we are in comparison. But at its time, all the other organism were ''very small'': the other guys you see in the linked image are not longer than your hand: all possible prey for ''Anomalocaris''. Apart from the latter, we can mention at least other three invertebrates which are stock in drawings: ''[[http://en.wikipedia.org/wiki/Hallucigenia Hallucigenia]]'', ''[[http://en.wikipedia.org/wiki/Opabinia Opabinia]]'', and ''[[http://en.wikipedia.org/wiki/Pikaia Pikaia]]''. The first has a so strange look that its name means "hallucination-generator": it was a sort of "worm" with long paired spikes for uncertain purpose, and long softed paired legs: the reconstruction of ''Hallucigenia'' has had an astounding ScienceMarchesOn tangle for many years, and it still remains one of the most enigmatic Cambrian animal: nobody knowns exactly in which phylum it has to be placed. ''Opabinia'' was related with ''Anomalocaris'', but had an even weirder look: maybe no other fossil animal resembles a fiction-related extraterrestrial thing more than ''Opabinia''. It had ''five eyes'' put in circular fashion on its head, and its mouth was pincer-like and at the end of a long, flexible proboscis. But the most important find is the third guy, ''Pikaia'': despite its rather insignificant appearence, it is the most well-known among ''vertebrate ancestor'', a sort of prehistoric relative of our [[http://en.wikipedia.org/wiki/Lancelet Lancelet]] (the closest vertebrate relative still-living today). This relevance has made ''Pikaia'' one of the unofficial symbols of Evolution, just like the ur-amphibian ''Ichthyostega'', the ur-bird ''Archaeopteryx'' and the ur-horse ''Eohippus''. But wait....have you see these critters in TV at least once? A hard thing, even if you watched [[WalkingWithDinosaurs Walking With Monsters]]. In this RuleOfCool-filled show, the ''only real'' Cambrian invertebrate to appear is....Guess what? Well, the superpredator ''Anomalocaris'' of course! The other two invertebrate guys shown up are... [[TheyJustDidntCare a modern jellyfish]] and an [[AnachronismStew anachronistical phacopid trilobite]] (remember that phacopids first evolved in the Ordovician, while Cambrian trilobites were very different-looking to the classic image we have when thinking about these animals). The absence of such awesome animals like ''Opabinia'' and ''Hallucigenia'' makes another egregious example of a missed opportunity, like the missing of the giant bird ''Argentavis''. Talking about ''Pikaia'', this time its missing is no problem for us: the aforementioned proto-vertebrate ''Haikouichthys'' did perform its role. Still another thing: if you watch the list of creatures from the Burgess Shale, you'll note almost all animals (the main exception being ''Anomalocaris'') have uncommonly short scientific names, most of them ending in '''-a'''. A rather amusing thing to read, and - let's face it - a ''true'' oasis of happiness among so many other unutterable, absurdely-difficult names.

** ''[[http://en.wikipedia.org/wiki/Argentavis Argentavis]]'': The aforementioned ''Teratornis'' had an earlier relative, which lived in South America 8 million years before: ''Argentavis'' (its name means "argentinian bird"). Why should we mention it separately? Well... simply because it deserves the GiantFlyer title more than every other prehistoric creature (beside pteranodonts and quetzalcoatls, obviously). Its wingspan was 25 ft (''as much as [[StockDinosaurs Pteranodon]]''); its weight 80 kg (as much as the two-times-wider-winged ''[[StockDinosaurs Quetzalcoatlus]]'', not to mention ''three times the weight of the Pteranodont''). Imagine a "flying ostrich" thing with [[ArabianNights huge roc-like wings]], a sharp beak and a love for carrion. With no doubt, the largest flying bird ever discovered. And yet, despite its coolness, ''Argentavis'' has yet to appear in fiction. And **heck**, it has actually had one single apparition in documentaries to date: "Paleoworld", as a ''side-note'' of Phorusrhacids! Since [[WalkingWithDinosaurs Walking With Beasts]] producers did recreate ''Argentavis'' world (the Sabretooth episode, in which "terrorbirds" did appear)... they made an egregious example of MissedMomentOfAwesome.

* [[http://en.wikipedia.org/wiki/Cambrian_Explosion Cambrian Fauna]]: Cambrian. The first Paleozoic Period, in which the famous "Cambrian Explosion" of life happened. The less-known thing is, we humans are ''unbelievably lucky'' if we know that remote event. At that time, animals just were starting to achieve hard parts in their body, and we already know that, usually, soft-bodied organisms do not preserve at all. The astounding luck is, one of the greatest exceptions of this ruthless rule are ''just some deposits from the Cambrian Period.'' : it almost seem Ol'Mother Nature [[BecauseDestinySaysSo has done this deliberately for ourselves...]]. The most famous and historically relevant is the [[http://en.wikipedia.org/wiki/Burgess_Shale]] in British Columbia, but still others are also known (for example in China). For obvious reason, our curiosity now reaches the top: which were the first animals (not counting protozoans) that thrived in our oceans? Well, the answer is not simple: we can divide them in two ensembles. One is made from those groups either still alive today or extinct several ages after the Cambrian: among the former, most non-arthropod / non-cephalopod invertebrate groups already seen; among the latter, the Trilobites. We'll talk here about the second ensemble: many Cambrian invertebrates were indeed ''exclusive of the Cambrian'' and didn't survive long enough, not even to reach the following period, Ordovician (in which the most famous Paleozoic critters, sea-scorpions, nautiloids, armored fish etc. appeared). Thus, is easy to imagine many of them were ''really'' [[OurMonstersAreWeird bizarre-looking]] to our limited point of view. We still know very very few things about their lifestyle, but their appearence is extraordinarily well-known, because these Cambrian deposits ''have preserved soft-bodies''; not only that, they have preserved them very well! It would be too long to mention [[http://en.wikipedia.org/wiki/Burgess_Shale_type_fauna all the members]] of the Cambrian Fauna: see [[http://www.google.it/imgres?imgurl=http://www.trilobites.info/burgess_community_sm.jpg&imgrefurl=http://www.trilobites.info/triloclass.htm&usg=__s0Eofooa0oLw4onLe4Slh3sbJ6g=&h=479&w=720&sz=125&hl=it&start=10&zoom=1&um=1&itbs=1&tbnid=3LpTQO2S2iy5RM:&tbnh=93&tbnw=140&prev=/images%3Fq%3Dcambrian%2Bfauna%26um%3D1%26hl%3Dit%26rls%3Dcom.microsoft:en-US%26rlz%3D1I7ADBF_it%26tbs%3Disch:1&ei=lyRVTZfKAcTrOYLpxYAF the image here]] for having an idea. It's immediately recognizable the bizarre shrimp-like animal in the center, by far the biggest creature in this fauna, and arguably the top predator. It is called ''[[http://en.wikipedia.org/wiki/Anomalocaris Anomalocaris]]'' (meaning "[[ExactlyWhatItSaysOnTheTin bizarre shrimp]]" indeed), and was a distant relative of arthropods with no articulated legs but with the same composed eyes of the Trilobites. Of course it is the most portrayed Cambrian animal in documentaries and illustrations, classicaly mentioned as "[[PrehistoricMonster the first prehistoric monster ever appeared on Earth]]"; actually, if alive today, the "terrible" anomalocarian would appear as a really [[{{Narm}} narmy thing]], a sort of 3 ft long lobster with a bit of jellyfish inside, nothing so dangerous for a tough-boned, tough-muscled, tough-skinned mammal we are in comparison. But at its time, all the other organism were ''very small'': the other guys you see in the linked image are not longer than your hand: all possible prey for ''Anomalocaris''. Apart from the latter, we can mention at least other three invertebrates which are stock in drawings: ''[[http://en.wikipedia.org/wiki/Hallucigenia Hallucigenia]]'', ''[[http://en.wikipedia.org/wiki/Opabinia Opabinia]]'', and ''[[http://en.wikipedia.org/wiki/Pikaia Pikaia]]''. The first has a so strange look that its name means "hallucination-generator": it was a sort of "worm" with long paired spikes for uncertain purpose, and long softed paired legs: the reconstruction of ''Hallucigenia'' has had an astounding ScienceMarchesOn tangle for many years, and it still remains one of the most enigmatic Cambrian animal: nobody knowns exactly in which phylum it has to be placed. ''Opabinia'' was related with ''Anomalocaris'', but had an even weirder look: maybe no other fossil animal resembles a fiction-related extraterrestrial thing more than ''Opabinia''. It had ''five eyes'' put in circular fashion on its head, and its mouth was pincer-like and at the end of a long, flexible proboscis. But the most important find is the third guy, ''Pikaia'': despite its rather insignificant appearence, it is the most well-known among ''vertebrate ancestor'', a sort of prehistoric relative of our [[http://en.wikipedia.org/wiki/Lancelet Lancelet]] (the closest vertebrate relative still-living today). This relevance has made ''Pikaia'' one of the unofficial symbols of Evolution, just like the ur-amphibian ''Ichthyostega'', the ur-bird ''Archaeopteryx'' and the ur-horse ''Eohippus''. But wait....have you see these critters in TV at least once? A hard thing, even if you watched [[WalkingWithDinosaurs Walking With Monsters]]. In this RuleOfCool-filled show, the ''only real'' Cambrian invertebrate to appear is....Guess what? Well, the superpredator ''Anomalocaris'' of course! The other two invertebrate guys shown up are... [[TheyJustDidntCare a modern jellyfish]] and an [[AnachronismStew anachronistical phacopid trilobite]] (remember that phacopids first evolved in the Ordovician, while Cambrian trilobites were very different-looking to the classic image we have when thinking about these animals). The absence of such awesome animals like ''Opabinia'' and ''Hallucigenia'' makes another egregious example of MissedMomentOfAwesome, like the missing of the giant bird ''Argentavis''. Talking about ''Pikaia'', this time its missing is no problem for us: the aforementioned proto-vertebrate ''Haikouichthys'' did perform its role. Still another thing: if you watch the list of creatures from the Burgess Shale, you'll note almost all animals (the main exception being ''Anomalocaris'') have uncommonly short scientific names, most of them ending in '''-a'''. A rather amusing thing to read, and - let's face it - a ''true'' oasis of happiness among so many other unutterable, absurdely-difficult names.

As said in StockDinosaurs, only ''few'' kinds of prehistoric mammals will appear in Fictionland, generally those from the Ice Ages. EverythingsBetterWithDinosaurs, useless to say it. But if there weren't dinos, extinct mammals as a whole would be much, ''much'' more popular than they are today: a lot of them were in RealLife as large and powerful as many stock dinosaurs. Not to mention the fact a consistent part of them were the ancestors of modern hairy, milk-producing vertebrates. In short, they would be ''very'' interesting guys to show in fiction. And yet most of them still remain docu-related animals - if they're lucky enough. Programs from the 2000s like ''[[WalkingWithDinosaurs Walking With Beasts]]'' and the ''IceAge'' film series tried to partially avert the trope, but even these shows didn't escape the EverythingsBetterWithDinosaurs fate: not only the well-known case of "Dawn of Dinosaurs". Though it's little-known, Walking With was initially intended to show ''prehistoric mammals'', but producers received money "only for a show about dinosaurs" - only after the dinosaurs' success they could start with ''Beasts'', changed to a simple sequel at that point. Here is a '''very''' partial list of extinct mammals. If you want to see more about the stock ones (Mammoths and Sabertoothed Cats) see StockDinosaurs.

** [[http://en.wikipedia.org/wiki/Evolution_of_the_horse Horse ancestors]]: The eternal symbol of Evolution. Almost the same level the Dodo is the icon of extinction. And yet, horse ancestors weren't so cool-looking compared to most other extinct [[http://en.wikipedia.org/wiki/Ungulate hoofed mammals]], really. The most famous of these is, obviously, the [[RuleOfCool less horse-like]] of them all: ''Eohippus'' --> ''Hyracotherium'' --> ''[[http://en.wikipedia.org/wiki/Eohippus Eohippus]]''. --> ''Protorohippus''. An almost-unbelievable ScienceMarchesOn affair has encircled horse's evolution, despite its iconic role in popular-science. Anyway, all this doesn't involve us so much. Expect to see this (whatever name is to be used) small, basal ungulate called ''horse'' anyway, despite it, actually, had nothing more in common with horses than with tapirs or rhinoceri: the "Hyracotheohippus stew" includes several different early ungulates, some of theme ''were'' horse-ancestors and some weren't. Systematics of primitive ungulates (many of them called [[http://en.wikipedia.org/wiki/Condylarthra Condylarths]]) is a total mess.

** ''[[http://en.wikipedia.org/wiki/Uintatherium Uintatherium]]'': As we'll say later, not all rhinoceros-looking fossil mammals were real rhinos; but they'll probably get [[DidNotDoTheResearch identified as such in popular media]]. The most well-known are ''Uintatherium'' and ''Brontotherium'', both found in huge numbers in several fossil deposits of Western Usa. The poor Uintathere is perhaps [[TheWoobie the most mistreated]] extinct mammal of them all: expect somebody describing its appearence as "[[PrehistoricMonster monstrous/scary]]". Right, it had six giraffe-like horns and two upper protruding tusks: but, honestly, ''Uintatherium'' if alive today would appear not more scary than an elephant, rhino, hippo or giraffe... Also expect a crack about its "tiny" brain (just what happens to its Woobiesaurian equivalent, ''[[StockDinosaurs Stegosaurus]]''), and just like the stego, expect the writer saying [[TooDumbToLive its dumbness being the real reason of its extinction!]] In RealLife, Uintatheres were among the very first mammals to reach large size (up to a modern-day rhino), and their body-plan was ''very successful'' at the time, to the point they roamed northern continents in huge numbers for million years in Early Cenozoic, before being substituted by the even larger Brontotheres (see below).

** ''[[http://en.wikipedia.org/wiki/Brontotherium Brontotherium]]'': This is the prototype of its group of mammals, the [[ExactlyWhatItSaysOnTheTin brontotheres]], whose cool name means "thunder beasts". While ''Uintatherium'' was not related with any modern hoofed mammals, Brontotheres were distant relatives of [[http://en.wikipedia.org/wiki/Perissodactyla horses, tapirs and rhinos]]. They had a more rhino-like look than uintathere, having one single "horn" on their nose: ''Brontotherium'' 's prominence was forked and slingshot-like, while that of ''[[http://en.wikipedia.org/wiki/Embolotherium Embolotherium]]'' (the brontothere portrayed in [[WalkingWithDinosaurs Walking With Beasts]]) was shovel-like and not forked. Like uintathere, brontotheres too roamed plains of the Northern Continents in huge numbers in Early Cenozoic: then they eventually gone extinct, perhaps because they weren't capable to adapt to the diffusion of the very first grasslands which replaced their former food (made of scrub and non-grass herbs).

** [[http://en.wikipedia.org/wiki/Proboscidea Other elephant relatives]]: There were A LOT of them in Prehistory: not so in {{Prehistoria}}. Don't expect to see any proboscidean in TV outside docus unless it's a Woolly Mammoth or an [[StockDinosaurs American Mastodon]], even though many of them were far cooler-looking than the latter. If you don't believe us, take a look on these: the shovel-jawed ''[[http://en.wikipedia.org/wiki/Platybelodon Platybelodon]]'' resembled a cross between an elephant and a hippo. The huge ''[[http://en.wikipedia.org/wiki/Deinotherium Deinotherium]]'' had two tusks ''on the lower jaw''. The ancestral ''[[http://en.wikipedia.org/wiki/Moeritherium Moeritherium]]'' (classicaly mentioned as "the first elephant") didn't resemble even an elephant: with its short trunk and short limbs, it was more similar to a modern tapir. But even more normally-looking proboscideans would appear cool-looking by our standards: other than the aforementioned giant mammoths, see the [[http://en.wikipedia.org/wiki/Anancus European Mastodon]] and its sword-like tusks, just as as example. And oh, don't forget some island-dwellers which lived in the Ice Ages and almost managed to survive until human history: the oxymoronic [[http://en.wikipedia.org/wiki/Dwarf_elephant Dwarf Elephants]]. Yes, they were real, and some ''sheep-sized''. Many of the larger elephant and elephant-relative bones (and the smaller ones too) which were found in the Mediterranean were identified by the ancient Greeks as the remaining bones of monsters, heroes and animals from the [[ClassicalMythology Age of Heroes.]] Some of these bones were identified as Cyclopes, but no elephant skulls were. The Fossils of Anceint Greece are way to fragment due to geologic forces (earthquakes and volcanoes) to allow something as fragile as a skull to survive intact.

** [[http://en.wikipedia.org/wiki/Paraceratherium Paracerathere]]: Here is Our Majesty, the largest land mammal ever lived (though some [[ScienceMarchesOn recent research]] seems to indicate that some mammoths were even larger). Despite its really gigantic size - it was as tall as an apatosaur up to the shoulders, and weighed as ''three'' elephants or, better, as three ''T. rex''es - it still had a quite slender, elegant frame: a sort of muscular giraffe with long neck, small head, and long, slender limbs. Its behavior itself was probably more giraffe-like than elephant-like, browsing the tree tops. In short, it was the new mammalian Brachiosaur. Lived at the middle of the Cenozoic (the Mammal Age). It's also a prime example of IHaveManyNames among prehistoric critters: now called ''Paraceratherium'', its traditional names are ''Indricotherium'' and ''Baluchitherium''.

** [[http://en.wikipedia.org/wiki/Chalicotheriidae Chalicotheres]]: The best example of MixAndMatchCritter among prehistoric mammals: they had the head of an horse, the body-shape of a gorilla, and sloth-like forelimbs with hooked claws for pulling down branches: some nickname them "sloth-horses". A very successful group of hoofed mammals, distantly related to horses and rhinos (like the aforementioned brontotheres); they roamed for a long time in most continents, and some [[WildMassGuessing think]] the famous "Nandy Bear" that could live in modern African rainforests is just a surviving chalicothere. The two most well-known family-members are the north-american ''[[http://en.wikipedia.org/wiki/Moropus Moropus]]'' and the Asian namesake ''[[http://en.wikipedia.org/wiki/Chalicotherium Chalicotherium]]'' - the latter was even stranger since literally ''knuckle-walked'' like a gorilla.

** ''[[http://en.wikipedia.org/wiki/Arsinoitherium Arsinoitherium]]'': Sometimes misspelled "Arsinotherium", it was the most peculiar-looking among the aforementioned "pseudo-rhinos", with its huge, yet light-weighed, hollow "double-horn". The same size of modern rhinoceroses, this animal is often described as a "cross between a rhino and a hippo" because of its short legs and amphibian habits: it lived along the coasts bordering the shallow seas which covered modern-day Egypt, together with the ur-elephant ''Moeritherium''. It's worth noting that, unlike ''Moeritherium'', ''Arsinoitherium'' was ''not'' an elephant-predecessor as said in [[WalkingWithDinosaurs Sea Monsters]], and maybe didn't have that tapir-like nose seen in the program: this mammal is so strange that it is put in its own mammalian order, the Embrithopods, only distantly related with elephants.

** [[http://en.wikipedia.org/wiki/Entelodontidae Entelodonts]]: Many hoofed mammals of the distant past were pig-like in shape: indeed, the pig-frame was the most primitive among "ungulates", still retained by some modern hoofed mammals, the best example being the tapir. Most prehistoric pseudo-boars were small, except Entelodonts: they were bison-sized at the most, and had several bony knobs on their head and jaws, resembling giant warthogs, but their tusks were much smaller than a warthog's or a babyrousa's, and didn't protrude out of the mouth. Their food habits are still unclear: they might be scavengers that drove away small predator from their kill, but also ate vegetation and might even be active hunters sometimes. North American ''[[http://en.wikipedia.org/wiki/Dinohyus Dinohyus]]'' (also called ''Daeodon'') is the largest and most depicted entelodont. [[WalkingWithDinosaurs Walking With]] has shown up an Asian unnamed relative, and affected its appearence [[CarnivoreConfusion to make it scarier]], exagerrating the opening of its mouth.

** ''[[http://en.wikipedia.org/wiki/Andrewsarchus Andrewsarchus]]'': One of the most enigmatic mammals, from the first part of the Cenozoic (the Eocene period). Only a skull is known, 3 ft long and vaguely wolf-like. Some argue it was the largest carnivorous land mammal ever, but we haven't any proof about that; it might be omnivorous instead. It was traditionally considered to be closely related to the much smaller [[http://en.wikipedia.org/wiki/Mesonychia Mesonychians]], the first meat-eating mammals which obtained a size larger than a house cat; however, [[http://scienceblogs.com/tetrapodzoology/2009/08/mesonychians_part_iii_andrewsa.php later]] [[http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0007062 phylogenetic studies]] indicate that it might have actually been a close relative of the aforementioned entelodonts (though obviously any phylogenetic placement is only tentative at this point). The mesonychians were once considered the ancestors of whales (see below) because of the shape of their skull that resembles the most primitive cetacean known, ''[[http://en.wikipedia.org/wiki/Pakicetus Pakicetus]]''; now we know [[ScienceMarchesOn hippopotamus]] is the closest relative of whales and dolphins. The fossil record of prehistoric hippos is poorly known; on the other hand, the similar-looking [[http://en.wikipedia.org/wiki/Anthracotheriidae Anthracotheres]] have a rich number of species described, they were probably the closest hippopotamus relatives, or even their ancestors.

** [[http://en.wikipedia.org/wiki/Evolution_of_cetaceans Early whales]]: ''All'' mammals were small and rodent-shaped at their beginnings. Then some became larger and more derived, but none with the same level as whales. The first whale ancestors appeared only 10 million years after the non-avian dinosaurs' extinction. Once thought to have descended from doglike mesonychids (see above) whales are now thought to be close relatives of artiodactyls (even-toed ungulates), such as camels, pigs, cattle and deer. The first whales probably spent much of their time on land. ''[[http://en.wikipedia.org/wiki/Ambulocetus Ambulocetus]]'' (the "walking whale") is a good example of this: still four-limbed, it was already a good swimmer, but still resembled anything but a whale. Among the first fish-shaped cetaceans, ''[[http://en.wikipedia.org/wiki/Basilosaurus Basilosaurus]]'' reached the length of a modern baleen whale, but was much more slender, almost eel-like. When first discovered, its elongated shape was misidentified for a mosasaur-like marine reptile: hence its strange, dinosaurian-sounding name ("king lizard"). At that time, all whales still were active hunters, like modern killer- and sperm- whales; the first filter-feeders appeared much more recently, when our planet turned colder and immense shoals of krill began to float in polar waters. Other cetaceans, however, remained small and active predators, originating our dolphins.

** The most primitive Ungulates: Once, "ungulates" (hoofed mammals) were believed a natural group of mammals; now ke know that several mammalian lineages reached the ungulate body-plan independently, and they do not make a real ensemble. Those which lived at the beginning of the Cenozoic were rather undifferentiated each other, and did not resemble most modern hoofed mammals. The two most famous are the small "ur-horse" ''Protorohippus'' and the large ''Uintatherium'', both from the Eocene epoch: among the other eocenic "ungulates", ''[[http://en.wikipedia.org/wiki/Coryphodon Coryphodon]]'' and ''[[http://en.wikipedia.org/wiki/Phenacodus Phenacodus]]'' are frequently portrayed in books. ''Coryphodon'' was perhaps the first land mammal to exceed 1 ton in weight, and was rather similar to an hippo in shape. ''Phenacodus'' was not larger than a dog: with its several small hoofed digits, it was similar to ''Eohippus'' with a very long tail, and it is often mentioned as the prototypical "basal ungulate". Just like ''Eohippus'', ''Phenacodus'' could have been a possible prey of the famous giant bird ''Gastornis''; while the massive ''Coryphodon'' and ''Uintatherium'' were too powerful to be threatened by any predator when adults, like modern rhinos and elephants.

** [[http://en.wikipedia.org/wiki/Ursidae Prehistoric bears]]: Bears are a very recent group. They have roamed our planet only since 5-10 million years. Many prehistoric bears were rather different than our grizzlies: for example, the North-American [[http://en.wikipedia.org/wiki/Arctodus short-faced bear]] had long limbs and [[ExactlyWhatItSaysOnTheTin bulldog-like snout]] and was probably an agile runner and specialized hunter. The most famous extinct bear is, however, the [[http://en.wikipedia.org/wiki/Ursus_spelaeus Cave Bear]], quite similar to a modern kodiak in shape and size. It is often portrayed as the archenemy of Neanderthals, because both lived in the same places (Ice Ages Europe) and were forced to share the same caves to repair themselves from the rigid Ice Age winters. Its fossil record is very abundant in European caves.

** Prehistoric [[http://en.wikipedia.org/wiki/Canidae canids]] and [[http://en.wikipedia.org/wiki/Hyaenidae hyenas]]: Prehistoric wolves and hyenas were not so different-looking than ours, but sometimes were larger. The [[http://en.wikipedia.org/wiki/Canis_dirus Dire Wolf]] has been often found in the same tarpits in which ''Smilodon'' remains have been discovered, along with several other American mammals (elephant relatives, ground sloths, but modern-living mammals as well); the most famous is [[http://en.wikipedia.org/wiki/La_Brea_Tar_Pits Rancho la Brea]], within Los Angeles. Among extinct hyenas we can mention the [[http://en.wikipedia.org/wiki/Cave_hyena Cave Hyena]], similar to modern spotted hyenas but living in northern territories during the Ice Ages. Some extinct canid were deceptively hyena-like: ''[[http://en.wikipedia.org/wiki/Borophagus Osteoborus]]'' from Middle Cenozoic is one example.

** [[http://en.wikipedia.org/wiki/Amphicyonidae Bear-dogs]] and [[http://en.wikipedia.org/wiki/Nimravidae Pseudo-cats]]: Before cat, bears, dogs and hyenas appeared on Earth, there were their pseudo-looking relatives, whose appearence was similar to their successors or a mix of these animals. The aforementioned ''Eusmilus'' was indeed a sabretoothed member of the pseudo-cat family. A [[AllAnimalsAreDogs very dog-like]] "bear-dog" appears in [[WalkingWithDinosaurs Walking With Beasts]].

** The most primitive [[http://en.wikipedia.org/wiki/Carnivora Carnivores]]: True carnivore (members of the order Carnivora) appeared soon after the start of the Mammal Age, but remained small and unspecialized for a long amount of time. In the Eocene most of them were still weasel- or genet-like like ''[[http://en.wikipedia.org/wiki/Miacis Miacis]]'' , but they already showed the separation in the two main branches still-living today: the [[http://en.wikipedia.org/wiki/Caniformia dog branch]] (dogs, bears, raccoons, weasels and ''seals'') and the [[http://en.wikipedia.org/wiki/Feliformia cat branch]] (cats, genets, mongooses and ''hyenas''). All modern large-sized carnivores from bears to lions, from wolves to the walrus, descend from weasel- shaped critters. However, many small carnivores retain still today their ancient shape/size: because of their smallness, they are much less abundant in fossil record and their evolution is less understood.

** [[http://en.wikipedia.org/wiki/Creodontia Creodonts]]: In Early Cenozoic, at the time "true" carnivores were still weasel-like, Creodonts occupied the ecological niche ruled by modern large carnivores. Very diversified in shape and size, they were more primitive and arguably slower-moving than our meat-eating mammals: this has been often cited as the cause of their extincion, but scientists aren't sure of that. ''[[http://en.wikipedia.org/wiki/Hyaenodon Hyaenodon]]'' is regarded as the stock creodont. The largest hyenodont species appears in Walking With as a formidable predator, but some hypothize it was mostly a scavenger.

** Non-cetacean marine mammals: While cetaceans' natural history is now well-known, that of [[http://en.wikipedia.org/wiki/Pinnipedia Pinnipeds]] (seals, sea-lions, walruses etc.) is still poorly-known: we are sure however, they descended from bear-like or otter-like ancestors, and are a more recent group than whales. On the other hand, the third group of sea mammals, [[http://en.wikipedia.org/wiki/Sirenia Sirenians]] (manatees and dugongs), are as ancient as cetaceans, but the first ones already had the shape of the modern ones. There was a forth group of sea-mammal in the Cenozoic, the little-known [[http://en.wikipedia.org/wiki/Desmostylia Desmostylians]], a sort of "herbivorous seals" which looked a bit like walruses, but ate weeds like hippos and were related to manatees.

** Prehistoric "insectivores": Traditionally we have put in this group all those mammals whose anatomy is comparable to that of most Mesozoic mammals: small size, generic mouse-like look and non-specialized teeth. Actually modern insectivores (bug-eaters) are very different among each other; while the most commonly known (hedgehog, mole, shrew) ''are'' closely related, many other less-familiar insectivores are not. Their resemblance is just due to the fact they still preserve a body-plan similar to the most common one in the Mesozoic, while non-insectivoran mammals modified it becoming more recognizable. Several "insectivores" are known from the Cenozoic's fossil record, but they, being usually small, are rather uncommon like rodents. Maybe the most famous and specialized is ''[[http://en.wikipedia.org/wiki/Leptictidium Leptictidium]]'', a hopping animal similar to a miniaturized kangaroo with a shrew-like head and teeth; not related with any modern mammal, ''Leptictidium'' appears the main character in the first [[WalkingWithDinosaurs Walking With Beasts]] episode.

** Mammals of prehistoric Australia: Australian mammalofauna hasn't changed much since the non-avian dinosaur extinction (not counting human influence of course): there have always been [[http://en.wikipedia.org/wiki/Marsupialia marsupials]] and [[http://en.wikipedia.org/wiki/Monotremata monotremes]] in the LandDownunder. Since modern Australian mammals are already so bizarre-looking, how would their predecessors have looked? Not unlike their descendents, really; but some were a bit larger. [[http://en.wikipedia.org/wiki/Procoptodon Giant Kangaroos]] were 10 ft tall, with a short tail and a flat snout; while [[http://en.wikipedia.org/wiki/Diprotodon Diprotodonts]] were even larger, ''rhino-sized'', but were wombat relatives, and thus vegetarian. Monotremes too were amazing: the [[http://en.wikipedia.org/wiki/Zaglossus Giant Echidna]] was as large as a sheep. Nevertheless, there was also an unique animal which has no modern relatives: the [[http://en.wikipedia.org/wiki/Thylacoleo Marsupial Lion]], so-called because of its body-shape and sharp claws, but with ''rodent-like incisors'' instead of the classic fangs. Scientist thought it was indeed vegetarian; now they know it was predatory, just like another unusual marsupial from South America: the aforementioned "marsupial sabretooth", ''[[http://en.wikipedia.org/wiki/Thylacosmilus Thylacosmilus]]''. Yes, there weren't only possums, once, in South America.

** [[http://en.wikipedia.org/wiki/Bat Prehistoric bats]]: Just like birds, bats are a very poorly-known group in fossil record, both for the same reason: their skeleton is way too fragile to fossilize well. Despite this, awesomely well-preserved bat remains have been discovered in the most famous fossil deposit from Early Cenozoic: [[http://en.wikipedia.org/wiki/Messel_pit Messel Pit]], in Germany. This deposit has also many, many other early mammals: among them, the aforementioned hopping bug-eater ''Leptictidium'' and the basal ungulate ''[[http://en.wikipedia.org/wiki/Propalaeotherium Propalaeotherium]]'' have been recently made famous by Walking With (even though the propalaeothere ''wasn't'' an early "horse" as said in the program). These and other mammals from this deposit are so well preserved that ''even their fur and stomach contents are known''. In short, we know'em almost like they were still-living animals. The very first bats have been discovered here, and show us all the traits associated with their modern relatives: fingered wings, large ears, and even structure for echolocating are known from these finds. This has lead scientist to make an intriguing hypothesis: perhaps were some sort of gliding proto-bats already living on Earth ''before'' pterosaurs and non-avian dinosaurs disappeared? This would also mean bat-winged critters ''did'' exist at the Age of Dinosaurs, thus making the "Mesozoic bat-winged fliers" thing partially TruthInTelevision.