History UsefulNotes / StockDinosaursNonDinosaurs

Mosasaur heads were similar to those of modern lizards, but with longer snouts. Like all living lizards and snakes, they'd have had fleshy lips. Like modern snakes, their mouths had notably loose hinges between the jaws; this allowed mosasaurs to swallow large prey without tearing them into pieces (not that they weren't incapable of doing so). The teeth were conical or specialized for crushing smaller species and serrated on the three largest species (the 40+-foot giants that are most often depicted), the upper ones placed in two rows on each half-jaw, again like modern snakes and monitors. According to stomach contents, mosasaurs were very generalist feeders: fish, sharks, squids, pterosaurs, early birds like ''[[UsefulNotes/StockDinosaursSaurischianDinosaurs Hesperornis]]'' and even smaller mosasaurs have been found.[[note]]This ''doesn’t necessarily mean'' they were cannibals, though: the preyed-upon mosasaurs might've been from different species than their predators. After all, modern orcas eat smaller dolphins.[[/note]] We don’t know if mosasaurs had a forked tongue and eyes that didn't close, like many modern squamates, nor if they had heat-sensors like some boas and rattlesnakes; these things usually don't preserve in fossils. Older depictions of mosasaurs usually gave them a rather crocodilian profile, with sword-shaped tails, but reevaluations of the body shape together with the discovery of a shark-like tail fluke on some exquisitely preserved specimens have led to newer reconstructions being more whale-like or ichthyosaurian in appearance, with a more massive upper torso and neck.

In paleoart ''Sordes'' can be either shown with or without the classic ''Rhamphorhynchus'' fin on its tail, but it is the ''only'' one among the pterosaurs found before the TurnOfTheMillennium that has always been shown "furred" and not naked or scaled like all the others (see also ''[[UsefulNotes/StockDinosaursSaurischianDinosaurs Avimimus]]'' for its non-bird-dinosaur equivalent). Some small ''Sordes''-looking pterosaurs are visible at the beginning of ''WesternAnimation/TheLandBeforeTime'' together with other small reptiles of various kinds, after Littlefoot had just hatched.

# '''Entry Time:''' 1988
# '''TropeMaker:''' ''WesternAnimation/TheLandBeforeTime''

''Sivatherium'' was indeed related to giraffes, but little resembled them. Stocky and short-necked, it looked more like a huge okapi, except with "antlers" quite similar to a moose's; these "antlers" were true ''ossicones'' like those of a living giraffe, firmly attached to the skull as seen in the ''Sivatherium's'' surviving relatives. Being a ruminant, it arguably "chewed its cud" like a cow or a giraffe in life. ''Sivatherium'' first appeared in the Pliocene and survived into the Ice Age, living in both India and Africa (the African ones were initially identified as its own animal ''Libytherium''); some think it's represented in ancient rock paintings in the Sahara and India, and alleged depictions have even been recovered from Ancient Sumeria. Many other extinct giraffe-relatives existed in the Cenozoic across Europe, Africa, and Asia: together, the form the family Giraffidae, of which only two members have survived to today: the proper giraffe and the okapi, both exclusive to Africa. Interestingly, most of them look more like the okapi, with the giraffe being a much more specialized member of the group -- not all "oddball" members of a group of animals are prehistoric!

''Daeodon'' ("dreadful tooth"; also called ''Dinohyus'', "terrible pig") was last of the entelodonts, as well as the largest and historically the most-often depicted entelodont, living alongside the chalicothere ''Moropus'' in Early Miocene North America (featured in ''Forgotten Bloodlines: Agate Springs'', where ''Daeodon'' is one of the focus animals alongside ''Moropus''). Daedon-like creatures appears in ''Series/TheLordOfTheRingsTheRingsOfPower'', and is accurately portrayed for a fantasy show. They are bigger than humans, have an boar-like even-toed ungulate appearance, hooves, and even the bony knobs entelodontids are known for. Yet in universe they are referred as wolves and are supposed to be related to the canid wargs. Other notable species include the previous mentioned ''Archaeotherium'' ("ancient beast") of Late Eocene-Early Oligocene North America and the group's namesake, ''[[http://en.wikipedia.org/wiki/Entelodon Entelodon]]'' of Late Oligocene Asia. The former was one of the smallest entelodonts, the size of a modern boar; the latter was more similar in size to ''Daeodon''.

''Daeodon'' ("dreadful tooth"; also called ''Dinohyus'', "terrible pig") was last of the entelodonts, as well as the largest and historically the most-often depicted entelodont, living alongside the chalicothere ''Moropus'' in Early Miocene North America (featured in ''Forgotten Bloodlines: Agate Springs'', where ''Daeodon'' is one of the focus animals alongside ''Moropus''). A daedon-like creature appears in Series/TheLordOfTheRingsTheRingsOfPower'', and is accurately portrayed for a fantasy show. They are bigger than humans, have the boar-like appearance, the toed ungulates like hippos, hooves, and even the bony knobs entelodontids are known for. Yet in universe they are referred as wolves and are supposed to be related to the canid wargs. Other notable species include the previous mentioned ''Archaeotherium'' ("ancient beast") of Late Eocene-Early Oligocene North America and the group's namesake, ''[[http://en.wikipedia.org/wiki/Entelodon Entelodon]]'' of Late Oligocene Asia. The former was one of the smallest entelodonts, the size of a modern boar; the latter was more similar in size to ''Daeodon''.

''Daeodon'' ("dreadful tooth"; also called ''Dinohyus'', "terrible pig") was last of the entelodonts, as well as the largest and historically the most-often depicted entelodont, living alongside the chalicothere ''Moropus'' in Early Miocene North America (featured in ''Forgotten Bloodlines: Agate Springs'', where ''Daeodon'' is one of the focus animals alongside ''Moropus''). Other notable species include the previous mentioned ''Archaeotherium'' ("ancient beast") of Late Eocene-Early Oligocene North America and the group's namesake, ''[[http://en.wikipedia.org/wiki/Entelodon Entelodon]]'' of Late Oligocene Asia. The former was one of the smallest entelodonts, the size of a modern boar; the latter was more similar in size to ''Daeodon''.

''Basilosaurus'' was at the centre of a peculiar hoax in the 1840s by the notorious huckster Albert Koch. Koch had come into possession of a large number of ''Basilosaurus'' fossils, the remains of at least six different individuals, which he assembled into a 114ft-long amalgam he dubbed "Hydrarchos harlani" ("Harlan's Water King"). Koch presented his creature as a real-life SeaSerpent and the inspiration for the [[Literature/TheBible biblical]] [[KrakenAndLeviathan Leviathan]], until after naturalist Jeffries Wyman correctly identified it as the hodgepodge of whale bones it was. Undeterred, Koch toured across Europe and USA with his "Hydrarchos", eventually selling it off to Kaiser Wilhelm IV of Germany. Koch's "Hydrarchos" was destroyed during WW2 by Allied air raids on Berlin; a second "Hydrarchos" he made after selling off his first one was lost in the Great Chicago Fire. Koch had previously pulled off a similar hoax with his 32ft-long mastodon amalgamation "Missourium", even twisting the tusks to point upwards and make it look scarier.

An unnamed chalicothere (based on ''Chalicotherium'' itself) is portrayed in the third episode of ''WWB'' as a rather torpid animal with a very [[PandaingToTheAudience giant panda]]-like face, that makes it look more harmless than other, more badass popular representations of chalicotheres. Here, it mainly appears as fodder for other large mammals of the time -- the predatory ''Hyaenodon'' and the scavenging entelodonts, to be precise -- while being mostly overshadowed by the colossal ''Paraceratherium''. ''Moropus'', on the other hand, is one of the star animals of the Nigel Marven-narrated documentary ''Forgotten Bloodlines: Agate Springs'', alongside the next animal on this list, the giant entelodont ''Daeodon''.

The much smaller (2ft long) ''Mesosaurus'' has a deceptive name: it was not related at all with the much more famous ''Mosasaurus'' -- the former name means "middle-lizard", the latter "lizard from the Meuse River" (in the Netherlands). Despite this, ''Mesosaurus'' did somewhat resemble in shape the old classic illustrations of mosasaurs, being elongated, with long toothed jaws, and a powerful sideward-undulating tail for swimming. But its legs were apt for walking, like modern crocs and unlike the paddle limbs of its almost-namesakes mosasaurians (the mesosaur's limbs were palmated-footed at the most). This makes ''Mesosaurus'' actually more similar to ''Nothosaurus'' or ''Champsosaurus'' than to a mosasaurid. Like ''Champsosaurus'', it's sometimes mislabeled in paleo-media as a crocodile-ancestor, or worse, a true crocodilian. In reality, ''Meosaurus'' lived in the Early Permian, disappearing long before the the ancestors of crocodiles evolved. Adapted for freshwater or estuarine/coastal life, ''Mesosaurus'' was one of the first vertebrates to re-evolve an aquatic lifestyle and return to the water. ''Mesosaurus''' numerous tiny, needle-like teeth were adept at catching small fish, but it was too small and ill-adapted for life in the open ocean. But because its fossils are known from both Africa and South America, it was one of the main fossils used as evidence for the existence of Pangea (alongside the mammal-ancestors ''Cynognathus'' and ''Lystrosaurus'' (see below) and the plant ''[[https://en.wikipedia.org/wiki/Glossopteris Glossopteris]]'').

The gorgonopsians' history in pop culture is convoluted. The famous Czech paleoartist Zdenek Burian first depicted a ''Sauroctonus'' interacting with some ''Scutosaurus'' [[https://i.pinimg.com/originals/45/38/30/45383040e2067086741fd593d84c48e7.jpg in one of his old paintings]], and they have appeared seldomly in educational books. The second ''VideoGame/DinoCrisis'' game included ''Inostrancevia'', inaccurately showing it as an armored monster living in volcanoes alongside Jurassic and Cretaceous dinosaurs. The 2007 TV show ''{{Series/Primeval}}'' made them famous by having ''Inostrancevia'' appear as the show's first MonsterOfTheWeek and then having it fight and kill a future-evolved flightless, predatory bat in the first season finale. The ''Walking with...'' series' 2005 entry ''Series/WalkingWithMonsters'' also included a gorgonopian that went unidentified in the show but has been confirmed in other material to be ''Gorgonops'' (although its size and coexistence with ''Scutosaurus'' make it more like ''Inostrancevia'').

Among mammals, those living during the Late Pleistocene Ice Age have classically been the most portrayed, because they lived alongside the most iconic hominins ([[AllCavemenWereNeanderthals Neanderthals]] and Cro-Magnons). But mammals from before that time occasionally appear, usually -- needless to say -- the [[RuleOfCool coolest-looking]] among them. It's not uncommon to see pre-Ice Age mammals erroneously depicted as living alongside the Pleistocene ones however.

''Quetzalcoatlus'' was not the only gigantic azhdarchid. Since the 90s, others have been discovered with a similar estimated wingspan, e.g. ''[[http://en.wikipedia.org/wiki/Arambourgiania Arambourgiania]]''. But at an estimated 250 kg, ''Hatzegopteryx thambema'' was the heaviest of them, and quite possibly the [[GiantFlyer biggest pterosaur]] (and flying animal in general) of all time, a real "[[{{Badass}} Badassodactylus]]".

''Basilosaurus'' has been a recent hit in documentary media since the 1990s and especially the 2000s; see ''Series/WalkingWithBeasts'' and ''Series/SeaMonsters'' for example. However, it hasn't received the same amount of attention in broader popular culture as other giant sea critters of the past, like ''[[StockNessMonster Elasmosaurus]]'', {{Megalodon}}, and ''[[Film/JurassicWorld Mosasaurus]]''. Its serpentine form however has been of great interest to cryptozoologists, with many proposing modern sea serpent sightings to be of surviving ''Basilosaurus'' or its descendants.

''Livyatan'' living during the Late Miocene, and the fossil beds it was found in have also produced {{Megalodon}}. It's also theorized that they had a similar taste in preferred prey: large marine mammals, such as baleen whales. Indeed, ''Livyatan'' hunted even more powerful prey than the modern giant squids eaten by sperm whales today, and it definitely would have had to directly compete with Megalodon for food. Perhaps ''Livyatan'' was even able to kill an adult Megalodon, like modern orcas do sometimes with the great whites. It also happens to be one of those prehistoric animals whose name is a reference, too. "Livyatan" is the Hebrew name for the [[Literature/TheBible Biblical]] sea monster [[KrakenAndLeviathan Leviathan]] (note that the word of "whale" in modern Hebrew is just "livyatan"), and "melvillei" is coined after Creator/HermanMelville, the author of ''Literature/MobyDick''.

# '''TropeMaker:''' Its size and power and its rivalry against {{Megalodon}}

Among the typical animals of the so-called "Cambrian Explosion" of life, ''Anomalocaris'' is the only one that has made some appearances in popular media: it seem especially popular in some Japanese cartoons, e.g. ''{{Franchise/Pokemon}}'' (as Anorith and Armaldo) and ''{{Franchise/Digimon}}'' (as "Anomalocarimon"). This because, [[BiggerIsBetter of course]], it was by far the largest Cambrian predator.

''Anomalocaris'' means "anomalous shrimp": this name reveals a singular RealLife case of MixAndMatchCritter. Initially the name was invented for one of its "arms", which was mistaken for the tail of a shrimp. Then its circular mouth and body were found separately, each of them believed in turn to have been distinct organisms: the mouth was first described as a sort of pineapple-like medusa named ''Peytoia'', while the body was named ''Laggania''. ScienceMarchesOn however, and later scientists found new fossils showing the "three" animals were actually fragments of a bigger animal, which was given the name ''Anomalocaris'' because that was the first name applied to it (a bit like the notorious case of [[UsefulNotes/StockDinosaursSaurischianDinosaurs "Apatosaurus"/"Brontosaurus"]]).

''Anomalocaris'' has been found to have been a distant relative of arthropods, more precisely a "panarthropod" of the dinocarid subgroup. At a first glance it resembled a sea scorpion like ''Pterygotus'' above, but unlike the latter it may have had a softer body, and lacked articulated legs but did have small lateral "finlets" to swim above the sea floor. However, it also had the same compound eyes as ''Pterygotus'', trilobites and modern horseshoe crabs. It had also a pair of moustache-like [[CombatTentacles appendages]] in front of its mouth (the alleged "shrimps" that gave it its name) instead of pincers, and a strange mouth placed below the head like that of a sturgeon, but with "teeth" placed in a circular fashion like [[LampreyMouth a lamprey]].

Despite their odd but relatively harmless appearance (they might recall swimming, legless lobsters for some), anomalocaridids were actually highly specialized predators, with mouths built for prey around 1/12 to 1/6 of their own size, to the point that they've often ([[PrehistoricMonster and unfairly]]) been labeled "the first [[SeaMonster sea monster]]s" in docu-media. In ''Anomalocaris'''s time every other organism was very small: creatures like ''[[UsefulNotes/PrehistoricLifeOtherExtinctCreatures Hallucigenia]]'' and ''[[UsefulNotes/PrehistoricLifeOtherExtinctCreatures Pikaia]]'' were hunted by smaller predators, such as ''[[UsefulNotes/PrehistoricLifeOtherExtinctCreatures Opabinia]]'' and ''Anomalocaris saron'' (the saron is an Eastern xylophone-like instrument, whose plates the animal's segmented body recalls). The latter was the species shown in ''Series/WalkingWithMonsters'', though ridiculously oversized (6ft. long!) and prone to attacking its own kind, even though neither its mouth nor arms could injure an equally-sized specimen in the way depicted.

''Anomalocaris'' was also described by some as the first active, intelligent predator capable of dismembering large prey: ''Walking With Monsters'' showed the animal tearing a whole trilobite to pieces with its tentacles. This ability is controversial, though, and it was more probable it simply grabbed small critters with its "arms" and then sucked them up whole. Regardless, it's quite possible that anomalocarids set up the important role of predators in ecology and evolution.

# '''TropeMaker:''' ''Series/WalkingWithMonsters'' and anime

Today, marine invertebrates are by far the most diverse animals on Earth: almost ''every'' zoological phylum is represented in the oceans, just like in the past. Among Paleozoic sea invertebrates (apart from trilobites and the earliest ammonites), eurypterids and nautiloids are the most iconic in docu-media.

Although the modern nautilus possesses a helix-shaped shell, many Paleozoic nautiloids possessed long, straight shells resembling ice cream cones. These nautiloids are dubbed "orthocones", and the most oft-depicted form is the Ordovician-Silurian genus ''Cameroceras'' ("chambered horn"). Popularly nicknamed the "giant orthocone", many paleo-books and documentaries will tell you that ''Cameroceras'' was the largest of all nautiloids, up to 9m/30ft in length. This interpretation most famously appeared in ''Series/SeaMonsters'', feeding on sea scorpions and giant trilobites. ''However'', this is no longer considered a valid interpretation -- as it turns out, those alleged 9m/30ft ''Cameroceras'' specimens actually belonged to a different genus, the already-known ''Endoceras'', and were in fact only 6m/20ft. Today, ''Cameroceras'' is now believed to have been about 1m/3ft long: although some experts think that ''Endoceras'' and ''Cameroceras'' are the same, potentially allowing the latter to regain its title. Regardless of identity, the giant orthocone was doubtlessly a formidable predator and certainly the biggest animal to have ever lived up to that point in Earth's history.

Ammonites were believed to be stony horns ("ammonite" comes from Amun, an Ancient Egyptian deity who was often portrayed with rams' horns), or petrified snakes -- some had fun sculpting snake heads on the shells' extremities to make them look like snakes!

The lesser-known belemnites (technically belemnoids), with their straight pointed shape, were believed to be stony arrows, or even the Devil's fingers! Belemnites were cephalopods living in the Mesozoic era together with ammonites, and probably gave rise to squid. Like ammonites, only their shells are usually preserved. This shell was straight and often arrow-shaped, and was ''inside'' the animal's body and invisible in life; belemnites would resemble simple squid or cuttlefish if alive today. Their lifestyle was more active than ammonites, and they were probably able to do the same things modern squid do: spraying ink, swimming using the lateral "fins", catching prey with their suckers, seeing images with their eyes. In popular media belemnites tend wrongly to be portrayed or described as proper squids, but technically they weren't. They too tend to be shown as ambient animals for Mesozoic or prehistoric placements.

Despite the abundance of their shells, their soft bodies are only rarely preserved and poorly known. They likely had ten tentacles, a beak, a small siphon for jet propulsion, and possibly even an ink sac. It's unknown if their tentacles had suckers like octopuses and squid, or lacked them like nautiluses, nor do we know if they had complex eyes to see images like octopuses and squid. Many were excellent swimmers, but others were slow-moving bottom-dwellers. Their diets likely varied from species to species, with some being active hunters and others being filter feeders. Their hard shells were excellent protection against predators, as shown by some ammonites with marks of teeth left by ichthyosaurs or mosasaurs which tried to break the shell in vain. Like nautiluses, their shells also let them function like miniature submarines, with small chambers they could fill with water or empty to control bouyancy and depth. Ammonites laid their eggs in coastal shallows and produced planktonic larvae, which made them extremely vulnerable to the devastating effects of the asteroid that ended the Cretaceous -- unlike nautiluses, which lay their eggs on the deeper seafloor and have babies that look just like tiny adults. Most ammonites were no bigger than a human hand, but some were as big as tractor tires. Many ammonite genera end with ''-ites'', ex. ''Ceratites'', ''Goniatites'', and so on, while many others end in ''-ceras'': ''Dactylioceras'' is one.

Today, marine invertebrates are by far the most diversified animals on Earth: almost ''every'' zoological phylum is represented in the oceans, just like in the past. Among Paleozoic sea-invertebrates (apart from trilobites and the earliest ammonites), sea-scorpions and nautiloid cephalopods are the most iconic in docu-media.

Two members of the latter two groups have a greater chance to eventually appear in fiction, though this has not happened yet: the giant sea-scorpion ''Pterygotus'' and the giant cephalopod ''Cameroceras''. Both only because, again, they're [[BiggerIsBetter bigger]] than their relatives. ''Pterygotus'' ("the finned one" or "the winged one") was 2m long, and like all its relatives, the Eurypterids, was ''not'' a marine scorpion, but closer to the modern "living fossil" ''Limulus'', the horseshoe crab (which, while we're at it, isn't a crab or any other kind of crustacean). ''Cameroceras'' ("chambered horn"), on the other hand, was distantly related with the modern ''Nautilus'' (another "living fossil"), but unlike the latter had straight chambered shell: hence the nickname "orthocone", meaning straight cone.

The potential interest toward them is tied to their size: ''Pterygotus'' was as long as a grown human; ''Cameroceras'' was much longer, as long as the armored fish ''Dunkleosteus''. They were the top predators of their seas (Silurian and Ordovician respectively). At a first glance, however, their appearance, though rather unusual by modern standards, wasn't so different from that of modern crustaceans and octopuses. The pterygotus resembled a slender lobster with big insect-like eyes and curious rear legs similar to paddles, for swimming; the "orthocone" resembled a squid inside an ice cream cone-like shell, though probably with more tentacles. MixAndMatchCritter fits well with both of them.

Contrary to what media usually tell you, ''Meganeura'' ("big nerve", a reference to its heavily-veined wings) was not a proper dragonfly, but a "griffinfly": basically an extinct relative of actual dragonflies and damselflies (order [[http://en.wikipedia.org/wiki/Odonata Odonata]]) and extremely similar to them, other than size.

With a wingspan like a crow, and not like an [[BiggerIsBetter eagle]] as is said in Series/WalkingWithMonsters, ''Meganeura'' has been called the largest-known true insect of all time (millipedes like ''Arthropleura'' are not insects), but its recently-discovered close relative ''[[http://en.wikipedia.org/wiki/Meganeuropsis Meganeuropsis]]'' ("similar to Meganeura") was just as big, if not bigger. Both had the same shape as modern dragonflies, with slender bodies, huge eyes, short antennae, powerful mandibles, and two pairs of independent-moving wings; they were arguably very powerful flyers like true dragonflies, perhaps able to fly as fast as many modern birds.

''Meganeura'' lived in the Carboniferous swamp-forests together with the giant millipede ''Arthropleura'' (below), while its bigger cousin ''Meganeuropsis'' lived in the Early Permian -- this still makes ''Meganeura'' the earliest known GiantFlyer. Unlike ''Arthropleura'', ''Meganeura'' was carnivorous (again, like modern dragonflies) and fed on smaller insects and maybe even small amphibians. Both animals were usually safe from the super predators of the time: the millipede's armor and the griffinfly's agility protected them against the crawling giant amphibians and the swimming fish.

In media, ''Meganeura'' is more common than its land-bound neighbor ''Arthropleura''. Like trilobites and ammonites, ''Meganeura'' tends to be an ambient animal in fiction, that exists mostly to show something prehistoric. Frustratingly, older works tended to portray ''Meganeura'' living [[AnachronismStew alongside dinosaurs]], despite the fact that it had already died out long before the dinosaurs arrived on the scene. A particularly confusing appearance of a ''Meganeura'' was in the first ''[[Franchise/JurassicPark Jurassic Park]]'' novel, where a cloned one was present in the park despite having gone extinct long before any mosquitoes or even amber would have existed -- conifer trees and mosquitoes appeared only after the Carboniferous period, when the "first giant flyer" was already gone, which raises the question of how they were cloned.

# '''Entry Time:''' 1885

Why did land arthropods reach [[BigCreepyCrawlies such a large size]] in the Carboniferous? [[note]]But don't forget most Carboniferous land arthropods were normal-sized; [[BiggerIsBetter obviously]], those don't gain much attention in media.[[/note]] Probably because the oxygen content at the time was much greater than in every other period. The tracheal respiratory system of insects and land arthropods prevents them from growing very large: over a certain size, this system just doesn't work. The upper limit an insect can grow to depends on the quantity of oxygen in the atmosphere; thus, more oxygen —> bigger size.

The myriapod ''Arthropleura'' ("articulated side") was the special case: as long as a human, it is the biggest known land arthropod of all time, and was also well-armored, to the point that it could be considered a living tank (its most known species' name, ''Arthropleura armata'', means "armored articulated side"). But like modern millipedes and unlike centipedes, it was an inoffensive herbivore that fed on the rotting vegetation extremely abundant in Carboniferous forests. This giant millipede didn't even resemble a millipede at first glance. Wide and flattened, it more resembled an overgrown trilobite, but actually there are modern millipedes that have a rather similar body shape to ''Arthropleura'', though obviously much smaller. We don't know if it was able to rear up like a cobra as portrayed in Series/WalkingWithMonsters, given its weight.

Remember earlier when we stated ''Arthropleura'' only got big because of the large amount of oxygen in the atmosphere? Well a new study [[https://jgs.lyellcollection.org/content/early/2021/11/19/jgs2021-115 shows]] that not only did it exist before the oxygen levels rose to ridiculous levels but it survive into the Permian when oxygen levels nosedived, giving the animal a range of about 45-50 million years on earth. It is now believed that their Extinction came about from the diversification of tetrapods who out competed them. On how it managed to survive without massive oxygen level is currently mystery but truly shakes up our understanding of these animals.

Despite this critter's size and appearance, ''Arthropleura'' historically got little presence in the media, but in recent years it's become a common sight in paleo-books and documentaries about life before the dinosaurs. The most noteworthy appearance of an ''Arthropleura'' in a non-educational work was ''Series/{{Primeval}}'', which [[RuleOfCool for some reason]] decided to portray it as a giant venomous ''centipede''.

Described by Cope during the Bone Wars from the Early Permian Red Beds of Texas (''Dimetrodon'' was also first described by Cope from the same geological terrains), ''Edaphosaurus'' means "pavement lizard" in reference to its teeth, which are packed together like the tiles of a floor. Like ''Dimetrodon'', several species are known, from less than a foot to over 11 feet in length . ''Edaphosaurus'' was bulkier-bodied and smaller-headed than the very similar''Dimetrodon'', sharing its carnivorous cousin's back sail, long tail and splayed legs. Its sail was more complex however: it had a more rounded shape and regularly-placed tubercles of uncertain purpose. Contrasting the pointier, more varied teeth of ''Dimetrodon'', ''Edaphosaurus'' had round, peg-like teeth all of the same shape and length. Its dentition, along with its large gut, tells us that it was a plant-eater -- in fact, it was one of the first large terrestrial vertebrate herbivores to evolve. It's also hypothesized to have eaten shellfish as a dietary supplement.

It's uncommon to see prehistoric invertebrates in Fictionland, but some are so common in ancient rocks (even cropping up in fossil markets and shops as well as popular paleo-books and magazines) that they've become familiar to the public nonetheless.

Some things have had more impact than others. Trilobites are among them. Their [[http:/en.wikipedia.org/wiki/List_of_trilobites extreme abundance]] in the 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 through the whole Paleozoic era, but became rarer and rarer after the Devonian, and none survived the devastating Permian-Triassic mass extinction: thus, they might be taken as the Paleozoic's unofficial symbol. Though their appearance could lead to them being confused with insects or crustaceans, they were actually not related to any modern arthropod. They are classified in between the two main arthropod groups: chelicerates (arachnids + sea spiders + horseshoe crabs) and mandibulates (hexapods + myriapods + crustaceans).

"Trilobite" means "three lobes". Their bodies were divided into three parts: the head, the segmented thorax, and the telson (the scute at the rear end of the body). But their flattened bodies also show three parts in the longitudinal sense, the middle segment and the two lateral ones. Like millipedes, they had many pairs of legs (up to 100), one pair of antennae, many pairs of gills, and two, usually large, compound eyes similar to those of insects; trilobites were among the first creatures capable of seeing images. They mainly lived in the benthic zone; some were diggers and others active swimmers. Some were able to curl up for protection, like many modern isopod crustaceans (pillbugs), which they're often compared to in appearance as well. Most were no bigger than a human hand, and the smallest were shorter than a human finger; the biggest were 3ft / 90 cm long, ex. ''[[http://en.wikipedia.org/wiki/Isotelus Isotelus]]''. Like the contemporary jawless fishes, trilobites only ate small objects, and were prey for other arthropods, cephalopods, and jawed fish. We don't know if trilobites were completely aquatic or came on land to lay their eggs. Their young were identical to the adults. The kinds of trilobites commonly shown in media usually come from the [[http://en.wikipedia.org/wiki/Phacopida Phacopid]] subgroup; good luck if you see an [[http://en.wikipedia.org/wiki/Agnostida Agnostid]] or a [[http://en.wikipedia.org/wiki/Proetida Proetid]].

In fiction, trilobites can often be seen in underwater visuals even in the Mesozoic, despite this being millions of years after their extinction: usually as ambient animals that skitter about on the ocean floor. They're much more common in older works, and tend to solely exist as a "Look, something that looks primitive! We're in prehistory alright!" type of thing.

Is there anyone who hasn't seen those spiral stony shells emerging from the surrounding rocks? Ammonites, more technically 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 they reached their prime in the Dinosaur Age. They went extinct at the end of the Mesozoic, when the asteroid struck. Even though it resembles an ammonite, the extant [[http://en.wikipedia.org/wiki/Nautilus Nautilus]] is not descended from them.

Despite the abundance of their shells, their soft bodies are rarely preserved and little-known. Like octopuses and squid, they certainly had the tentacles and beaks typical of cephalopods, but the number of tentacles is uncertain. They may have had more than eight to ten tentacles, more like a nautilus than a squid. It's unknown if their tentacles had suckers like octopuses and squid, or lacked them like nautiluses. Nor do we know if they sprayed ink or had complex eyes to see images like octopuses and squid.

With their heavy shells, ammonites were probably slow swimmers; they were surely predators like every other cephalopod, but they probably caught only small prey. Their hard shells were excellent protection against predators, as shown by some ammonites with marks of teeth left by ichthyosaurs or mosasaurs which tried to break the shell in vain. Though most ammonites were no bigger than a human hand, some reached a diameter of 3m/10ft (smaller than a giant squid in length, but heavier in weight, ex ''[[http://en.wikipedia.org/wiki/Titanites Titanites]]''). Many ammonite genera end with ''-ites'', ex. ''Ceratites'', ''Goniatites'', and so on, while many others end in ''-ceras'': ''Dactylioceras'' is one.

In media, ammonites are always shown with the classic curly, laterally-flattened shell; however, the shells of some Cretaceous ammonites showed unusual forms. Some had [[https://upload.wikimedia.org/wikipedia/commons/thumb/4/46/Hamites.jpg/250px-Hamites.jpg loosely uncoiled shells]], some had [[http://www.thefossilforum.com/uploads/gallery/album_1575/med_gallery_10275_1575_20734.jpg u-shaped shells]], some had [[https://redlegagenda.files.wordpress.com/2015/11/hypotumilittes.jpg?w=600 spiny tower-like shells]], some just had [[https://s-media-cache-ak0.pinimg.com/736x/3a/06/07/3a060722f2ba3abd280625fd62910403.jpg straight shells]], and others had [[https://www.tonmo.com/attachments/conv_302072-jpg.55598/ shapes so bizarre]], no one is sure how they survived.

Ammonites, like trilobites, are common as ambient animals in paleo-media, though their presence in Mesozoic works at least makes more sense seeing as they were ''extremely'' common back then and their fossils are among the most commonly found. So common, in fact, that individual ammonite species are used as "index fossils", with their presence in layers of rock denoting specific geological time zones.