The critters in this page pertain to groups of "biota" (= living beings) that have by old-fashioned biologists been quoted as "lower-ranking" than the so-called "higher animals" aka mammals + birds. [[note]] Reptiles may get placed in either one category or the other depending on scientific age and their subgroup. In the past, all reptiles were usually labeled as "lower animals", but [[ScienceMarchesOn today]] the closest-to-mammals/birds ones (dinosaurs, pterosaurs, and sometimes therapsids and crocodilians) tend to be upgraded, while non-croc living reptiles and their ancestors (and the extinct sea reptiles as well) tend to be still considered more similar to "lower animals".[[/note]]

However, modern scientists do not accept such an unfairly "racistic" distinction. Furthermore, "lower animals" often show biological traits and behaviours traditionally considered typical of mammals and birds: social attitudes, parental care, intelligence, even some "warm-blood" abilities. On the other hand, in popular media they may be treated as stupid/unfeeling brutes even to this day. Documentaries not excluded: within the ''[[WalkingWithDinosaurs Walking With]]'' series, for example, ''Walking With Dinosaurs'' and ''Walking With Beasts'' show dinosaurs and mammals as smart/social/caring creatures, while the meaningfully-named ''Walking With [[PrehistoricMonster Monsters]]'' and ''[[SeaMonster Sea Monsters]]'' focus mainly to non-dino reptiles and to all the animal groups listed below, with only animals with bones shown as being smart/social/caring (YouFailBiologyForever).

We humans should be more grateful to extinct "lower beasts" however: several of them gave rise to many modern animals, and some did that to Mankind itself (yes, there were not only APES among our ancestors!). And don't think they were boring, uninteresting creatures: anything but, as you'll see soon.


In paleontology, the word "amphibian" has traditionally had a much broader meaning than that commonly attributed. Amphibians have been all [[ tetrapods]] (four-limbed vertebrates) excluded amniotes (reptiles + mammals). Today, even scientists tend to restrict the world to indicate only modern frogs, salamanders, 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, and non-caecilian animals.

Lissamphibians excluded, prehistoric amphibians 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. 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 synapsids and Mesozoic mammals, they have not gained much attention in pop culture. If they appear at all in fictional works, they'll be simply described as "giant amphibians".

Hopping, crawling, and digging: ''[[ Triadobatrachus]]'', ''[[ Karaurus]]'', ''[[ Andrias]]'', and ''[[ Eocaecilia]]''

* The only real amphibians in modern taxonomy, lissamphibians (frogs + salamanders + caecilians) appeared in the Triassic together with the first dinosaurs, but their deepest origins and their relationship with extinct amphibian groups are still unclear. The first frogs (''Triadobatrachus'' is the most cited example) were already like the modern ones, only with shorter hind legs less adapted for hopping. Frogs have possibly been the most evolved amphibians ever, with their complex social behaviours and the ability to produce loud vocal sounds (this ability is atypical for a non-mammal / non-archosaur vertebrate). On the other hand, extinct salamanders have retained the primitive crawling shape of early amphibians. It's curious the case of ''Andrias scheuchzeri'' (a close relative of the modern Japanese Giant Salamander) which was initially believed a ''man dead during the Biblic Great Deluge'' ("Andrias" just means "man" in Greek). About the legless worm-like caecilians, they are as little known in palaeontology as they are in RealLife. Their fossils are extremely rare, but they are believed to have had small limbs at the start of their evolution (ex. ''Eocaecilia'').

Boomerang-heads, eel-bodies, and whip-tails: ''[[ Diplocaulus]]'', ''[[ Phlegethontia]]'', and ''[[ Urocordylus]]''

* Lepospondyls were among the most numerous and diversified "amphibians" in the Carboniferous. They could have been the closest relatives of lissamphibians, and perhaps their ancestors. Usually with long bodies and weak limbs, they lived mainly in water or in soil. Some were like salamanders, ex. the whip-tailed ''Urocordylus''; other were limbless and eel-like, ex. ''Phlegetontia''. But the most interesting one is certainly ''Diplocaulus''. 2 ft long and having lived in Early Permian North America, its unique boomerang-like head makes it one of the most bizarre-looking prehistoric animals and a very common sight in paleo books (even though it has not appeared in ''Walking With Monsters'' or other CGI documentaries). The purpose of its head protrusions has made real headaches to paleontologists (A swimming device? A display tool? A mean to excavate the bottom of lakes?) Some have even suggested the shape of the head prevented ''Diplocaulus'' to be swallowed by larger amphibians such as ''Eryops''!

When amphibians were like crocs 1: ''[[ Eryops]]'', ''[[ Cacops]]'', ''[[ Platyhystrix]]'', and ''[[ Crassigyrinus]]''

* The most successful and diversified group of palaeoamphibians, temnospondyls are often described in documentary media as "croc-like": however, their jaws and teeth were smaller and weaker than a crocodile's, but they should nonetheless be efficient predators. The most famous (and perhaps the most portrayed amphibian in paleo-art together with ''Diplocaulus'' and ''Ichthyostega'') is ''Eryops''. 8 ft long and weighing equal to two adult humans, it was a massive animal with a short tail and weak limbs, but had a very alligator-like head, with eyes placed above the skull and a large snout. Living in North American Early Permian, ''Eryops'' was mainly aquatic, and when on dry land it could have fallen prey to the superpredator ''[[StockDinosaurs Dimetrodon]]''. Other Permian relatives were more terrestrial: ''Cacops'' and ''Platyhystrix'' had an armor on their back to protect them from land predators. ''Platyhystrix'' is remarkable for its dorsal spines very similar to a ''Dimetrodon'''s, maybe sustaining a "sail". Even though not a temnospondyl is also worthy of note ''Crassigyrinus'', as an example of how paleo-amphibians were diversified to each other: living in the Carbonifeorus, it was a very specialized water-loving animal with tiny limbs, just like what happened to some modern salamanders (the olm, the mudpuppy, the amphiumas, the sirens).

When amphibians were like crocs 2: ''[[ Mastodonsaurus]]'', ''[[ Trematosaurus]]'',''[[ Gerrothorax]]'', ''[[ Metoposaurus]]'', and ''[[ Koolasuchus]]''

* Temnospondyls survived well the huge Permian mass extinction and made their way in the Triassic: only competition with croc relatives at the end of the period caused their decline and their nearly total extinction before the Jurassic. The most famous Triassic amphibian has been ''Mastodonsaurus'' (improperly meaning "mastodon lizard", and sometimes misspelled "Mastodontosaurus"). It was one of the very first "giant amphibian" discovered to science, in the first half of the 1800 century. Lived in Early Triassic Europe before true dinosaurs like ''[[StockDinosaurs Plateosaurus]]''. 5 m long, it was one of the biggest paleo-amphibians ever, remarkable for its massive body and 4 ft long head with a couple of strange protruding teeth. Also very large was ''Trematosaurus'', more similar to a gharial in shape. On the other hand, ''Gerrothorax'' was much smaller and a bit similar to the unrelated boomerang-headed ''Diplocaulus''; interestigly, it shows neoteny (that is, adults retained the external gills of their larval stage, like the modern axolotl). Few temnospondyls reached the Late Triassic: among them, the North American ''Metoposaurus'' was able to see ''[[StockDinosaurs Coelophysis]]'' in RealLife. In the latest decade a new temnospondyl was unexpectedly discovered in Cretaceous terrains: ''Koolasuchus'' was probably an isolated Australian late survivor which managed to resist the competition with freshwater reptiles. It shows both in WalkingWithDinosaurs and in Disney's ''Disney/{{Dinosaur}}'' (rather incorrectly in the latter, in truth).

Egg shells, what an invention!: ''[[ Seymouria]]'', ''[[ Proterogyrinus]]'',''[[ Westlothiana]]'', and ''[[ Diadectes]]''

* The "amphibians" cited here are collectively called reptiliomorphs ("reptile-shaped"), were more related to amniotes (reptiles + mammals) than to every amphibian mentioned above. More terrestrial than the latter, they progressively evolved the typical traits of amniotes, but we don't know when these traits appeared exactly: waterproof skin, water-storing lungs and kidneys, and egg shells. The latest invention was crucial for vertebrate evolution: embryos inside shelled eggs were able to develop and to hatch out of water, and the descendants of the reptiliomorphs became able to survive in arid environments. Traditionally the most known reptiliomorph has been ''Seymouria'', which was once considered the "missing link" between reptiles and amphibians, or alternatively the very first reptile appeared. 2 ft long, it lived in Early Permian North America like ''[[StockDinosaurs Dimetrodon]]'', and was possibly one of its most frequent preys. Well-known are also the anthracosaurs, the biggest "amphibians" in the Carboniferous (some reached 9m in length!): the croc-sized ''Proterogyrinus'' is one of them. Also in the Carboniferous lived ''Westlothiana'', a tiny lizard-like animal that was briefly considered "the first reptile" in the 1990s. Last example, the Early Permian ''Diadectes'': similar to an iguana, it was possibly one of the first land vertebrates that evolved (partial or total) vegetarianism.

Limbs, what an invention!: ''[[ Ichthyostega]]''

* ''Ichthyostega'' has been one of the most iconic paleo-amphibians. Found in Greenland, [[note]] HilariousInHindsight, during most the prehistory Greenland was ''really'' a Green Land covered with forests; the ice cap formed only 30 million years ago in the Cenozoic. [[/note]], it lived before all the animals above, in the Devonian Period. It has been considered the "very first land vertebrate" for about a century, and the common ancestor of all tetrapods (mammals + birds + reptiles + amphibians). Like ''Archaeopteryx'', ''Ichthyostega'' has been mentioned as a "missing link" between two main animal classes (fish-amphibians in this case), and like the "ur-bird" and the "ur-horses", portrayed as an icon of Evolution. However, since the 1990s new intermediate forms between fish and land animals have been found; ''Tiktaalik'' is just one example (see the Fish section). Like many other basal tetrapods ''Ichthyostega'' was a big animal, 5 ft long and weighing like a adult human. This "half-fish / half-amphibian" was one of the first animals that developed true limbs, already similar to modern animals except for one thing: it had ''seven'' digits for each foot (later vertebrates have no more than five). Its body plan, however, had still several fishy traits: streamlined body, fish-like scales, and a powerful tail with a ''fin'' on its top. Even though most portraits show it crawling on dry land, today scientists think ''Ichthyostega'' lived mainly in water, and [[ScienceMarchesOn recently-made researches]] suggest its limbs were ''not'' used for walking on dry soils but only on the bottom of lakes and rivers. In ''Walking With Monsters'' its close relative ''Hynerpeton'' is shown in the traditional mainly-terrestrial way, but also with many unlikely traits typical of MODERN amphibians - like frogs, it has loud voice, naked skin, and lays eggs just the same shape of the frogs' ones.


"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 (except they are... in the same way birds are dinosaurs). 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.

Lungs, what an invention! (1) ''[[ Coelacanthus]]'', ''[[ Macropoma]]'', and ''[[ Ceratodus]]''

* Sarcopterygians, aka "lobe-finned fish" or "lobefins". They should better be called proto-amphibians rather than fish: their blood circulation is double like land vertebrates, not simple like typical fish; their fins are bony and fleshy, and their nostrils are connected with their mouth (those of fish aren't). And some can even ''breathe air'' like us, other than absorbing oxygen in water with the usual gills. The latter are meaningfully called lungfish, they have one or two true lungs which originally were simple protrusions of the digestive tube. Lungfish are very few today: the most archaic is the Australian one, ''Neoceratodus'', with robust paired "fins". Its name means "new Ceratodus": ''Ceratodus'' is the most abundant prehistoric lungfish, and was virtually identical to ''Neoceratodus''. However, the most famous modern lobe-finned fish is ''Latimeria'', the only surviving coelacanth. Prehistoric coelacanths, too, were virtually identical to their modern descendents: one of the most common in fossil record is ''Macropoma'' from the Mesozoic; the namesake of the group ''Coelacanthus'' lived earlier in the Paleozoic. Unlike lungfish, coelacanths (also known as "actinists") have been exclusively aquatic: unable to breathe air, they are the most "fishy" among the lobe-finned fish. It's worthy to note that during the Dinosaur Age lungfish and coelacanths were very abundant: coelacanths swam in great numbers in the sea, while lungfish lived in oxygen-poor swamps, sometimes obligated to "walk" out of water when the water pools dried out just like modern lungfish.

Lungs, what an invention! (2) ''[[ Eusthenopteron]]'', ''[[ Hyneria]]'', and ''[[ Tiktaalik]]''

* Even though more closely related with US than with true fish, lungfish and coelacanths were less close to terrestrial vertebrates than some fossil lobefins, the basal tetrapodomorphs (called "rhipidists" in older sources). Among them, there was the common ancestor of all tetrapods aka land vertebrates, but we don't know which was really ''the'' ancestor. The traditionally most cited is ''Eusthenopteron''. Its shape recalled a bit that of the famous ur-amphibian ''Ichthyostega'', but smaller (60 cm), with fleshy paired fins instead of true legs, classically fishy dorsal and anal fins, and a curious three-lobed caudal fin reminiscent of Poseidon's trident. Its lifestyle was probably like a lungfish's, and was also able to breath air with primitive lungs and get occasionally out of water to escape drought. Its almost-identical relative ''Hyneria'' was much bigger (3-4 m long), and [[BiggerIsBetter because of its size]] was chosen by ''Walking With Monsters'' producers instead of ''Eusthenopteron'' as the representative of Sarcopterygii (and it was oversized). However, it is shown only to give a predator to the early tetrapod ''Hynerpeton'', and with no mention at all about its role as one of the tetrapods' forerunners (in effect it was eating its descendant). In the 2000s some new animals were discovered, which appear evolutionarily in the middle between a ''Eusthenopteron'' and an ''Ichthyostega'': an excellent example is ''Tiktaalik''.

Bones, what an invention!: ''[[ Leedsichthys]]'', ''[[ Lepidotes]]'', ''[[ Leptolepis]]'', and ''[[ Xiphactinus]]''

* Actinopterygians, aka "ray-finned fish" or "rayfins". Or, more simply, "the fish". They are by far the most common fish today (95% of all fish species!), but in the Dinosaur Age they were only one of the several fish groups roaming seas and freshwaters. The most evolved rayfins, teleosts, became widespread only in the Cretaceous. Almost all modern ray-finned fish are teleosts. However, most familiar teleosts appeared only after the K-Pg extinction, in the Mammal Age. There were no goldfishes, swordfishes, seahorses, piranhas, ocean sunfishes, deep sea anglers,... in the Cretaceous (only herrings, tarpons, and few others). However, non-teleost rayfins were already common in the Mesozoic: among them, gars, sturgeons and their relatives. And then, there were things such as ''Leedsichthys'', a Jurassic fish with no modern relatives that was ''as big as a large whale'', maybe the greatest fish of all times. [[note]] Maybe not bigger than a modern whale shark however, and with a toothless mouth which indicates an inoffensive filter-feeding attitude like the latter [[/note]] Another non-teleost fish was ''Lepidotes''. It was one of the most common fish, with more than 100 species that lived during the whole Mesozoic timespan. Similar to a carp, it was actually not related with any modern fish: its primitiveness is revealed by its heavy scales similar to an armor. These scales are sometimes found inside the rib cages of other animals, e.g. the fishing dinosaur ''[[StockDinosaurs Baryonyx]]''. Since the Cretaceous all these early forms have been outcompeted by teleosts, which were more agile thanks to their lighter scales. One of the most common was ''Leptolepis'', a sort of ancient herring. Perhaps the most famous Cretaceous rayfin is ''Xiphactinus'': also similar to a herring but with teeth, it was 5-6m long (like a great white shark), and a voracious predator in competition with the giant sea reptiles of the time. Along with sharks and mosasaurs, fishes like this could have contributed to bring the ichthyosaurs to their early extinction.

Jaws, what an invention!: ''[[ Palaeoniscus]]'', ''[[ Cheirolepis]]'', and ''[[ Acanthodes]]''

* Together, ray-finned fish and lobe-finned fish make the traditional Osteichthyes aka bony fish. Indeed, a bony skeleton was their main invention - all the earlier fish groups had cartilaginous skeletons, while their bones were only ''outside'' their body in the form of scales and teeth. Bony fish (both lobefins and rayfins) appeared in the Paleozoic era, 200 million years before the first dinosaur. Among the earliest ray-finned fish, ''Palaeoniscus'' and ''Cheirolepis'' resembled a cross between a shark and a modern bony fish: mouth placed downwards and asymmetrical caudal fin like the sharks'; fins, opercula, and smooth scales like the bony fish's. Curiously some extant archaic rayfins like the sturgeon still preserve this [[MixAndMatchCritter mixed look]]. In the Paleozoic there was also a unique fish group that went totally extinct before the Mesozoic: the acanthodians (so-called from their namesake ''Acanthodes''). They were externally similar to the earliest rayfish above, but with a cartilaginous inner skeleton like a shark. Their name means "spiky" from their spiny fins, and have been nicknamed "spiny sharks", but they were actually closer to bony fish than to sharks. Together, sharks, acanthodians, bony fish and placoderms (see below) have one thing in common: jaws. See also "Tough Guys" below.

Shark tales 1: ''[[ Cladoselache]]'', ''[[ Stethacanthus]]'', ''[[ Xenacanthus]]'', and ''[[ Helicoprion]]''

* If you ask a paleontologist about what are the most common vertebrate fossils, (s)he'll answer you "shark teeth". However, these teeth are usually found isolated - ironically, the remaining skeletons are among the rarest fossil finds (sharks' cartilage don't fossilize well unlike bone). Even though sharks made only a small percentage of the modern fish species (about 5%), they were a very successful group in the past, even more diversified than they are today. But stop a moment. What is a shark, exactly? In common sense, sharks are things like the great white or the bull shark; but zoologists often use this word to indicate every cartilaginous fish, or more technically, every Chondrichthyes. Palaeontologists usually give the same meaning to "shark", too. So, the first ever sharks appeared in the Devonian period 400 million years ago, and since then have changed very little: sharks are often cited as "living fossils". More precisely, the modern kinds of shark appeared in the Cretaceous: earlier sharks were only distantly related with them. Examples are ''Cladoselache'', ''Stethacanthus'', and ''Xenacanthus'' (all from the Devonian period), and also a little known modern fish, the deep sea chimaera (also called ratfish or rabbitfish). The latter has preserved to this day the mixed shark/bony fish anatomy of the acanthodians and the earliest rayfins. ''Cladoselache'' was more like a true shark, with uncovered gills and tooth-like scales covered in enamel (its fossils have preserved prints of soft tissues), but its mouth was strangely placed at the top of its head. ''Xenacanthus'' and ''Stethacanthus'' were more bizarre. The former had an eel-body and a long filament protruding from its head; the latter is nicknamed "ironing-board shark" from its flat head prominence with many dentines on the top. Maybe only males had these things, which resemble the much smaller tubercle of the male chimaera. (if so, they would have been courtship devices). But the perhaps weirdest shark ever is ''Helicoprion'', whose teeth were placed in a spiral line inside its mouth![[note]]It now appears that ''Helicoprion'' may actually belong to the chimaera lineage.[[/note]]

Shark tales 2: ''[[ Hybodus]]'', ''[[ Ptychodus]]'', and ''[[ Cretoxyrhina]]''

* Triassic and Jurassic sharks were still primitive, but with a more modern look. One of the most common was ''Hybodus'', whose shape recalls a typical predatory shark but with small horns on its head. Other relatives became flatter and similar to a ray: ''Ptychodus'' is one example. If we imagine to swim in Cretaceous waters, however, we'll see sharks virtually identical to the modern ones. ''Cretoxyrhina'' (nicknamed "the Ginsu Shark") was very similar to a great white shark. It was one of the top predators of the Late Cretaceous North American inland sea, in competition with mosasaurs, plesiosaurs, and the bony fish ''Xiphactinus''. But we could also encounter another kind of fish which little resembles a shark, but technically ''is'' a true shark: ray and skates. They appeared in the same time of the commonly intended "sharks", and also little changed their anatomy during the times.

Shark tales 3: The [[ Megalodon]] shark

* It's usually accepted that the biggest / most spectacular prehistoric animals lived in the Dinosaur Age: well, sharks are a notable exception. The biggest known predatory shark ever lived ''just a few million years ago'', at the time of the first hominids! [[RuleOfCool Obviously]], this animal is often shown in documentary media: for example, its open jaws are often depicted with [[ThreateningShark some people inside]] to show how immense they are. Recently, this animal has fascinated even the Fiction World, to the point {{Megalodon}} has become a trope on its own. But wait: Megalodon (literally "big tooth") is ''not'' the name of its genus: it's that of its species. The full scientific name is ''Carcharodon megalodon'' or ''Carcharocles megalodon''. [[note]] If it was an extremely close relative of the great white shark (''Carcharodon carcharias''), the correct name is ''Carcharodon''; if not, is ''Carcharocles''. [[/note]]. Like the most impressive extinct beasts, the megalodon is often victim of sensationalism. Some sources describe it 30 m long, like a blue whale; actually it was only slightly over half this length. Still, it remains the biggest known fish and largest and most successful (with a tenure of 20 million years, when most last just one) apex predator ever. It could have been a specialist whale hunter, and its bite marks have been found in whale skeletons: but could also have fed on smaller prey, too. We don't know why it went extinct; maybe because of climatic changes that deprived it of its main food source, in particular the closing of the Central American Seaway, which was an important hunting and migration area. One final note about Megalodon; it was so successful it held back the evolution of whales, which underwent a third explosion in diversity right after its extinction (therefore, the theory orcas outcompeted the shark is highly unlikely).

Tough guys 1: ''[[ Bothriolepis]]'', ''[[ Coccosteus]]'', and the other Placoderms

* The Devonian is rightly called "the Fish Age". Almost every main fish group was present in Devonian waters: lobe-finned fish, ray-finned fish, cartilaginous fish, acanthodians, and several jawless fish (see further). But the perhaps most typical Devonian fish group is another: the placoderms. Their name means "skin with plates", and are nicknamed "armored fish"; their scales were notably thick and broad and covered their forebody like a true armor. However, this armor was still flexible and didn't make a "shell", making these fish more agile than their armored predecessors "ostracoderms"; unlike the latter, they were active predators. There were two main placoderm groups: antiarchs and arthrodires. The former had bizarre pectoral fins more similar to crustacean legs than fins, and lived near the bottom of the seas: ''Bothriolepis'' is the most known example. The latter had strange scissor-like teeth for cutting meat, and probably lived in more open waters. Ex. ''Coccosteus''. There is a curious thing about the evolutionary origin of jaws and teeth: the former arose from the first pair of ''gills'' of the earliest jawless fish; while the teeth had the same origin of ''scales''. After all, modern sharks still have enamel-covered scales on their body, the same shape of their teeth (only smaller). [[note]] The reptilian and bird scales have nothing to do with fish scales: the latter are pieces of bone covered or not with enamel; the reptilian ones are simple horny protrusion of the skin, like our nails. [[/note]] In a sense, you could even say teeth are the ''only'' fish scales we human still preserve.

Tough guys 2: ''[[ Dunkleosteus]]'' (once called "Dinichthys")

* Most placoderms were small. But ''Dunkleosteus'' makes a ''real'' exception. 30 ft long, the size of an orca it was only outmatched by its larger but gentler cousin ''Titanichthys'' and an obscure chimera known as ''Parahelicoprion'' for the title of largest animal in the Paleozoic. It was the same shape of the ''Coccosteus'' above, with the same kind of armor and the same strange scissor-like teeth. It was evidently the top predator of its time (Devonian), able to chop up even the toughest preys. In older sources it is called ''Dinichthys'' ("terrible fish"); the much less awesome name "Dunkleosteus" means "Dunkle's bone". Despite its impressiveness, ''Dunkleosteus'' has not gained much attention outside paleo books; in [[Series/WalkingWithDinosaurs Walking With Monsters]] it appears as one of the "[[PrehistoricMonster monsters]]" encountered by Nigel Marven during his time travel, and to fit better the role is portrayed [[RuleOfScary overscary]], with cat eyes, blood-red color, and unproven cannibalistic attitudes.

Tough guys 3: ''[[ Cephalaspis]]'', ''[[ Pteraspis]]'', and the other "Ostracoderms"

* Welcome to the Aspis family. Most "ostracoderms" ("shelled skin") have this suffix. Despite this, they ''don't'' make a real fish group: every armored fish devoid of jaws is traditionally called with this name, but they are actually distinct lineages, some closer to ''jawed fish'' than to other ostracoderms. Compared with placoderms, ostracoderms' armor was more complete, covering the whole body, and formed a true shell at the head level. Despite their {{Badass}} look they were very harmless creatures; their size was from a thumbnail up to a human hand, and with their tiny mouths they could only have feed on tiny food items like algae, small invertebrates, etc... They often fell victim to predators like the sea scorpions, cephalopods and jawed fish that were strong enough to go through their thick armored skin. One successful ostracoderm lineage is the osteostracans, whose prototype is the flat-headed ''Cephalaspis''. Another is the anaspids, more streamlined and with a lighter armor. The heterostracans had long snouts; ''Pteraspis'' is their prototype. Finally, the thelodonts, which where the most closely related with jawed fish (and maybe their ancestors).

Our earliest origins: ''[[ Haikouichthys]]'' and the [[ Conodonts]]

* However, ostracoderms were ''not'' the most primitive fish; they were already very evolved animals, with complex brains, fins, and keen senses (''Cephalaspis'' seemingly shows even electric sensors!) Their anatomy is unusually well-known because the inner portion of their head shows the prints of the brain, nerves, inner ear, and other soft tissues. [[note]]Ostracoderms and the other jawless fish shared a curious anatomical trait: one single nostril on their head (all jawed vertebrates share two paired nasal openings like us humans).[[/note]] Actually ostracoderms descended from armor-less fish, among them the very first fish appeared. Sadly, as soft tissue don't usually fossilize, they are virtually unknown by science. One exception is ''Haikouichthys'' from the Cambrian period, similar to the famous invertebrate lancelet, or also to the larval stage of the modern lamprey (the so-called ammocoetes). It was a tiny animal the size of a human nail, and was probably a harmless filter feeder living in the bottom-seas. Incredibly, ''Walking With Monsters'' managed to transform even this unconspicuous critter in a "terror": here, a shoal of ''Haikouichthys'' is seen feeding on the flesh of a wounded ''Anomalocaris'' like modern lampreys and hagfish would do. Actually, lampreys and hagfish (aka the cyclostomates) are very evolved parasitic animals capable to feed on large items despite their lacking of jaws; their evolution is very poorly known. Finally, we could not forget the enigmatic conodonts. These tiny fossils similar to toothed jaws (conodont means "cone tooth") have been a real headache for scientists (invertebrates? early vertebrates? worms?). Today we know they belonged to early jawless fishes that lived during the whole Paleozoic, but their lifestyle is still uncertain; maybe they were the ancestors of the lampreys.



When thinking about animal fossils, our mind usually goes on the petrified 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 although 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.

The first eyes: [[ Trilobites]]

* Some things are more important than others. Trilobites are among them. Their [[http:/ extreme abundance]] in fossil record had made them "index fossils": that is, Paleozoic terrains can be easily recognized ''just because'' they almost certainly contain at least one trilobite. As a group, trilobites lived in the whole Paleozoic era, but became rarer and rarer after the Devonian, and no one survived the Permian-Triassic mass extinction. Even though their appearance could make them confused with crustaceans, they were actually not related with any modern arthropod; they are classified in the middle between the two main arthropod groups: chelicerates (arachnids + sea spiders + horseshoe crabs) and mandibulates (hexapods + myriapods + crustaceans). "Trilobite" means "three lobes". Their body was divided in three portions: the head, the segmented thorax, and the telson (the scute at the rear-end of the body). But their flattened body also shows three portions in the longitudinal sense, the middle one and the two lateral. Like a millipede they had many pairs of legs (up to 100), one pair of antennae, and two usually large eyes similar to those of insects: trilobites were among the first creatures capable to see images. They mainly lived in the benthic zone; some were diggers, other active swimmers; some were able to curl themselves for protection. Most were not bigger than a human hand; the biggest were 3 ft long. Like the contemporary jawless fishes, trilobites only ate small items, and were prey for other arthropods, cephalopods, or jawed fish. We don't know if trilobites were totally aquatic or came to land to lay their eggs. Their young were identical to the adults. The kinds of trilobites commonly shown in media pertain usually to the Phacopida subgroup; good luck if you see an agnostid or a proetid trilobite.

Crabs and pseudo-crabs: Prehistoric [[ Crustaceans]] and [[ Xiphosurans]]

* Today, crustaceans are by far the most abundant water arthropods. Their prehistoric relatives were like the modern ones, and have always been an important group. However, in the Paleozoic another group of aquatic arthropods were even more diversified: the early chelicerates, more related with ''spiders'' than to crabs. The most spectacular water chelicerates were the so-called sea scorpions (see the following paragraph); the smaller xiphosurans were just as abundant. Like the coelacanth and the nautilus, they have classically been mentioned as "living fossils". Indeed, the modern ''Limulus'' (the horseshoe "crab") is just the only surviving xiphosuran, and the only surviving aquatic chelicerate (except for the little-known sea spiders). All the other chelicerates became terrestrial, forming the arachnids (spiders, scorpions, mites and others). Xiphosuran means "sword tail". Contrary to what is believed, the "sword" at the end of the horseshoe crab is not venomous or dangerous at all, is only a mechanical device to overturn again the animal when capsized. Many extinct xiphosurans were identical to our modern ''Limulus'', and probably behaved the same; our horseshoe "crab" lives mainly in the bottom of the seas like trilobites, feed only on small items, but comes ashore to lay its eggs. Curiously, its young are very similar to an adult trilobite.

Our distant enemies? ''[[ Pterygotus]]'' and the other Eurypterids

* When talking about evolution, the superpredators are usually described as a sort of BigBad guys that try to destroy our distant ancestors, almost as their precise purpose was to delete Man's modern presence on Earth. Just see ''[[Series/WalkingWithDinosaurs Walking With Monsters]]'' for an egregious example. When the portrayals are about Mesozoic life this treatment is typically reserved to dinosaurs (see [[UsefulNotes/PrehistoricLifeNonDinosaurianReptiles The origin of Mammals]]); in Paleozoic settings, however, the classic choice has been the eurypterids (also called Gigantostracians), better known as the [[BigCreepyCrawlies sea scorpions]]. They were indeed related with modern scorpions (and maybe their ancestors), but technically they ''were not'' scorpions. They hadn't the venomous sting, and resembled more slender lobsters than scorpions. Their had big composed eyes like insects, scorpion-like pincers, and their rear pair of legs were flattened and used to swim; they arguably lived both in the bottom and in open waters. We don't know if they came on land to lay their eggs. Eurypterids were active predators, and the biggest ones were among the apex predators especially in the Silurian period; in the following Devonian they were outcompeted by jawed fish like ''Dunkleosteus'', but managed nonetheless to survive until the Permian. ''Pterygotus'' was one of the biggest eurypterids (the length of a human), and one of the biggest arthropods of all times along with the extinct millipede ''Arthropleura'' and the modern Giant Japanese Crab. ''Pterygotus'' is the "sea scorpion" traditionally most portrayed in media, [[BiggerIsBetter because of its size]] of course. Ironically, however, its even larger (and more freaky-looking) cousin, ''Jaekelopterus'', the largest arthropod ever, never appeared in media.

Out of water, at last! ''[[ Palaeophonus]]'', ''[[ Brontoscorpio]]'', ''[[ Arthrolycosa]]'', ''[[ Rhyniella]]'', and other non-insect land arthropods

* Within the evolution of animal life, it is universally agreed that arthropods and vertebrates have been the two animal groups which reached the best results. Cephalopod molluscs, too, are very complex creatures; but they ''never'' managed to come on land. Arthropods and vertebrates did that, but it was the former which made the first step on dry land, in the Silurian period. Vertebrates joined them only later in the Devonian. Even when out of the liquid element arthropods and vertebrates have continued to co-exist and to co-evolve, and this competition has made both more and more perfected. It's actually meaningless saying arthropods have been the vertebrates' worst enemies, and that the latter had to fight a "war" against spider-scorpions-insects (as said in the preface of ''[[Series/WalkingWithDinosaurs Monsters]]''); indeed, arthropods have unwillingly ''helped'' us vertebrates to became those successful beings we are. Among the very first land arthropods were the first TRUE scorpions and the first myriapods (millipedes and centipedes). Critters such as ''Palaeophonus'' were already identical to a modern scorpion; the same about the earliest myriapods. Spiders appeared a bit later, in the Carboniferous (ex. ''Arthrolycosa''); the first non-insect hexapods (hexapod = six legs) evolved in the Devonian (''Rhyniella''), but the first winged TRUE insects took their first flight in the Carboniferous forests: they were the very first flying animals ever, and the ''only'' flyers until pterosaurs made their appearance in the Triassic, followed by birds and finally bats. In the Carboniferous, land arthropods became often huge; two in particular have become a staple in paleo-books and documentaries: ''Arthropleura'' and ''Meganeura'' (see below). They have even made some apparitions in Fiction, too. [[note]]Curiously, the more impressive "giant millipede" ''Arthropleura'' has entered Fictionland only recently, while the "giant dragonfly" Meganeura can be also seen in older fictional works. [[/note]] ''Walking With'' has also popularized other critters: the huge true scorpion ''Brontoscorpio'', the alleged giant spider ''Megarachne'' (it was actually an eurypterid) and the awe-inspiring giant ants seen in ''Beasts''. All, more or less, affected by RuleOfCool in the show.

Everything's better with Euras: ''[[ Arthropleura]]'' and ''[[ Meganeura]]''

* Why did land arthropods reach such a large size in the Carboniferous? [[note]]But don't forget most Carboniferous land arthropods were normal-sized; [[BiggerIsBetter obviously]], they don't gain much attention in media.[[/note]] Probably because the oxygen content at the time was much greater than every other period. The tracheal respiratory system of insects and land arthropods prevents them to reach big size: over a determined size, this system just doesn't work. The maximum an insect can reach depends also to the quantity of oxygen in the atmosphere; thus, more oxygen --> bigger size. The myriapod ''Arthropleura'' was the UpToEleven case: as long as a human, it is the the biggest known land arthropod of all times. But was an inoffensive herbivore that fed on the rotting vegetation extremely abundant in the Carboniferous forests. In truth, this "giant millipede" didn't even resemble a millipede. Wide and flattened, it resembled more a overly-long trilobite. Actually there are modern-day millipedes that have the same body-shape of ''Arthropleura'', though obviously much smaller. About ''Meganeura'', it was a griffinfly (basically a giant dragonfly relative); with a wingspan like a crow, it is the biggest known TRUE insect of all times (millipedes are NOT insects!), and a very powerful flyer like modern dragonflies. Unlike ''Arthropleura'', ''Meganeura'' was carnivorous and fed on smaller insects and maybe even small amphibians. Both animals got usually unattacked by the super-predators of the time: the millipede's armor and the griffinfly's agility protected them against giant amphibians and fish.

!!Bugs Everywhere! TRUE 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 larches.

Remember ''Film/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 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 [[note]]Technically these were the first hexapods, since springtails are no longer considered proper insects by modern entomologists: however, we follow the traditional view because it's more convenient.[[/note]], later than scorpions and millipedes: they were still wingless as modern [[ springtails]] and [[ 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.

[[ Insect evolution]] has always been related with that of terrestrial plants. 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, especially 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 modern birds and placental mammals are today the most 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. Keep this in mind, every time you crush a bug.


No other animal group has had a greater importance in paleontology than molluscs. Their fossils are extremely abundant, to the point that many rocky formations are mainly made of cemented mollusc shells. Among molluscs cephalopods deserve a mention apart, being much more evolved than the others. Together with arthropods, cephalopods are the extinct invertebrates you have more chances to see in media - at least, the documentary ones: you hardly can see a trilobite, an ammonite or a sea scorpion in Fictionland. If it happens, it would be a simple cameo, and good luck if the animal is mentioned.

Ammon's horns: [[ Ammonites]]

* Is anyone that has never seen those spiral stony shells emerging from the surrounding rocks? Ammonites (technically the ammonoids) have always been among the most iconic fossil invertebrates, together with the trilobites. Like the latter, they have been used as "index fossils", but for the Mesozoic era. Actually, some ammonites lived in the Paleozoic, but reached their prime in the Dinosaur Age. They went definitively extinct at the end of the Mesozoic, when the comet stroke. [[note]] Even though it resembles an ammonite, the extant nautilus is not an ammonite descendant. [[/note]] Despite the abundance of their shells, their soft bodies are rarely preserved and little known. Like octopuses and squids, they had certainly tentacles and the "beak" typical of cephalopods; but the number of tentacles is uncertain. Maybe they had more than 8-10 tentacles, more similarly to the nautilus (see below) than to a squid. It's unsure if their tentacles had suckers like octopuses and squids, or had not them like a nautilus. And we don't know if they sprayed ink, nor if they had complex eyes to see images like octopuses and squids. With their heavy shell, ammonites should have been slow swimmers; they were surely predators like every other cephalopod, but they probably caught only small preys. Their hard shell was an excellent protection against predators, as shown by some ammonites with marks of teeth left by an ichthyosaur or a mosasaur which tried to break their shell in vain. Though most ammonites were no bigger than a human hand, some reached the diameter of 2 m (still much smaller than a modern giant squid). In media, ammonites are always shown with the classic curly, laterally-flattened shell; however, the shells of some Cretaceous ammonites reached an unusual form.

Stony arrows: [[ Belemnites]] and extinct Octopuses and Squids

* Extinct cephalopods have given fuel to many legends, even before paleontology itself was "invented" by [[http:/ Georges Cuvier]] at the end of the 1700 century. Before that, those strange things today called fossils were believed to be Nature's jokes to the Earth's flowers. (Only Creator/LeonardoDaVinci recognized correctly their nature, but his discovery was long ignored). And then, there are more specific legend about cephalopod fossils. Ammonites were believed stony horns ("Ammonite" comes from Ammon, a legendary ram), or petrified snakes. [[note]] Some had fun to sculpt a snake-head on the shell's extremity to make it like a snake! [[/note]] The less-known belemnites (technically the belemnoids), with their straight pointed shape, were believed stony arrows, or even the Devil's fingers! Belemnites were cephalopods living in the Mesozoic era together with ammonites, and probably gave rise to squids. Like ammonites, only their shell is usually preserved. This shell was ''inside'' the animal's body and invisible in life; belemnites would resemble simple squids or cuttlefish if alive today. Their lifestyle was more active than ammonites, and probably they were able to do the same things modern squids do (spraying ink, swimming using the lateral "fins", catching preys with their suckers, seeing images with their eyes). True modern squids became widespread in the Cretaceous, as well as the first octopuses; these mollusks usually have no shell inside, or at least only a remnant of shell (ex. the famous cuttle-bone). Some Cretaceous squids were as large as a modern giant squid.

Finding Nemo: ''[[ Orthoceras]]'', ''[[ Cameroceras]]'', and the other "Nautiloids"

* Some fossil animals' names recall literary characters, rather than mythical things: nautiloids (literally "similar to the Nautilus") are so-called from the modern ''[[ Nautilus]]'', whose name (meaning "ship" in Greek) incidentally recalls [[Creator/JulesVerne Nemo's submarine]] (we're talking about the human captain, NOT the cartoon fish!). Actually, nautiloids are an artificial assemblage of all cephalopods which were neither ammonoids, octopodes nor coleoids. They include both the modern nautilus and the most ancient cephalopods, widespread in the Paleozoic. Their traits were probably like those of the nautilus: their shell was divided in sections which could be filled alternately with water or with air like in a submarine. This allowed them to regulate their buoyancy (ammonoids had a similar inner-shell anatomy and probably did the same). As the nautilus' eyes are simple chambers lacking any lens and incapable of forming images, this was probably true for other nautiloids as well. They should have had dozen of sucker-less tentacles, and were probably slow swimmers. However, many Paleozoic nautiloids had straight conical shells, not curly like the nautilus; ''Orthoceras'' is a good example. Its shell shows even traces of its original colors. The ''Walking With'' series has popularized a close relative, ''Cameroceras'', chosen as the prototypical Paleozoic cephalopod only because it [[BiggerIsBetter was 10m long]].


[[folder: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 ''Disney/{{Fantasia}}'' showed several ''modern'' critters to symbolize the early evolution of invertebrates, but few or nothing among the ''really'' prehistoric ones. The ''Walking With'' series did the same: only modern jellyfish, 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. Among modern land arthropods expect to see dragonflies, scorpions, centipedes, spiders, cockroaches, beetles, and sometimes crickets. They would be oversized: roaches the size of a rat, scorpions as big as cats, and so on. Finally, let's not forget a staple in every Paleozoic or Mesozoic sea: a jellyfish, used as the symbol of the most ancient forms of life.

Clams and Pseudo-clams: [[ Rudists]] and [[ Prehistoric ''Lingula'']]

* Gastropods, scaphopods, bivalves, brachiopods, chitons, monoplacophorans: which is the intruder? All these invertebrate groups were "shellfish", and all but one were molluscs: brachiopods weren't. They were only distant mollusc relatives, and more related with the coral-like bryozoans (see "Sessile invertebrates" below). As a whole, molluscs and brachiopods are extremely abundant in fossil record of all ages, from early Paleozoic up to the modern era. However, while molluscs are still a dominant group in modern seas, brachiopods are nearly extinct today, and thus cites as "living fossils". The most representative is probably ''Lingula'' ("small tongue"), a clam-like, filter-feeding animal that lives anchored to the sea floor with a fleshy protrusion (the "tongue"); prehistoric ''Lingula'' have been identical to the modern one since the Early Ordovician! Among extinct non-cephalopod molluscs are worthy of note the rudists. Exclusively Cretaceous, these clams are notable both for their often great size (some were as tall as a human), and for their unique shape. They can be described as giant cups with a lid: the lower valve (the one attached to the sea bed) was conical and much bigger than the flat upper valve. Like ''Lingula'', rudists were probably almost motionless creatures that filter-fed on tiny organisms.

We love geometry: [[ Cystoids]], [[ Blastoids]], and [[ Prehistoric Crinoids]]

* Crinoids, echinoids, asteroids, [[note]] NOT [[UsefulNotes/TheSolarSystem those]] asteroids! [[/note]] ophiuroids, holoturoids, blastoids, cystoids, carpoids: which is the intruder? To some extent the carpoids (see the following paragraph); all the others were confirmed echinoderms. The asteroids ("star-like") are the starfish; ophiuroids are nicknamed "brittle stars" or "serpentine stars"; the echinoids ("husk-like") are the sea urchins and sand-dollars; while the holoturioids are the sea cucumbers or trepang. Thanks to their hard "skeleton", all these groups (except for the soft-bodied sea cucumbers) are common fossils, and have roamed the seas since the start of the Paleozoic. However, we're going to talk more about other three less familiar groups of echinoderms: crinoids, blastoids and cystoids. Crinoids ("sea lilies") are the only ones still living, but are today a rarer sight than the four groups above; like brachiopods, they are considered "living fossils". They have been not-very-movable filter-feeders, and like all echinoderms they resemble more plants than animals: symmetrically rayed and with several "arms" that make them looking like ferns or flowers (hence "sea lily"). Adult echinoderms lack eyes, limbs, heads (but have a mouth nonetheless) and they usually lack a right/left side of their body - however, their tiny planktic larvae ''do have'' bilateral symmetry. The astonishing thing is, echinoderms are among the ''closest relatives of vertebrates.'' About blastoids and cystoids, they are exclusively fossil, were similar to crinoids but without the "arms"; their lifestyle was probably like the sea lilies'. Also worthy mention were the (exclusively fossil as well) edrioasteroids, perhaps similar to sand-dollars or sea-urchins.

Odd relatives: [[ Graptolites]] and ''[[ Cothurnocystis]]''

* In Prehistory, some odd-looking invertebrates were even closer relatives of us vertebrates than echinoderms themselves: graptolites and calcichordates (or homalozoans). Graptolites are among the most common fossils in the Paleozoic, and used as index fossils alternatively to trilobites. They resembled floating water plants, but the "plant" was ''not'' the whole organism. They were colonial animals like modern corals, and the single individuals were actually ''inside'' the colony. Like brachiopods and crinoids, graptolites too were passive filter-feeders. About calcichordates (remember, they are the carpoids above), they have been variably classified as primitive echinoderms, graptolite relatives, or even true chordates (that is, the group including tunicates + lancelets + vertebrates aka US). Calcichordates lived in the bottom seas, were movable animals (and bilaterally symmetrical unlike a typical echinoderm), with an armor and a sort of "tail". [[note]] Note that only vertebrates and other true chordates had a tail: tail-looking structure in invertebrates are ''never'' real tails: even the scorpion's one is just the extremity of its abdomen, with the anus ''near'' the sting! [[/note]] However, one of the most depicted calcichordate, ''Cothurnocystis'', lost the bilateral symmetry altogether for inexplicable reasons.

Survival of the toughest: [[ Prehistoric Sessile Invertebrates]]

* This is a merciless law even in palaeontology. Only hard parts of the organisms' bodies usually fossilized: bones, shells, armors, jaws, teeth, and whatnot. Many modern invertebrate groups which haven't tough elements left little fossil record (if they did). For examples, most "worms" (annelids aka segmented worms, nematodes aka round worms, platyhelmintes aka flatworms, and many others) are virtually unknown in paleontology, and their evolution is only a guess. This is also true for coelenterates - that is, the cnidarians (jellyfish, sea anemones, hydrae, siphonophores) and the ctenophores (comb jellies). At least, the totally soft ones; fortunately, corals (which are also cnidarians) build tough external skeletons that fossilize well, and their extinct relatives are well-known since the start of the Paleozoic. The same about the unfamiliar bryozoans (moss animals), very similar but not related at all with corals but with the brachiopods. Finally, the enigmatic sponges (which many zoologist hardly consider real animals) are also frequent fossils. They too have had an inner "skeleton" made of limestone (and sometimes glass-like silicon or a horny material, but they usually don't fossilize); one extinct group of possible sponge relatives were the archaeocyathans.

A treasure in the rocks: [[ Foraminiferans]], including [[ Nummulites]]

* Foraminifers ("forams" for friends) are ''really'' a treasure in the rock, in all senses. They have contributed to confirm the DeepImpact theory about dinosaur extinction; their shells have contributed to form several sedimentary rocks around the world; and they are cool on their own, with their immense variety of shapes. The biggest forams, the nummulites, look often like literal COINS emerging from the rocks ("nummus" means coin in Latin); they are used as "index fossils" for the Cenozoic era, and have also created the material for the Egyptian pyramids! But wait: what are actually the foraminifers? Originally, scientists thought they were molluscs or mollusc-like critters; today we known they weren't even real animals. They were "protozoans", aka single-celled organisms with animal traits. Most other one-celled "animals" have left very few fossil material (if they did); the ancestors of ''Amoeba'', ''Paramecium'', ''Euglena'', ''Vorticella'', and so on are a mystery. Even the radiolarians: their shell is siliceous, and silicon usually dissolves before fossilising.

!!Once upon a time... CAMBRIAN ANIMALS

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 [[ 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, 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 appearance 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 [[ all the members]] of the Cambrian fauna: see [[ the image here]] for having an idea. The bizarre shrimp-like animal in the center is immediately recognisable, by far the biggest creature in this fauna, and arguably the top predator. It is called ''[[ Anomalocaris]]'' (meaning "[[ExactlyWhatItSaysOnTheTin bizarre shrimp]]" indeed -- it's a coincidence as the name was invented for one "arm", that was mistaken for separate organism), and was a distant relative of arthropods with no articulated legs but with the same compound eyes of the trilobites. Of course it is the most portrayed Cambrian animal in documentaries and illustrations, classically mentioned as "[[PrehistoricMonster the first prehistoric monster ever appeared on Earth]]". Actually, if alive today, the "terrible" anomalocaridid would appear as a really [[{{Narm}} narmy thing]], a sort of 3 ft long, shell-less, pincer-less (It does have CombatTentacles and a LampreyMouth) lobster, nothing dangerous for a tough-boned, tough-muscled, tough-skinned mammal we are in comparison. Nonetheless, anomalocaridids were highly specialized predators, with a mouth build for prey around 1/12 to 1/6 of their own size.

However, at the ''Anomalocaris''' time, every other organism was ''very small'': the other creatures you see in the linked image are not longer than your hand, all possible prey for anomalocarids. [[note]] Except those which were so small that a full grown ''Anomalocaris canadensis'' (the largest known species) would have ignored them, focusing on larger prey[[/note]]. Creatures like ''Hallucigenia'' and ''Pikaia'' were hunted by smaller predators, such as ''Opabinia'' and ''Anomalocaris saron''. The later was the species shown in ''Series/WalkingWithMonsters'', though ridiculously oversized (6 ft. on a ''A. saron''!?) and prone to attack its own kind, even though neither its mouth nor grasps could injure an equally sized specimen in the way it was depicted, let alone possibly eating it.

Anomalocharis also deserves a mention as the first active, intelligent predator capable of dismemberment, and quite possibly setting up the important role of predators in ecology and evolution.

Apart from Anomalocaris, we can mention at least other three invertebrates which are stock in drawings: ''[[ Hallucigenia]]'', ''[[ Opabinia]]'', and ''[[ 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 soft 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 mouth which was actually located behind the proboscis. But the most important find is the third guy, ''Pikaia'': despite its rather insignificant appearance, it is the most well-known vertebrate ancestor, a sort of prehistoric relative of our [[ lancelet]] (the closest extant vertebrate relative). 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 [[Series/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 looked very differently 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.

Talking about ''Pikaia'', this time it's 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, absurdly-difficult names.

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 [[ Petrified Woods]], the most famous being that in Arizona), other less-striking but even more significant, such as prints of leaves (very common in some deposits) and even the fossilized ''pollen'' which has allowed us to understand not only the composition of ancient flora, but even the climate they lived in. And, naturally, the aforementioned [[Film/JurassicPark amber]] which has often caught insects inside, of course.

A flowering smell in the Cretaceous: Prehistoric [[ Magnolias]], [[ water lilies]], and [[ true palms]]

* The most familiar plants today are the angiosperms aka flowering plants, including most modern trees, bushes, herbs, but also apparently non-flowering critters such as grass, palms, bamboos, and even some "seaweed" (''Posidonia''). But as a group, they appeared only in the Cretaceous. Or, at least, became widespread only in that period. In modern taxonomy the angiosperms are called magnoliophytes (literally magnolia plants). Indeed, the magnolia was one of the earliest flowering plants ever appeared, in the lower Cretaceous. This is the most commonly shown angiosperm in paleo works, which often portray herbivorous dinosaurs like ''Iguanodon''s and ''Triceratops''es eating magnolia leaves. [[note]] It was hypothesised that dinosaurs have actually helped flowering plants to became more widespread [[/note]]. Among the other earliest angiosperms are water lilies. The first palm trees also appeared in the Cretaceous (but note that most Cretaceous palm-looking trees were NOT palms, see further). However, most modern flowering greens - roses, apples, figs, oaks ad infinitum - appeared (or became a main component of the vegetation) only AFTER the dinosaur extinction. The angiosperms' success is tied to their relationship with pollinating animals, especially insects (see in the Arthropod section above), but also to those mammals/birds which still aid them to disperse their seeds by eating their fruits, or by other means. However, some flowering plants returned again to traditional strategies, using the WIND to disperse their pollen like the more archaic pines/firs do. Among them, ironically, are the most evolved and successful ones: the Poaceae, aka the grasses. See below.

Thank you grass!: Prehistoric [[ Gramineans]]

* In the Early Mammal Age landscapes were already similar to those surrounding us today... except for one thing: grasslands were still totally missing. Prairies and savannah appeared only 30-20 million years ago in the middle of the Cenozoic. Actually, [[ScienceMarchesOn recent research]] has shown that grasses were ''already'' living in the Cretaceous: but they still didn't form ''grasslands'', they grew isolated within the undergrowth. Grasslands have had a crucial role in Earth's ecosystems: all modern herbivorous mammals living in the modern African savannah (just to make one example) were able to evolve ''just'' thanks to grass. They developed special teeth to cope with this especially harsh green food, and thanks to the scarcity of trees, they were able to become bigger and faster. We humans have to be grateful to the grasses, too. All cereals and most fodder belong to this family of plants, as well as bamboo and sugar cane, other than the common grass naturally. However, their importance has been even greater than what you might think: if the grasses didn't evolve million years ago... you would not be here to read this. Simply, without grasslands, the human race still would look like big apes. (see [[UsefulNotes/PrehistoricLIfeMammals in the Mammal section]]).

Dinosaur tree: Prehistoric [[ Ginkgos]]

* In the Dinosaur Age, however, most land plants had no flowers. Non-flowering plants belonged to two main ensembles: those reproducing with seeds, and those reproducing with spores. The former are traditionally called "gymnosperms", but are actually more than one group of plants not particularly closely related to each other. The most familiar gymnosperms are, obviously, the conifers (see below). In paleo-books, however, you can often read the name "''Ginkgo biloba''". This is, indeed, the ''only'' surviving member of a whole group of seed plants (the Ginkgophyta) that was among the dominant greens in the Mesozoic. Its special status makes the ginkgo often cited as a ''living fossil''. However, it doesn't look like a pine or a fir: with its wide leafs and fruit-like seed, it resembles a normal-looking flowering plant. Indeed, ginkgophytes are probably the closest angiosperm relatives. Even though the modern ginkgo is widespread around the world as a ornamental tree, its wild ancestor lives only in Eastern Asia.

A resiny smell in the Jurassic: Prehistoric [[ Pines and firs]], [[ Redwoods]], [[ Podocarps]], and [[ Monkey puzzles]]

* Fictional media typically make us believing the trees from the Mesozoic were ''all'' palm-shaped. If non-palmlike tree appear, they usually have the shape of an angiosperm. Pines, firs, spruces, larches, cypresses and cedars are usually unseen in Fictionland... maybe because are usually associated with ''cold'' in the writers' mind (while {{Prehistoria}} is ''always'' a very hot world filled with volcanoes....). However, in RealLife things were very different. Conifers were among the dominant plant groups in the whole Mesozoic, and a common food for camarasaurs, camptosaurs, centrosaurs, cetiosaurs, chasmosaurs, corythosaurs, and so on. However, there were not only pines and firs [[note]]better, their ancestors adapted to a warmer climate than the modern ones.[[/note]] at the time: more common were some kinds of conifers which are rare or extinct today. For example, the araucarians (monkey puzzles), the podocarps, the yews, and the more spectacular of all, the sequoia trees. [[note]]Modern sequoias are nicknamed "mammoth trees" for their size.... but a mammoth would appear ''really'' a midget next to its green namesake! [[/note]] If you think sauropods were the real titans of the Jurassic, think again: a ''Giraffatitan'' near a redwood would appear like a house cat near a fully grown man.

Palms, or not? ''[[ Glossopteris]]'', [[ Pseudo-Cycads]], and prehistoric [[ Cycads]]

* These are the Mesozoic seed plants that more resemble the ones seen in the fictional Dinosaur Age. They ''did'' resemble palm trees, but were NOT related at all with them. Cycads are the only ones still living, often used to embellish our cities. Bennettitales or cycadeoids ("pseudo-cycads") went extinct at the end of the Mesozoic. These two groups were very abundant at the dinosaur times, but were already present before the Triassic (as well as the little-known Cordaitales, maybe the ancestors of the conifers). About pteridosperms (the "seed ferns"), they are so called because of their external look, but were ''not'' true ferns: ferns do reproduce with spores. Seed ferns were among the very first seed plants ever appeared, in the Devonian, and survived until the Cretaceous. One of them, the Triassic ''Glossopteris'', has been used to demonstrate the Pangaea hypothesis: its fossils have been found in every southern continent, showing landmasses were still united at the start of the Dinosaur Age.

The Mesozoic undergrowth: Prehistoric [[ Ferns]] and [[ Horsetails]]

* One of the worst errors in popular media (sometimes even the documentary ones) is to portray ''grasslands'' in the Mesozoic. Arguably, writers think grass is the simplest kind of plant ever... thus, the first ever appeared on Earth. As seen above, grass are actually the ''most evolved'' plants and among the latest to become widespread on our planet. In the Dino Age, the dominant small-sized land plants were much, much more primitive: ferns, fern relatives and horsetails. These are collectively called pteridophytes and their modern descendants still make a wide portion of the undergrowth in many forests. In the Mesozoic, ferns and horsetails already made the forests' undergrowth, but also made true "prairies" where trees were absent. Only in the Mammal Age fern prairies were definitively substituted by grass prairies. But don't think ferns and horsetails were always small: in Prehistoria there were also giant horsetails and tree ferns, both deceptively similar to trees. In some places, they still live today: the 10m tall ''Equisetum giganteum'' is still growing in tropical landscapes. And tree ferns are still present in Australia and New Zealand - the LandDownUnder and its little neighbor are a real mine of "living fossils": not only the platypus, the kiwi, or the tuatara...

The Paleozoic overgrowth: ''[[ Lepidodendron]]'' and ''[[ Sigillaria]]''

* After all, Mesozoic vegetation wasn't so different than ours. Right, most land plants at the dinosaur times were mostly pine-like, palm-like or fern-like, and flowering plants were still a minority... but widespread conifer forests are still present today in northern territories. But if our time machine could bring us to the Carboniferous (aka the Coal Age, 100 million years before the Triassic), landscapes would appear REALLY a sorta Otherworld. At the time, all the plant groups cited so far were either a small portion of Earth' vegetation, or they haven't still appeared. The dominant plants were the so-called lycopods (named after ''Lycopodium'', a tiny plantlet which is one of the few kinds surviving today). Many of them would resembled extraterrestrial trees if alive today: ''Lepidodendron'' and ''Sigillaria'' are two often cited examples. Their trunk was scaly, they sometimes had only ''two'' branches; and some were huge, taller than a building! Despite their powerful look, they were quite fragile giants: giant lycopods easily fell down during the frequent Carboniferous storms. The rotting logs then carbonized, becoming the fossil coal we burn today (hence "Carboniferous", meaning "coal-making"). It's worth noting lycopods, ferns and horsetails have always been strictly tied with water; their spores can develop in adult individuals only in humid habitats, and this explains why they were so common in the Carboniferous swamp world. Then, in the following Permian period the Earth mostly dried out, and giant lycopods weren't able to survive the change. It was seed plants that have become the more successful plant groups since that: seeds are a bit like the reptiles' shelled eggs, well-adapted to sprout in arid environment.

The "first tree": ''[[ Archaeopteris]]''

* Sometimes it seems paleontologists have fun making unwilling jokes with scientific names. While the traditional "first bird" is called ''[[StockDinosaurs Archaeopteryx]]'', one of the first land plants ever appeared is the almost homonymous ''Archaeopteris''! But wait, ''Archaeopteryx'' means "ancient wing", ''Archaeopteris'' means "ancient fern". This plant lived in the Devonian (before the Carboniferous), just when the proto-amphibian ''Ichthyostega'' made the first step on dry land; it was one of the first terrestrial plants to develop the size of a tree. Since at the time land animals were very few and mostly carnivorous or detritivorous, ''Archaeopteris'' and its relatives were able to spread worldwide but never far from water, just like amphibians did. Their appearence was that of a tree fern: indeed, the fern-like is considered one of the most primitive body plans among terrestrial plants.

The "first shoot": ''[[ Cooksonia]]''

* However, plants went on land ''before'' the amphibians. In the Silurian period (before the Devonian) there were already some aquatic plants emerging out of water; ''Cooksonia'' is an often cited example. These tiny plantlets had their roots still underwater, but their "branches" grew out of the water level, capturing extra light. Terrestrial plants are actually very evolved creatures and have done a hard work to create their adaptations to survive outside the liquid element. Among them, a vascular system (that is, tiny vessels for the flow of the lymph), waterproof skin, and fibres to make their stalks more robust against gravity.

[[WesternAnimation/AvatarTheLastAirbender It's a giant mushroom...MAYBE IT'S FRIENDLY!]]: ''[[ Prototaxites]]''

* This species was first described in 1843, and for the longest time experts couldn't decide ''what'' it was. Many thought it was a conifer tree (its name means "First yew"), others thought it was a giant aquatic algae. It wasn't until 2007 that scientists confirmed it was indeed a FungusHumongous! Since this thing grew up to 8 meters, it would've been the tallest organism of its time. Many are still confused as to how such an organism could grow like that without photosynthesis.

Plants?: Prehistoric [[ Mosses]], [[ Algae]], [[ Fungi]], and [[ Lichens]]

* These so-important living beings in modern world are very little known in paleontology. Their "bodies" fossilize very rarely, but they surely have been main components of both water and dry land ecosystems since the Paleozoic. However, only bryophytes (mosses, hornworts and liverworts) can be called "plants" without going in error. Algae (seaweed) and fungi (mushrooms, toadstools, moulds, yeasts) are NOT true plants in modern systematics (fungi cannot even perform photosynthesis!). And lichens are not even true organisms: they are the results of a symbiotic relationship between a fungus and an alga.

[[folder:The origin of Life]]

The creatures here are from the Precambrian, and lived/originated ''before'' the other organisms listed in all the other "Prehistoric Life" pages. Talking about them is hard matter even for the most skilled biologists. Our mind has trouble to imagine how the first living beings actually looked, even more how they lived... However, not everything is unknown to us.

Animals, or plants?: [[ The Ediacara creatures]]

* We are so accustomed to divide the visible-to-the-naked-eyes creatures between plants and animals, it's hard imagining critters that were neither. The Ediacaran biota (often improperly called "Ediacaran fauna") match all this. They lived even BEFORE ''Anomalocaris'' and the other Cambrian animals, and their body plans are even more enigmatic to us. One of the most mentioned is ''Spriggina'', similar to a fern. Like the Burgess Shale, is a very lucky thing that some fossil deposits have preserved these soft-bodied creatures to our days. However, we could recognize some modern invertebrate groups: for example, one of these Ediacarans is a very archaic mollusc. This would mean modern invertebrate groups were still living before the famous "Cambrian explosion" of life. Maybe, even our earliest vertebrate ancestors, but this is unproven.

The first Earthlings: [[ Prehistoric Stromatolites]] and other bacteria

* One-celled organisms are usually not preserved in fossil records (the aforementioned foraminifers are a well-known exception). However, we're sure the first Earthicans were bacteria. [[note]]For [[GeniusBonus expert readers]]: we're talking about bacteria in broader sense, including also the Archaea.[[/note]] They have been the simplest form of life, even lacking the nucleus which is the hallmark of the Eukarya - that is, animals + plants + fungi + algae + protozoans + other less-known organisms, ''all'' with nucleate cells. Some bacteria, the photosynthetic cyanobacteria (improperly called "green-blue algae") have built strange rocky structures called stromatolites (they produce them still today); the most ancient stromatolites are from 2,000 million years ago, ''three'' times earlier than the first multi-celled organisms. They are among the most ancient form of life that has left some fossils. It's worthy noting that parasitic bacteria (those that carry diseases) could only have appeared ''after'' multi-celled organisms: otherwise [[FridgeLogic which creature could have they infected?]] The same about the non-living viruses: [[note]] They are basically simple aggregates of proteins, lipids, and a bit of DNA or RNA capable to self-replicate: if we consider them "living", then we'd do the same with the chromosomes inside our cells, which are also aggregates of DNA and proteins able to replicate themselves.[[/note]] they should have appeared only ''after'' the apparition of true living things for the same reasons. (Some viruses infect bacteria, mind this). How life as a whole has originated is one of the most fascinating fields within human knowledge, but here we're outside paleontology and science in general. This is mainly speculation and philosophy, even though molecular biologists are doing great efforts to found the answer.