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Useful Notes / Stock Dinosaurs (Non-Dinosaurs)

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The following extinct animals, to quote Lore Sjoberg, "are not technically speaking dinosaurs but end up in the dinosaur section of the plush toy aisle nonetheless." This can get quite confusing, as no matter what your dictionary tells you, scientists have been waffling on the subject of dinosaurs for as long as there has been a name for them.

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Flying Reptiles

Pterosaurs (usually called pterodactyls in media and in pop language) are often referred as the "flying dinosaurs". They were closely related to them, but were not true dinosaurs.

    Pterosaurs in Media 

In Real Life, pterosaurs were the dominant large flying creatures in the Age of Dinosaurs, coexisted with their land-dwelling relatives for 160 million years, and eventually went extinct together with the last dinosaurs. As with dinosaurs, there are several issues about pterosaur portrayals in media. They go much further than simple Anachronism Stew and Misplaced Wildlife, they regard every aspect of pterosaurian biology. Here, it’s easy to imagine pterosaur scientists crying more than every other colleague.

  • In fiction, these reptiles usually act as airborne terrors to menace humans and/or other animals, usually grabbing them with improbable eagle-like feet and being magically strong enough to lift and carry their victims in flight, often giving them to their nestlings just like eagles. In Real Life pterosaurs had very weak legs with non-opposable digits and caught their food with their mouths instead. And they didn't have any nestlings to feed: pterosaurs reproduced like lizards, burying and abandoning their soft eggs, until the hatchlings (termed "flaplings" by some paleontologists) emerged, strong-boned and ready to fly on their own.
  • Especially in older media, they are often portayed with bat wings, tying into the whole Dinosaurs Are Dragons thing. Actually their wing membranes were sustained by only one overly-long digit, the fourth one (not the fifth as sometimes shown), which was as robust as the rest of the forelimb. The first, second and third fingers were normal-sized and protruded from the anterior wing-edge like the first digit of modern bats. While most media nowadays have done away with the bat wings, more persistent is the depiction of the wings as loose, bat-like flaps of skin — in Real Life, the wing membranes were thin but taut sheets of muscle, containing several distinct layers of complex muscle fibers which essentially made them into shape-shifting organs for on-the-fly adjustments.
  • We don’t know at all what kind of sounds they emitted in Real Life, but expect to hear them screeching loudly and continuously (usually in a mixed crow-vulture-seagull manner), and also fanning their wings as noisily as possible.
  • They tend to be represented as always huge. In Real Life there were many types of pterosaurs (just like modern birds) and they were astonishingly diverse in size, ranging from the size of a crow up to a small airplane.
  • They weren't dinosaurs, nor were they birds. Furthermore, they were not even the ancestors of any modern fliernote : instead, they were only relatives of dinosaurs (and thus birds, of course).

Its worth noting, however, that Science Marches On has been a crucial factor in pterosaur portrayals. Like dinosaurs, pterosaurs have undergone a sort of scientific "renaissance" since the seventies. Before that, they were considered cold-blooded creatures covered in scales and very unlike modern birds. Scientists used to think pterosaurs had weak wing muscles and fragile wing membranes; this would've meant pterosaurs were only awkward gliders — contrasting with the popular view of them as powerful fliers. Since the "renaissance" paleontologists now believe pterosaurs were the first ever vertebrates to be able to fly properly, and nowadays it's clear they were active and efficient fliers with large brains, good eyesight, excellent sense of balance, skin covered in down-like structures (just like the most bird-like theropods), and with high metabolic rates. Due to the structure of their wings, pterosaurs would have been particularly adept at soaring (a bit like modern albatrosses), but they were also able to flap their wings.

Most pterosaurs discovered thus far appear to have lived in marine, coastal, or other watery habitats, but more dry land-loving kinds surely existed as well: some of the smallest species were probably able to climb trees. They were mainly predators of small prey (insects, fish, small land vertebrates etc. according to the species), but some may have been fruit-eaters. Some (especially Pterodaustro) were flamingo-like filter feeders. Like dinosaurs, we don't know what coloration they had, though different kinds of pterosaurs surely had different colors. Modern artists often depict them with motifs reminiscent of those of modern birds, but may also portray them with duller colors (as happens with dinosaurs). Pterosaurs' locomotion on land has long been a mystery; their footprints were only first discovered in the 1990s. Scientists now think most or all pterosaurs were quadrupedal. Despite all these discoveries and theories, even today the pterosaurs remain one of the most enigmatic groups of prehistoric beasts, as their fossil record has always been one of the scarcest.

Sadly, all the issues above are usually glossed over in pop-media, even today. See Ptero Soarer to get into this in depth.

    Stock Pterosaurs 

Very few pterosaurs have been portrayed in non-documentary media, despite their notable variety in Real Life. Among pterosaurs listed here, only three can be called pterodactyls without being totally wrong: Pteranodon, Quetzalcoatlus, and of course Pterodactylus. The other two, Rhamphorhynchus and Dimorphodon, were more primitive than the former and are usually called rhamphorhynchs.

Surprisingly, stock pterosaurs are not (necessarily) the biggest/coolest-looking ones — three out of five are no bigger than an eagle or a stork. Instead, they were among the very first scientifically-described species, in the 19th century. Pterodactylus, Rhamphorhynchus, and Dimorphodon (the mid-sized ones) were discovered in Europe before the 1820s (the decade in which the first dinosaurs were named). The last two were initially classified as Pterodactylus and recognized as distinct only after the 1820s. Initially scientists were doubtful if pterosaurs were really fliers: since no modern reptile (in traditional sense) can fly, some thought they were swimmers using their membranes as flippers, while others believed they were terrestrial. And some, surprisingly, already postulated they were furry like mammals (even though most classical depictions show them scaly). The notion that they were covered with filamentous structures has re-emerged only since The '70s thanks to new fossil finds of that period (Sordes)

With its 7m/24ft wingspan, Pteranodon was found in the USA in the last quarter of the 19th century, during the "Bone Wars." note  Its sheer size ("Whoa the biggest flier ever!") and its crest soon made it the new iconic pterosaur, and it still holds that status today.

Several interesting new pterosaurs were discovered in the second half of the 20th century, but only one managed to achieve some consideration in the media: Quetzalcoatlus, because it was the only one clearly bigger than Pteranodon, and the new "biggest flying animal ever." In the 2000s, Ornithocheirus gained some popularity as well thanks to a memorable appearance in Walking with Dinosaurs, but only because it was (wrongly) described as the biggest flying animal that ever existed. The others (Dsungaripterus, Pterodaustro, Tapejara, Eudimorphodon, Sordes, and so on) were largely ignored outside of dino-books and documentaries. If you’re looking for these and other non-stock pterosaurs, see here.

Giant Flier, but not Toothy: Pteranodon ***

Pteranodon lived 86-84 million years ago on what were then the shorelines of Kansas and other midwestern U.S. states. It had the typical traits of the most evolved pterosaurs, the pterodactyloids (aka literal pterodactyls). It had an elongated head, weak hindlimbs, only a hint of a tail, and very long wings with a huge "wing-finger," while the other digits were very small and may have been almost useless. It was one of the most specialized flying animals that ever lived, but very clumsy on land, where it arguably walked slowly on all fours.

It was thought pteranodonts lived a bit like modern seashore birds, laying their eggs on cliffs and using ascendant winds to take off. However, the takeoff method is now known to have been wrong; rather, pteranodonts, like all pterosaurs, could vault from level ground with their wings. Roosting on cliffs is not entirely unlikely, though. Like the modern albatross, they may have been vagrant or migratory. Contrary to what is sometimes said, Pteranodon probably didn’t survive enough to see the meteorite — its fossil record ends a dozen million years before the mass extinction. Until 2018, only azhdarchids were known from fossils as late as 65 mya; one of them was Quetzalcoatlus (see below). Findings early in 2018 revealed that pteranodontids and their smaller, more derived relatives the nyctosaurids also reached that point, though Pteranodon itself still hasn't left any fossils from that time.

The backwards-pointing crest is the most striking feature of Pteranodon. It was laterally flattened in Real Life, but in media expect to see it with a conical shape, often resembling a horn. The real purpose of this crest is still unclear. It is traditionally described as a sort of balancing pole to better balance the long head, or as a rudder to keep it stabilized during flight. However, this doesn’t explain why only males had such a big crest, while the females’ one was extremely shortened. It was once thought long- and short-crested individuals belonged to different species. note  This bony protrusion may have simply been a display device, as is hypothesized as well for Stegosaurus’ plates, Triceratops’ horns and frill, Spinosaurus’ "sail," and so on. This could explain why the males’ one was so big compared with the females.

In popular portrayals, an ever-present mistake is to show Pteranodon as toothed. When present, these teeth usually resemble those of the other well-known pterosaur, Rhamphorhynchus (see below). The fact that the genus’ name ends in odon (meaning tooth in Greek) may mislead people. Actually, odon is preceded by the Greek "privative a-" (becoming an- when followed by a vowel). Thus, anodon means toothless (see also Ludodactylus).

In Real Life, Pteranodon was basically a giant pelican in behavior. Its long toothless beak was useful for catching fish, and the shape of its lower jaws seem to show a sort of "pouch" to store fish in flight, though this is not certain. It was once thought that Pteranodon would snatch fish on the fly with its beak, but now it's believed that it would have dived into the water and swam for food (again, much like a brown pelican). If alive today, Pteranodon wouldn't be the danger for humans that it is in media. Weighing only about 20kg note , it was too light to lift a 70kg man off the ground. And even if it could have done so, it wouldn't have used its weak hindlimbs, but its mouth instead. Finally, since its beak was straight and smooth-edged, a child could easily have escaped it by wriggling.

Pteranodon’s nifty crest on its skull, along with the fact that it held the size record for almost a century, has made it THE pterosaur in popular imagination. Its iconic status among pterosaurs could be partially justified. It’s not only one of the first-discovered pterosaurs, but perhaps also the most common in the fossil record. Hundreds of specimens are known, while most other pterosaur genera are much, much rarer, often known from a single individual. The vast majority of pteranodonts belong to the species everyone knows, Pteranodon longiceps.

  1. Entry Time: 1925
  2. Trope Maker: The Lost World (film)

Smaller Flier, but Toothy: Rhamphorhynchus **

Rhamphorhynchus ("sharp beak") was first found in Germany in the 19th century, and lived in the Late Jurassic in the same location as several other pterosaurs and also Archaeopteryx and Compsognathus. It was the second named pterosaur after the prototypical Pterodactylus (see below), and the first one known with a long tail. It’s the namesake of the primitive pterosaurs called Rhamphorhynchoids. Like Archaeopteryx, Rhamphorhynchus has left exquisite remains. Some specimens with prints of wing membranes have been known since the 19th century. It was just these Rhamphorhynchus that definitively showed pterosaurs were airborne critters, not water-dwelling as believed by some at the time.

Rhamphorhynchus had a wingspan of about 2m/6ft, relatively short wings, a narrow snout slightly pointing upwards note , robust hindlimbs, and long tail. Two recognizable traits are the protruding teeth and the diamond-shaped "fin" set vertically on the tip of its tail. As Rhamphorhynchus lived in coastal lagoons, the teeth were probably apt to either catch fish in flight or catch them by swimming and diving. The typical tailfin was made of soft tissue (it’s known only thanks to prints in the rocks).

Rhamphorhynchus’ tail has often been compared with a dragon’s or a devil’s, and the large teeth give it a deceptively "menacing" look (actually it wouldn’t be more dangerous than a gull if alive today). We now know it was covered in hair-like structures like its close relative Sordes pilosus (which just means "hairy devil").

Its striking look, the earliness of its discover and the completeness of many remains have contributed to make Rhamphorhynchus the second most commonly portrayed pterosaur in media — especially older media. In particular, the Pellucidar series features the Mahars - a race of psychic Rhamphorhynchus. And Harryhausen's movie One Million Years B.C. shows a huge, short-tailed (and tailfin-lacking) rhamphorhynch winning an aerial battle against an equally huge (but correctly toothless just for once) pteranodont. The species has become quite rare today — pterosaurs shown in the most recent movies generally are Pteranodon or (more often) imaginary Giant Fliers.

Like Pteranodon, Rhamphorhynchus tends to be portrayed incorrectly in fiction, often as big as a Pteranodon or even bigger. Another classic mistake is to show rhamphorhynchs with flexible tails (a bit like what happens to "raptors") and often ending with triangular, arrow-like fins, like here. Actually their tail was stiffened by bony tendons, and was a steering device during flight. note  Finally, a very Undead Horse subtrope is to apply the "dragonish" rhamphorhynchoid tail to every other pterosaur, especially Pteranodon. Actually pterodactyloid pterosaurs had stubby tails without distinction.

  1. Entry Time: 1940
  2. Trope Maker: Fantasia

Huge, Mythical Beast: Quetzalcoatlus *

This has been considered the ultimate Giant Flyer among prehistoric animals. Lived in North America at the very end of the Cretaceous 70-65 mya (but some think its distribution was worldwide). Quetzalcoatlus was discovered in the 1970s in Texas from incomplete remains. Its wingspan was estimated from 10m/35ft up to 16m/50ft, with the lower range being the most likely. Of course, pop-media have often followed the higher one. This "living airplane" took Pteranodon's reputation over as "the biggest flier ever" in those years. Its describer named it from an Aztec divinity: Quetzalcoatl, the "feathered snake" - the animal itself is often called "the quetzalcoatl". Its name also recalls that of the modern Quetzal, the long-tailed bird who was sacred to the Aztecs.

Weighing about 80 kg like a adult human, Quetzalcoatlus was long described as similar to an upscaled Pteranodon (which weighed less-than-half). Indeed, both animals had a long toothless beak and an atrophied tail. Some depictions show Quetzalcoatlus with a small cranial crest, others show it crestless. Compared to Pteranodon, Quetzalcoatlus had much longer, stronger hindlimbs, a bigger body, a longer, stiffer neck, and shorter, wider wings with the "hands" closer to the wingtips than to the shoulders. Its diet has long been an enigma (Fish? Small reptiles? Carrion?). In the 2000s, scientists re-studied its anatomy, and today Quetzalcoatlus is thought to have a mainly terrestrial animal, walking on its four long limbs, and eating small land critters like a stork. note 

The astonishing thing is, in spite of being as tall as a giraffe when on land, Quetzalcoatlus could still fly — even though some scientists still doubt that such a large critter could actually take off. If it really was a flier, giving its size it should have been an extremely powerful flier, capable of frequenting several habitats, and maybe even traveling worldwide. An almost-identical relative, Hatzegopteryx, was described from Europe in 2002. It was estimated even bigger than Quetzalcoatlus, with a 36 to 39ft wingspan and was probably more menacing, with a more muscular frame and a shorter neck.

Despite its impressiveness, Quetzalcoatlus has received great attention only in dino-books and documentaries, while is still rare in films and dino-stories. No matter that, with its size and terrestrial habits, it could have been the only stock pterosaur potentially dangerous for humans if alive today. A downsized Quetzalcoatlus flying robot capable of flapping its wing was built in the 1990s, although it did not have the proportions that the animal is now known to have had (a case of Science Marches On).

  1. Entry Time: 1990s
  2. Trope Maker: Dinotopia books

The first-named Reptile of the Mesozoic: Pterodactylus *

Rarely will you see any other pterosaur in fiction, but if you do, it will either be Pterodactylus or Dimorphodon. In the original novel The Lost World (1912), the two scientists argue if the pterosaurs they meet are one of the two. Whatever kind they were, they are enormously oversized — even bigger than a Pteranodont. In Real Life both were not bigger than a large seagull. In recent stories, Pterodactylus and Dimorphodon are rarely portrayed, but have traditionally been common in documentaristic media due to their historical relevance.

Pterodactylus was the first fossil recognized by science as belonging to a prehistoric animal completely different to the modern ones (well before the first dinosaurs); this happened in year 1809, when concepts like "extinct" and "antediluvian" (the word "prehistoric" came later) were still highly controversial. Obviously, Pterodactylus was the very first flying reptile ever found, and even early paleontologists tended to refer to the whole group as 'pterodactyls' long before the name pterosaur was coined; this explains why pterodactyl has become the stock name of pterosaurs.

Several Pterodactylus species were recognized in the past. Today only one has remained valid, Pterodactylus antiquus ("ancient winged finger"), about the same size of a Rhamphorhynchus. Some alleged Pterodactylus species were described from individuals no bigger than a sparrow: this led the genus to be described as "one of the tiniest pterosaurs ever." Recent research suggests these specimens were actually juveniles, which deceptively resemble miniaturized adults. The fact that newborn pterosaurs were virtually identical to adults is a very recent discovery (made in the 2000s) which astonished scientists: none of the extant fliers shows powered flight soon after its birth.

Pterodactylus was one of the first pterodactyloid pterosaurs to appear (Late Jurassic Europe), and shared its habitat with the more archaic Rhamphorhynchus. Its body shape was more similar to a miniaturized pteranodont than to a rhamphorhynch, with long, thin jaws, elongated wings, weak hindlimbs, small "wing-hands," and stubby tail. Usually depicted as a generic-as-it-gets pterosaur, the latest findings show it had a small crest made of skin on the back of its head. Moreover, its apparently generic teeth could have been specialized for something — traditionally described as a fish- or insect-hunter, Pterodactylus could have been a filter feeder in coastal lagoons (though not so specialized as another relative, Pterodaustro) or perhaps a wader/prober like a shorebird.

  1. Entry Time: 1854
  2. Trope Maker: Crystal Palace Park

Primitive Bighead: Dimorphodon *

Dimorphodon was a rhamphorhynchoid that lived in Early Jurassic, 190 mya - the most ancient of the five stock pterosaurs. Found in England, it shared with Rhamphorhynchus the elongated stiffened tail, but we don't know if it had a "fin." Its more striking trait is its oversized skull, even bigger than the body itself! Despite appearances, the head of Dimorphodon was lightened by wide openings in the skull, and the animal couldn’t have had trouble lifting it, a bit like modern toucans and hornbills with their beaks.

Its name, "two-shaped teeth," recalls that of the famous Dimetrodon ("two-measured teeth"). It had two kinds of teeth (while most pterosaurs had only one or none). Some teeth were bigger and sparse among the smaller ones. With this kind of dentition, the feeding habits of Dimorphodon have always been matter of speculation. It could have been a fisher, a hunter of small land animals, an insectivore, or all these things. Newer evidence reveals that the latter two were more likely, however, as it has few to no adaptations for fishing, but many for terrestrial hunting and leaf-litter grubbing.

Dimorphodon is often depicted as a frequent flyer (the Dinotopia books even portray it as an Instant Messenger Pigeon!), but later research suggests that it was quite the opposite. While Dimorphodon could fly, it was also rather heavy for such a small animal, making flight rather strenuous for it. It's believed that, like similarly loaded birds, Dimorphodon would have only flown in times of emergency. Interestingly, this is not an illustration of Dimorphodon's primitiveness, as many pterosaurs before it were excellent flyers. This likely means that Dimorphodon's poor flight ability was actually an evolutionary adaptation.

More archaic than Rhamphorhynchus, Dimorphodon shows several primitive traits which betray how dinosaurs and pterosaurs were closely related. The three free wing-fingers were strong and large-clawed, not unlike those of a feathered theropod (indeed, its species name, macronyx, means "large claw"). The hindlegs were long and powerful, and the animal was believed to have walked bipedally used its long tail for balance, but this is unlikely. Its stocky skull was more similar to a theropod dinosaur than to a pterosaur, with nasal openings on the tip of the nose (most pterosaurs had nostrils just in front of the eyes). A strange anatomical feature is one elongated digit in each hindfoot, which could have been attached to the wing membrane. If so, the dimorphodont could have used it to better-control the flight, like modern bats do with their feet. More evolved pterosaurs lost this super-toe altogether. Despite its primitive anatomy, Dimorphodon was fully pterosaur with all the pterosaurian traits. (See also Eudimorphodon.)

Dimorphodon doesn't typically appear in the media beyond dinosaur books. However, this might be due for a change with the release of Jurassic World, which had Dimorphodon as a featured creature (naturally in the "winged menace" role).

  1. Entry Time: 1912
  2. Trope Maker: The Lost World

Other pterosaurs

Sorry, these ones aren't here. If you're looking for Dsungaripterus, Nyctosaurus, Pterodaustro, Tropeognathus, Cearadactylus, Tupandactylus, Anurognathus, Eudimorphodon, Sordes, and others, see here.


Marine Reptiles

Similarly, these animals are often collectively referred to as "marine dinosaurs," but this time they were not close relatives of true dinosaurs; some of them were not even related to each other. There were semiaquatic dinosaurs (Spinosaurus, for one), not to mention modern-day diving birds such as penguins, but none of them were completely marine in the way that these reptiles were.

    Sea Reptiles in Media 

Four main groups of sea reptiles can be recognized in media: plesiosaurs, ichthyosaurs, mosasaurs, and pliosaurs. In Real Life there were other sea-going reptiles in the Mesozoic, but being less impressive than the former, they don’t gain much attention (except for the giant turtle Archelon, which shows up occasionally). As with most prehistoric animals, only the largest will be mentioned from each group: Elasmosaurus for plesiosaurs, Liopleurodon for pliosaurs, and Tylosaurus for mosasaurs — with the exception of the ichthyosaurs. Ichthyosaurs will be represented only by Ichthyosaurus, which was actually small for the group, though that won't stop writers from making it bigger. However, in old media Plesiosaurus is frequent as well, even though was a very small member of the eponymous group (but don’t worry: it is regularly shown oversized as well).

Interestingly, unlike dinosaurs, marine reptiles were already well-known to science at the beginning of the 19th century. Their fossil record is overall wealthier and better-preserved than that of the dinosaurs. Significantly, the very first "antediluvian" reptiles to enter into narrative media were not dinosaurs, but the ichthyosaur and the plesiosaur which battle each other in the novel Journey to the Center of the Earth written by Jules Verne in 1864. Both animals were enormously oversized and depicted in a very fanciful way: more like Mix-and-Match Critter-type sea monsters than their Real Life counterparts. The "ichthyosaur" is similar to a mixup of whales, crocodiles, dragons and snakes, and doesn't have the familiar fish-like shape of a real Ichthyosaurus. The plesiosaur is a bit more realistic, but has a serpentine neck and the shell of a sea turtle. However, some of these errors are due to Science Marches On, as we’ll see in the individual sections below.

Possibly thanks to Verne, the battle between prehistoric marine reptiles has become stock in paleo-art and pop culture, just like its land-based equivalent of the carnivorous vs. herbivorous dinosaur. One of the opponents is always a long-necked plesiosaur, while the other may alternate between a mosasaur (known plesiosaur predators), an oversized Ichthyosaurus (other ichthyosaurs were plesiosaur predators, but not this one), or a pliosaur (graphic Real Life evidence exists in the form of a decapitated plesiosaur). In these portrayals, ichthyosaurs, mosasaurs, and pliosaurs tend to be used indifferently, often confused each other and portrayed as generic giant swimmers.

Another long-standing cliche makes sea reptiles the pterosaurs' archenemies. You've probably already seen the scene of a prehistoric leviathan emerging abruptly from the surface of the sea, grabbing a giant flying reptile with its jaws (the victim is usually Pteranodon), and dragging it underwater to eat itnote . In Real Life this would be possible only for the biggest mosasaurs and pliosaurs, and even then, we don't have any evidence that either of these preyed on pterosaurs; in fact, we have more evidence that large fish, predatory dinosaurs, and marine crocodiles would have fancied a leathery-winged snack. Giant ichthyosaurs did roam the seas, but in their time pterosaurs were still very small. Even though giant plesiosaurs like Elasmosaurus could have interacted with giant pterosaurs, their small mouths were unable to swallow whole Giant Fliers like Pteranodon. Pteranodon bones have been discovered in the belly of a plesiosaur fossil, but they come from a small, female or juvenile pterosaur, not a gigantic male, and in any case they were probably shaken about before being eaten, or more likely scavenged.

    Stock Sea Reptiles 

Flippered Brontosaurs: Elasmosaurus & Plesiosaurus ***

Plesiosaurs (more correctly, plesiosauroids) are among the most distinctive marine reptiles, and lived worldwide throughout the Mesozoic, 210-65 mya. With their long necks, massive bodies, short tails, small heads, and four paddle-like limbs, their appearance may recall that of a flippered brontosaur, but they were actually very different from sauropod dinosaurs. They were carnivorous, like all known marine reptiles. With their small mouths, they arguably ate only small prey, like fish, juvenile reptiles, or shellfish. Their hunting techniques are still a matter of discussion — active hunting, ambush predation, bottom-feeding or even partial filter-feeding are all possible. They had pointed teeth which protruded from their jaws, but were perhaps covered by lips in the living animals. For obvious reasons, expect to see plesiosaurs with ever-visible teeth sticking outside their mouth, often oversized and more protruding than in Real Life, resembling the fangs of boa or python snakes.

The association with snakes and turtles seems a constant when describing plesiosaurs. Even scientists used to describe these animals as "a turtle in a snake’s body" or "a snake in a turtle’s body." Their bodies were actually shaped somewhat like sea turtles' (though lacking a shell, of course), and their necks had a huge number of vertebrae (76 in Elasmosaurus!). Classic depictions show plesiosaurs with extremely flexible necks capable of coiling and darting like a snake. Science Marches On however, and it was discovered in the 2000s (thanks to simulations in CGI) that their necks were much more rigid than previously thought, a bit like what has happened to sauropod dinosaurs. Unlike ichthyosaurs (see below) their skin still seemingly preserved small scales, but we don't know how they were colored.

These animals are traditionally described as slow swimmers, using their four flippers as oars and awkwardly propelling their bulk through the water. In classic art, plesiosaurs are usually portrayed in a swan-like posture when surfacing, and often use their necks as periscopes when swimming underwater. According to biomechanical studies, they'd have kept their neck straight to better plough the water, and used their flippers to literally "fly" underwater, though the exact movement of the flippers is still uncertain (see also the pliosaurs, below). Plesiosaurs may have been among the most skilled swimming animals of all time. Like whales compared to dolphins, larger species may have been less agile than smaller ones. Some portrayals show plesiosaurs with a fluke at the end of the tail, but this is only speculative. If present, it acted only as a rudder, as a plesiosaur's tail was too weak to propel the animal.

The most commonly shown species in recent media is Elasmosaurus, while Plesiosaurus is more common in older works. Elasmosaurus was one of the largest plesiosauroids, 40ft/13m long (about as long as a grey whale), but since only a small portion of its length was the body, it weighed "only" 8-10 tons (about as heavy as a large killer whale). The 20ft/7m long neck made more than half the entire length, and was actually longer than the body. Living in the Late Cretaceous in the inland Western Interior Seaway of North America, Elasmosaurus was discovered in the U.S.A. shortly before the famous Bone Wars. Its describer, Edward Cope, made an astounding mistake in his first attempt to rebuild its skeleton by putting the head at the end of the tail (see Prehistoric Life - Non-Dinosaurian Reptiles), and this explains why the animal in the oldest paleo-art has a short neck and an extremely long tail. The prototypical Plesiosaurus was the first described plesiosaur (1810s), before even the earliest-discovered dinosaurs, Megalosaurus and Iguanodon. First found in England, it was much smaller (16ft long), lived earlier (at beginning of the Jurassic) and was proportionally shorter-necked and longer-headed than Elasmosaurus — though popular portrayals sometimes show it as a miniature elasmosaur, with a longer neck and smaller head than in Real Life.

Possibly thanks to their dinosaurian look and the association with snakes, plesiosaurs have been the most iconic and depicted sea reptiles in media. Like dinosaurs and pterosaurs, expect to see them as scary monsters with a killing attitude towards humans. If alive today, even the biggest Elasmosaurus wouldn't be more aggressive than most whales (although they could unintentionally overturn your tiny boat or raft). Needless to say, almost every time a plesiosaur shows up, someone will bring up the Loch Ness Monster.

  1. Entry Time: 1854 (Plesiosaurus); 1933 (Elasmosaurus)
  2. Trope Maker: Crystal Palace Park (Plesiosaurus); King Kong (1933) (Elasmosaurus)

Flippered Tyrannosaurs: Liopleurodon & Kronosaurus **

The long-necked plesiosauroids belong to the Sauropterygia supergroup, which also includes the Pliosaurs (or pliosauroids, so-called from their obscure namesake, Pliosaurus) and other lesser-known groups of sea reptiles. Together, plesiosauroids and pliosauroids make the Plesiosauria, a.k.a. "plesiosaurs" in broader sense, originating from the same common ancestor in the Triassic seas. The relationship of sauropterygians to modern reptiles has long been unclear. Once, they were placed with ichthyosaurs in their own subgroup, and not related with any still-living reptilian group. Today, plesiosaurs sensu lato (pliosaurs included) are not thought to be closely related to ichthyosaurs. They seem distantly related to modern lizards or maybe turtles, rather than to crocodiles and dinosaurs.

Like plesiosauroids, pliosauroids were widespread throughout the Mesozoic, 218-65 mya. Both subgroups shared the same body plan, with rigid bodies, short tails, and two pairs of powerful flippers — perhaps moved alternately to produce a typical "double-wing" swimming effect (as seen in Walking with Dinosaurs). The difference is in front of their shoulders. Pliosaurs had very short, stocky necks, and their heads were far bigger than that of an Elasmosaurus. Their teeth were less numerous, but much longer and stronger: like elasmosaurs, expect to see them visible when the mouth is closed, even though they may have been hidden by lips in Real Life. Despite the differences in proportion, the head anatomy of plesiosaurs and pliosaurs was the same. Both had eyes and nostrils placed above to see out of water when the rest of the head was submerged. Both shared a singular trait: each nostril had two chambers like fish, possibly giving them a directional sense of smell. We don’t know if they passed more time near the surface or in the deeps, but some think pliosaurs were more deep-sea creatures than plesiosaurs.

Pliosaurs were variably-sized, some were no bigger than dolphins, but the biggest ones are candidates for the title of largest sea reptile ever — though their size has often been exaggerated. Among the latter, Liopleurodon and Kronosaurus were some of the top predators of the late Jurassic and early Cretaceous oceans respectively. First-found in Australia in 1924 and once estimated at 16m long (10m is more likely), Kronosaurus is named for Cronus, a Greek Titan who devoured his own offspring (most of the Olympians among them). Liopleurodon was found in Europe in the late 19th century and was very simlar to the former, but more primitive and with less teeth. As is usual with marine superpredators, both are usually depicted as merciless ever-hungry killing machines.

Despite this, pliosaurs have been the least-portrayed group of sea reptiles, and still remain mainly creatures of documentaries. Kronosaurus was long the most commonly-shown pliosaur in books and documentaries until 1999, when a memorable appearance of an extraordinarily oversizednote  Liopleurodon on Walking with Dinosaurs rapidly made it the new iconic member of the family. In the show, an old male Liopleurodon was described weighing 150 tons (a bit less than the blue whale) and the biggest predator of all time. In particular, the scene in which he chomps an ichthyosaur to pieces disturbed many viewers (though the sad final scene where he’s stranded like a whale and slowly dies gives it a bit of "humanity"). To give an idea about how the animal remained impressed in pop consciousness: all successive depictions have shown Liopleurodons with the WWD blue-white color pattern.

For some reason, unlike dinosaurs and pterosaurs, marine reptiles are usually shown with dull colors even in modern portrayals. However, some of them might have been very colorful, like modern tropical seagoing animals. Another species that is starting to rise in popularity is Pliosaurus funkei, known in popular culture as Predator X. At an estimated 13 metres and 25 tons in weight (originally it was over 15 metres and 45 tons but Science Marches On), it's likely that it was the largest of this group, and this was coupled with a bite that was estimated to be four times that of T. rex.

  1. Entry Time: undetermined (Kronosaurus); 1999 (Liopleurodon)
  2. Trope Maker: Paleo-art (Kronosaurus); Walking with Dinosaurs (Liopleurodon)

Fish, Dolphin, or Lizard? Ichthyosaurus **

Ichthyosaurs have the very evocative name of "fish-lizards": they really resembled large fish in shape and swimming style, but recall modern dolphins as well thanks to their flippers and their long snouts. Like fishes and unlike dolphins, they had four flippers (foreflippers were usually bigger) and an upright caudal fin.

As a group, ichthyosaurs were the most ancient marine reptiles, and were widespread from the Middle Triassic until the Late Cretaceous, 245-90 mya, but went extinct 25 million years before the KT extinction for unclear reasons. Once, ichthyosaurs, plesiosaurs and pliosaurs were put together in their own group, the "euryapsids", unified by having a single pair of fenestrae on the top of the skull. Today, "euryapsids" are firmly put in the diapsid group (which also included dinosaurs, pterosaurs and all living reptiles except maybe turtles). Ichthyosaurs were among the very first diapsids to have evolved: since they are not related to any modern animal group (thus preventing good comparisons), they still remain quite mysterious critters.

Descended from a still-unknown land-dwelling ancestor (remember, every lineage of marine reptiles descended from four-limbed terrestrial reptiles), ichthyosaurs were the most marine of all marine reptiles and never came onto land, not even to lay eggs. In fact, their young were born alive just like modern dolphins, as we can see in some fossils of mothers dead with their offspring just getting out of their body. We now know that plesiosaurs also reproduced in the same way and probably never left the water either — even though the scene of a long-necked plesiosaur which crawls on the seashore like a sea lion is a staple in artwork. Ichthyosaurs are extremely abundant in fossil record: several individuals are preserved with soft tissue and, sometimes, even the imprint of the whole body. Thanks to the latter, we know they had a dorsal fin and a crescent-shaped caudal fin as well as the four paired "flippers". A strange thing is the backbone curved downwards at the tail level, and filled the lower lobe of the caudal fin, not the upper one — the exact opposite of modern sharks.

Their eyes were notably large for good vision; most portrayals show ichthyosaurs with round pupils and no eyelids, like a typical fish. Skull nasal openings were just in front of the eyes, but the nostrils might have been on top of the head like modern whales (though this is totally speculative). Their skin was smooth and hydrodynamic like a dolphin, as shown in fossil prints: they were perhaps the only reptiles ever whose skin was totally scaleless, convergently with cetaceans. The mouth was usually filled with acute teeth: most ichthyosaurs ate fish, but ammonites and other shellfish were also on their menu. We don't know what percent of time they passed underwater; they may have been able to extract some oxygen directly from the water like modern sea turtles, but they certainly did breath regularly like every reptile.

The resemblance to dolphins has classically led artists to show ichthyosaurs jumping out of water in a dolphinish style, but this is not proven. Unusually for extinct reptiles, "fish-lizards" often escape the fate of being portrayed as "monsters"... at least in modern documentaries. Originally, ichthyosaurs were depicted as more crocodile- or mosasaur-like, with no caudal or dorsal fins. The famous "ichthyosaur" in Verne’s novel is based on this early interpretation. Several other fictional ichthyosaurs have then been inspired by the original.

Today, more updated ichthyosaurs are a regular sight in dino-books. They’re very useful for showing evolutionary mechanisms, providing a classic example of convergent evolution with fish and cetaceans. On the other hand, they're rarely seen in recent stories, much less than the long-necked plesiosaurs. Maybe they're not that exotic-looking, or just not impressive enough to attract writers’ interest. The species shown is always Ichthyosaurus, because was the first discovered in the 1810s in England, before the first known dinosaurs, and the prototype of the group. While it was only 8-10ft long in Real Life, expect to see it oversized and overly scary. If shown to proper scale, expect to see is resemblance to dolphins played up heavily; it's likely that its dolphin-like appearance is precisely why Ichthyosaurus maintained "stock" status instead of being displaced by bigger ichthyosaurs. And never mind that some other ichthyosaurs (Temnodontosaurus, Cymbospondylus, Thalattoarchon, Shastasaurus, Himalayasaurus, Shonisaurus), being 25ft long or more and at least two of them being apex predators that killed huge prey, would be very apt for the role. The absence of the Shastasaurian ichthyosaurs (see below) is particularly strange: with some as large as a sperm whale, they may be the biggest known sea reptiles, and much bigger than the much-hyped ''Liopleurodon''.

  1. Entry Time: 1854
  2. Trope Maker: Crystal Palace Park

Giant Sea-Serpents?: Tylosaurus & Mosasaurus **

The most recent group of Mesozoic sea reptiles, mosasaurs, more properly the Mosasaurids, lived worldwide in the Late Cretaceous, at the end of the Age of Dinosaurs. They replaced ichthyosaurs in their ecological niche and coexisted with the last plesiosaurs. While ichthyosaurs and plesiosaurs were not closely related to any modern reptile, mosasaurs are the only prehistoric animals which literally deserve the title of "giant lizards". They belong to the Squamates (lit. "the scaly ones"), the clade containing modern lizards and snakesnote , and were closely related to modern snakes and monitor lizards. Indeed, due to their elongated shape, they have often been compared with the legendary sea serpent, and often depicted with a speculative dragon-like crest running along their back in much old art.

Descended from monitor-like lizards, mosasaurs often reached gigantic sizes, but exaggerations tend to be common. Some sources speak of 20m long animals, though most giant mosasaurs were probably no more than 10m long. With their slender bodies, they were also less heavy than the robust plesiosaurs and pliosaurs. To be more hydrodynamic, they may have lost the original lizard scales and developed a smooth skin texture (like ichthyosaurs but unlike plesiosaurs), but some skin prints seemingly show they preserved scales on their bodies. Their tails were long and laterally-flattened: like sharks and ichthyosaurs and unlike plesiosaurs, they swam by swinging their tails side-to-side. It's been confirmed that at least some were ovoviviparous (that is, producing eggs that hatch inside the mother’s body). Thus, they would have had no need to come ashore to reproduce, and could live entirely in water. Their limbs fin-like may be further proof. All marine reptiles described here obtained their flipper-like limbs in the same way as modern cetaceans, embedding their original digits in one single fleshy mass, and enormously multiplying the number of phalanges (ichthyosaurs took this to an extreme).

Mosasaur heads were similar to those of modern lizards, but with longer snouts. Like the latter, 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 (which they could still do). 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 Hesperornis and even smaller mosasaurs have been found.note  We don’t known 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. However, it is interesting to know that a fairly close relative of both Mosasaurus and Tylosaurus, Platecarpus, is known to have a tail fluke on the dorsal and ventral sides of the tail, akin to sharks. It's thus possible that all mosasaurs shared this feature. Older depictions of mosasaurs usually gave them a rather crocodilian profile, with sword-shaped tails, but recent reevaluations of body shape together with the discovery of the Platecarpus tail fluke have led to newer reconstructions being more massive in the upper torso and neck, somewhat whale-like or ichthyosaurian in appearance.

Like pliosaurs and ichthyosaurs, mosasaurs are a staple in documentaries, but are not so common in fiction. Most giant leviathans with huge jaws seen in fiction tend to be generic monsters a la Verne, rather than exact species of sea reptiles. And don’t rule out seeing mosasaurs confused with sharks.

Tylosaurus and the clade's namesake Mosasaurus are the stock members of the mosasaur family; needless to say, they're among the largest, up to 10-15m long. The former was found during the Bone Wars in the U.S.A. The latter has a much more fascinating story. Found in the Netherlands near the Meuse river at the end of the 1700 (hence its name), Mosasaurus was not only the first prehistoric sea reptile ever discovered, but the second fossil recognized by science as belonging to a Mesozoic reptile, after Pterodactylus. See also Prehistoric Life - Non-Dinosaurian Reptiles.

In 2015, a (slightly oversized) Mosasaurus received top billing alongside a pack of trained Velociraptors, the already-iconic Tyrannosaurus rex and Chris Pratt in the hit film Jurassic World. The image of her leaping out of the water to be fed a shark was the second major marketing image used for the film (the first being Chris Pratt riding a motorcycle alongside the raptors), and it's been suspected that this film might help contribute to the species becoming more popular among a whole new generation of paleontology geeks. It was also regarded as the most accurate animal in the film despite being slightly oversized, which is quite an achievement in a film series that acknowledges its own lack of scientific accuracy.

  1. Entry Time: 1854 (Mosasaurus); undetermined (Tylosaurus)
  2. Trope Maker: Crystal Palace Park (Mosasaurus); Paleo-art (Tylosaurus)

The Biggest Sea-Reptiles?: Shonisaurus & Shastasaurus *

Among the rarely-seen marine reptiles in Fictionland, the giant ichthyosaur Shonisaurus popularis deserves special mention because it's been frequently depicted in popular dinosaurs books since its relatively recent discovery.

In a sense, Shonisaurus ("Shoshone lizard") could be considered the ichthyosaurian equivalent of the giant pterosaur Quetzalcoatlus. Both were discovered in The '70s in the central USA, but their geological epochs were widely different: Quetzalcoatlus lived at the end of the Dinosaur Age, Shonisaurus at the start of it, in the Late Triassic. The wingspan of Quetzalcoatlus was also about the same as the total length of Shonisaurus popularis, 12-15m.

Shonisaurus was commonly accepted to have been the biggest ichthyosaur ever, and also the largest animal of the Triassic period — as long as the longest "prosauropods" (sauropod predecessors like Plateosaurus) but heavier, 20-30 tons, comparable to a humpback whale or a medium-sized sauropod; but the recently- discovered Shastasaurus sikanniensis (a species of the traditionally smaller triassic ichthyosaur Shastasaurus) has revealed to have been even bigger, 20-22m long, and the biggest sea-reptile known to science. Shastasaurus sikanniensis was originally considered a species of Shonisaurus, and some still argue that it should be considered so; if true, Shonisaurus would detain the record of "the Largest Ichthyosaur".note 

Shonisaurus and its relatives together comprise the Shastasaurians (once named Shastasaurids), an early lineage of true basal ichthyosaurians that went extinct in the mass extinction at the end of the Triassic, along with several non-dinosauria reptiles (the "thecodonts" or basal archosaurs, the rhynchosaurs, etc.), and most mammal ancestors. Shastasaurians had a typical ichthyosaurian fishy or dolphinish shape, but with a more primitive tail rather similar to that of the mosasaurs, longer hindflippers than most ichthyosaurs, and fewer or none teeth in their mouths. Shonisaurus popularis had small teeth only in the front mouth, Shastasaurus sikanniensis totally lacked them. Their lifestyle is uncertain: they could be like sperm-whales in respect to dolphins or orcas, swimming slower than other ichthyosaurs and eating fish or cephalopods of small/medium size, but not hunting giant marine preys the size or bigger than them like orcas do.

  1. Entry Time: 1980s
  2. Trope Maker: Documentary media

Other sea reptiles

Sorry, these aren't here. If you're looking for Stenopterygius, Eurhinosaurus, Opthalmosaurus, Cryptoclidus, Muraenosaurus, Peloneustes, Macroplata, Plotosaurus, Clidastes, Globidens, Opetiosaurus, and others, see here.


Other Extinct Reptiles

Extinct relatives of modern reptilians are not as common as the above, but some have gained attention in the media. Ancestral extinct reptiles are even rarer sights, but many of them are very interesting and peculiar.

    Extant Reptiles in Media 

Ancient Colossal Turtle: Archelon **

Archelon ischyros lived in the Late Cretaceous inland shallow sea which once covered the Great Plains of the U.S. Discovered at the start of the 20th century, it shared its habitat with Elasmosaurus, Tylosaurus, and the flying Pteranodon. Its size and armor made adult Archelon virtually immune to predators — though in WWD an Archelon is shown killed by a giant mosasaur, but the latter was oversized.

Not all Mesozoic reptiles were exotic by modern standards. Archelon was simple a sea turtle. But it perfectly fits the subtrope that everything was huge in dinosaur times: it's among the largest known fossil turtles — 4m/13ft long and weighing several tons, Archelon was two to three times bigger than the biggest modern turtle (the Leatherback turtle), confirming Turtle Power is Truth in Television. However, it was not the ancestor of modern sea turtles: it belonged to a different lineage, the Protostegids, which went extinct along the other giant reptiles at the end of the Cretaceous. Its name is a Portmanteau of arche (primeval) and chelon (turtle).

As turtles and tortoises have remained virtually unchanged since their first appearance in the Triassic, Archelon had the same traits seen in modern chelonians: beaked jaws, forelimbs transformed into strong flippers (with multiple phalanges, as usual for sea reptiles), weaker hind-flippers and a short tail. However, its armor was lighter than most modern turtles, and the shell may have been leathery instead of horny. The modern turtle which mostly resembles Archelon might just be the leatherback. As modern species of sea turtles eat very different items (some eat shellfishes, others seaweed, and some jellyfishes), we don’t know what Archelon’s preferences were. Almost certainly it came ashore to lay its eggs like its relatives.

Among Archelon’s appearences in fiction, the most remembered is in Harryhausen's One Million Years B.C.. The turtle is the first animal cavemen encounter in the island, upsized to be as big as a house. Surprisingly, many viewers think it was live-acted by a Real Life turtle, but it too is stop-motion like most other animals here. An Archelon also appears in The Land Before Time series. A Pokémon based on Archelon made its debut in Pokémon Black and White; a two-stage fossil Pokémon, Tirtouga and Carracosta are interesting, as even fully-grown they're actually smaller than their real-world inspiration.

  1. Entry Time: 1966
  2. Trope Maker: One Million Years B.C.

The Super Crocs of the Mesozoic: Deinosuchus & Sarcosuchus *

Deinosuchus ("terrible crocodile", also called Phobosuchus "fearsome crocodile"), belonged to the eusuchians, a.k.a. the true crocodilians. This gigantic alligator (thus more correctly called "Super Gator" than "Super Croc") appeared only in the Cretaceous but had the same anatomy we see today. More precisely, it was closer to alligators and caimans than to true crocodiles. Like gators, Deinosuchus' skull had wide strong jaws and relatively blunt teeth. Its head was as long as a full-grown man, but the length of its body is unknown because little more than the skull has thus far been found. By comparison with modern american alligators, Deinosuchus may have reached 15m in length and weighed more than a Tyrannosaurus.

Its home was freshwater basins in Late Cretaceous North America, but it could also have frequented the inland sea that divided the continent at the time. Since its fossils date to more than 70 mya, Deinosuchus probably didn't live long enough to meet T. rex in Real Life, but only the latter's smaller relatives, like Albertosaurus. It is usually shown in docu-media ambushing giant dinosaurs like a Nile Croc does with zebras, expecially hadrosaurs like Parasaurolophus or Corythosaurus, but its actual lifestyle is unknown — maybe it feeded mainly on large fish or othet water creatures such as small freshwater plesiosaurs/mosasaurs, turtles, smaller crocs, or champsosaurs (see below). Its reproductive methods are also unknown, but probably it built nests on riverbacks for its eggs like modern crocodilians.

Sarcosuchus imperator ("Emperor meat-eating croc") lived earlier than Deinosuchus, in Early Cretaceous, and was found originally in Northern Africa in the 1970s together with some dinosaurs like Ouranosaurus that could have been its prey. It was still too primitive to be an Eusuchian, but resembled one in shape: with its long thin jaws, it recalled closely the modern gharial of India. It was about the same size of Deinosuchus but more slender; some remains from South America are also known possibly belonging to it or to a close relative. Like Deinosuchus, its lifestyle is only a guess.

For VERY obvious reasons, Deinosuchus and Sarcosuchus are popular crocodilian choices in the world of Dinosaur Media, though they're not quite as common in mainstream works as they are in educational ones. Naturally, their size and abilities will usually be exaggerated, though curiously they tend to avoid foraging into Prehistoric Monster territory due to the fact that they were essentially scaled-up alligators/gharials, and we have plenty of them in the modern day to use as points of referencenote . One noteworthy appearance of Deinosuchus was the fourth The Land Before Time film, in which a cantankerous Deinosuchus appears as one of the two main villains (partnered with an equally disagreeable proto-bird, Ichthyornis), while another was the protagonist of the last episode of the 2006 Prehistoric Park, wherein Nigel brings one back to the present for his dinosaur zoo. Sarcosuchus appeared in the 2003 miniseries Chased By Dinosaurs, with a rather minor role in the story — basically the only purpose of the programers was to add another giant reptile along with the others met by Nigel in his Time Travel.

  1. Entry Time: the 2000s
  2. Trope Maker: The Walking with Dinosaurs franchise

Titanic Snake and Mega Lizard: Titanoboa & Megalania *

It's not common to see snakes in prehistory media, even documentaries; however, in recent years Titanoboa ("titanic boa") has been gaining in popularity.

This huge snake was found only in 2009, and lived in what is today Colombia (South America) just few million years after the extinction of the dinosaurs. It was one of the top predators in this Paleocenic world (unlike the famous bird Gastornis, which recent research indicates was a herbivore). Although it was not as big as sometimes reported ("only" one or two meters longer than the biggest green anacondas or reticulated pythons), Titanoboa was more heavily-built, and may have weighed an impressive 1 ton; green anacondas reach 200 kg at the most, reticulated pythons slightly less so. Despite the early period at which it lived, Titanoboa was closely related to modern constrictors (the Boid family), more to true boas and anacondas than to true pythons, and like all them it arguably preserved vestigial hindlimbs in the form of small "spurs". It was not venomous, and probably gave birth to live offspring like the closer boas/anacondas (pythons lay eggs and take care of them by coiling around them).

The Komodo dragon-like Megalania prisca (Megalania = "big tearer") has been known far longer; it was described by Richard Owen (the dinosaurs' Trope Namer) in the 19th century. It was an extinct goanna (the name for Australian monitor lizards), and was extremely closely related to modern ones, to the point that it's often put today in the same genus, Varanus (and thus renamed Varanus priscus). It was about twice the length of the largest living monitor, the Komodo dragon, and was one of the top predators of Ice Age Australia, in competition with the marsupial lion and some land-dwelling crocodilians (the Mekosuchines). Whatever the name, this giant monitor is the largest-known fully terrestrial lizard of all time. Its behavior was arguably similar to that of modern goannas, and like them almost surely had a snake-like forked tongue to detect odors from the soil, and likely laided eggs (oviparous) like all modern monitors. Megalania went extinct only a few thousand years ago, along with many Australian megafauna, at about the same time as the extinction of the woolly mammoths; it may have been killed at least indirectly by the fires created by the first prehistoric human colonizers of the Land Down Under.

  1. Entry Time: the 2000s
  2. Trope Maker: Documentaries

Other extinct modern reptiles

Sorry, these aren't here. If you're looking for Kaprosuchus, Meiolania, Homoeosaurus, Bavarisaurus, Dinilysia, and others, see here.

    Primitive Reptiles in Media 

Crocodiles or Dinosaurs?: Postosuchus, Rutiodon, Desmatosuchus, Erythrosuchus & Proterosuchus *

"Thecodont" ("teeth in sockets") is a now-abandoned term at least in cladistics for basal archosaurs or their close relatives that were neither dinosaurs, nor pterosaurs, nor crocodilians. They were all from the Triassic, and were the real dominant reptiles of this geological period, to the point that dinosaurs are often quoted as their natural successors in the following Jurassic and Cretaceous periods. However, at least initially they were in competition with Triassic mammal-ancestors and proto-mammals. Many "thecodonts" went extinct at the mass-extinction at the end of the Triassic: the latest ones lived alongside the first dinosaurs like Coelophysis and Plateosaurus, but others went extinct earlier. Research since the 2000s indicates that some "thecodonts" weren't true archosaurs.

The most striking ones were perhaps the giant Rauisuchians of the Late Triassic, because they were theropod-like predators in competition with the first carnivorous dinosaurs. Walking with Dinosaurs popularized one of them, the North American Postosuchus, found in 1985 in Texas. There were also the herbivorous, heavily-armored Aetosaurs (Desmatosuchus being the most famous), and the aquatic and very croc-like Phytosaurs (Rutiodon being the most-often portrayed), both groups also often of large size and living throughout the Triassic period. Proterosuchians like Erythrosuchus and the namesake Proterosuchus roamed only the start of the Triassic, but were also as large as many modern crocodilians.

  1. Entry Time: 1990s/2000s
  2. Trope Maker: Various CGI documentaries

Dino-Ancestors?: Euparkeria, Lagosuchus, Ornithosuchus & Saltoposuchus *

Perhaps the most common thecodont in popular dinosaur books and documentaries has been Euparkeria, often wrongly cited as an ancestor of the dinosaurs because of its partially-bipedal shape. Just 3ft long, this small archosauriform lived in the Early Triassic in the same epoch as many therapsids (Cynognathus, Lystrosaurus, Thrinaxodon, etc.), giant amphibians (Mastodonsaurus etc.), and other much larger quasi-archosaurs (Erythrosuchus, Proterosuchus, etc.). Some of these animals (Cynognathus, giant amphibians, and its fellow archosauriforms) were all potential predators of Euparkeria. Euparkeria capensis means "Parker's good (animal) of the Cape" because was found in South Africa, at the start of the 20th century.

The even smaller Lagosuchus (only one foot long, and thus called "rabbit-croc") was an actual ancestor of dinosaurs, but lived in Middle Triassic Argentina. Some sources have wrongly classified it as "the first dinosaur" (see also Herrerasaurus). It may have had some feather-like or hair-like structures in its body, like the related pterosaurs and dinosaurs.

Before the discovery of Lagosuchus in the 1970s, other "thecodonts" were considered the direct ancestors of dinosaurs, especially the European Saltoposuchus ("hopping-footed croc") and to a lesser degree Scleromochlusnote  — and some were often even considered early proper dinosaurs (more precisely early theropods), notably the 12 ft long Ornithosuchus ("bird-croc"), the 2 ft long Saltopus ("hopping foot", see Prehistoric Life - Other Small Theropods for this), and the large, 20 ft long Teratosaurus (see Prehistoric Life - Large Theropods for this). Ornithosuchus, Teratosaurus and Saltoposuchus (but not Saltopus, a close dino-relative like Lagosuchus) were actually more closely related to crocodilians than to dinosaurs or pterosaurs; the same is true of the Rauisuchians and Aetosaurs above. Phytosaurs, on the other hand, were long believed to be direct crocodile ancestors, but according to recent research they are not even archosaurs sensu stricto, just like Euparkeria.

  1. Entry Time: undetermined
  2. Trope Maker: Popular dinosaur books and other media

Giant Neck and Scissor Beak: Tanystropheus & Hyperodapedon *

These guys were among the oddest and most specialized reptiles ever, despite their smaller size compared to many other reptiles of the Mesozoic. They were primitive archosaur-relatives like Euparkeria, but unlike the latter they have never been considered "thecodonts", not even in the past. Both lived across the Triassic.

Tanystropheus was 4-5m long and notable for its enormously long neck compared with its shorter body and tail, to the point that it could be mistaken for a plesiosaur at a glance. But had true, if short, legs, not flippers like the latter, and was probably amphibious and a hunter of small aquatic prey. Once considered a plesiosaur ancestor, it actually belonged to its own group of archosaur-relatives. In Sea Monsters it is shown losing its tail like many modern lizards do, after Nigel Marven tempted to stop it by grabbing the tail. This is actually an invention of the show, because Tanystropheus was not a true lizard (unlike the mosasaurs, which also did not lose their tails like modern monitors); furthermore, it's unlikely that such a damaged animal of its size would still be able to swim correctly by using its tail as a propeller as shown in the program.

Hyperodapedon was very different: it was an herbivorous land reptile of the successful group of archosauromorphs named the Rhynchosaurs. The latter could be mistaken for true archosaurs of the Triassic like the "thecodonts" or even for contemporaneous mammal ancestors like the Dicynodonts. Curiously, the rhynchosaurians were once considered relatives of the modern tuatara despite the two animals' different appearance. Hyperodapedon (more traditionally called Scaphonyx) is portrayed in paleo-art because of its strange owl-like "face": it had an uncinated beak with a split in its upper half which the lower half fitted into when the mouth was closed, and eyes pointing forwards just like an owl. This reptile and its closest relatives have usually been described as sluggish critters unable to flee to the faster predators of the time like the rauisuchians and the first meat-eating dinosaurs, but this might not be true: the rhynchosaurs' short splayed limbs and bulky body don't mean they were slow and harmless, and Scaphonyx's parrot-like bill was powerful enough to deliver nasty bites to its attackers, like the beak of a modern macaw parrot or snapping turtle.

  1. Entry Time: Undetermined
  2. Trope Maker: Popular dinosaur books and other media

Gliding Lizards: Kuehneosaurus, Coelurosauravus, Longisquama & Sharovipteryx *

Kuehneosaurus and Coelurosauravus were much smaller than the two reptiles above, just a few feet long, but both deserve the popular nickname of "gliding lizards" — the first one was even a close relative of Lepidosaurs (snakes, lizards and tuataras). Both animals had protruding ribs, but not because they were especially skinny: these rib protrusions pointed sideways from the body and were connected by skin like the famous Dimetrodon sail, forming wings for gliding from one tree to another. Today, a modern true lizard convergently evolved a similar gliding mechanism, the so-called "flying dragon" of southeastern Asia (Draco volans). Coelurosauravus (whose odd name means "coelurosaur ancestor") was portrayed in the series Primeval as a human's pet.

Longisquama means "long scale": today regarded as an archosaur-relative, its classification has long been a headache for paleontologists. Also a few feet long like Kuehneosaurus but found in the former USSR in The '70s, it has usually been considered a gliding creature like the latter, using the eponymous "long scales" to cross the air like a modern flying squirrel, but this is not certain. As its huge protrusions resembled feathers a bit, it was even believed to be an ancestor of birds in the past — and anyway, the Science Marches On story of this enigmatic critter has been extremely convoluted. Another "gliding lizard", this time with bat-like skin-membranes, was Sharovipteryx ("Sharov's wing"); this one was hypothized in the past to have been the ancestor of pterosaurs. Longisquama insignis (its full name, meaning "notably long scale") appears in Dinosaur as a sorta flying chameleon using its scale-things as the feathers of actual wings.

  1. Entry Time: Undetermined
  2. Trope Maker: Popular dinosaur books and other media

Swimming Reptiles of the Triassic: Nothosaurus, Placodus, Askeptosaurus & Mixosaurus *

These reptiles (and the ones of the next paragraph) were only unified by the fact that were aquatic but less specialized than the classic marine reptiles within the main folder above. They were also usually smaller-sized than them.

Nothosaurus ("false lizard") looked a bit like Tanystropheus, but its neck wasn't as excessively long, and it was actually related to the ancestors of plesiosaurs. Like the long-necked plesiosaurians, Nothosaurus had needle-like teeth set in elongated but weak jaws; unlike plesiosaurs, it had a well-developed tail for swimming by undulating like a mosasaur, and short, splayed true legs with palmated feet. Because of the latter feature, it and the other nothosaurs have often been portrayed as sort of like seals or sea otters of the Triassic, coming onto land to lay their eggs but feeding with agility in the water on fish and shellfish. Askeptosaurus italicus was apparently similar to a nothosaur, but belonged to a more archaic group: the Thalattosaurs (lit. "sea lizards", even though the askeptosaur is believed a freshwater-dweller), once put together with the champsosaurs in the artificial assemblage of the Eosuchians (meaning "dawn crocs").

Placodus, the prototype of the eponymous Placodonts, was similar in overall shape to Nothosaurus but more massively-built and much shorter-necked, with powerful short jaws and flat crushing teeth for eating shellfish. Apart from this, its lifestyle was probably analogous to Nothosaurus, and like the latter it swam using its tail. Placodus ("plate-tooth") had also light armor consisting of a line of bony plates running along its whole backbone, but the most derived placodonts like Henodus developed literal shells and were very turtle-like (a classic case of convergent evolution).

Mixosaurus has traditionally been the most familiar primitive ichthyosaur, also from the Triassic. It had already the classic head, neck and body of the more known/derived Ichthyosaurus, but its tail fin was still small, because the vertebrae of its tail don't show the downward bend of the derived ichthyosaurs, and we don't know if it had a dorsal fin or not. Smaller than Ichthyosaurus (some individuals were only 1m long), Mixosaurus might recall an ichthyosaur with a mosasaurian tail, or even a tiny mosasaur that looked like a dolphin.

  1. Entry Time: Undetermined
  2. Trope Maker: Popular dinosaur books and other media

Crocodilians and Non-Crocodilians: Metriorhynchus, Geosaurus, Teleosaurus & Champsosaurus *

Champsosaurus lived as late as the Cretaceous; it belonged to a particular lineage of archaic reptiles, the Neochoristodera (once put in the Eosuchians as said above), which arose in the Triassic and managed to survive beyond the great dinosaur extinction, just like turtles, crocs, tuataras, lizards, and snakes. But unlike all them, they went extinct not long after the start of the Mammal Age, long before humans appeared. Champsosaurus was like an undersized, 1.5m-long crocodile in shape (its name means "croc-lizard"), and sometimes is wrongly portrayed in documentary media as a true crocodilian living alonside others like the "supergator" Deinosuchus.

True crocodile-relatives, on the other hand, were the Jurassic Metriorhynchus, Geosaurus, and Teleosaurus (which are here for comparison, but should more correctly be put together with Deinosuchus and Sarcosuchus). However, unlike the mostly freshwater modern alligators and kin, they adapted to a fully marine lifestyle. Metriorhynchus ("moderated snout" because of its thin jaws) and the very similar Geosaurus were both Late Jurassic: they lose their armor altogether, developed a caudal fin very similar to an ichthyosaur or a mosasaur, and their limbs became similar to paddles, though still not proper flippers like those of a plesiosaur, ichthyosaur, mosasaur, or sea turtle. When they and their relatives (the aptly-named sea crocodiles, ex. Dakosaurus) appear in docu-media, they're portrayed as underdog predators of their time with respect to giant plesiosaurs (Liopleurodon) and in competition with primitive sharks like Hybodus, ichthyosaurs like Ophthalmosaurus, or small long-necked plesiosaurs like Cryptoclidus. Teleosaurus was a more archaic Jurassic sea-crocodile, resembling a small gharial in shape: it still had a light dorsal armor, weak but still land-adapted legs, and normal tail. Some sculptures of it are portrayed in the Crystal Palace Park of London together with other more famous Mesozoic reptiles — unusually, still accurate today.

  1. Entry Time: Undetermined
  2. Trope Maker: Popular dinosaur books and other media

Early Reptiles?: Scutosaurus, Pareiasaurus, Mesosaurus & Hylonomus *

When discussing the origin of Amniotes, the clade consisting of true reptiles (including birds!) + true mammals and their ancestors, the first amniotes to appear on Earth are usually and traditionally called "reptiles". But the four animals in this section, according to many experts today, were more properly in the middle between Diapsids ("reptiles" in a narrower sense) and mammal-ancestors (the Synapsids). The first three are placed in a third, smaller group called Anapsids — often also called parareptilians, lit. "near-reptiles", because they were probably closer to the diapsids than to the synapsids. It's worth noting that for a long time turtles were considered Anapsids as well, but today are believed to be Diapsids, possibly related to plesiosaurs or even archosaurs.

Scutosaurus means "shield lizard", and was once considered an ancestor of turtles. It was one of the biggest and most heavily-armored anapsids ever, weighing 1 ton (comparable to a bison) and covered with armor on its back — recalling more an Ankylosaurus than a tortoise. Like the armored dinosaurs, it was vegetarian; it had a thickened skull and blunt teeth all similar to each other; its limbs were semi-erect and stocky, and the tail was very short. Pareiasaurus, the namesake of the scutosaur' group (the Pareiasaurians) was similar but without the armor. All these traits make Scutosaurus and Pareiasaurus closely resemble the mammal-like "reptile" Moschops (except that the latter lacked the dorsal armor of the scutosaur). Both lived slightly later than Moschops, in the Late Permian, and were possibly among the animals wiped out by the gigantic mass extinction that separated the Permian from the Triassic — the worst to have happened since multicellular organisms evolved, even more destructive than the one that ended non-avian dinosaurs.

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 central Europe). Despite this, Mesosaurus did somewhat resemble in shape the old classic illustrations of mosasaurs, being elongated, with long toothed jaws, and a powerful sidewards-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. The group of the mesosaurs actually lived in the Permian, and disappeared before the first croc-like archosaurian diapsids evolved.

Hylonomus, similar to a 1-foot-long lizard, is still today considered the first undisputable reptile, hailing as far as the Carboniferous period (even earlier than the Permian). Even though Casineria, discovered in 1999, is today often considered the earliest-known true amniote, the latter's fossil is too fragmentary to be sure. Hylonomus was long considered an Anapsid, but today is mostly classified as a Diapsid relative, thus belonging to a different lineage than the Pareiasaurians and Mesosaurians above. In the 1990s, Westlothiana (also from the Carboniferous) seemed to take the record over from Hylonomus for the "first amniote" title, but now is mostly regarded as only an near-amniote, thus an "amphibian" (sensu lato).

  1. Entry Time: Undetermined
  2. Trope Maker: Popular dinosaur books and other media

Other primitive reptiles

Sorry, these aren't here. If you're looking for Trilophosaurus, Drepanosaurus, Megalancosaurus, Helveticosaurus, Hupehsuchus, Shringasaurus, Claudiosaurus, Procolophon, Elginia, Milleretta, Captorhinus, and others, see here.

Mammal-like "Reptiles"

At least pterosaurs and the above-mentioned seagoing and terrestrial animals are almost all from the same time period, the Mesozoic. Don't even get us started on how Synapsids (the "mammal-like reptiles", or, more properly, proto-mammals) are sometimes labeled dinosaurs, even though the most famous of them lived far earlier, in the Paleozoic.

    Mammal-Ancestors in Media 

Most (non-mammalian) synapsids lived well before the appearance of the first dinosaur; indeed, synapsids were the very first large land vertebrates and diversified much during their time on Earth, until most of them were wiped out in the huge Permian mass extinction. In the Brave New World that followed, the few surviving species were progressively outcompeted by archosaurs, the group containing dinosaurs, pterosaurs and crocodilians. The last kinds of non-mammal therapsids (the most derived mammal-ancestorsnote , while the most basal ones were traditionally named "pelycosaurs") were depleted at the end of the Triassic in another mass extinction.

Anyway, all these creatures have extraordinary relevance to the history of evolution because they were the ancestors of true mammals and thus of mankind , and yet they haven't gained popularity like that of the dinosaurs, probably because of their relatively small size compared to dinos like T. rex or the sauropods. The only exception is below.

Sail-Backed Lizard or Sail-Backed Mammal?: Dimetrodon ***

Dimetrodon lived in North America 280 million years ago, in the Permian period (just before the Triassic). It is the only mammal-like "reptile" whose popularity matches that of the stock dinosaurs, thanks to its mohawk-esque crest (sail) on its back. Its iconic status among mammal-like reptiles is partially justified by its fossil abundance — dozens of specimens are known, juveniles included. As one might expect at this point, it was discovered in North America during the Bone Wars, in the second half of the 19th century.

The most classical of its numerous known species is Dimetrodon limbatus. Being a very early mammal-ancestor, it was not a proper therapsid, and was once classified among the "Pelycosaurs". It still had a lizardy shape, with long tail, long body, splayed legs, and skull with a small braincase. Fossil prints show a lizard-like gait. Other traits, on the other hand, were quite mammalian: a laterally-flattened trunk (not wider-than-taller like most modern reptiles); a solid skull with one single pair of temporal openings placed near the maxillary hinge (the so-called "synapsid" condition also seen in mammals, humans included); and differently-shaped teeth — Dimetrodon just means "teeth with two lengths." Even though all teeth were conical, the anterior ones were small and crammed together like incisors, while the longest teeth were in the place mammals have usually their canines. Behind them, the posterior teeth were small and not apt for chewing food unlike our molars, but are somewhat analogue to those seen in primitive insectivorous mammals. More derived synapsids like Cynognathus (below) achieved a clearly mammalian anatomy, with more erect limbs, shorter tails, larger brains, and teeth very similar to mammals.

Its "sail", sustained by elongated vertebral spines, has always been a headache for scientists. The classic theory considers it a thermoregulating device. Turned to face the solar rays, it could have captured heat like a solar panel; turned parallel to them, it would have been more like a radiator, dispersing heat. Considering its desert habitat, this hypothesis remains a good one. Other theories are mating or threat display, inter-specific identification, and so on. It may have been that the sail served all these purposes. Among external features, Dimetrodon might also have had some sparse hair, hints of external ears and maybe even proto-milk glands. These things are totally uncertain, and given its primitiveness, are unlikely. The coloration is totally speculative — living in harsh habitat, it was likely brownish like modern desert mammals, but its sail could have been vividly coloured and/or able to change colors for display purpose. Sadly, synapsid soft tissues are virtually unknown. No eggs or nests are known from Dimetrodon; we don’t even know if it was oviparous, or viviparous like modern mammals (though if the latter, it evolved viviparity independently).

Dimetrodon is usually described as the top predator of its time, shown hunting early "amphibians" like Eryops, Diplocaulus, Seymouria etc., as well as what could be called its Non-Identical Twin, Edaphosaurus (see below). Its crest, its deceptively reptilian appearance and the fact that it was a large carnivore make Dimetrodon a predestined victim of Dinosaurs Are Dragons and Prehistoric Monster both in fiction and in docu-media. However, if you put it next to other famous prehistoric animals, Dimetrodon would appear rather narmy. If we imagine a battle against a Tyrannosaurus, Deinosuchus, Smilodon or Mosasaurus, the primitive and relatively small dimetrodont would always be the loser — this might also be true if it were pitted against modern predators (lions, Kodiak bears, Nile crocodiles, etc.), as well as most ancient and modern giant herbivores. But in Permian landscapes, Dimetrodon was still faster and more powerful than every other land animal, definitively debunking the Narm thing.

Although Dimetrodon is more closely related to you than to any dinosaur, and predated the first dinosaur by at least a country mile of geologic time, it is often mixed with dinosaurs in toy collections just because it looks cool. In movies and comics, it may even show up living with cavemen. Expect it to look like a giant iguana with scaly skin. Actually, scales are strictly a reptilian thing, and Dimetrodon hide was probably naked like modern hairless mammals, with some hardened fish-like belly scales left over from its amphibian ancestry. Its shape makes Dimetrodon the most abused animal within the Slurpasaur trope. For example, in the 1970 film version of Journey to the Center of the Earth some Caribbean iguanas with ridiculous crests on their backs live-act Dimetrodons, which of course attack the humans.

  1. Entry Time: 1940
  2. Trope Maker: Fantasia

More a Wolf than a Reptile: Cynognathus *

If you've seen it in an illustration, you probably thought at least once "Oh, this thing looks like a big dog!" Cynognathus ("dog jaws"), unlike Dimetrodon, was a true therapsid, belonging to the therapsid subgroup called Cynodonts ("dog teeth"). These were the most advanced and mammal-like of all the mammal-ancestors, with a very mammalian look, certainly at least some hair and quasi-mammalian dentition. They were also among the smallest therapsids, being mostly cat-sized; even Cynognathus, the largest known, was still no bigger than a German Shepherd.

Found in South Africa at the end of the 19th century, Cynognathus crateronotus (its only known species) has traditionally been considered the prototypical cynodont and, more generally, the prototypical "mammal-like reptile" in documentary media, and it has also been cited as one of the unofficial symbols of Evolution, as one of the "missing links" between reptiles and mammals (just like Archaeopteryx, the "missing link" between reptiles and birds).

Despite this, Cynognathus has not received much attention outside non-fictional works, maybe due to being not so impressive-looking compared with Dimetrodon or, naturally, dinosaurs. However, it is very common in popular prehistory-related media as the most classic example of a particularly mammalian-looking synapsid, typically described as "dog-like" and/or "wolf-like", in contrast with the primitive "lizard-like" Dimetrodon (which more often tends to be considered a dinosaur because of this). Cynognathus is also often portrayed as an excellent predator, and in Real Life it may have been as powerful as Dimetrodon in spite of its smaller size (it was about half the length of the latter), possibly even capable of killing therapsids bigger than itself, like the herbivorous dicynodonts (don't confuse them with cynodonts: they were two distinct lineages of therapsids).

Even though was almost certainly hairy, its hair would have been less dense than modern mammals. Unlike Dimetrodon, Cynognathus has never been portrayed with scaly hide; at most, it's given just naked skin. We don’t know if Cynognathus and other cynodonts had external ears or mammary glands (two distinctive mammalian traits), but the odds they had them were obviously greater than the primitive Dimetrodon. Like the latter, we have no idea how Cynognathus was colored. Media tend to depict cynodonts like it and Thrinaxodon (and other carnivorous therapsids like the apparently-similar but more primitive gorgonopsids) with a brown color scheme, but this might not have been the case in Real Life. The usually-bland coloration typical of mammals is thought to be an adaptation for darkness – according to scientists, every modern mammal (even diurnal ones like us humans) descend from night-dwellers. Nocturnal habits, however, developed within the synapsid lineage only in the Triassic, to avoid competition with dinosaurs (or at least, that’s what most scientists say). If true, this would mean non-mammalian therapsids like Cynognathus could have been very colorful, like many modern reptiles and birds.

  1. Entry Time: undetermined
  2. Trope Maker: Popular prehistory media

The Dimetrodon's vegan Twin: Edaphosaurus *

After Dimetrodon, Edaphosaurus is the only "pelycosaur" (aka basal synapsid) which has some chance of appearing in non-documentary media — at least indirectly: sometimes Dimetrodons with a sail more similar to Edaphosaurus are seen in fictional works, ex. in The Land Before Time.

Described by Cope during the late 1800s Bone Wars in the Early Permian "red bed" formations (Dimetrodon was also first described by Cope from the same geological terrains), Edaphosaurus can be translated "ground lizard", but actually 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 small to large. Edaphosaurus was more bulky-bodied but otherwise very similar to Dimetrodon, with a sail on its back, long tail and splayed legs. Its sail was more complex however: it had a more rounded shape and its spines had regularly-placed tubercles of uncertain purpose. Edaphosaurus head was much smaller than Dimetrodon and with round teeth all of the same shape and length. With this dentition, it was arguably herbivorous, but it's also hypothized that it could have eaten shellfish as a dietary supplement.

Living alongside Dimetrodon in Early Permian North America, it probably used its "sail" the same way as the former, but obviously this cannot be known for certain. Edaphosaurus is sometimes shown in paleo-art, books, and programs like Walking With Monsters as one of Dimetrodon's possible preys. This might be plausible (Edaphosaurus was arguably a slower runner), though if so, Dimetrodon almost certainly hunted young Edaphosaurus more often than the massive adults.

  1. Entry Time: undetermined
  2. Trope Maker: its resemblance with Dimetrodon

A very successful Guy: Lystrosaurus *

Dicynodonts ("two dog-like teeth") were the most diversified group of non-mammalian therapsids, living from the Late Permian up to the very end of the Triassic (and possibly even the Early Cretaceous, but this is not confirmed). They were very diversified in size and shape, but all were herbivorous (or perhaps omnivorous) and shared very specialized dentition: they had only two teeth in their upper jaw and none in the lower one, coupled with a tortoise-like beak in front of the teeth. We don't know if they had some hair or were still totally naked.

The most iconic dicynodont is probably Lystrosaurus ("shovel lizard"). Others include the prototypical Dicynodon (see below), the small Diictodon, the large Kannemeyerids like Kannemeyeria and Placerias (see again below), and the enormous elephant-sized Lisowicia found only in 2019 — the latest one is currently the biggest known therapsid by far.

One of the first animals to have recuperated after the Permian-Triassic extinction event, Lystrosaurus was one of the most successful animals of all time. Its remains have been discovered everywhere in southern continents, even Antarcticanote . Thanks to this, Lystrosaurus has been used as one of the classic proofs of the Pangaea supercontinent hypothesis. The size of a medium pig and thus bit bigger than Cynognathus, Lystrosaurus has the typical dicynodontian shape: bulky, stubby-tailed, with strong semi-erect limbs, and the typical dentition made up of only the two upper tusk-like "canines". Formerly, it was depicted as a freshwater dweller like a hippo, but now is mostly believed to have been a grazing land animal. In paleo-art, it is often shown as the favourite prey of Cynognathus (the two could have met in what today is South Africa). In Walking With Monsters, Lystrosaurus is shown as very similar in behavior to modern wildebeest, living in immense noisy herds, crossing a river in a mass, and dying by drowning or being killed by "primitive crocodiles" (they were actually archosaur relatives).

  1. Entry Time: 2004
  2. Trope Maker: Walking With Monsters

Hulky Beast: Moschops *

Moschops ("calf's face") is the most famous member of a peculiar subgroup of basal therapsids: the Dinocephalians, "terrible heads", much more primitive than the cynodonts like Cynognathus and also more basal than dicynodonts like Lystrosaurus. It was one of the biggest among all mammal-ancestors as well (the size of a small rhino), making even the biggest Dimetrodon species small in comparison — but was still much smaller than the most popular dinosaurs.

Moschops capensis (the name of the classic species) was characterized by powerful front legs longer than its hind legs: this, combined with its massive chest and muscular neck, gave to it a rather Hulky frame. It had also partially splayed front limbs, more erect hind limbs, and a short but well-developed tail. Even though little-visible in a mount or painting, the most specialized trait of Moschops is the thickened skull roof, a bit like that of a giraffe but without the "horns" of the latter (its relative Estemmenosuchus had some horn-like protrusions). The purpose of its hard head is not known: headbutting rivals or predators is a possibility (like a giraffe indeed), making it sort of an earlier version of the true dinosaur Pachycephalosaurus, but it could alternatively just have been for display.

Moschops' teeth were small and blunt, and all rather similar to each other, unlike most other synapsids (Dimetrodon included), but they were enough for taking vegetation of the harsh landscapes it inhabited. It lived in Middle Permian South Africa (hence the species name capensis); some portrayals wrongly show it living alongside Dimetrodon or Cynognathus, but it actually lived in a time period between the two, later than the former and earlier than the latter.

Old sources often wrongly depicted Moschops with reptilian scales (like most mammal-ancestors), and even with an erroneous line of reptilian tubercles along its neck, back and tail (a bit like an iguana crest but blunter). We don't know if it had some hair on its body like Cynognathus above or was naked-skinned like a modern rhinoceros. It's sometimes said to have had a "third eye" in the middle of its skull; actually this "eye" was just a tiny bunch of light-sensitive cells shared by many other primitive vertebrates (such as the modern tuatara).

  1. Entry Time: undetermined
  2. Trope Maker: Popular prehistory media

Proto-Sabertooth?: Inostrancevia *

The gorgonopsians ("monstrous faces") were the top predators of the Late Permian, but they were killed off by the huge mass extinction that divides the Paleozoic from the Mesozoic. More slender and usually smaller than dinocephalians, they are nicknamed "sabertooth" just like their mammalian namesakes; however their upper canines, though longer than most therapsids, were far less developed than those of a saber-toothed cat. They include the prototypical Gorgonops, the wolf-sized Lycaenops ("wolf face") and Sauroctonus, but the perhaps most portrayed has been (of course) a larger genus, the cow-sized Inostrancevia. It is named after a Russian geologist, and is perhaps the biggest of the whole group.

Gorgonopsians, Cynognathus and other carnivorous therapsids are often described as looking like dogs; indeed, in modern depictions, this resemblance is even more evident than in the older, more reptilian portraits. As usual for synapsids, whether or not the gorgonopsids laid eggs and/or had mammary glands is still unknown.

The gorgonopsids' history in pop culture is convoluted. The Czech paleoartist Zdenek Burian first depicted a Sauroctonus interacting with a Scutosaurus in one of his old paintings and they have appeared seldomly in educational books. The second Dino Crisis game included Inostrancevia, inaccurately showing it as an armored monster living in volcanoes alongside Jurassic and Cretaceous-period animals. The Primeval series made them famous by having Inostrancevia appear in the first episode, while BBC's documentary series Walking With Monsters included the eponymous Gorgonops in the third and final episode, enlarged up to the size of Inostrancevia.

  1. Entry Time: undetermined
  2. Trope Maker: documentary media

Fur and Whiskers: Thrinaxodon *

After Cynognathus, the most represented among the Cynodonts is the cat-sized Thrinaxodon: for example, it appeared in "New Blood" episode of Walking with Dinosaurs (identified simply as "cynodont", oversized and misplaced).

Also found in South Africa at the end of the 1800 century like the cynognath, Thrinaxodon ("trident tooth") has sometimes been cites as "the most mammal-like among mammal-like reptiles": but recent research indicates it was actually one of the most basal cynodonts, even more basal than Cynognathus itself. With its small size, compact body, short but robust legs and short tail, it probably lived in self-digged burrows like a modern badger, an could have been a hunter of small animals like the american badger (Taxidea taxus) or an omnivore like the eurasian badger (Meles meles). Careful analysis of its skull show the thrinaxodont was certainly covered with fur, and has also sensitive whiskers just like modern mammals.

  1. Entry Time: 1999
  2. Trope Maker: Walking With Dinosaurs

Proto-Tusks?: Placerias *

Placerias hesternus was another member of the Dicynodont subgroup of therapsid, from the same habitat of Coelophysis in Late Triassic southern U.S.A. It was bigger and more evolved than Lystrosaurus above, weighing 1 ton and with a body-shape rather similar to the herbivorous dinocephalians like Moschops or pareiasaurs like Scutosaurus. Its very large head was typical of a dicynodont however, with only two upper teeth and a round tortoise-like beak. Its most striking feature is the shape of this pair of teeth: instead of protruding downwards like most other dicynodonts, they pointed forwards like elephant-like short tusks.

In Walking with Dinosaurs, Placerias is represented as a particularly slow animal moving a bit like a giant tortoise, but experts think despite its bulky shape and stocky limbs it was able to move faster than what's seen in the show. Its tusks were probably powerful weapons against its enemies, predatory "thecodonts" like the armored Parasuchians and Rauisuchians, and the comparatively more gracile theropod dinosaurs of the time (coelophysoids and herrerasaurians).

  1. Entry Time: 1999
  2. Trope Maker: Walking With Dinosaurs

The First known Mammal-Ancestor: Dicynodon *

The first mammal-like "reptile" ever described was Dicynodon ("two dog-like teeth") in the middle of the XIX century, the time in which Darwin popularized his revolutionary concept of evolution.

His pupil Thomas Huxley (nicknamed "Darwin’s Mastiff") proposed a surprisingly modern hypothesis, that land vertebrates should be divided in only two branches instead of the Linnaean tripartition mammals-birds-reptiles. These lineages were: theropsids ("beast-looking", not to confound with therapsids) and sauropsids ("lizard-looking"). The former were basically the mammals; the latter were the reptiles (including dinosaurs and birds). Since Dicynodon was initially not thought a mammal ancestor, in Huxley’s classification it was put in the "sauropsid" branch. This was the start of the tradition to classify these animals as reptiles, and to depict them with reptilian traits. Even though the relationship therapsid-mammal was cleared at the start of the 20th century, the mammal-like "reptiles" thing has endured until the 21th century.

Dicynodon lived in Late Permian Southern Africa, and is the official prototype of the Dicynodont subgroup of therapsids. Lived in Late Permian, before Lystrosaurus and Placerias, was relatively small-sized compared with the latter two, but with the usual only-two-toothed dentition of the group. Due to the earliness of its discover it is also the only mammal-ancestor portrayed in the Crystal Palace Park of London — with oversized upper "canines" and, worse, with a totally erroneous turtle-shell.

  1. Entry Time: 1856
  2. Trope Maker: Crystal Palace Park

Other synapsids

Sorry, these aren't here. If you're looking for Ophiacodon, Sphenacodon, Cotylorhynchus, Tapinocephalus, Anteosaurus, Titanosuchus, Robertia, Kannemeyeria, Lisowicia, Sauroctonus, Lycaenops, Lycosuchus, Bauria, Ericiolacerta, Massetognathus, Oligokyphus, and others, see here.

Extinct Mammals

Even prehistoric mammals are sometimes mislabeled dinosaurs. Colloquially, this is often true of prehistoric amphibians or even prehistoric fish and invertebrates, and also existing critters that are considered "living fossils" (the coelacanth, tuatara, horseshoe crab, nautilus, etc.), and mammals that went extinct after the dawn of recorded history.note 

    Mammals in Media 

Among mammals, those living in the Ice Age have classically been the most portrayed, because they lived alongside the most iconic hominins (Neanderthals and Cro-Magnons). But earlier mammals of the Cenozoic Era (the Mammal Age) occasionally appear, usually — needless to say — the coolest-looking among them.

Portrayals of prehistoric mammals have usually been more accurate than those of prehistoric reptiles since large extinct mammals both have left more numerous remains than the latter, and are easier to "bring to life" correctly in media by comparing directly them with their modern relatives — though this doesn't entirely prevent inaccurate reconstructions. A good percentage of them received an increase in popularity just after the Turn of the Millennium thanks to Walking with Beasts and CGI cartoons, but others (especially the Ice Age ones) have been popular since long before then.

    Ice Age Mammals 

The Symbol of the Ice Age: the Woolly Mammoth & the American Mastodon ***

Mammoths and mastodons often show up in anything dealing with prehistory: you can even see them living in tropical volcano-filled worlds alongside dinosaurs, but thankfully they are usually associated with the Ice Ages.

The species most commonly portrayed of these is Mammuthus primigenius (lit. "primeval mammoth"), better-known as the woolly mammoth, or THE mammoth par excellence. Probably the most iconic non-dino prehistoric animal of all, thanks to its resemblance to an elephant with huge curly tusks and dense hair, but also to the countless, extraordinarily well-preserved specimens with soft tissues found both in northern Eurasia and northern North America. These findings have long made it one of the most accurately-portrayed of all prehistoric animals, and one of the very rare extinct animals almost as scientifically well-known as a still-living animal. However, the real cause of its extinction during the Pleistocene epoch remains unclear.

Despite its familiarity, even this animal is not spared misconceptions and mistakes in its portrayals. The most common error is thinking the woolly mammoth was larger than modern elephants: actually the "woolly" was the same size as its tropical, 21st-century cousins — perhaps this is due to the confusion with other mammoth species that were a bit larger, like the Columbian or Imperial mammoth (Mammuthus columbi). Also note that only males had the typical huge, curled tusks; the females' tusks were not that different from those of modern elephants. As preserved fossil hair is often rich reddish-brown, some depictions show woollies with this color; actually, this is due to a chemical change in the hair during the intervening thousands of years. When alive their hair could be black, as seen in both Walking with Beasts and Prehistoric Park, or pale "ginger" or even blond.

It's worth noting that mammoths, scientifically speaking, were just another genus of elephant, since they belonged to the same family, the Elephantidae. The Asian elephant (Elephas maximus) is slightly more closely related to mammoths (Mammuthus) than to its more distant modern African relatives (Loxodonta africana and Loxodonta cyclotis) — thus mammoths (and mastodons) weren't the direct ancestors of elephants as is sometimes claimed. Closely related to the several Mammuthus species were the members of the genus Palaeoloxodon, the "straight-tusked elephants"; the best-known of them is Palaeoloxodon antiquus. This was an elephantid of the Ice Ages, but living in warmer climates, bigger than the woolly mammoth and about the same size as the Columbian mammoth. Other recently-extinct elephantids underwent a high degree of insular dwarfism, some becoming as small as an average sheep or pig.

On the other hand, the proper mastodons (whose common name curiously means "breast-tooth") were not true elephants, but just distant relatives of both mammoths and surviving elephants, and were much more primitive within the phylogenetic tree than the Elephantidae. The scientific name of the commonly-known species of mastodon, Mammut americanum, is partially misleading: it was American indeed, but not a mammoth, and had shorter limbs and a couple of small teeth in the lower jaw, unlike true mammoths. Other species of the genus Mammut lived in Eurasia in the same period.

Like the woolly mammoth, the American mastodon has left exquisite remains (such as those in the Californian tarpits). It lived during the Ice Ages, but in warmer climates than Mammuthus primigenius, and was neighbour and possible prey of the sabertooth Smilodon fatalis. Interestingly, in some languages the adjective "mastodontic" has become a household word as a synonym of "huge," "enormous," but the animal wasn't actually that big compared with other extinct proboscideans (it was a bit smaller than a bush elephant). For other extinct elephant relatives, see some entries below and Prehistoric Life.

  1. Entry Time: N/A for the woolly mammoth, which has been a cultural icon since prehistory. 1864 for the mastodon.
  2. Trope Maker: Journey to the Center of the Earth (Mastodon)

Knife-Teeth: Smilodon & Machairodus, aka the "Saber-Toothed Tigers" ***

Saber-toothed cats, with their distinctive fangs, are just as iconic in pop culture as the woolly mammoths, and the only other mammals worthy of three stars here. Mammoths and sabertooths (sabretooths in UK) have traditionally competed for the title of most iconic Ice Age mammal — just like Brontosaurus and Tyrannosaurus for title of most iconic dinosaur.

There were many species of saber- or sabre-toothed felines, but the ones you'll likely see are the North American Smilodon fatalis ("fatal knife-tooth") and the South American Smilodon populator ("devastator knife-tooth"), which was larger but whose name sounds less cool when said out loud (even if its specific definition is awesome). The nearly-identical Old World genus Machairodus ("sword-tooth")note  has also been quite common, at least in non-fictional works. Estimated at around a thousand pounds in maximum weight, S. populator was one of the largest cats to have ever lived (the same size as the extinct American lion and cave lion), and was probably a descendent of S. fatalis, which was closer in size and weight to a bulky modern lion.

Although sabertooths belongs to the cat family Felidae, they are in a separate branch of that clade from modern felines, the hard-to-pronounce Machairodontines (named after Machairodus); thus, the name "saber-toothed tiger"note  popularly applied to these creatures is not correct at all. The "tiger" thing has led to them being shown roaring with the same sound as an actual tiger or a lion, though only the big cats of the genus Panthera (that is, lions, tigers, jaguars and leopards) can produce such a roar thanks to the structure of their larynxes, which is unique to this genus. Although the structure of the small bones in sabertooths' throats were set up for roaring, it's uncertain if these roars were identical to that of modern big cats.

In media, Smilodons will also probably use their sabers for every conceivable task, like slaying herbivores the size of mastodons or Megatherium with a single stab, despite the fact that most real sabertooths (as well as their relatives, the scimitar-tooths and dirk-tooths) had relatively delicate fangs that could not safely be used for stabbing. Instead, they probably slashed out the throats of prey from below. And they may be depicted as striped, just like a literal tiger, which — in S. populator 's case — isn't completely impossible, given that it lived on grasslands.

Expect to see Smilodon, Machairodus etc. frequently interacting with humans, as our ancestors' main predators; in Real Life other carnivores such as the aforementioned prehistoric lions were probably more common predators of hominins. And expect to see them living alongside woolly mammoths. Even though they were contemporary, their habitats in Real Life were largely different, with Smilodon preferring warmer climatesnote . And, naturally, don't rule out seeing saber-toothed cats somehow living alongside dinosaurs, and in the worst-case scenario, fighting against a ''T. rex''.

In Real Life, Smilodon was an animal exclusive to the Americas (the New World), filling the niche the other sabertooths, Machairodus for example, were occupying in the Old World (Europe, Asia, Africa). Smilodon and kin were among the most specialized members of the Carnivoran order of mammals. Its hindlegs were shorter than its forelegs, like hyenas and some bears, and a stubby tail; it was powerful but quite slow-moving, and agile only in a straight line: in other words, a Mighty Glacier. The lower jaws were more gracile than modern big cats', and had a loose hinge that allowed them to open incredibly wide (convergently with hippos), but were not apt for delivering powerful crushing bites, similar to snakes' jaws (venomous snakes have often upper fangs surprisingly similar to a sabertooth's). Smilodon had the biggest/longest fangs among all saber-toothed cats; this, together with its body size, might explain why it's become the most famous member of the group (and often cited as THE sabertooth par excellence). Only the earlier, distantly-related pseudo-cat Eusmilus had fangs of comparable size.

The "sabers" of Smilodon were arguably used only for slashing the throat of prey that had already been subdued with its bodybuilder-like forearms; the molars were smaller than those of modern cats but the incisors were bigger, and more apt than the canines for tearing off flesh from its preys' bodies. Smilodon is often portrayed living in wolf-like packs with both sexes actively hunting, though this is considered controversial by some scientists as there is not enough actual evidence to support it. Some artists have even depicted smilodonts with a totally speculative lion mane, linked with the pack behavior which is practiced by lions but unusual for other modern felines.

Saber-toothed cats went extinct 10,000 years ago, after the Ice Age ended. Like the mammoths, theories have been raised as to how they died off, such as due to climate change thanks to the end of the Ice Age, the lack of big prey for them to hunt, or humans changing their habitat by setting fires, killing off their food supply. Anyway, it's certain that they didn't evolve into modern cats, because as mentioned above, they were from a distinct cat lineage from modern felines.

  1. Entry Time: 1903 (Smilodon fatalis); 2001 (Smilodon populator)
  2. Trope Maker: The paintings of Charles R. Knight (Smilodon fatalis); Walking with Beasts (Smilodon populator)

Big Beast: Megatherium **

One of the largest and most spectacular land mammals that ever lived, Megatherium americanum was the same size as an elephant or a T. rex: it reached 5m when standing fully erect, like a giraffe but much heavier. Indeed, the name "Megatherium" means... well... big beast.

This is probably the most famous extinct mammal that doesn't really look like an ancient version of its still-living cousins, and is probably also the most famous one whose name ends in -therium. While mammoths and mastodons could be regarded as the "brontosaurs" of their time and sabertooths the "tyrannosaurs", the megathere (but also the woolly rhinos and glyptodonts below, and to some extent, also the cave bear) can be considered the "Ice Age Triceratopses and/or Stegosauruses": that is, the Giant Herbivorous Tanks of their time.

Megatherium lived just a few thousand years ago in South America, and ancient humans knew it, to the point that they actually might have used it and other relatives as a living pantry! Megathere remains have been discovered in ancient caves, and it is thought that some human hunters enclosed some of these animals in those caves.

In old reconstructions, Megatherium was shown with a horse-like head and sometimes a giraffe-like tongue to reach foliage on the tree tops. The horse head and giraffe tongue are probably mere fantasies, but the high-browsing habits aren't; indeed, the robustness of its body allowed it to stand on only its hind feet (which, curiously, had only one claw each) and on its robust tail like a tripod, while the three-clawed, bear-like forefeet were used to pull down branches. Actually, our "big beast" was neither a horse nor a giraffe relative, nor was it a giant bear... it was a sloth. More precisely, the stock animal within the group called giant ground sloths, which are not only related to modern sloths, but also to anteaters and armadillos, and not to ungulates or carnivores. Thanks to some fossilized pieces of skin we know that the megathere had long hair like a modern sloth, but also osteoderms, small lumps of bone in its skin, as a kind of armor. Thanks to its size, dense hair, and osteoderms, it probably had no predators as an adult, except of course humans.

An extremely controversial idea is that ground sloths might have supplemented their diet with meat that they scavenged from predators such as sabertooths by chasing them away from their kill. There isn't much to support this theory other than Rule of Cool, though.note  This didn't stop Walking with Beasts from depicting Megatherium chasing some Smilodons away from their kill and eating it, and since then, it has been forever cemented as an omnivore in video games such as Zoo Tycoon and Ark Survival Evolved note  Some portrayals take this depiction Up to Eleven by having it be an active hunter, knocking over animals like the tank-like glyptodonts to tear open their soft belly, almost like it was a mammalian version of Tyrannosaurus rex.

Megatherium is the most well-known species of ground sloth, due to being the largest. Like Smilodon, it's commonly depicted alongside the aforementioned mammoths, despite being strictly South American (mammoths never reached this continent).note Megalonyx was the sloth species that was common in North America, but it was about half the size of its more famous cousin. It was first described, believe it or not, by president Thomas Jefferson!note 

The most famous ground sloth in fiction is Sid from the Ice Age franchise, who is only about the size of a human, and resembles no ground sloth in real life, much less Megatherium. He looks more like a modern tree sloth, which the animators did indeed model him off of. In prehistoric terms, though, he seems to be closest to the Nothrotheriops (or Shasta ground sloth) at least in terms of appearance. The most bizarre portrayal of these critters would have to be in the 1948 B-movie Unknown Island, where a ground sloth was depicted as a strange, roaring predator that resembles a cross between a gorilla and a bear.

  1. Entry Time: 1854
  2. Trope Maker: Crystal Palace Park

Extinct Hairy Rhinos: the Woolly Rhinoceros & Elasmotherium **

Mammoths weren't the only "woolly" creatures that lived in the Ice Age. Special mention should be given to the slightly less famous but still notable woolly rhinos, the "ceratopsids" of their time.

Elasmotherium sibiricum ("Siberian thin-plate beast"), also known as the unicorn rhino, is often confused with the proper woolly rhino (Coelodonta antiquitatis, "hollow tooth of antiquity") because of their similar appearance. However, the latter was no larger than modern white rhinos and had two horns as well; it was closely related to the modern Sumatran Rhinoceros, the smallest extant rhino species (and the only one with some hair on its body). Elasmotherium was much larger (5 tons, like a modern bush elephant) and with a single horn... on its forehead rather than its nose, and perhaps as long as a grown man; hence unicorn rhinoceros. It was not closely related to any of the five modern rhinoceros species, but still belonged to the rhino family, the Rhinocerotidae.

Both rhinos lived in the Ice Age in cold climates, alongside mammoths in northern Asia, but the elasmothere had a more southerly range than the proper woolly rhino, and while both lived east of the Urals, only Coelodonta was found in Europenote ; the woolly rhino Coelodonta lived alongside the other, more popular woolly (guess what) in the same frozen landscapes. Interestingly, both the elephantine "woolly" and the rhinocerotine one (we're always talking about Coelodonta) have left soft parts of their bodies other than bones, hair and horns included.

It's important to note that rhino's horns are not made of bone like the horns of bovids and deer, but of hardened hair, and don't usually preserve as fossils. The anterior curved horn of the proper woolly rhinoceros was laterally flattened, and some have speculated it used it to free the terrain from snow to reach the vegetation below, like modern caribous do with their hooves and antlers (and like woolly mammoths may have done with their tusks). We don't know what size the elasmothere's horn actually was, because it has never found; considering the shape of its skull, however, it must have been very large. Both rhinos went extinct without leaving descendants. The "unicorn rhinoceros" is often thought to have been the inspiration for the Unicorn myths found all over Eurasia in one form or another when still alive, but this is mere speculation. There's a chance the unicorn rhino might have lived into historic times, but the anecdotes and depictions of these creatures might just as well refer to one-horned bulls or animals frozen in the permafrost like mammoths are known to have been. Once again, it appears humans did these creatures in just as things were getting better.

  1. Entry Time: 1918 (Coelodonta), 2006 (Elasmotherium)
  2. Trope Maker: The Land That Time Forgot (Coelodonta), Prehistoric Park (Elasmotherium)

Large Ice Age Bears: the Cave Bear & the Short-Faced Bear **

Among the prehistoric mammals of the order Carnivora, the most famous after the saber-toothed cats are the giant bears (again from the Ice Ages).

The most well-known is the cave bear (Ursus spelaeus, meaning "cave bear" in Latin), so-called because its remains are extremely abundant in European caves. Quite similar to a modern Kodiak bear in shape and size, but with a bigger hump on its shoulder and a more prominent skull, the cave bear was perhaps the closest relative of brown/grizzly/kodiak bears (Ursus arctos), and usually depicted with the same brownish color of the latter (as cave paintings suggest).

It had classically been described as the archenemy of Neanderthals and Cro-Magnon humans, because both humans and bears lived in the same places (Pleistocene Europe) and were forced to share the same caves to protect themselves from the frigid Ice Age winters. But it's more probable that Neanderthals and Cro-Magnons were actually the worst enemies of cave bears, and some think they could even have contributed to the bears' extinction. Studies show the cave bear to have been to an almost pure herbivore, like the living giant panda, living on a strict diet of berries and shrubs (though, like pandas, it may have supplemented its diet with meat every now and then). In fact, the inflexibility of its diet may also have contributed to its extinction.

The North American short-faced bear (Arctodus simus, lit. "short-muzzled toothed bear"), in contrast to its stockier cousin, had long limbs, a bulldog-like snout, and (it's usually thought) an almost purely carnivorous diet. At first glance, it seems like it would be an agile and fast runner, and a very powerful hunter. However, more recent studies show that its limbs were too gracile to wrestle large prey to the ground, and too fragile for sharp turns, the latter of which are required for a fast-running hunter. More likely, it was a scavenging "kleptoparasite" that stole prey from other predators by scaring them away with its large size. On the other hand, very few animals can live entirely on scavenging (vultures are an exception, as they can fly for miles without eating), hinting that it may have been an omnivore like other bear species.

Expect these two bears to be confused in pop culture despite being quite different in appearance, and the short-faced bear being more related to the South American Spectacled Bear (Tremarctos ornatus) than the modern grizzly (while the cave bear was a close relative of every other Ursus species). Also expect the cave bear to be depicted as a hunter of large prey despite having a mostly herbivorous diet judging from the wear on its teeth. Another thing to note is that despite most books describing the short-faced bear as the largest bear, that title actually belongs to its South American relative Arctotherium ("bear beast").

  1. Entry Time: 1897 (cave bear); 2000s (short-faced bear)
  2. Trope Maker: A Story of the Stone Age (cave bear); recent documentary media (short-faced bear)

Living-Tank Mammals: Glyptodon & Doedicurus **

After ankylosaurs went extinct, evolution decided to create their perfect mammalian equivalents: the glyptodonts. They were basal placentals of the same group as the giant ground sloths (the Xenarthrans or Edentates), but evidently more related to armadillos rather than to sloths. Despite the old name "edentate" means "no teeth" (a reference to anteaters, which are xenarthrans as well), both ground sloths and glyptodonts had strong molar-like teeth to grind up vegetation, but small or no frontal teeth.

Glyptodonts lived in South America for a dozen million years, before going extinct only a few thousand years ago: in other words, they had the same history as their cousins, the giant sloths. Both groups were herbivores, and glyptodonts fortunately have never been depicted as meat-eaters or predators in popular media unlike their relatives. Rather, they have often been compared with giant tortoises because of their shell-like armor and short "hoofed" feet. Like the megatheres, as adults they feared no predators (not even the saber-toothed cats), except of course humans. The size of the largest glyptodonts tend to be sometimes exaggerated in docu-media; they were actually much smaller than Megatherium, being not taller than an adult man — but their mass was nonetheless as much as a small car, and thanks to their heavy armors they weighed perhaps two tons, like a modern rhino or hippo (which is still much smaller than an Ankylosaurus).

There is a secret behind giant sloths' and glyptodonts' success: their backbone. It was far, far stronger than that of any other mammal, thanks to special protrusions (the xenarthral bones, hence the name "Xenarthrans" given to their group) in their vertebrae that permitted them to carry such heavy bodies around without suffering back pain.

Glyptodon ("sculpted tooth") is the prototypical and most well-known glyptodont, with a round upper shell like a tortoise coupled with a small round head and short rigid tail, but it's also worth mentioning Doedicurus ("pestle tail": this is the one seen in Walking With Beasts, Zoo Tycoon 2, and ARK Survival Evolved). It was almost identical to Glyptodon, but with its long flexible tail covered in massive spikes at the end, it was the most stegosaur- or ankylosaur-like of all glyptodonts, easily able to kill even a smilodont with a single blow from its "Medieval mace". These two were also among the biggest glyptodonts, and thus the most-often depicted. In truth, the doedicurus' spiky tail-end would have been even more dangerous for enemies than the Ankylosaurus' more rounded one — recalling more a stocky Stegosaurus "thagomizer".

Glyptodonts' dorsal armor was the strongest among any land vertebrate, tortoises excluded. It was made of a single piece consisting of several scutes fused together, smooth and usually round, unlike ankylosaurs and armadillos whose armor was more flexible (and spiky in the case of ankylosaurs). With their compact frame, pillar-like legs, and rigid armor, glyptodonts were probably slower-moving than ankylosaurs and armadillos, but still faster than a Galapagos tortoise. Despite these differences, the glyptodont's armor was astonishingly similar to an ankylosaur's; only the upper parts of the body were covered, the underbelly was unarmored like ankylosaurs and hairy like modern armadillos; the head had a "shield" again like ankylosaurs and armadillos, and their tail was also covered by bone all around it.

Like Megatherium, Glyptodon was known to ancient humans; we now know human hunting wiped out these species, as the species on islands were the last to go, and as there is evidence of human hunting and change in their habitat. Ancient humans often used the biggest glyptodonts' dorsal armors as body armor for themselves. Now, only far smaller xenarthrans survive; armadillos (which were not glyptodont descendants but only relatives), tree sloths (not Megatherium descendants), and true anteatersnote , all Central/South American, except for the nine-banded armadillo, which has in the past few centuries colonized part of the USA.

  1. Entry Time: 1864
  2. Trope Maker: Journey to the Center of the Earth

Big Badass Wolf: the Dire Wolf **

The dire wolf (Canis dirus) was a recently-extinct wolf exclusive to the Americas, famous for being bigger/stronger than our wolves, and possibly a hunter of giant bison like Bison priscus in competition with saber-toothed smilodonts and extinct American lions (Panthera leo atrox). It has been often found in the same tar pits in which Smilodon remains have been discovered, along with several other American mammals (elephant relatives, ground sloths, and modern mammals as well); the most famous is Rancho la Brea, in Los Angeles. This animal could be considered the mammalian "raptor" of the Ice Ages.

In real life, the dire wolf wasn't much larger than the modern grey wolf (Canis lupus), and probably not too different in appearance. However, it had a much more powerful bite, well over twice that of its relative (and thus often compared to that of a hyena). This would allow it to be a fair competition to other predators at the time. It ranged from as far north as Canada to as far south as South America (though only in the northern and western areas, due to the obstacle presented by the Andes). Like the bears above, neither of which left descendants in modern world, the dire wolf is not the ancestor of modern wolves.

Surprisingly, this canid is less common in works set in prehistoric times, and more common in fantasy works such as Dungeons & Dragons and, most famously, in A Song of Ice and Fire and its television adaptation Game of Thrones. When it appears, expect it to be double the size of a real grey wolf, despite not being much larger in real life. Expect it also to be described in books as "the biggest canid ever", though some Borophagines (nicknamed "hyena-dogs") that lived well before it were actually larger, as well as some extinct true hyenas (which are not canids at all but distant feline relatives).

  1. Entry Time: 1996
  2. Trope Maker: A Song of Ice and Fire

Up To Eleven Trophy: Megaloceros *

Now we return in the world of the hoofed mammals (remember that rhinos are true ungulates, but mammoths & elephants are not), this time with an artiodactyl, aka an even-toed hoofed mammal.

The most spectacular extinct deer, this is also one of the most-depicted extinct mammals in prehistory books because of its antlers, but is rather uncommon in Fictionland. Megaloceros simply means "big horn": continuing the Running Gag of comparing Ice Age mammals with dinosaurs, Megaloceros could be considered the "hadrosaur" of its time, for its huge size but slender running frame, spectacular head ornamentation like that of the Parasaurolophus, and its ecological niche as prey for other mammals (humans included), just like "duckbills" in the Cretaceous.

But wait: even though it is commonly referred to as the Irish elknote , Megaloceros (also called "Megaceros" in older sources, with the same meaning of "big horn") was more closely related to the European fallow deer — indeed, in many sources it is more generically named the "giant deer". It wasn't the largest deer ever — though it was as large as a moose, even bigger deer lived elsewhere in the Ice Age — but its antlers were another matter: they would make a modern moose's antlers look puny. Each one was as long as the entire animal's body (each as tall as an adult person, as mentioned in Walking With Beasts), and each weighed more than 100kg — more than any other known deer species.

As with all modern deer (except for reindeer and caribou), only males had such headgear, which in reality more resemble a moose's flat antlers than the typical deer's branched ones. Some scientists believe that the antlers alone were the cause of its extinction, having grown too bignote , and making the animal too clumsy... but this is uncertain. Megaloceros males were stronger than females but probably just as agile (as with extant deer species): if their antlers actually were too big, evolution probably would have just made them smaller at some point. The species Megaloceros giganteus ("gigantic big-horn") lived in Europe in the Ice Ages alongside woolly mammoths and other large mammals, and was possibly prey for ancient humans (Walking with Beasts show Cro-Magnons successfully killing one adult male Megaloceros that was tired after a combat with another male); its nickname "Irish elk" is due to its remains being very common in Oireland. Its huge antlers are often found isolated in this country, and have even been used as a tool to cross small streams! Other Megaloceros species were more common in continental Europe, but were less impressive than the Irish one and had differently-shaped antlers.

Eucladoceros ("well-ramified horn") and Cervalces ("moose-deer") were other large, spectacularly large-antlered, extinct true deer (Cervalces had a smaller set of antlers, but had a larger body than the megaloceros), but other prehistoric cervids (the "deer family" of artiodactyls) had more normal-sized headgear. Other prehistoric mammals with big antler-like things above their heads, like Sivatherium and Synthetoceras, were artiodactyls but not of the deer family (the former a giraffe, the latter a relative of the chevrotain or mouse deer, family Tragulids); they may nonetheless be wrongly presented as "deer" in docu-media. Of course, none of these real or pseudo-deer were direct ancestors of modern deer species.

  1. Entry Time: 1854
  2. Trope Maker: Crystal Palace Park

Bigfoot?: Gigantopithecus *

This extinct primate is surely the most popular today in media (human ancestors excluded, of course) also because of its size. Other giant primates of the past include baboons like Dinopithecus, and giant lemurs of ancient Madagascar.

According to the most recent research, Gigantopithecus was a relative of the orangutan, but also convergently exhibited gorilla-like characteristics. Found in Southern Asia from China to India, its name means "giant ape", and with good reason. It's estimated to have measured up to 10 feet when standing upright, twice as tall as a modern silverback gorilla; sort of midway between a Real Life gorilla and King Kong.

Sadly, the only parts that can be described for certain are the jaws and teeth, while the rest of the body has yet to be recovered; the shape of the teeth show us it was a plant-eater, possibly specialized to a bamboo-based diet just like a gorilla, to the point that some experts think competition with the giant panda actually drove it to extinction. Gigantopithecus lived alongside the asiatic Homo erectus before going extinct, but we don't known how they interacted with each other due to the scarcity of remains of either.

At least part of the reason this ape has entered stock territory is due to some scientists speculating that it might have been the inspiration for the mythical yeti (especially since it was also discovered in the Himalayas). Some cryptozoologists have taken these theories Up to Eleven, speculating that not only did it survive to modern times, but at least one lineage migrated to North America and evolved into Bigfoot. Thanks to this radical theory, Gigantopithecus has been mentioned in virtually every Bigfoot documentary.

There are quite a few problems with this theory. First of all, there is absolutely zero fossil evidence that it survived that long, much less that it made it to North America. It's quite unlikely that such a large creature could go unnoticed for so long without leaving some sort of proof of its existence. Secondly, since the creature was specialized for eating mostly bamboo, it's doubtful it would survive in a temperate environment without its preferred diet, much less spread throughout North America.

Despite this, the "Gigantopithecus = Bigfoot" theory is so popular that the ape is often depicted in models and illustrations in an upright stance like a man, just to fit with this idea. Since all we have are its jaw and teeth, it's hard to be sure, but judging by its relationship with other apes, it most likely walked on its knuckles like most great apes do today. Since primates that habitually stand and walk upright require a specialized foot structure extremely different from that of other apes, Gigantopithecus evolving a similar foot structure to that of humans would be a radical case of convergent evolution. Also, if it was as large as believed, its immense weight would cause great stress on its ankles and would be better-distributed by walking on all fours.

In The New '10s, Gigantopithecus made two notable film appearances. First, there was the villainous pirate Captain Gutt in Ice Age: Continental Drift. Then in The Jungle Book, a 2016 remake of the 1967 Disney classic, King Louie was changed from an orangutan to a Gigantopithecus to avert Misplaced Wildlife (orangutans live in South Asia but they survive only in Indonesia and Malaysia, not in India where the story is set). The latter appearance could very well place this creature in the public's mind for quite a long time, since not only was he quite humorous, being voiced by Christopher Walken and all, but he was much more menacing than his 1967 counterpart, chasing Mowgli through the ancient temple ruins in a memorably chilling sequence. At least both film appearances correctly depict Gigantopithecus as an orangutan-like ape, walking quadrupedally on its knuckles as opposed to upright like a human.

  1. Entry Time: The New '10s
  2. Trope Maker: Yeti and Bigfoot documentaries, and the two aforementioned films

South American Tapir-Camel: Macrauchenia *

Macrauchenia was another famously enigmatic prehistoric creature that lived in the Ice Age (but also earlier); its best-known species is Macrauchenia patachonica, meaning "Patagonian long/big llama". It did indeed resemble a llama or humpless camel in appearance, but actually belonged to a long-extinct group of mammals called the Litopterns, with no modern relatives — though recent research shows this group to be a sister group to Perissodactyls, the odd-toed ungulates.

The size of a horse, one of its most distinct features is its nostrils, which on the skull were located on its forehead like in tapirs and in the proboscideans (elephants, mammoths, and so on) . This results in it always being depicted with a flexible tapir-like proboscis. However, if you compare a tapir skull to that of Macrauchenia, you can see that the tapir has a bony projection on its forehead to hold the proboscis in place, which Macrauchenia lacks. Therefore, it's more likely the animal had a bulbous trunk similar to that of a Saiga antelope.

Another distinctive feature of the Macrauchenia is its leg bones, which were not only built for extremely high speeds, but also some of the sharpest turns of any herbivorous mammal. This makes sense when you realize it evolved alongside the famous terror birds, which were not only fast runners but, like most birds, had very good color vision, meaning camouflage was useless. Other predators of Macrauchenia included a group of carnivorous marsupial-relatives common in South America named Sparassodonts, like Borhyena and the saber-toothed Thylacosmilus, and, after the Great American Interchange, North American "invaders" like cougars, jaguars, the giant bear Arctotherium, and, most famously, Smilodon.

Macrauchenia lasted a good seven million years from the Late Miocene to the Late Pleistocene, until it went extinct after humans entered South America. Pop culture appearances include Walking with Beasts, the Ice Age franchise, and even an episode of Futurama. However, when it appears in non-documentary fiction, don't expect it to be referred to by name — like the vast majority of prehistoric mammals.

  1. Entry Time: 2001
  2. Trope Maker: Walking with Beasts

South American Hippo-Rhino: Toxodon *

Though slightly less often-portrayed than Macrauchenia, Toxodon also make occasional appearances in media, e.g. in the Prehistoric Park series — in which is shown as the main herbivore of the time and as a Smilodon's prey, substituting in this role for Macrauchenia of Walking with Beasts.

Toxodon ("bow tooth") was bigger than the "tapir-camel", being one metric ton or so in weight, and was probably the most common plant-eating mammal in the South American Pleistocene (the Ice Age), but lived also earlier, since the Miocene. Like Macrauchenia, it wasn't closely related to any modern group of ungulates. Toxodon belonged to the Notoungulates, lit. "the southern ungulates", and was one of the biggest and latest-surviving members of the group.

Its look may recall for some that of a stockily-built, hornless buffalo, but it had a wider mouth-opening and strong incisors like a horse. Its body and limbs were stockier than cattle, and the feet had four or five digits with small "hooflets"; thus, it has been classically compared with a hornless rhino or a small-headed hippo. Like the pre-ice Age Uintatherium and Arsinoitherium, Toxodon was once thought to have been a slow-moving animal — today we believe it was capable of running rather quickly (as shown in Prehistoric Park, where one is shown even keeping pace with Nigel Marven's vehicle). The toxodont was arguably not as fast as Macrauchenia, but thanks to its massive frame it was a harder target to fight and defeat for predators than the more slender tapir-camel.

These two South American guys lasted a sufficient length of time that they could have met humans in the past, like their neighbors, the giant ground sloths and glyptodonts.

  1. Entry Time: 1912
  2. Trope Maker: The Lost World (1912)

Ice Age Bison: Bison priscus *

Among the megafaunal mammals that roamed North American Pleistocenic landscapes (in a time when humans still lived only in Africa and Eurasia), besides the more famous mammoths, mastodons, sabertooths, ground sloths, and dire wolves, there were also several species of true bison (belonging to the scientific genus Bison).

The most famous is probably the Steppe Bison, Bison priscus (perhaps the one live-acted in the last episode of Walking with Beasts), closely related to the two modern species (Bison bison, the familiar American bison, and Bison bonasus, the rarer European bison or wisent). It was, however, a bit bigger than both, similar in size to the largest modern wild bovine, the so-called "Indian bison" or gaur (Bos gaurus, probably more closely related to domestic cattle). The Steppe bison had, more strikingly, longer horns than its two living kin — more like those of an African Cape buffalo or Indian water buffalo. It also lived in contemporaneous Eurasia, from which it actually originated.

An especially famous specimen of Bison priscus was found mummified in Alaska in 1979; nicknamed "Blue Babe" because of the color it has assumed, its frozen meat was still edible (its discoverers actually ate a chunk of it!) and its corpse shows perhaps signs of attack from Ice Age American lions (Panthera leo atrox).

  1. Entry Time: Undetermined
  2. Trope Maker: Documentary media

Paleo-Camels: Aepycamelus and Camelops *

The giant "giraffe-camel" Aepycamelus is the most famous extinct camelid, and lived earlier than Bison priscus, in Miocene North America. Other big, more modern-looking camelids like Camelops ("camel face") roamed North America later, in the Ice Ages. The latter was also found in the famed pleistocenic tarpits whose most iconic animal is Smilodon (a possible predator of it).

In older media Aepycamelus is often called "Alticamelus": both names mean "lofty camel", but Aepy is Greek, Alti is Latin. It was indeed taller than the already-tall modern dromedaries (up to 3m), but not much heavier: it was slender and had especially long limbs and neck, convergent with modern giraffes. Unlike the most primitive camelids, Aepycamelus had already the typical flattened toes with small hooves of modern camels and llamas, but isn't known to have had a fatty hump on its back.

  1. Entry Time: Undetermined
  2. Trope Maker: Documentary media

Ancient Rodent: Castoroides *

It's not common to see prehistoric rodents and other usually small-sized mammalian groups like rabbits, bats, "insectivores", or pangolins in popular media. However, this guy tends to be a bit more commonly-seen than the others.

Castoroides, the giant beaver, means "similar to a beaver" (Castor fiber in Latin): indeed it was of the same rodent family as modern beavers, the Castorids, but was as large as a small bear (three times heavier than the capybara, the largest modern rodent) and with extremely powerful incisors, possibly the most powerful ever among rodents, and arguably able to bring down even tougher trees than modern beavers. It lived in Ice Age North America and was thus a member of the Ice Age megafauna, but it wasn't the biggest rodent ever — some South American rodents were as large as a large cattle or a small rhinoceros! Due to its size and massive build, shared also by modern beavers, Castoroides was probably rather slow-moving on land, and may have been prey for the saber-toothed cats, American lions, and dire wolves. The main difference from modern beavers other than the size is that Castoroides was more land-dwelling, and thanks to its cylindrical tail it looked more similar to a large muskrat or coypu than to a beaver at a first glance.

Another prehistoric rodent fairly common in docu-media is the so-called "horned gopher", Ceratogaulus (formerly known as "Epigaulus"), was not related to ground squirrels (genus Spermophilus and others of the family Sciurids) or pocket gophers (the family Geomyids, commonly known as simply "gophers"), but belonged to an extinct family of rodents: the Mylagaulids. The prefix Cerato- ("horned") indicates its peculiarity: an unique two-forked bony projection above its nose no other rodent has ever had, recalling that of the more famous and totally unrelated brontothere Megacerops, or even that of the pseudo-deer Synthetoceras. This makes this critter the smallest known horned mammal of all time. Apart from this, the epigaulus was not so different from other rodents of the past and the present: it resembled a horned guinea pig in size and shape, and lived before the giant beaver Castoroides, in Miocene and Pliocene prairies of North America.

  1. Entry Time: Undetermined
  2. Trope Maker: Popular paleo-art

Giant Rhino-Wombat and Giant Koala-Roo: Diprotodon and Procoptodon *

Now we enter the realm of extinct Marsupials. Diprotodon ("two teeth in front") was related to modern wombats, but was a lot bigger: the largest species reached the size of a rhinoceros. With its robust limbs and massive body, it literally looked like a hornless rhino or a small-mouthed hippo, and also several extinct ungulates like the South American Toxodon or the early Coryphodon.

Indeed, Australian marsupials have undergone an extraordinary case of convergent evolution with placental mammals. Among differences between diprotodonts and ungulates, other than (of course) their reproductive system, is that the former had the same rodent-like incisors seen in modern wombats. We know that the diprotodon's hide was not naked or toughened like a modern rhino or hippo, but hairy like a wombat, and it had a pouch with a backward-facing opening just like the latter.

Procoptodon deserved the title of "giant kangaroo" more than modern giant Red or Grey kangaroos (Macropus rufus and Macropus giganteus). It was taller and more massively-built than both, with a shorter tail and more robust forelimbs. It's also known as the short-faced kangaroo because of its flattened muzzle, which looked like a koala's. Its pouch was similar to modern female kangaroos, but its hindfeet had a single horse-like hoof each — the only digit present on each foot.

Unlike modern kangaroos, which are all grass-grazers, Procoptodon was arguably a browser of trees, and recent research seems to indicate it was too heavy to hop on two legs, and walked instead rather like an erect ape or an ostrich. For this reason, it would have maintained a different stance from its modern relatives, by keeping its heels off the ground and standing on its hoofs.

These two giant mammals from the Land Down Under are more excellent examples of Mix-and-Match Critter-s, and the two most commonly-portrayed herbivorous prehistoric marsupials in media because of their size.

  1. Entry Time: Late 1990s
  2. Trope Maker: The Prehistory of Australia (documentary)

Marsupial Cats?: Thylacoleo & Thylacosmilus *

Modern Australia was also home to a unique animal which has no close modern relatives, with its contemporary the koala, wombat and the Diprotodonts above being closest despite being herbivores: Thylacoleo, ("pouched lion"), nicknamed the "marsupial lion", with its species name, carnifex, meaning "executioner". Related to it but much smaller were the recently-discovered Priscileo and Wakaleo.

The marsupial lion was so-called because its body shape, sharp claws, and short head remember modern big cats, but unlike the latter, it had rodent-like incisors (like wombats) instead of the classic fangs, and "guillotines" instead of carnassial molars that it used to slice the neck of prey to kill it instantly.

Scientists once thought Thylacoleo was herbivorous like a wombat or rabbit because of its incisors; they now know it was predatory. Not only that, it may have been the most efficient mammalian predator ever. Despite being no bigger than a jaguar, some think it was able to kill even the Diprotodonts and giant kangaroos above! The combination of Velociraptor-like claws in its forelimbs and guillotines in its mouth proved an efficient killing arsenal. If not for the fact there were two larger, faster, equally well-armed reptilian predators — Quinkana, a terrestrial crocodile, and the better-known giant monitor lizard Megalania prisca — it would have been the continent's unrivalled predator.

All three critters, modern animals adapted to today's world, met an untimely end at the hands of humans, as they set fires to grow different plant species, which starved their prey to extinction. The same fate occurred to all species of marsupial "wolves", the other main mammalian predators of prehistoric Australia other than the "lion", whose only species to have survived into the modern age, the famous "Tasmanian wolf" (Thylacinus cynocephalus), missed the chance to be observed by modern wildlife lovers only by a matter of decades.

Though not "marsupials" per se (and thus possibly lacking a true "pouch" just like some South American opossums), Sparassodonts were a closely-related lineage of carnivorous mammals that dominated South America before the Pliocene. The largest and most well-known of these was Thylacosmilus atrox ("atrocious pouched knife").

The same size as the marsupial lion, Thylacosmilus had two upper fangs virtually identical to actual saber-toothed cats (and possibly used in the same way), but unlike the latter, they were ever-growing like an elephant's tusks or rodent's incisors. To protect these fangs, the lower jaw has a couple of bizarre bony sheaths covered with skin, which could have given it a curious drooping-lipped appearance.note 

The most curious thing, however, is Thylacosmilus was not Australian at all: it was South American. Together with the other (non-saber-toothed) sparassodonts such as the bear-like Borhyena and the weasel-like Cladosictis, Thylacosmilus long occupied the mammalian predator niche in South America. It was one of the top predators in this landmass, in competition with terror birds and large crocodilians... before becoming extinct for unclear reasons. It was long thought that true placental sabertooths outcompeted it to extinction, but it appears sparassodonts were gone long before placental carnivores arrived. Furthermore, research published in 2020 seems to show that Thylacosmilus had a decidedly un-catlike hunting style. Instead of using its huge teeth to stab its victims' throats, as saber-toothed cats are believed to have done, it probably used them to slash open their abdomens and feed on their internal organs.

In old illustrations, both Thylacosmilus and Thylacoleo are often portrayed with a literal cat-like external appearance, with the same eyes, ears, body, or even retractable claws of real felines, but since both weren't related with them at all, this could be considered artistic license. Sadly, neither the giant herbivores of Australia nor the two "marsupial cats" appear in Walking with Beasts; interestingly, the producers initially planned a seventh episode with Australian Ice Age fauna — thus giving at least Thylacoleo the chance to appear — but this program never materialized.

  1. Entry Time: Undetermined
  2. Trope Maker: Their resemblance with big cats

A Cold Safari: the Cave Lion, the American Lion & the Cave Hyena *

True prehistoric cats weren't all sabertooths; there were also more normal-looking ones, which make up the subfamily Felinae (Felis = "cat" in Latin), while sabertooths comprise the Machairodontinae. The former are nicknamed by paleontologists "biting cats", the latter "stabbing cats"; it's easy to see why.

The most well-known "biting" extinct cats were the American lion (Panthera leo atrox: atrox = "atrocious") and its Eurasian cousin, the cave lion (Panthera leo spelaea: spelaea = "from caves"), both simply larger, Ice Age subspecies of the modern lion (Panthera leo), and well-adapted to live in colder climates along with the northern species of mammoths. Some think they were the main predators of ancient humans, but this is not certain. According to some prehistoric paintings, they had no manes.

In Walking with Beasts a cave lion has a minor role in the episode dedicated to the woolly mammoths: here it's correctly depicted mane-less (unlike in other paleo-artistic works), but with an odd snow-white color to its fur and even small "sabers" like a "stabbing cat"; actually its teeth were identical to those of every other "biting cat", and its coloration was brownish, like a modern lion but paler.

Similarly, the cave hyena is regarded today as a simple subspecies (Crocuta crocuta spelaea) of the well-known African spotted hyena (Crocuta crocuta), but in the past both the lions above and the hyena were considered true distinct species, albeit closely related to their namesakes. The cave hyena lived alongside the cave lion in Ice Age Eurasia, but compared with the more famous cave bear they were less associated with caves. The Ice Age hyena was arguably similar in appearance and behavior to its Savannah equivalent, but with thicker fur against the cold. However, in Prehistoric Park cave hyenas are not CGI but live-acted by modern spotted hyenas.

  1. Entry Time: 2001/2006
  2. Trope Maker: Walking with Beasts (cave lion); Prehistoric Park (cave hyena)

Dino-Sized Mammoths: the Columbian Mammoth and the Steppe Mammoth *

People often assume that mammoths were bigger than modern elephants. This is wrong if we're talking about the stock mammoth, the hairy, curly-tusked, tundra-dwelling woolly mammoth that everyone knows, but it is true about certain other mammoth species.

There were indeed many mammoth species in Real Life, and as a group they lived throughout most of the Ice Ages. The largest ones did challenge Paraceratherium for the title of largest land mammal ever, weighing 15 tons or more (comparable to a medium sauropod dinosaur), while a modern elephant and a woolly mammoth are "only" 4-6 tons (like a big ceratopsid or stegosaur).note  The most famous are the American Columbian mammoth (Mammuthus columbi — an older synonym is Imperial mammoth, Mammuthus imperator) and the lesser-known Asian Steppe mammoth (Mammuthus trogontherii), both the same size and very similar to each other. Other smaller members include Mammuthus meridionalis, the "southern mammoth" living in Southern Europe and West Asia, and Mammuthus africanavus, the African ancestor of the mammoths, living in Africa — the land from which mammoths originated. Giant mammoths of the columbi species have been discovered in famous U.S. tar pits like La Brea along with mastodons, saber-toothed Smilodon fatalis and many other mammals (prehistoric camels, giant ground sloths, giant wolves, pronghorns, American lions and so on), some of them still living today and others that went extinct after the Ice Ages.

The lesser popularity of the giant mammoths (despite their size) compared to the woolly one is probably due to their more "normal" appearance. They were more similar-looking to modern elephants than to the popular image of a "mammoth" because they were mostly hairless and with straighter tusks, though longer and more curved than every modern elephant — 3m long and weighing 200kg or more, they were the biggest/longest teeth known so far in the Animal kingdom. Giant mammoths inhabited relatively warmer climates, and their greater size was enough to preserve heat without a woolly coat. Think the mûmakil from The Lord of the Rings; okay, not quite that big (nor six-tusked), but generally similar in appearance. It's likely that the giant mammoths of the Ice Age steppes feared no predator as adults.

Mammoths as a whole actually thrived even after the end of the Ice Age, as there was more food available. Therefore it was almost certainly humans changing their habitat that drove them to extinction, evidenced by the fact that populations on islands lasted much longer than in the more easily-accessed mainland areas.

  1. Entry Time: Undetermined
  2. Trope Maker: Documentary media and gigantic skeletons in museums

Lilliputians or Cyclopes: the astonishing Dwarf Elephants *

Among extinct members of the elephant clan, don't forget some island-dwellers which lived in the Ice Ages and managed to survive until in recorded history: the oxymoronic dwarf elephants. Yes, they were REAL, and some were even sheep-sized.

Most of them lived in the Mediterranean islands; especially famous is Palaeoloxodon falconeri, the Sicilian/Maltese dwarf elephant. But others lived elsewhere; there were some dwarf mammoths living on the Channel Islands off southern California and on Wrangel Island off eastern Siberia (the latter managed to survive until about 4,000 years ago, contemporaneous with Ancient Egypt). All achieved their dwarfism probaby due to a lack of abundant vegetation and/or because they lost the necessity to defend against big mainland predators. These species were all driven to extinction by humans.

There's a theory that elephant and other proboscidean bones found in the Mediterranean were identified by the ancient Greeks as the remains of monsters, heroes and mythical animals from the Age of Heroes. Some of these bones were identified as cyclopes, due to the alleged misunderstanding of the elephant's nasal opening, placed where cyclopes would have their one eye. But... this is a myth on its own. No elephant skulls were found, as is often claimed. The fossils of Ancient Greece and Italy are far too fragmentary due to geological forces — earthquakes and volcanoes like the Sicilian Etna (where cyclopes were said to live, according to Homer's Odyssey) to allow something as fragile as a skull to survive intact.

  1. Entry Time: Undetermined
  2. Trope Maker: The oddness of their size and the association with the cyclops myth

    Pre-Ice Age Mammals 

A Run for the Future: the Horse Ancestors *

Now we'll go before the Ice Ages and meet the so-called "horse ancestors" (more precisely, the equid ancestors). Even though little-portrayed in more mainstream media, they are more familiar than other pre-Ice Age mammals because they have always been among the symbols of evolution, almost as much as the dodo is the icon of extinction. Horse ancestors weren't so cool-looking compared to most other extinct hoofed mammals: they mostly resembled their modern namesake at a glance. The most famous of these forerunners are, obviously, the least horse-like of them all (at least averting Bigger Is Better for once, as they were also the smallest): Eohippus ("dawn horse") and Hyracotherium ("mole beast"), often considered the same animal in the past.

An almost-unbelievable Science Marches On affair has actually encircled horses' evolution, despite its iconic role in popular science. This evolution was not as linear as shown in popular science books and elsewhere, though it's certain that equine ancestors progressively lost their digits from four or three to one for each foot, their heads became loftier to see farther, their limbs became nimbler to run faster, their overall size costantly increased, and their teeth progressively adapted from browsing forest vegetation to grazing the grass of the first grasslands to appear in the Miocene epoch (middle Cenozoic). Horse evolution has often been cited as a symbol of progress in general (also due to the historical fame of the horse as a "noble" animal), forgetting that modern animals are actually not "better" than the older ones only because they reached our time; every animal is adapted to the environment of its own period.

Of course, expect to see the small, basal ungulates Hyracotherium and Eohippus called "horses" anyway, despite their possibly having nothing more in common with horses than with tapirs or rhinos (the other living odd-toed ungulates); moreover, the "Hyracotherium-Eohippus" stew has included several other early ungulates, some of which were horse ancestors and some of which weren't. Sadly, systematics of the earliest ungulates is still a total mess.

Among confirmed horse ancestors, they make a sort of pun if read together. Mesohippus ("middle horse"), still small and with three fingers for each limb, was still a forest browser like Eohippus; Merychippus ("grazing horse"), also with three digits, was larger, more horse-like and grazed Miocene grasslands; Pliohippus ("more horse") was very similar to a modern equine in size and shape, and had the familiar one-hoofed toe. They are the most commonly-shown in media, but there were in reality dozens of other -hippus, almost all of them North American. Also worthy of note, however, are Hipparion (meaning "pony" in Greek) and Hippidion (lit. "little horse"), which break the theme of having -hippus as prefix instead of suffix; they also break the geographic rule, the first being an Old World critter, the second South American, both offshoots of the horse tree which didn't leave any descendants. Remember that all modern equines descended from North American ancestors.note  There were also a few exceptions of the "-hippus" rule, such as Anchitherium (another Eurasian offshoot but earlier than Hipparion or Hippidion: the latest two survived almost until today).

Oh, and: all the animals above were not only the horse's ancestors, but also the donkey's and zebra's — and also the lesser-known wild asses of Africa and Asia. Also note that despite their different appearances and habits, modern equids are so closely related to each other they're all placed in a single genus, Equus — while, by comparision, the modern five rhinoceros species are put in four different genera despite being all called "rhinos" in common speech: Diceros (the black rhino), Ceratotherium (the white rhino), Dicerorhinus (the Sumatran rhino), and the namesake Rhinoceros (both Indian and Javan rhinos). The genus Equus also includes two recent historical extinctions: the African quagga, a kind of zebra with incomplete stripes, and the European tarpan, one of the ancestors of the domestic horse. See below for them.

Whenever the putative "ur-horse" Hyracotherium/Eohippus shows up in media, expect it to be portrayed as a Red Shirt, usually falling prey to the giant flightless bird Gastornis/"Diatryma". Now that science has marched on, we know it's highly unlikely for the bird to have any interests in the small ungulates due to its probably herbivorous diet — though the "ur-horses" might nonetheless have been prey for other animals of the time, being "as large as a fox terrier", to use a classic description in paleo-books. Among fictional appearances, the most notable was perhaps Ray Harryhausen's cowboys-versus-dinosaurs film The Valley of Gwangi. On the other hand, confirmed horse ancestors like Mesohippus, Merychippus, Pliohippus, Hipparion, and Hippidion have little chance of ever appearing in non-documentary media.

  1. Entry Time: Undetermined
  2. Trope Maker: Portrayals of their evolutionary sequence in pop science books

Saber-Toothed Rhino: Uintatherium *

Not all fossil mammals that looked like rhinoceroses actually were, although they'll probably get identified as such in popular media. Among the most well-known is Uintatherium ("Uinta Mountains' beast"), found in huge numbers in several fossil deposits in the western USA (but also in China). Like several other early mammals, it was described for the first time during the Bone Wars — Marsh called it "Dinoceras", "terrible horn", but the animal was redesignated Uintatherium by Joseph Leidy. For some, however, it recalls more a hippo than a rhino because of its upper pair of tusks (hence the term "saber-toothed" above).

The uintathere is perhaps the most mistreated extinct mammal of them all. Expect somebody describing its appearance as "monstrous" or "scary". True, it had three pairs of giraffe-like "horns" and the two aforementioned upper protruding tusks, but, honestly, if Uintatherium were alive today, it would probably appear no more scary than an elephant, rhino, hippo or giraffe. Also expect a crack about its allegedly slow movement and its "tiny" brain (just like what happens to Stegosaurus), and just like the stegosaur, expect the writer to cite its slowness and/or stupidity as the reason for its extinction. Though they had comparatively short limbs and feet, similar in shape to an elephant's, this wouldn't necessarily have prevented uintatheres from running with speed if necessary — again, just like modern elephants, or rhinos, or hippos.

In Real Life, uintatheres were among the very first mammals to reach large sizes (about as large as a modern-day rhino), and their body plan was very successful at the time, as they roamed the northern hemisphere in huge numbers for millions of years in the early Cenozoic (in the Eocene epoch, to be precise), before being outcompeted by the even larger brontotheres and the first true rhinos. Uintatheres are usually depicted with rhino-like hide and sideways-pointing ears, a bit like a cow; sadly, we don't have remains of soft tissues from them, so we don't know how their skin and ears really looked.

Rather strangely, the famous franchise Walking with Dinosaurs doesn't mention uintatheres in any of its pieces, despite them having been among the most iconic early big herbivores in the Mammal Age. This could be seen as a missed opportunity to talk more accurately about these animals, also because uintatheres are scientifically better-understood than many other kinds of mammals from the Eocene epoch. In more mainstream media, on the rare occasions they appear, they are frequently mislabeled "prehistoric rhinos" or even ceratopsids.

  1. Entry Time: Uncertain
  2. Trope Maker: Educational media

Thunder Beast: Megacerops, aka "Brontotherium" *

Megacerops (formerly called Brontotherium... these Brontos just can't keep their names) is the prototype and the most well-known member of its group of mammals, the Brontotheres, ("thunder beasts"), also called Titanotheres ("titanic beasts").note  While Uintatherium was not related to any modern hoofed mammals (belonging to the extinct mammalian order called Dinocerata), brontotheres were Perissodactyls (odd-toed ungulates), thus distant relatives of horses, tapirs, and rhinos. The biggest brontotheres were almost Triceratops- or elephant-sized (larger than the biggest uintatheres), but still smaller than other giant herbivorous mammals of prehistory, like the giant mammoths and the guy we'll see in the next chapter.

Also first discovered during the Bone Wars (this time by Cope, and also officially described by Leidy with the older classical name "Brontotherium"), Megacerops had a more rhino-like appearance than the uintatheres, having one single "horn" on its nose, and no tusks. Unlike rhinos, however, brontotheres' protrusion was bony and not made of hardened hair, and thus its shape has preserved in fossils, unlike the latter. The horn of the North American Megacerops was forked with round points (rather slingshot-like), while that of its Asian cousin Embolotherium (the brontothere portrayed in Walking with Beasts, as a protective mother toward its dead calf) was shovel-like and not forked. Both had notably concave heads if seen from the side, with the eyes rather near the top, and also a big hump on their shoulders like a bison. They had four digits on the front feet and three on the back, like the ur-horse Eohippus and modern tapirs (true rhinos always have three toes on each foot). Like uintatheres, we don't know if brontotheres were hairy like bovines or "naked" like rhinos.

Like uintatherians, brontotherians roamed plains of the northern continents in huge numbers in the Early Cenozoic; compared with uintatheres, they tend to be portrayed as more active and faster-running in paleo-art, and more overall similar to true rhinos, but still rather unintelligent because of their smaller brains. Note, however, that small brains don't necessarily mean low intelligence; after all, dinosaurs are today well-known to have been intelligent and social creatures despite having even smaller brains than those of the brontotheres and uintatheres.

Brontotheres eventually went extinct perhaps because they weren't able to adapt to the diffusion of the first grasslands, which replaced their former food sources (scrub and non-grass herbs). Like uintatheres, expect to see brontotheres identified as rhinoceroses or ceratopsians in popular works. Despite this, it seems that their closest living relatives among odd-toed ungulates were the equids (horses and their kin), and not the rhinoceroses!

  1. Entry Time: Uncertain
  2. Trope Maker: Educational media

The Giant of the Giants: Paracera-Indrico-Baluchi-therium *

Here is Our Majesty, the biggest land mammal that ever lived; though some recent research indicates that some giant mammoths and, even more recently, the Asian straight-tusked elephant Palaeoloxodon namadicus were heavier, neither were as tall as Paraceratherium.

Its size was immense; it would make modern pachyderms look small in comparison. It was 5m up to the shoulders, as tall as a Brontosaurus; reached 7.5m/24ft when holding its head high, 5ft taller than the tallest giraffe; and weighed 15 tons, as much as three elephants or three T. rexes (some earlier estimates made it even heavier than that: up to 30 tons, as much as a brontosaur!). Contrasting with all this, it had a quite slender, elegant frame: a sort of muscular giraffe with a long straight neck, small hornless head, and long, slender limbs with three hoofs each, like a rhino — indeed, it was a close rhino relative. Its behavior was probably more giraffe-like than elephant- or rhinoceros-like, browsing the tree tops and walking with long steps like a giraffe. In short, it was the mammalian equivalent to a sauropod.

It lived in Oligocene, in the middle of the Cenozoic, later than brontotheres and uintatheres, and was only the biggest member of a whole group of extinct "rhinos" (or rather, rhino relatives): the hyracodontids, most of which were horse-sized and more similar to horses than to rhinoceroses. Our record-holder is also a prime example of I Have Many Names among prehistoric critters: now called Paraceratherium ("near-horned beast"), its traditional names are Indricotherium ("Indrik's beast") and Baluchitherium. This last name is the oldest, and most frequent in older books: it means "beast from Baluchistan" because was originally found in this Asian region (straddling Pakistan and Iran). Some think this critter went extinct because it became too large, and when its habitat dried out, it was unable to find sufficient food; but this is only a supposition.

A young "indricothere" is the main character of the third episode of Walking with Beasts. To indirectly illustrate how big the adults of its species are, the beginning of the episode shows its mother defending it just after it's born against a pack of Hyaenodons (see below), the latter being described as "as big as rhinos" but still appearing tiny next to the adult indricothere.

  1. Entry Time: Undetermined
  2. Trope Maker: Its size

Shovels, Forks, and Spears: Platybelodon, Deinotherium, & Anancus *

Let's return to extinct elephant relatives... there were A LOT of them in prehistory, not only woolly mammoths and American mastodons. Many of them were even cooler-looking than those two, though all (except the most primitive, such as Moeritherium below) shared a similar shape to a modern elephant, with long pillar-like limbs, short feet with round nails, short necks, small tails, and compact bodies. It was their mouths and teeths that were very different.

Gomphotherium, for example, resembled a cross between an elephant and a hippo, with its shovel-like lower jaws; Platybelodon was similar but took this to an extreme, with a huge mouth opening. Both belonged to the subgroup of proboscideans called the Gomphotheres, whose Platybelodon is the most commonly-shown member in media. Smaller than modern elephants, these animals were once classified within the "mastodons", but the latter has been found to be an artificial assemblage of archaic proboscideans, only united by one thing: they had a pair of tusks both in the upper jaw and in the lower. In Platybelodon, Palaeomastodon, Gomphotherium, Phiomia, and other "gomphotheres" (or similar forms), the upper ones were small and normal-looking; the lower tusks were placed on the tip of the jaw, and were flat and very untusk-like, possibly used to "gather" ground-level vegetation like a literal shovel. One gomphotherian, Amebelodon, had expecially long "shovels" on a relatively short mandible; others, like Stegotetrabelodon, had more pointy lower tusks.

Gomphotheres are often shown with bizarre flat trunks, but this is actually unproven — trunks have no bones, so they didn't fossilize. However, recent studies suggest gomphotheres had elephant-like trunks instead, as the tusks show signs of wear suggesting the animals were browsers as opposed to feeding on water plants as previously suggested. Interestingly, The Lord of the Rings's Mûmakil were shown in The Film of the Book with a pair of gomphothere-like lower tusks.

Other "mastodonts" were more similar to elephants, but even they would appear unusual to modern eyes: Anancus arvernensis, nicknamed the "European mastodon", with its straight, spear-like upper tusks (while the lower ones were almost missing), was similar in shape both to the more primitive American mastodon (Mammut americanum) and, convergently, to the more derived straight-tusked elephants of the genus Palaeoloxodon. Anancus was one of the closest relatives of the proper elephants and mammoths, but even closer (forming the sister clade outside the elephant-mammoth group) were the stegodonts ("roof-tooth"). Among them, Stegodon ganesa (named after the elephantine goddity Ganesha) had huge parallel tusks so close to each other that illustrations show the animal as obligated to keep its trunk to the side of both tusks!

A more primitive proboscidean lineage includes the genus Deinotherium ("terrible beast"). Unlike the mastodonts and gomphotheres, deinotheres had only two tusks like modern pachyderms, only they grew from the lower jaw like a two-pronged fork, and were curved downward. The function of these tusks is still uncertain, possibly stripping the bark from trees. Deinotheres lived throughout the Cenozoic era, and some managed to survive long enough to meet our first human ancestors in Africa.

Some Asian deinotheres were as big as the aforementioned giant mammoths: the largest one (Deinotherium giganteum) lived before the appearance of the australopithecines. This one is shown in Walking with Beasts, wrongly placed in Pliocenic Africa, oversized (described "as tall as a giraffe but 14 times heavier") and portrayed as a serious hazard for Australopithecus. Here a sexually-excited male tries to kill every "ape-man" he encounters (like modern male elephants often do while in musth), but this behavior is merely speculative, and since deinotheres were among the most distant elephant relatives among proboscideansnote , this may be unlikely. The African deinotheres were actually never bigger than a modern Asian elephant.

Like mastodons and gomphotheres, we don't how deinotheres' trunks or ears were shaped, but probably the trunk was cylindrical and as long as those of modern elephants (again, unlike what appears in WWB). Of course, we don't know for sure if ancient proboscideans could trumpet like modern elephants do. It's highly probable that at least true mammoths (and the strictly-related palaeoloxodonts) did trumpet, since they were extremely closely-related to modern elephants. Similarly, we don't know how much hair extinct proboscideans had on their bodies (if any); woolly mammoths and American mastodons of the genus Mammut are exceptions only because they have preserved soft tissue other than bones.

  1. Entry Time: 1864
  2. Trope Maker: Journey to the Center of the Earth

A Dinosaur of a Whale: Basilosaurus *

The first whales evolved early in the Mammal Age, in the Eocene, from terrestrial ancestors related to modern even-toed hoofed mammals (especially hippopotamuses). Most early cetaceans were medium-sized, but not Basilosaurus cetoides ("whale-like king lizard").

This one reached the length of a modern baleen whale or sperm whale: up to 20 m/60 ft, longer than most stock marine reptiles — though still much shorter than a blue whale (Balaenoptera musculus). In spite of its length, the basilosaur weighed "only" 20 tons, less than shorter modern whales like the 30-ton humpback (Megaptera): this because it was much more slender, to the point that it's sometimes described as "eel-like".

But wait, why does its name end in -saurus?!? Well, when first discovered, its elongated shape was misidentified as a mosasaur-like marine reptile: hence its strange, reptile-sounding name, meaning "king lizard". There was an attempt to rename it Zeuglodon to fix the error, but nomenclature rules prevented that.

Its first remains were discovered in North America in the 19th century, and more were found in the 20th century in Egypt, which at the time Basilosaurus lived was mainly occupied by a shallow sea. For long the basilosaur was one of the few early cetaceans known by science, together with Protocetus, Dorudon, and others. Pakicetus, Ambulocetus and other "archaeocetans" were discovered only during or after The '80s, along with the more modern-looking toothed whales Odobenocetops and the huge Livyatan. In Basilosaurus' time, all whales were still active hunters, like modern orcas and sperm whales, but still with differentiated teeth: the anterior ones pointed, the posterior serrated, an old legacy which betrays their origins from land mammals.

Basilosaurus with its size was arguably the top predator of its oceans, potentially preying on every other creature of its world — like mosasaurs, plesiosaurs, and ichthyosaurs did in the Dinosaur Era, and like the armored fish Dunkleosteus did before dinosaurs evolved. However, it may have been a less able swimmer than modern cetaceans because of its primitiveness. Since soft remains have not been preserved, we don't know if the basilosaur's tail fluke was already identical to modern whales/dolphins, or smaller and/or shaped differently, nor if it had a dorsal fin. Unlike modern whales, it retained the tiny remnants of its hindlegs (which were maybe used to lock mating pairs' bodies together), as shown in its fossils.

Basilosaurus has been a recent hit in documentary media since the 1990s and especially the 2000s; see Walking with Dinosaurs for an example. But it hasn't received the same amount of attention in broader popular culture as other giant "leviathans" of the past (Elasmosaurus, Megalodon, Mosasaurus). In 2001's Walking with Beasts it's shown initially throwing a shark in the air like modern orcas do often with sea-lions, but then is shown struggling for survival in the empty-of-prey seas it swam in. In 2003's Sea Monsters, it's depicted with the same appearance as in the former, as the fourth most dangerous sea predator of prehistory after Carcharodon megalodon and two stock sea reptiles, the "giant mosasaur" and the famously oversized Liopleurodon. Note that the more modern whale Livyatan was not yet discovered when the program was broadcast (it was found only in The New '10s); this explain its absence in the show despite being even more powerful in Real Life than Basilosaurus, as it's thought to have hunted large baleen whales (see also the fish folder below).

  1. Entry Time: 2001
  2. Trope Maker: Walking with Beasts

Badasso-Therium: Andrewsarchus *

Andrewsarchusnote  ("Andrews' ruler") is one of the most enigmatic mammals, from the first part of the Cenozoic (the Eocene period) like the uintatheres and the brontotheres. As its complete name suggests (Andrewsarchus mongoliensis) it was discovered in Mongolia, during the same American expedition led by Roy Chapman Andrews (hence the name) in which Velociraptor was first found.

Only one single skull is known, about 1m/3ft long and vaguely wolf-like. Andrewsarchus has classically been called the largest carnivorous land mammal ever (hence our nickname "Badasso-Therium"). But there isn't any hard proof of that; it might have been omnivorous instead, and of course its overall size can only be guesstimated. It is often depicted as a scavenger of large herbivores' carcasses, but has also been shown as an active hunter. Andrewsarchus was traditionally considered to be closely related to the much smaller Mesonychids, and depicted with small hooves on its feet like the latter. However, later phylogenetic studies indicate that it might have actually been a close relative of the Entelodonts (large even-toed ungulates resembling boars in shape), though obviously any phylogenetic placement is only tentative at this point.

In Walking with Beasts, Andrewsarchus is shown with the overall shape and color of a gigantic civet (a small African carnivore), and crushing a sea turtle with its jaws that was crawling on the beach to return to the sea after having laid its eggs, but obviously this is another invention of the show without paleontological proof. According to modern hypotheses, the real Andrewsarchus was also smaller than it appears in the show.

  1. Entry Time: 2001
  2. Trope Maker: Walking with Beasts

Elephant or Pig?: Moeritherium *

How did elephants look when they were just starting to evolve? Not really like pachyderms. The most classic ur-elephant is Moeritherium, found in Egypt in the Eocene period. It's been called "the first elephant", but some proboscideans were even more basal, ex. the fox-sized Eritherium, the medium-sized barytheres and numidotheres, and perhaps even the giant Deinotheres above.

Moeritherium ("Lake Moeri's beast") didn't resemble an elephant at all. No bigger than a large pig, with short tusks, hippo-like limbs and (possibly) pig-like snout, it was also more like a tapir than an elephant in appearance. Living in a mixed aquatic-terrestrial habitat, the moerithere is often thought to have been an amphibious animal a bit like a modern hippopotamus, but its actual lifestyle is still unknown. In Walking with Beasts it's shown as a potential prey for the giant early whale Basilosaurus, which however fails in its attack.

Moeritherium lived alongside the much bigger horned herbivore Arsinoitherium in the same habitat. Like the ur-horse Eohippus, Moeritherium has often been shown in textbooks as the start of the evolutionary trip of its group, the Proboscidea, passing through deinotheres, mastodonts, gomphotheres, stegodonts etc. and ending with modern elephants and mammoths. Its look tends to vary a bit in classic paleo-art: some depict Moeritherium as a sort of boar-thing with dense hair, while others show it naked-skinned and more looking like a hippopotamus, but always with an elephant-like short trunk.

  1. Entry Time: Undetermined
  2. Trope Maker: Textbooks portraying elephant evolution

The Pharaoh's Megahorn: Arsinoitherium *

Together with Andrewsarchus this has always been one of the most enigmatic prehistoric giant mammals, despite (unlike Andrewsarchus) being known from complete skeletons. It wasn't a true elephant relative like Moeritherium (being outside the order Proboscidea), but was perhaps the most peculiar, and at the same time the most striking-looking, among the prehistoric "pseudo-rhinos".

Arsinoitherium means "Arsinoe's beast": Arsinoe was an ancient Egyptian queen, hence the nickname "Pharaoh's Megahorn" we have given it here. It is sometimes misspelled "Arsinotherium" without the "i" in the middle because so it's easier to pronounce. Arsinoitherium lived in the Eocene epoch, a bit later than Uintatherium but earlier than the brontotheres, and was of similar size and body shape to the former. Once, both Uintatherium and Arsinoitherium were placed in the same mammalian order, the "Amblypods" ("short foot") together with the lesser-known Pantodonts, but Science Marches On and recent research says otherwise: Arsinoitherium was an Afrothere like elephants (though not one of their ancestors), while the uintatherians and the pantodontians were probably Laurasiatheres, closer to true ungulates but also to carnivorans and bats (and, more distantly, to rodents and primates).

Arsinoitherium's most visible peculiarity is by far its huge, yet lightweight, hollow "quadruple-horn", which rivals in size and oddity the crests of the hadrosaurian dinosaurs or the frills of the ceratopsians. This thing was sometimes even asymmetrical (like caribou antlers), with one main branch longer than the other: for some, it's a bit similar to a cross between a brontothere's forked horn and a Irish elk's antler. The exact purpose of this huge headgear has been a headache for experts. Defense? Courtship device? Or even thermoregulation? We don't even know if only males had it.

The same size as modern rhinos and hippos, this animal has often been also described as a cross between the two, because of its short robust legs ending with "hooflets", and probably amphibious habits. Indeed, the arsinoithere lived along the coasts bordering the shallow seas which covered what's now Egypt together with the ur-elephant Moeritherium (possibly amphibious as well), and probably ate both land vegetation and sea plants.

Both Arsinoitherium and Moeritherium were portrayed in the Walking with Dinosaurs series (though in different spinoffs), in the episodes in which the predatory whale Basilosaurus is the main character. In the show, Arsinoitherium is shown with a short trunk like a tapir (and thus looking like simply a bigger, horned version of the Moeritherium), but the trunk is improbable, because the shape of the nasal opening of the skull doesn't show points of attachment for a trunk, even a small one.

Finally, let's mention a lesser-known arsinoitherian peculiarity: its teeth were more numerous than most four-legged mammals (though similar to cetaceans), and not clearly differentiated into incisors, canines, and molars. This mammal is so strange that it is placed in its own mammalian order: the Embrithopods, fairly close to proboscideans, sirenians, hyraxes, and the extinct Desmostylians.

  1. Entry Time: Undetermined
  2. Trope Maker: Its horn

Gorilla-Horses or Sloth-Bears: Chalicotherium & Moropus *

Chalicotheres are typically regarded as some of the best examples of Mix-and-Match Critter among prehistoric mammals, even more than Arsinoitherium. They had the head of a horse, the body shape of a gorilla, and bear-like forelimbs with hooked claws for pulling down branches or excavating the soil in search of roots: some nickname them sloth-horses.

Like sloths, chalicotheres probably weren't especially fast runners compared with other ungulates because of their frame (yes, they were ungulates!), but were nonetheless powerful and muscular animals and arguably not an easy target for predators, unlike what's shown in Walking with Beasts. We don't know how long/dense their hair was, as with almost all prehistoric mammals (except those found frozen in ice or stuck in ancient tarpits, which have often preserved some remains of skin).

A very successful group of hoofed mammals, chalicotheres, despite their un-ungulate-like appearence, were perissodactyls or odd-toed ungulates, distantly related to horses, rhinos and tapirs (like the aforementioned brontotheres), but their body plan was quite modified from the original ungulate shape — more so than any other ungulate except for obviously the cetaceans, which descend directly from land artiodactyls — with the nails of some chalicotheres more resembling claws than hooves. Chalicotheres roamed for a long time in most continents, and some think the famous "Nandi bear" that allegedly lives in modern African rainforests is a surviving chalicothere.

The two most well-known family members are the North American Moropus and the Asian namesake Chalicotherium, both from the middle of the Cenozoic. The former (lit. "silly foot" because its nails had a split in the middle) was the more horse-like in appearance of the two, with forelimbs not much longer than hindlimbs, and probably walked like a normal ungulate. The latter (half again taller than a human) had forelegs twice the length of its hindlegs, and its "hands" had huge curved sloth-like claws which obliged it to literally knuckle-walk like a gorilla to protect them against damage, just like modern giant anteaters do (and probably most extinct ground sloths as well). Similar to Chalicotherium but smaller was the European Anisodon.

An unnamed "chalicotere" (arguably Chalicotherium itself) is portrayed in the third episode of WWB as a rather torpid animal with a very giant panda-like face, that makes it look "cuter" or more harmless than other, more badass popular representations of chalicotherians. Here, it mainly appears as simple fodder for other large mammals of the time — the predatory Hyaenodon and the scavenging entelodonts, to be precise. Another species, the African Ancylotherium, was shown in the fourth episode of Beasts as an inoffensive, easily-frightened neighbor of the australopithecines. This one in Real Life was closer to Moropus than to Chalicotherium, and was one of the last surviving genera of chalicotherians: it reached the Early Pleistocene epoch, before ultimately going extinct probably due to the changing colder climate conditions (not counting the improperly-named cryptid Nandi bear, of course).

  1. Entry Time: undetermined
  2. Trope Maker: documentary media

Terminator Pig or Hippo-Pig: Daeodon *

Let's return to the even-toed ungulates: alongside the giant Deer Megaloceros, there was another, very different-looking kind of extinct artiodactyl that has achieved some popularity: the Entelodontids.

They were among the several prehistoric artiodactyls that resembled boars in shape and possibly habits. Entelodonts ("complete teeth") had the same overall body plan as pigs, and were once thought to be closely related to them, but have recently turned out to be closer to hippos and whales. They were bison-sized at the most, and the bony knobs on their heads and jaws made them resemble giant warthogs. But their tusks were straight like those of peccaries, much smaller than a warthog's or a babirusa's, and didn't protrude out of the mouth. The exact shape of their snout is unknown, but it's unlikely that they had pig-like noses as sometimes shown, especially given the recent theories which classify them as hippo relatives.

The food habits of these critters are still unclear: they might have been scavengers that drove away small predators from their kill, but also ate vegetation, and might even have been active hunters sometimes, a bit like the omnivorous modern wild boars. Thanks to their strong jaws, they would've been able to crush the bones of corpses to reach the softer marrow inside. The bony knobs on their heads may have protected them against rivals during fights, as shown by "scars" on the skulls of some specimens left by the canines of their conspecifics — they probably could open their mouths wider than boars (but not to the same degree as hippos).

North American Daeodon (also called Dinohyus, "terrible pig") is the largest and historically the most-often depicted entelodont, living alongside the chalicothere Moropus in the Miocene. Walking with Beasts showed an unnamed Asian relative living alongside the "indricothere", and altered its appearance to make it scarier, exaggerating the opening of its mouth (it's given no cheeks at all, more similar to a cetacean than to a hippopotamus) and also making it particularly noisy and overly aggressive toward every animal it encounters. Here the entelodonts also appear almost-naked like a warthog or babirusa, but we don't know if in reality entelodontids were mostly covered in bristles like a wild boar or peccary, or not.

Archaeotherium ("ancient beast") and the prototypical Entelodon were also Asian. The former was one of smallest and most ancient entelodonts, the size of a modern boar; the latter was more similar in size to Daeodon. Extinct true pigs of the Suid family included Kubanochoerus, Metridiochoerus, and others: see Prehistoric Life - Mammals for these.

  1. Entry Time: Late 1980s
  2. Trope Maker: Dino-Riders (identified as "giant warthogs")

Spectacular Horns: Sivatherium & Synthetoceras *

These mammals were also artiodactyls, but similar to deer or moose in shape. Sivatherium giganteum was one the biggest ruminants ever; the largest species was heavier than an average bison, and 2.5m tall at the shoulder — as massive as a giraffe, though less tall.

Sivatherium was indeed related to giraffes, but little resembled them. Stocky and short-necked, it had "antlers" quite similar to a moose's, or a pronghorn's if you prefer; these "antlers" were true ossicones, 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. Some think it's represented in ancient cave paintings in the Sahara and India; Sivatherium lived both before and during the Ice Age, going extinct only recently, and roamed across the Old World (where humans underwent most of their evolution). Among the other Giraffids, only two animals have survived to today: the proper giraffe and the smaller okapi, both exclusive to Africa.

Synthetoceras is more enigmatic. From Miocene North America, it resembled in shape a common deer or antelope, but had three horns placed on the head surprisingly similarly to a Triceratops, and the nasal horn was long and two-pronged like that of "Brontotherium" (Megacerops). It was actually more related to camelids than to deer and antelopes, and since camelids also ruminate, Synthetoceras probably did the same. As with the above-mentioned Megaloceros, Synthetoceras may be wrongly identified as a true deer in media.

  1. Entry Time: Undetermined
  2. Trope Maker: Popular science books

Early Hooves: Coryphodon & Phenacodus *

Among the earliest mammals traditionally classified among the "ungulates", these two have been among the relatively most common in popular paleo-media.

Coryphodon was one of the biggest mammals of the Eocene, the size of a large cattle (but still smaller than Uintatherium, the brontotheres, and Arsinoitherium) and lived roughly alongside the famous bird Gastornis. It was very similar to a hornless uintathere, with small tusk-like canines like the latter, and was once classified together with them in the same order of mammals, the "amblypods"; today Coryphodon is considered a highly derived member of the Pantodonts (the first large, plant-eating land mammals). Though smaller than other later herbivorous mammals, as an adult the coryphodont probably feared no predators.

Phenacodus was much smaller (about the size of the better-known Eohippus), and also lived in the Eocene. It was very generic, with dentition suited for various foods (probably was a mainly-herbivorous omnivore), and with an archaic long tail typical of the earliest "hoofed mammals". It was probably a relative of the perissodactyls or even a true primitive member of this group. When the giant bird Diatryma/Gastornis was believed to have been the superpredator of the Early Cenozoic, Phenacodus was considered one of its possible prey, just like Eohippus. It was once considered a herbivorous member of the Condylarths (see further).

  1. Entry Time: Undetermined
  2. Trope Maker: Media portraying the early Mammal Age

Meat-Eater, but not Carnivore: Hyaenodon *

Although "carnivore" literally and commonly just means "meat-eater", in cladistics it refers to members of the order Carnivora (the less ambiguous term for members of this group is "carnivoran"). The vast majority of large carnivorous land mammals are carnivorans — bears, canids, cats, hyenas — but there are exceptions: not counting marsupials like the pseudo-felines Thylacosmilus & Thylacoleo (see further), there were also the Creodonts.

Creodontians were related to true carnivorans, but were more primitive. They had smaller brains (like most early mammals that lived before the Ice Age), and with different cheek teeth than true carnivorans; they nonetheless often had powerful jaws with a stronger bite than modern carnivores (Creodont means "meat tooth").

Hyaenodon (often misspelled "Hyaenadon"), the most iconic and portrayed creodont in media, has a name that is not mere coincidence: despite being more similar in shape to a short-limbed, long-tailed wolf, it had the typical crushing jaws/teeth of a hyena — hence the name, "hyena tooth". Scientists tended to depict the hyaenodont as a scavenger because of this, but since Real Life spotted hyenas are more often active hunters, contrary to popular belief, the bone-crushing jaws of their ancient namesake don't rule out more predatory behavior.

Indeed, in the third episode of Walking with Beasts, an oversized Hyaenodon (the biggest species in reality was no larger than a bull, and not "as big as rhinos" as said in the show!) is the main predator of the story, capable of killing with extreme ease two-ton chalicotheres, and digesting even their teeth — based on modern hyenas, which can dissolve bones in their stomachs. But these claims are mere speculation: note that most modern meat-eating mammals can't digest bones, much less enamel-covered teeth. It may also have been shown as more agile than it was in Real Life, since a large specimen of Hyaenodon was arguably rather slow-moving compared with modern wolves, cats, or hyenas, not only being heavier but also having shorter feet. In the show the hyaenodon appears as a dog-like critter with a look kind of similar to the famous Thylacine or Tasmanian wolf, and growling in the same manner as an Angry Guard Dog when approaching the young indricothere in a pack — again, there's no proof of wolf-like pack behavior or even growling. In short, it's portrayed like a gigantic cross between a wolf and a hyena, but in reality it was related to neither. Note also that other creodonts were even bigger than the hyaenodont, ex. the one-ton Megistotherium.

  1. Entry Time: 2001
  2. Trope Maker: Walking with Beasts

Cats and Dogs Imitators: Eusmilus & Amphicyon *

Other extinct mammals were true carnivores, but deceptively looked like members of modern families of the carnivorans (felids, canids, ursids, hyaenids etc.).

Eusmilus ("true saber"), for example, was an almost-perfect copy of a saber-toothed cat of the Felidae in shape, size, and anatomy, but actually belonged to a distinct lineage of feliforms, the Nimravids. It lived earlier than Smilodon and the other true sabertooths, and had shorter legs but particularly long sabers, almost as long as Smilodon's and longer than other true saber-toothed cats like Homotherium or Megantereon. Its behaviour and predation style is uncertain; some say Eusmilus was less intelligent than smilodonts and their kin, but that's only a guess.

Amphicyon means "half-dog", an apt term because it was related to canines but was not one of them — it's the namesake of its own family of carnivores, the caniform Amphicyonids. Its size and appearence were rather in the middle between a long-tailed wolf and a slender bear; according to recent classifications, the Amphycyonids were closer to the bears than to the dogs, and were also related to raccoons and mustelids (weasels, martens, badgers, otters, wolverines etc.). It's uncertain if it was a pure carnivore like a lion or an omnivore like most bears. Like Eusmilus, Amphicyon existed in the middle of the Mammal Age, in the Neogene period, well before the Ice Ages.

  1. Entry Time: Uncertain
  2. Trope Maker: Popular media about Cenozoic animals

Small bipedal Bug-Eater: Leptictidium *

Leptictidium, despite its look, was totally different from the the two rodents Castoroides and Epigaulus described in the previous folder: it was a smallish (the size of a medium dog), short-armed and long-legged "insectivore" found in Europe from the start of the Mammal Age, once put in the Insectivorans or in the equally artificial group named Proteutherians ("first eutherians"); today is placed in the eponymous Leptictidians.

It's probably the most famous of those mammals which were preserved in the German Messel Tarpits (see Prehistoric Life - Mammals), and it's always been one of the most peculiar of them all — others include early pangolins, hedgehogs, early bats, primitive ungulates, small carnivores, and ancient primates. Arguably because of its Mix-and-Match Critter looks, it was chosen as the main character of the first episode of Walking with Beasts, set in Eocene Germany.

Leptictidium was not related to any modern mammalian group, not even modern "insectivores" like hedgehogs, moles or shrews, and looked more like a small kangaroo or a jerboa. But we don't know if it actually hopped like a kangaroo like in WWB or ran like a miniature dinosaur; some portrayals prefer the first choice, others the second. Anyway, judging from its teeth, it was arguably a predator of insects or small vertebrates. Additionally, we don't know if it had a mobile nose like a shrew.

  1. Entry Time: 2001
  2. Trope Maker: Walking with Beasts

The Ancestor of Whales?: Mesonyx *

Mesonyx ("middle-nail") was similar in size and shape to a strange dog or hyena with a big head and long tail, but with hoof-like nails like Phenacodus or Eohippus. It was one of the first mammalian predators/scavengers comparable in size to a human — but still smaller than the allegedly meat-eating bird Gastornis; thus it was once considered an underdog of the latter. But its fame is due mainly to the fact it and its relatives (together called Mesonychians) were once thought to have been the ancestors of the cetaceans: it was said they roamed the coasts in search of dead fish and carcasses, and that this was the kick-off of the evolution of whales.

Together, Mesonyx, Phenacodus and other less-known early mammals were put together in the artificial grouping named the Condylarths. Interestingly, Andrewsarchus has traditionally been depicted as an oversized Mesonyx because was considered a giant relative of the latter. This could explain why the Walking With Beasts producers decided to show it near the shore in search of turtles in its first relevant scene.

  1. Entry Time: undetermined
  2. Trope Maker: Popular books depicting whale's evolution

When Whales Were Wolves: Pakicetus & Ambulocetus *

All mammals were small and rodent-shaped in their evolutionary beginnings. Some became larger and more derived after the extinction of the dinosaurs, but none to the same level as whales.

The first cetaceans probably spent much of their time on land, feeding on dead fish and drowned animals. Pakicetus ("Pakistan whale") is the traditionally most-portrayed of them. Found in Pakistan in the late 20th century, it was still four-limbed and looked nothing like a whale, but had a long tail (the typical archaic trait of the earliest ungulates), anticipating the powerful muscular tail of later cetaceans. It was already a good swimmer, but probably swam using its legs like land mammals and seals — not yet its tail, which arguably acted as a rudder. Its nostrils were still placed at the top of its snout like a land mammal, but its ears already showed specializations for hearing underwater like a modern whale (we don't know if it had still external ears or had already lost them). This combination of land and water adaptations makes Pakicetus another excellent example of a Mix-and-Match Critter.

Discovered only in the early 1990s (a decade after Pakicetus), Ambulocetus natans (lit. "walking whale") was also found in Pakistan. It was similar to the former but bigger, with shorter limbs, palmated feet, and a more powerful tail. At the time of its discovery it was celebrated in media as the "missing link" between the still terrestrial-looking Pakicetus and more modern whales like Basilosaurus. Maybe because of this fame, Ambulocetus was chosen as the archetypical early whale in 2001's first episode of Walking with Beasts, but was incorrectly shown in Europe instead of Asia and interacting with critters known from the German Messel Tarpits like Leptictidium above. In the show, Ambulocetus was portrayed as a hairy croc-like swimmer and an ambush-hunter of small land mammals, like a modern Nile crocodile; actually, like Pakicetus, its precise appearence and lifestyle is unknown. It may have been a specialist fish-hunter, like modern otters.

Both these early whale-ancestors had the same two tooth shapes in their jaws as Basilosaurus, but being descendants of true ungulates, Pakicetus may not have been completely zoophagous, unlike the most fishy basilosaur. Recent research seems to indicate, however, that Ambulocetus was already fully aquatic, thus not really deserving the name "walking whale", but nomenclature rules being what they are, it's stuck with it.

  1. Entry Time: End of the 20th century
  2. Trope Maker: Documentary media about whale evolution

Mammals Win: Plesiadapis, Purgatorius & Didelphodon *

Plesiadapis was an archaic primate that lived at the start of the Cenozoic, similar to a lemur but with gnawing teeth like a rodent. Purgatorius (named after Purgatory Hill) was a small shrew-like placental that lived both before and after the Great Dinosaur Extinction, considered a distant primate-relative. nt. Didelphodon ("possum tooth") was, as its name suggests, an extinct relative of modern marsupials.

As the latest two were both found in the Hell Creek formation, they would've coexisted with Tyrannosaurus rex and Triceratops. Purgatorius has been famous because it used to be considered the earliest primate or primate-ancestor, often imagined similar to the modern tree-shrew in look; so is frequently-mentioned in the sources talking about the evolution of humans together with the more "evolved" Plesiadapis.

Didelphodon used to be a very obscure animal until year 1999: it became abruptly famous in that year when was portrayed in the WWD “Death of a Dynasty” episode as the annoying mammal stealing eggs. In the show, and official science, it was depicted as a badger/tasmanian devil like creature, but now is known to resemble and behave more like an otter, so the WWD portrayal is very inaccurate now. Yet it is still commonly seen as the main “Hell Creek mammal” together with Purgatorius. The group Didelphodon belongs to (Stagodontidae) went extinct 66mya with the dinosaurs, though the Early Cenozoic Eobrasilia ("early brazilian)" might be a member of the group.

  1. Entry Time: undetermined for Plesiadapis and Purgatorius; 1999 for Didelphodon
  2. Trope Maker: the discussion about human origins (Plesiadapis, Purgatorius); Walking with Dinosaurs (Didelphodon)

    Historically-Extinct Mammals 

Cattle Ancestor: the Aurochs *

This animal is not strictly prehistoric, but like the Dodo bird, went extinct in the Modern Era thanks to humans.

The aurochs (whose scientific name, Bos primigenius, means "primeval ox") was the biggest European land mammal together with the wisent (European bison) among those that survived the Ice Ages and managed to reach recorded history. It's a classic imprecision in media to say the aurochs was a prehistoric animal; this is not completely wrong, since it was widespread during the Ice Ages both in Europe and in Asia alongside woolly mammoths, woolly rhinos, cave bears and so on, but strictly "prehistoric" creatures are those that disappeared before the dawn of civilization (roughly 4000 B.C.).

Also known as the urus or the ure, the aurochs was a powerful animal but sometimes oversized in media: it was actually no bigger than the modern wild bovines. It roamed ancient forests, and was probably a browser/grazer. Its predators would have included cave lions, cave hyenas, modern wolves and brown bears, from which it defended itself with its robust horns and rapid charges — it was a fast runner despite its weight. It gave birth to one calf per time after a long gestation, and like all modern ruminants it chewed its cud to better digest plant matter.

The aurochs was already known by prehistoric European people, the Neanderthals and the Cro-Magnons (aka the first European Homo sapiens), who often depicted it in cave art — Lascaux in France and Altamira in Spain, for example — together with many other extinct and extant animals they hunted. Ancient Celtic, Greek, Roman and Medieval peoples too knew the animal, often mentioning it in literature as a particularly dangerous wild game, or as a symbol of power, or (in the case of the Celts) even as a divinity. Some peoples painted images of it on their war shields.

But since Medieval and Renaissance times, reduction of the forests it lived in, coupled with extensive hunting, made the aurochs rarer and rarer, until it disappeared definitively in the 17th century together with another large European animal, the tarpan horse (see below). The European bison managed to escape the same fate only thanks to a bunch of individuals saved Just in Time in one small forest between Poland and Belarus, in the 1800s.

The aurochs has left an extremely crucial legacy in modern times, however: around the end of the Ice Age, 10,000 years ago, some aurochs (yes, not aurochses or aurochsen) were domesticated by humans. This domestication was one of the most successful and important ever: their descendants became the bulls, oxen, and cows (Bos taurus), whose contribution to mankind's development, as everyone knows, has been fundamental.

Interestingly, there are very archaic cattle breeds that strongly resemble the aurochs, and some have been reintroduced in ancient European forests (ex. Bialowieza between Poland and Belarus, the same place that saved the last European bison) — resurrecting, at least partially, the memory of the ancient presence in Europe of their wild ancestor.

  1. Entry Time: European Antiquity
  2. Trope Maker: Undetermined (maybe Pliny the Elder or Aristoteles, both naturalists)

Horse Ancestor: the Tarpan *

The tarpan was a true wild horse (Equus ferus: "ferus" = wild, "Equus" = horse in Latin) that lived in Europe until the Modern Age, but was depleted by humans along with the aurochs — however, some archaic domestic horse breeds resemble the tarpan, and are visible in some European parks, just like cattle breeds that resemble their own wild ancestor.

The tarpan was a smallish, greyish horse very similar to the living conspecific Przewalski's horse (see below) and the equally rare wild asses of Asia and Africa: all of them combined a donkey-like mane with normal horsy tail. Its behavior was no different from modern wild equids, roaming grasslands and steppes in large herds to defend itself from predators. The tarpan too was depicted in prehistoric caves like the aurochs, and mentioned in classic European literature throughout the centuries as "the wild horse". Both the aurochs and the tarpan arguably shared the same voice (mooing and neighing respectively) as their domestic descendants, and both had a quite long gestation of 10-11 months, but the tarpan being an odd-toed ungulate didn't ruminate like modern equines and unlike bovines.

  1. Entry Time: Uncertain
  2. Trope Maker: Mentions in classic literature

Zebra-Horse: the Quagga *

All modern equines are so similar to each other in anatomy that they are all included in a single genus: Equus. This genus, as mentioned in the "horse ancestors" chapter, originated on the North American prairies during the Pleistocene (the Ice Age), and then spread throughout Eurasia toward the Bering strait, and later to Africa through the Sinai passage. Modern "wild" (or rather, feral) horses of North America, Asia, Australia etc. actually descend from domestic horses returned to the wild — except for the Mongolian Przewalski's horse (another subspecies of Equus ferus, the original wild horse), probably extinct in nature but still surviving in few zoos and parks.

The quagga (Equus quagga) was an unusual-looking kind of zebra with stripes only in the front part of its body. It was closely related to the modern plains zebra (they may even be the same species), but unlike the latter it lived only in the southernmost part of Africa - making it the southernmost kind of modern equine together with the once critically-endangered Mountain Zebra. The quagga's lifestyle was probably identical or very similar to the surviving zebras, but sadly, it was overhunted by European settlers in recent centuries together with some kinds of South African antelopes it shared the land with, notably the Bluebuck. Being less skittish and more robust than other zebra species, the quagga was probably well-suited for domestication, making it all the more wasteful that it was instead hunted to extinction. The quagga is mentioned in the first Jurassic Park book as an example of a recently-extinct species of animal that could possibly be cloned in the park.

  1. Entry Time: Uncertain
  2. Trope Maker: Embalmed mounts in natural history museums and animal books

Gentle Giant: the Steller's Sea Cow *

The story of this mammal is a particular Tear Jerker. The Steller's sea cow (Hydrodamalis gigas, also "Rytina gigas" in older systematics) was not a cow, despite the name, but a giant relative of modern manatees and dugongs — that is, a large Sirenian (and not a cetacean at all, but a distant relative of elephants).

9m long and weighing as much as a large African elephant, and much more than an elephant-seal, a walrus, or a true manatee (genus Trichechus), it was similar to the latter in shape but with smaller head and flippers, rougher hide, and the same whale-like fluke as a dugong (genus Dugong), which it was more closely-related to. It used to swim slowly and peacefully in the cold waters of the Northern Pacific coasts along with sea otters and sea lions, grazing kelp and seaweed with its unusual toothless jaws. Like modern manatees it gave birth to one offspring at a time after a long gestation, and thus was not an especially fast breeder.

When the first European settlers (among them the researcher Georg Steller, who first described it, hence the common name of the animal) arrived at Wrangler Island and the nearby seas in the 1700s, they first reported its existence to the Western world, finding that the sea cow was already rare at that time, with only few thousand individuals left. Unfortunately, hunters and whalers soon saw it as a great source of food and animal grease because of its size, and also noted that it was a relatively easy animal to kill, more so than the bigger and/or faster cetaceans nearby. The result was that the giant sirenian went extinct merely 27 years after its discovery — while most other historically-extinct mammals and birds were depleted at least one century after Western people learned about them.

Today, the most endangered sea mammals include animals much smaller than the sea cow, but still large compared with many other mammals: among them, the Chinese river dolphin, the Californian porpoise, and the Mediterranean and Hawaiian monk seals (the Caribbean one is already gone). Among historically-extinct land mammals we can mention the Mediterranean pika, a short-eared relative of rabbits and hares.

  1. Entry Time: Uncertain
  2. Trope Maker: Documentary media

Extinct or Not?: the Thylacine *

This mammal is not strictly prehistoric either, to the point that it could actually still be alive today. Nonetheless, like the animals above, it has left several fossils from prehistoric times.

In popular media the thylacine (Thylacinus cynocephalus, lit. "pouched dog with a dog head") is known as the marsupial wolf, the Tasmanian wolf, or the Tasmanian tiger. Wolf, because its shape and size effectively recall that of a long-tailed, round-eared wolf — to the point that it's often cited as an example of convergent evolution with true canids. Tiger, because of its coloration, which was vaguely similar to the eponymous cat but with a simpler design: wide black stripes on the rear of its back upon an otherwise uniformly brownish body.

But this mammal is/was neither a canine, nor a feline; it was of the same systematic group as kangaroos or koalas! More precisely, it was related with smaller still-living carnivorous marsupials of Australia like the Tasmanian "devil" (Sarcophilus harrisii), the weasel-like quolls (Dasyurus), the ant-eating Numbat (Myrmecobius fasciatus), and several mouse-like animals nicknamed "marsupial mice". It's called Tasmanian because Europeans found it only on the island of Tasmania, but in the past the thylacine also lived on mainland Australia — until it was dethroned by the dingo, an ancient breed of domestic dog brought in the Land Down Under by the ancestors of Aborigines thousands of years ago.

Like the dodo, the aurochs, the moa, the elephant bird, the great auk, the passenger pigeon, the Steller's sea cow, the quagga, the tarpan, etc., the thylacine is often and rightly mentioned as an example of Man's irresponsibility. This also because its possible extinction happened only in the 20th century — old black-and-white films exist showing the animal alive in zoos, and reveal that it could open its mouth rather widely. It was hunted to extinction mainly because Tasmanian farmers of the 19th and 20th centuries considered it a serious peril for their livestock, expecially their sheep but also their poultry. This was only partly true, however, because the animal mainly hunted wild game. The alleged ferocity of the thylacine was notably exagerrated by several reportages and citations in books and encyclopedias as well. These accusations of viciousness and perilousness (even toward humans) were among the excuses that led to it and its placental namesake, the grey wolf (Canis lupus) and the tiger (Panthera tigris) being driven to endangerment or extinction from many countries worldwide.

Sometimes, alleged sightings of "the last thylacine" occur in newspapers, but for now none of them is confirmed. Among portrayals in popular media, this animal has made appearances in 1980s anime, wrongly identified as a strang "striped wolf", and as a possible danger for not only livestock but the humans themselves — even though in Real Life there have never been any reports of thylacines attacking humans directly. Like many modern Australian/Oceanian animals it shows up also in the cartoon series Tazmania.

  1. Entry Time: Undetermined
  2. Trope Maker: Uncertain, possibly the Wild Mass Guessing about its survival

Other extinct mammals

Sorry, these aren't here. If you're looking for Protosiren, Desmostylus, Titanohyrax, Homotherium, Borophagus, Cynodictis, Viverravus, Pelorovis, Titanotylopus, Protoceras, Prolibytherium, Remigtonocetus, Eurhinodelphis, Merycoidodon, Anoplotherium, Thalassocnus, Stegotherium, Palaeocastor, Phoberomys, Icaronycteris, Planetetherium, Dinopithecus, Archaeoindris, Phascolonus, Palorchestes, Zaglossus, and others, see here.

Prehistoric Amphibians

Extinct amphibians are interesting, and the stock ones are almost always from before the dinosaurs (though, of course, authors frequently forget that and put them in dinosaur settings anyway).

    Amphibians in Media 

The "First Vertebrate with Limbs": Ichthyostega *

Ichthyostega is one of the most iconic paleo-amphibians, together with Diplocaulus and Eryops below. Found in Greenland — Hilarious in Hindsight, during most the prehistory Greenland really was a green land, covered with forests; the ice cap formed only 30 million years ago in the Cenozoic — Ichthyostega lived before all the animals mentioned above, in the Devonian Period, when flying insects didn't yet exist and the very first forests had just started to grow. It was considered the very first land vertebrate for about a century, and the common ancestor of all tetrapods (mammals + birds + reptiles + amphibians). Like Archaeopteryx and Cynognathus, Ichthyostega has been cited as a "missing link" between two main animal classes (fish and amphibians in this case), and like the "ur-bird" and the "ur-mammal", portrayed as an icon of Evolution. However, since the 1990s new intermediate forms between fish and land animals have been found; Acanthostega and Tiktaalik are just two examples (see the Fish section).

Like many other basal tetrapods, Ichthyostega was a big animal, 5ft long and weighing as much as an adult human. This half-fish/half-amphibian was one of the first animals that developed true legs, already similar to modern animals except for one thing: it had seven digits on each foot (later vertebrates have no more than five). Its body plan, however, had still several fishy traits (Ichthyostega indeed means "roof fish"): a streamlined body, fish-like scales, and a powerful tail with a true fin on top. Though classical portrayals show it crawling on dry land, today scientists think Ichthyostega lived mainly in water, and recently research suggest its limbs were not used for walking on dry soil 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's given a loud voice and scale-less skin, and lays eggs that are just the same shape as frog eggs.

  1. Entry Time: Unknown
  2. Trope Maker: Educational media

The "Hammerhead Salamander": Diplocaulus *

Diplocaulus was two feet long and lived in Early Permian North America (contemporary with the famous Dimetrodon). Its unique boomerang-like head makes it a very bizarre-looking prehistoric animal and a very common sight in paleo books (though it has not yet appeared in Walking With Monsters or other CGI documentaries). The purpose of its head protrusions has been a headache 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 fromg being swallowed by larger amphibians such as Eryops (below)!

Diplocaulus (meaning "double-stem" — while Diplodocus means "double-beam"), despite its appearence, was not a member of the group comprising modern amphibians (the Lissamphibians): it was a Lepospondylian, a Carboniferous/Permian group whose shape only coincidentally recalled that of modern salamanders and newts. Its eyes and nostrils were placed on the top of its flattened head, and were very close to each others (the exact opposite of a modern hammerhead shark), which gave it what may have been a rather funny appearance if seen from above. It was mainly aquatic, probably swimming with its tail and/or walking on the bottom of the water bodies with its five-toed feet. Diplocaulus arguably fed upon small water critters, and could have fallen prey to larger fish, amphibians, and perhaps also the super-predator Dimetrodon.

  1. Entry Time: Unknown
  2. Trope Maker: Its skull

The "Alligator Amphibian": Eryops *

Temnospondyli (lit. "cut vertebrae") were the most successful paleo-amphibians in Real Life, thriving from the Late Carboniferous to the Late Triassic (with one holdout reaching the Cretaceous). The most iconic of them has traditionally been Eryops megacephalus ("big-headed drawn-out face"). 2.4m/8ft long and weighing as much as two adult humans, it was the size of a small crocodile, and has indeed classically been compared with crocs in documentary media. But Eryops was more massively-built than a modern-day crocodilian; it had a shorter tail, lacked armor on its back, and its limbs were comparatively weaker, making it probably more awkward than a croc on land. Still, it had a very alligator-like head, with eyes placed above the skull and a large snout. Its teeth were different from those of a gator, though, being more numerous and thin, more like a gharial's.

Living in North American Early Permian, Eryops is believed by most experts to have been mainly aquatic — other contemporaneous relatives, such as Cacops and Platyhystrix, were more terrestrial. Eryops was arguably a predator of other smaller paleo-amphibians such as Diplocaulus above and also fish and invertebrates, but when on dry land it could have fallen prey to Dimetrodon. Nonetheless, it can't be ruled out that it could have raided Dimetrodon and Edaphosaurus nests and hatchlings if it got the chance.

  1. Entry Time: Unknown
  2. Trope Maker: Educational media

The Biggest Amphibian Ever?: Mastodonsaurus *

From the Early Triassic Period comes the even larger Mastodonsaurus. Its name means "mastodon lizard", and sometimes is misspelled "Mastodontosaurus". It was one of the very first giant amphibians discovered to science, in the first half of the 1800s, and portrayed in the London Crystal Palace Park as "Labyrinthodon". It was the namesake of the Labyrinthodonts ("labyrinth teeth"), the catch-all name for non-frog, non-salamander and non-caecilian extinct amphibians — so-named because many had teeth with strange convoluted "labyrinthic" patterns of enamel inside them for uncertain purpose.

Mastodonsaurus (so-named for its size) lived in Europe before the first dinosaurs like Plateosaurus or the North American Coelophysis. 5m long, it was long considered the biggest paleo-amphibian ever, but this title was later taken by Prionosuchus. Nonetheless, Mastodonsaurus remains remarkable for its massive body, powerful limbs, and its 1.2m/4ft-long head with a couple of strange protruding teeth in the lower jaw, which may have perforated the upper jaw in life (though this detail is usually ignored in paleo-books). During the Triassic, giant amphibians like these became rarer and rarer, becoming outcompeted by the ancestors of crocodilians.

  1. Entry Time: 1854
  2. Trope Maker: The Crystal Palace Park in London

Amphibian or Reptile?: Seymouria *

Reptiliomorphs ("reptile-shaped") were transitional animals between amphibians and the first Amniotes (reptiles, birds and mammals). Traditionally the best-known among these half-amphibian/half-reptiles has been Seymouria baylorensis. The genus name comes from the town of Seymour, Texas, near where it was discovered; the species name from Baylor County. Seymouria used to be described in textbooks as the "missing link" between reptiles and amphibians, or alternatively the very first reptile. In the latter case, it was considered a "cotylosaur" (the catch-all name for the earliest reptiles).

Only 60cm long, it was much smaller than the other creatures above (except for Diplocaulus), and lived in Early Permian North America alongside the latter and Eryops. It was more terrestrial than them, and had a greater chance of meeting Dimetrodon in Real Life; it was possibly one of its most frequent prey. In Walking With Monsters, however, it's shown mainly as a potential thief of the latter's eggs. Despite its similarity to reptiles, Seymouria still laid shell-less eggs from which tadpoles hatched in water, as some fossils show.

  1. Entry Time: Unknown
  2. Trope Maker: Educational media

Other prehistoric amphibians

Sorry, these aren't here. If you're looking for Triadobatrachus, Karaurus, Eocaecilia, Phlegetontia, Platyhystrix, Cacops, Branchiosaurus, Gerrothorax, Metoposaurus, Eogyrinus, Westlothiana, Diadectes, and others, see here.

Prehistoric Fish

It's not often that you'll see prehistoric fish in paleo-media, but when you do, it will usually be these guys. The first two are the most common, expecially the one at the top of the list.

    Fish in Media 

Jaws on Steroids: Megalodon ***

It's usually accepted that the biggest/most spectacular prehistoric animals lived in the Age of Reptiles. Well, sharks give us a notable exception. The biggest known predatory shark ever lived just a few million years ago, at the time of the first hominids!

Obviously, this animal is often shown in documentary media: for example, its open jaws are often depicted with some people inside to show how immense they are. Recently, this animal has fascinated the world of fiction, to the point that Megalodon has become a trope on its own. Megalodon (literally "big tooth") is not the name of its genus; it's that of its species. The full scientific name used to be Carcharodon megalodon; today it's Carcharocles megalodon. It was believed to have been an extremely close relative of the great white shark (Carcharodon carcharias); today it's placed in a different family convergently similar to the great white's, but still in the same order of true sharks — the Lamniformes, which also include the long-tailed thresher sharks, the filter-feeding basking shark, and the deep-sea megamouth shark, among others.

Like the most impressive extinct beasts, Megalodon is often a victim of sensationalism. Some sources describe it as 30m/90ft long, nearly as big as a blue whale; palaeontologists estimate it at just over a third to just under two thirds of this length. Still, it remains one of the biggest known fishes of all times as well as the biggest known predatory shark, and one of the most successful apex predators ever, with a tenure of 20 million years. Only Livyatan and other recently-discovered huge-toothed giant predatory whales related to the modern sperm whale were true rivals, being its contemporaries in the same seas.

Like these predatory whales, Megalodon may have been a specialist hunter of large cetaceans, and its bite marks have been found in whale skeletons, but it could also have fed on smaller prey. We don't know why it went extinct; possibly because of climatic changes that deprived it (and its mammalian rivals as well) of their main food sources, in particular the closing of the Central American Seaway, which was an important hunting and migration area. It is hypothesized that Megalodon held back the evolution of cetaceans themselves, which underwent a third explosion in diversity right after its extinction — therefore, the theory that orcas outcompeted the shark is highly unlikely.

Megalodon is probably the one prehistoric creature that gets almost as much sensationalism as Tyrannosaurus rex: from frequent, fraudulent reports of it still patrolling the seas to erroneous portrayals of it chomping on Mesozoic marine reptiles (despite not appearing until long after those creatures had gone extinct), Megalodon is frequently cast as the ultimate sea predator. This obviously cannot be verified — in the Walking with Dinosaurs spinoff Sea Monsters, it's portrayed as "only" the third-most-dangerous marine superpredator of Prehistory, after the sea reptiles Tylosaurus and Liopleurodon, but before the fish below.

  1. Entry Time: Late 1990s/early 2000s (pop culture)
  2. Trope Maker: Documentary books on the shark buff side, Meg in pop culture

Giant Armored Killer Fish: Dunkleosteus *

Most placoderms (armored fishes that went extinct well before the dinosaurs evolved) were small. The big exception is Dunkleosteus.

19ft long, the size of a great white sharknote , it was only outmatched by its larger but gentler cousin Titanichthys ("titanic fish") and an obscure chimera known as Parahelicoprion for the title of largest animal in the Paleozoic era (the geological era before the Mesozoic). It was the same shape as the smaller and lesser-known Coccosteus, with the same kind of armored head and the same strange scissor-like "teeth" (actually plates of sharpened bone). It was evidently the top predator of its time (the Devonian, the same period in which the "ur-amphibian" Ichthyostega lived), able to chop up even the toughest prey.

Studies of its jaw reveal that it probably sucked up food like a vacuum, using its bone plates to slice prey into chunks with a bite force of 4400 pounds — possibly the strongent bite of any animal that ever lived. Its fossilized vomit has been found too, indicating that it often regurgitated the armour and bones of its prey. Also of interest is that several Dunkleosteus fossils preserve evidence of being attacked by other Dunkleosteus, which has led some to suggest that they were active cannibals.

In older sources it's referred to as Dinichthys ("terrible fish", which, however, may be a separate animal); the much less awesome name Dunkleosteus means "Dunkle's bone" after a museum curator.

Despite its impressive size, apex predator status, and "living tank" appearance, Dunkleosteus has not gained much attention outside of paleo books; in Walking with Dinosaurs it appears as one of the "monsters" encountered by Nigel Marven while time-traveling, and to better fit the role is portrayed as excessively scary, with cat eyes and blood-red coloration note . Here, it's the fifth-most-dangerous superpredator of all time, after two marine reptiles, Megalodon, and the early whale Basilosaurus.

  1. Entry Time: 1956
  2. Trope Maker: Documentary and book media

Overgrown Herring?: Xiphactinus *

Xiphactinus shares several traits with Dunkleosteus. It was only slightly smaller (6 meters long at most), and much smaller than Megalodon; however, if alive today, it would be one of the largest non-shark fishnote  — at least in mass: the modern deep-sea giant oarfish can reach 30ft or more in length, but is much more slender than Xiphactinus was.

Another common trait with Dunkleosteus is that it was in older media known by another name: "Portheus molossus". Xiphactinus audax means "courageous sword ray"; the meaning of "Portheus" is uncertain, but molossus refers to an early breed of mastiff. Indeed, its protruding lower jaw slightly resembles that of a bulldog; this, together with its long pointed teeth, clearly indicates it was a predator. But unlike Dunkleosteus, it didn't cut the prey into pieces, but swallowed them whole (like most modern bony fish). Indeed it was a primitive Teleostean, the most evolved subgroup of bony fish today, and a distant relative of herrings and tarpons. It was only larger than them, and thus with a not-at-all exotic appearance compared with many fish of the Paleozoic — not only placoderms like Dunkleosteus but also acanthodians, early sharks, lobe-finned fish, and the ostracoderms (some of them are below).

In documentary media, Xiphactinus or "Portheus" is typically portrayed as an underdog predator, which gulps big items like the swimming bird Hesperornis but in turn falls victim to the dominant marine reptiles of the Cretaceous (especially large mosasaurs like Tylosaurus). Sea Monsters oversized it a bit, and showed it as one of the dangers in the most perilous sea of prehistory (nicknamed Hell's Aquarium by Nigel Marven in the program). Obviously, in mainstream media it's largely ignored as is usual for the ray-finned fish (actinopterygians) of the past (Lepidotes, Leedsichthys, etc.) because of its "generic fish" look compared with other giant sea-dwellers of the past like reptiles, cetaceans, giant sharks, cephalopods, etc.

  1. Entry Time: Uncertain
  2. Trope Maker: Educational media

Fish or Amphibian?: Eusthenopteron *

This animal is classically mentioned in paleo-books coupled with Ichthyostega, to show how vertebrates came onto land for the first time. The long-named Eusthenopteron means "strong fin". Its shape recalled a bit that of the famous ur-amphibian above, but smaller (60cm), 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 similar to a lungfish's, and like a lungfish was probably also able to breath air with primitive lungs and occasionally crawl out of the water to escape drought.

Its almost-identical relative Hyneria was much bigger (3-4m long), and because of its size was chosen by Walking With Monsters producers instead of Eusthenopteron as the representative of Sarcopterygians, aka the "lobe-finned fish" (and, of course, was scaled up still further). However, it's shown only to provide a predator to the Ichthyostega relative Hynerpeton, and with no mention at all of its role as one of the forerunners of land vertebrates: in effect it was eating its descendant!

  1. Entry Time: Uncertain
  2. Trope Maker: Educational media

Fish or Shellfish?: Cephalaspis & Pteraspis *

Cephalaspis and Pteraspis are perhaps the two most-depicted Ostracoderms in paleo-media — at least, non-fictional media. As ostracoderms, they were small critters similar to strange modern bony fish at a glace; actually, they were more similar to the so-called "jawless fish" like the modern lamprey and hagfish, and likewise lacked jaws. Unlike the latter, they had armored heads and bodies, which made them look more like the aforementioned placoderms such as Dunkleosteus.

But unlike Dunkleosteus, Cephalaspis and Pteraspis were totally harmless creatures, and much, much smaller: some Pteraspis were no longer than a human finger. They were also very different from lampreys and hagfish, being inoffensive filter-feeders or bottom-feeders of tiny food items, not parasites or scavengers of large animals like the as-yet nonexistent giant bony fish or cetaceans.

These two ostracoderms lived from the Silurian to the Devonian, in the middle of the Paleozoic. Walking With Monsters chose to show Cephalaspis as the prototypical ostracoderm, as fodder for giant "scorpions" (see below) and as a salmon-like migrator, but this last behavior is only speculative — and rather unlikely, since they were probably slower swimmers compared with most modern fish. But it's always Rule of Cool that wins...

  1. Entry Time: Uncertain
  2. Trope Maker: Educational media

Other prehistoric fish

Sorry, these aren't here. If you're looking for Coelacanthus, Mawsonia, Dipterus, Palaeoniscum, Hybodus, Stethacanthus, Helicoprion, Climatius, Bothriolepis, Coccosteus, Arandaspis, Drepanaspis, Birkenia, Haikouichthys, the Conodonts, and others, see here.

Prehistoric Invertebrates

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.

    Invertebrates in Media 

The First successful Invertebrates: the Trilobites ***

Some things have had more impact than others. Trilobites are among them. Their 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 Permian-Triassic mass extinction. Though their appearance could lead to them being confused with 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 long, ex. 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 Phacopid subgroup; good luck if you see an Agnostid or a Proetid.

In fiction, trilobites can often be seen in underwater visuals (even in the Mesozoic, despite this being millions of years after their extinction) 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.

  1. Entry Time: Unknown
  2. Trope Maker: Educational media.

The Symbol of the Mesozoic: the Ammonites ***

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. note 

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 Titanites)note . 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 loosely uncoiled shells, some had u-shaped shells, some had spiny tower-like shells, some just had straight shells, and others had 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.

  1. Entry Time: Unknown
  2. Trope Maker: Educational media.

The First Giant Flyer: Meganeura **

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 Odonata) and extremely similar to them, other than size. With a wingspan like a crownote , Meganeura has been called the largest-known true insect of all time (millipedes like Arthropleura are not insects), but its recently-discovered close relative Meganeuropsis ("similar to Meganeura") was actually a bit bigger. Both had the same shape as modern dragonflies, with slender bodies, huge eyes, 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 Giant Flyer. 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 — and given its size, possibly ramp up the Squick factor. Frustratingly, older works tended to portray Meganeura living 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 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.

  1. Entry Time: 1885
  2. Trope Maker: Educational media.

The Super-Millipede: Arthropleura *

Why did land arthropods reach such a large size in the Carboniferous? 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 Up to Eleven case: as long as a human, it is the 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. note  We don't know if it was able to rear up like a cobra as portrayed in Walking With Monsters, given its weight.

Despite this critter's size and impressive appearence, 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 Primeval, which for some reason decided to portray it as a giant venomous centipede.

  1. Entry Time: 2005
  2. Trope Maker: Walking With Monsters

Ancient Sea Critters: Pterygotus & Cameroceras *

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 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 appearence, 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.

  1. Entry Time: undetermined for Pterygotus; 2003 for Cameroceras
  2. Trope Maker: educational books (Pterygotus); Sea Monsters (Cameroceras)

Unshelled or Shelled?: the Belemnites *

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 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.

  1. Entry Time: undetermined
  2. Trope Maker: educational media

The First Predator: Anomalocaris *

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. Digimon (as "Anomalocarimon"). This because, of course, it was by far the largest Cambrian predator.

Anomalocaris means "anomalous shrimp": this name reveals a singular Real Life case of Mix-and-Match Critter. 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. Science Marches On 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 "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 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 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 (and unfairly) been labeled "the first sea monsters" in docu-media. In Anomalocaris's time every other organism was very small: creatures like Hallucigenia and Pikaia were hunted by smaller predators, such as Opabinia and Anomalocaris saron. note  The latter was the species shown in Walking With Monsters, 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.

  1. Entry Time: Early 2000s
  2. Trope Maker: Walking With Monsters and anime

Other prehistoric invertebrates

Sorry, these aren't here. If you're looking for prehistoric crustaceans, rudists, brachiopods, bryozoans, cystoids, blastoids, graptolites, chalcicordates, nummulites, and others, see here.


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