Science, Tech, Math › Animals & Nature Prehistoric Reptile Pictures and Profiles Share Flipboard Email Print Animals & Nature Dinosaurs Prehistoric Mammals Basics Paleontologists Carnivores Dinosaurs & Birds Herbivores Marine Reptiles Amphibians Birds Habitat Profiles Mammals Reptiles Wildlife Conservation Insects Marine Life Forestry Evolution View More By Bob Strauss Science Writer B.S., Cornell University Bob Strauss is a science writer and the author of several books, including "The Big Book of What, How and Why" and "A Field Guide to the Dinosaurs of North America." our editorial process Bob Strauss Updated March 17, 2017 01 of 37 Meet the Ancestral Reptiles of the Paleozoic and Mesozoic Eras Wikimedia Commons Some time during the late Carboniferous period, about 300 million years ago, the most advanced amphibians on earth evolved into the first true reptiles. On the following slides, you'll find pictures and detailed profiles of over 30 ancestral reptiles of the Paleozoic and Mesozoic Eras, ranging from Araeoscelis to Tseajara. 02 of 37 Araeoscelis Araeoscelis. public domain Name: Araeoscelis (Greek for "thin legs"); pronounced AH-ray-OSS-kell-iss Habitat: Swamps of North America Historical Period: Early Permian (285-275 million years ago) Size and Weight: About two feet long and a few pounds Diet: Insects Distinguishing Characteristics: Long, thin legs; long tail; lizard-like appearance Essentially, the skittering, insect-eating Araeoscelis looked like any other small, lizard-like proto-reptile of the early Permian period. What makes this otherwise obscure critter important is that it was one of the first diapsids--that is, reptiles with two characteristic openings in their skulls. As such, Araeoscelis and other early diapsids occupies the root of a vast evolutionary tree that includes dinosaurs, crocodiles, and even (if you want to get technical about it) birds. By comparison, most small, lizard-like anapsid reptiles (those lacking any tell-tale skull holes), such as Milleretta and Captorhinus, went extinct by the end of the Permian period, and are represented today only by turtles and tortoises. 03 of 37 Archaeothyris Archaeothyris. Nobu Tamura Name: Archaeothyris; pronounced ARE-kay-oh-THIGH-riss Habitat: Swamps of North America Historical Period: Late Carboniferous (305 million years ago) Size and Weight: About 1-2 feet long and a few pounds Diet: Probably carnivorous Distinguishing Characteristics: Small size; powerful jaws with sharp teeth To the modern eye, Archaeothyris looks like pretty much any other small, scurrying lizard of the pre-Mesozoic Era, but this ancestral reptile has an important place in the evolutionary family tree: it's the first known synapsid, a family of reptiles characterized by the unique number of openings in their skulls. As such, this late Carboniferous creature is believed to have been ancestral to all subsequent pelycosaurs and therapsids, not to mention the early mammals that evolved from therapsids during the Triassic period (and went on to spawn modern human beings). 04 of 37 Barbaturex Barbaturex. Angie Fox Name: Barbaturex (Greek for "bearded king"); pronounced BAR-bah-TORE-rex Habitat: Woodlands of southeast Asia Historical Epoch: Late Eocene (40 million years ago) Size and Weight: About three feet long and 20 pounds Diet: Plants Distinguishing Characteristics: Relatively large size; ridges on lower jaw; squat, splayed posture If you're a paleontologist who wants to generate headlines, it helps to throw in a pop-culture reference: who can resist a prehistoric lizard named Barbaturex morrisoni, after the Lizard King himself, the long-deceased Doors frontman Jim Morrison? A remote ancestor of modern iguanas, Barbaturex was one of the largest lizards of the Eocene epoch, weighing about as much as a medium-sized dog. (Prehistoric lizards never quite achieved the huge dimensions of their reptile cousins; compared to Eocene snakes and crocodiles, Barbaturex was an insignificant runt.) Significantly, this "bearded king" competed directly with comparably sized mammals for vegetation, another indication that Eocene ecosystems were more complicated than once believed. 05 of 37 Brachyrhinodon Brachyrhinodon was ancestral to the modern Tuatara (Wikimedia Commons). Name: Brachyrhinodon (Greek for "short-nosed tooth"); pronounced BRACK-ee-RYE-no-don Habitat: Woodlands of western Europe Historical Period: Late Triassic (230 million years ago) Size and Weight: About six inches long and a few ounces Diet: Insects Distinguishing Characteristics: Short size; quadrupedal posture; blunt snout The Tuatara of New Zealand is often described as a "living fossil," and you can see why by looking at the late Triassic Tuatara ancestor Brachyrhinodon, which lived over 200 million years ago. Basically, Brachyrhinodon looked almost identical to its modern relative, except for its smaller size and blunter snout, which was presumably an adaptation to the type of food available in its ecosystem. This six-inch-long ancestral reptile seems to have specialized in hard-shelled insects and invertebrates, which it crushed between its numerous, small teeth. 06 of 37 Bradysaurus Bradysaurus. Wikimedia Commons Name Bradysaurus (Greek for "Brady's lizard"); pronounced BRAY-dee-SORE-us Habitat Swamps of southern Africa Historical Period Late Permian (260 million years ago) Size and Weight About six feet long and 1,000-2,000 pounds Diet Plants Distinguishing Characteristics Bulky torso; short tail First things first: while it's amusing to imagine otherwise, Bradysaurus has nothing to do with the classic TV series The Brady Bunch (or the two subsequent movies), but was simply named after the man who discovered it. Essentially, this was a classic pareiasaur, a thick, squat, small-brained reptile of the Permian period that weighed as much as a small car and was presumably much slower. What makes Bradysaurus important is that it's the most basal pareiasaur yet discovered, kind of a template for the next few million years of pareiasaur evolution (and, considering how little these reptiles managed to evolve before they went extinct, that's not saying much!) 07 of 37 Bunostegos Bunostegos. Marc Boulay Bunostegos was the late Permian equivalent of a cow, the difference being that this creature wasn't a mammal (a family that didn't evolve for another 50 or so million years) but a type of prehistoric reptile called a pareiasaur. See an in-depth profile of Bunostegos 08 of 37 Captorhinus Captorhinus. Wikimedia Commons Name: Captorhinus (Greek for "stem nose"); pronounced CAP-toe-RYE-nuss Habitat: Swamps of North America Historical Period: Early Permian (295-285 million years ago) Size and Weight: About seven inches long and less than a pound Diet: Insects Distinguishing Characteristics: Small size; lizard-like appearance; two rows of teeth in jaws Just how primitive, or "basal," was the 300-million-year-old Captorhinus? As the famous paleontologist Robert Bakker once phrased it, "If you started as a Captorhinus, you could end up evolving into just about anything." Some qualifications apply, though: this half-foot-long critter was technically an anapsid, an obscure family of ancestral reptiles characterized by the lack of openings in their skulls (and represented today only by turtles and tortoises). As such, this nimble insect-eater didn't really evolve into anything, but went extinct along with most of its anapsid relatives (such as Milleretta) by the end of the Permian period. 09 of 37 Coelurosauravus Coelurosauravus. Nobu Tamura Name: Coelurosauravus (Greek for "grandfather of the hollow lizard"); pronounced SEE-lore-oh-SORE-ay-vuss Habitat: Woodlands of western Europe and Madagascar Historical Period: Late Permian (250 million years ago) Size and Weight: About one foot long and one pound Diet: Insects Distinguishing Characteristics: Small size; moth-like wings made of skin Coelurosauravus is one of those prehistoric reptiles (like Micropachycephalosaurus) the name of which is disproportionately larger than its actual size. This strange, tiny creature represented a strand of evolution that died out by the end of the Triassic period: the gliding reptiles, which were only distantly related to the pterosaurs of the Mesozoic Era. Like a flying squirrel, the tiny Coelurosauravus glided from tree to tree on its taut, skin-like wings (which looked uncannily like the wings of a large moth), and it also possessed sharp claws to grab securely onto bark. The remains of two different species of Coelurosauravus have been found in two widely separated locations, western Europe and the island of Madagascar. 10 of 37 Cryptolacerta Cryptolacerta. Robert Reisz Name: Cryptolacerta (Greek for "hidden lizard"); pronounced CRIP-toe-la-SIR-ta Habitat: Swamps of western Europe Historical Epoch: Early Eocene (47 million years ago) Size and Weight: About three inches long and less than an ounce Diet: Probably insects Distinguishing Characteristics: Small size; tiny limbs Some of the most puzzling reptiles alive today are the amphisbaenians, or "worm lizards"--tiny, legless, earthworm-sized lizards that bear an uncanny resemblance to blind, cave-dwelling snakes. Until recently, paleontologists were unsure where to fit amphisbaenians on the reptile family tree; that has all changed with the discovery of Cryptolacerta, a 47-million-year-old amphisbaenian possessing small, almost vestigial legs. Cryptolacerta clearly evolved from a family of reptiles known as lacertids, proving that amphisbaenians and prehistoric snakes arrived at their legless anatomies via a process of convergent evolution and are not in fact closely related. 11 of 37 Drepanosaurus Drepanosaurus (Wikimedia Commons). The Triassic reptile Drepanosaurus possessed single, oversized claws on its front hands, as well as a long, monkey-like, prehensile tail with a "hook" on the end, which was clearly meant to anchor it to the high branches of trees. See an in-depth profile of Drepanosaurus 12 of 37 Elginia Elginia. Getty Images Name: Elginia ("from Elgin"); pronounced el-GIN-ee-ah Habitat: Swamps of western Europe Historical Period: Late Permian (250 million years ago) Size and Weight: About two feet long and 20-30 pounds Diet: Plants Distinguishing Characteristics: Small size; knobby armor on head During the late Permian period, some of the biggest creatures on earth were the pareiasaurs, a plus-sized breed of anapsid reptiles (i.e., those lacking characteristics holes in their skulls) best typified by Scutosaurus and Eunotosaurus. While most pareiasaurs measured 8 to 10 feet long, Elginia was a "dwarf" member of the breed, only about two feet from head to tail (at least to judge by this reptile's limited fossil remains). It's possible that Elginia's diminutive size was a response to the hostile conditions toward the end of the Permian period (when most anapsid reptiles went extinct); the ankylosaur-like armor on its head would also have protected it from hungry therapsids and archosaurs. 13 of 37 Homeosaurus Homeosaurus. Wikimedia Commons Name: Homeosaurus (Greek for "the same lizard"); pronounced HOME-ee-oh-SORE-us Habitat: Woodlands of Europe Historical Period: Late Jurassic (150 million years ago) Size and Weight: About eight inches long and half a pound Diet: Insects Distinguishing Characteristics: Small size; quadrupedal posture; armored skin The tuatara of New Zealand is often referred to as a "living fossil," so different from other terrestrial reptiles as to represent a throwback to prehistoric times. As far as paleontologists can tell, Homeosaurus and a handful of even more obscure genera belonged to the same family of diapsid reptiles (the sphenodonts) as the tuatara. The amazing thing about this tiny, insect-eating lizard is that it coexisted with--and was a bite-sized snack for--the huge dinosaurs of the late Jurassic period, 150 million years ago. 14 of 37 Hylonomus Hylonomus. Karen Carr Name: Hylonomus (Greek for "forest mouse"); pronounced high-LON-oh-muss Habitat: Forests of North America Historical Period: Carboniferous (315 million years ago) Size and Weight: About one foot long and one pound Diet: Insects Distinguishing Characteristics: Tiny size; sharp teeth It's always possible that a more ancient candidate will be discovered, but as of now, Hylonomus is the earliest true reptile known to paleontologists: this tiny critter scuttled around the forests of the Carboniferous period over 300 million years ago. Based on reconstructions, Hylonomus certainly looked distinctly reptilian, with its quadrupedal, splay-footed posture, long tail, and sharp teeth. Hylonomus is also a good object lesson in how evolution works. You might be surprised to learn that the oldest ancestor of the mighty dinosaurs (not to mention modern crocodiles and birds) was about the size of a small gecko, but new life forms have a way of "radiating" from very small, simple progenitors. For example, all mammals alive today--including humans and sperm whales--are ultimately descended from a mouse-sized ancestor that scurried beneath the feet of huge dinosaurs more than 200 million years ago. 15 of 37 Hypsognathus Hypsognathus. Wikimedia Commons Name: Hypsognathus (Greek for "high jaw"); pronounced hip-SOG-nah-thuss Habitat: Swamps of eastern North America Historical Period: Late Triassic (215-200 million years ago) Size and Weight: About one foot long and a few pounds Diet: Plants Distinguishing Characteristics: Small size; squat trunk; spikes on head Most of the small, lizard-like anapsid reptiles--which were characterized by a lack of diagnostic holes in their skulls--went extinct at the end of the Permian period, while their diapsid relatives prospered. An important exception was the late Triassic Hypsognathus, which may have survived thanks to its unique evolutionary niche (unlike most anapsids, it was a herbivore) and the alarming-looking spikes on its head, which deterred larger predators, possibly including the first theropod dinosaurs. We can thank Hypsognathus and its fellow anapsid survivors like Procolophon for turtles and tortoises, which are the only modern representatives of this ancient reptile family. 16 of 37 Hypuronector Hypuronector. Wikimedia Commons Name: Hypuronector (Greek for "deep-tailed swimmer"); pronounced hi-POOR-oh-neck-tore Habitat: Woodlands of eastern North America Historical Period: Late Triassic (230 million years ago) Size and Weight: About six inches long and a few ounces Diet: Insects Distinguishing Characteristics: Small size; long, flat tail Just because a prehistoric reptile is represented by dozens of fossil specimens doesn't mean it can't be misunderstood by paleontologists. For decades, the tiny Hypuronector was assumed to be a marine reptile, since experts could think of no other function for its long, flat tail than underwater propulsion (it didn't hurt that all those Hypuronector fossils were discovered in a lake bottom in New Jersey). Now, though, the weight of the evidence is that the "deep-tailed swimmer" Hypuronector was actually a tree-dwelling reptile, closely related to Longisquama and Kuehneosaurus, that glided from branch to branch in search of insects. 17 of 37 Icarosaurus Icarosaurus. Nobu Tamura Name: Icarosaurus (Greek for "Icarus lizard"); pronounced ICK-ah-roe-SORE-us Habitat: Woodlands of eastern North America Historical Period: Late Triassic (230-200 million years ago) Size and Weight: About four inches long and 2-3 ounces Diet: Insects Distinguishing Characteristics: Small size; butterfly-like appearance; extremely light weight Named after Icarus--the figure from Greek myth who flew too close to the sun on his artificial wings--Icarosaurus was a hummingbird-sized gliding reptile of late Triassic North America, closely related to the contemporary European Kuehneosaurus and the earlier Coelurosauravus. Unfortunately, the tiny Icarosaurus (which was only distantly related to pterosaurs) was out of the mainstream of reptile evolution during the Mesozoic Era, and it and its inoffensive companions had all gone extinct by the start of the Jurassic period. 18 of 37 Kuehneosaurus Kuehneosaurus. Getty Images Name: Kuehneosaurus (Greek for "Kuehne's lizard"); pronounced KEEN-ee-oh-SORE-us Habitat: Woodlands of western Europe Historical Period: Late Triassic (230-200 million years ago) Size and Weight: About two feet long and 1-2 pounds Diet: Insects Distinguishing Characteristics: Small size; butterfly-like wings; long tail Along with Icarosaurus and Coelurosauravus, Kuehneosaurus was a gliding reptile of the late Triassic period, a small, inoffensive creature that floated from tree to tree on its butterfly-like wings (pretty much like a flying squirrel, except for some important details). Kuehneosaurus and pals were pretty much out of the mainstream of reptile evolution during the Mesozoic Era, which was dominated by archosaurs and therapsids and then dinosaurs; in any event, these gliding reptiles (which were only remotely related to pterosaurs) went extinct by the start of the Jurassic period 200 million years ago. 19 of 37 Labidosaurus Labidosaurus. Wikimedia Commons Name: Labidosaurus (Greek for "lipped lizard"); pronounced la-BYE-doe-SORE-us Habitat: Swamps of North America Historical Period: Early Permian (275-270 million years ago) Size and Weight: About 30 inches long and 5-10 pounds Diet: Probably plants, insects and mollusks Distinguishing Characteristics: Large head with numerous teeth An otherwise unremarkable ancestral reptile of the early Permian period, the cat-sized Labidosaurus is famous for betraying the earliest known evidence of a prehistoric toothache. A specimen of Labidosaurus described in 2011 showed evidence of osteomyelitis in its jawbone, the most likely cause being an uncontrolled tooth infection (root canals, unfortunately, weren't an option 270 million years ago). Making matters worse, the teeth of Labidosaurus were unusually deeply set in its jaw, so this individual may have suffered for an excruciatingly long time before it died and happened to be fossilized. 20 of 37 Langobardisaurus Langobardisaurus. Wikimedia Commons Name: Langobardisaurus (Greek for "Lombardy lizard"); pronounced LANG-oh-BARD-ih-SORE-us Habitat: Swamps of southern Europe Historical Period: Late Triassic (230 million years ago) Size and Weight: About 16 inches long and one pound Diet: Insects Distinguishing Characteristics: Long legs, neck and tail; bipedal posture One of the strangest ancestral reptiles of the Triassic period, Langobardisaurus was a small, slender insect-eater whose hind legs were considerably longer than its front legs--leading paleontologists to infer that it was capable of running on two legs, at least when it was being chased by larger predators. Comically, judging by the structure of its toes, this "Lombardy lizard" would not have run like a theropod dinosaur (or a modern bird), but with an exaggerated, loping, saddle-backed gait that wouldn't have looked out of place on a Saturday morning kids' cartoon. 21 of 37 Limnoscelis Limnoscelis. Nobu Tamura Name Limnoscelis (Greek for "marsh-footed"); pronounced LIM-no-SKELL-iss Habitat Swamps of North America Historical Period Early Permian (300 million years ago) Size and Weight About four feet long and 5-10 pounds Diet Meat Distinguishing Characteristics Large size; long tail; slender build During the early Permian period, about 300 million years ago, North America was teeming with colonies of "amniotes," or reptile-like amphibians--throwbacks to their ancestors from tens of millions of years earlier. The importance of Limnoscelis lies in the fact that it was unusually large (about four feet from head to tail) and that it seems to have pursued a carnivorous diet, making it unlike most "diadectomorphs" (i.e, relatives of Diadectes) of its time. With its short, stubby feet, though, Limnoscelis couldn't move very fast, meaning it must have targeted especially slow-moving prey. 22 of 37 Longisquama Longisquama. Nobu Tamura The small, gliding reptile Longisquama had thin, narrow plumes jutting out from its vertebrae, which may or may not have been covered with skin, and the exact orientation of which is an enduring mystery. See an in-depth profile of Longisquama 23 of 37 Macrocnemus Macrocnemus. Nobu Tamura Name: Macrocnemus (Greek for "large tibia"); pronounced MA-crock-NEE-muss Habitat: Lagoons of southern Europe Historical Period: Middle Triassic (245-235 million years ago) Size and Weight: About two feet long and one pound Diet: Insects Distinguishing Characteristics: Long, slender body; frog-like hind legs Yet another prehistoric reptile that doesn't fit easily into any specific category, Macrocnemus is classified as an "archosaurimorph" lizard, meaning that it vaguely resembled the archosaurs of the late Triassic period (which eventually evolved into the first dinosaurs) but was in fact only a distant cousin. This long, slender, one-pound reptile seems to have made its living by prowling the lagoons of middle Triassic southern Europe for insects and other invertebrates; otherwise, it remains a bit of a mystery, which will unfortunately remain the case pending future fossil discoveries. 24 of 37 Megalancosaurus Megalancosaurus. Alain Beneteau Name: Megalancosaurus (Greek for "big-forelimbed lizard"); pronounced MEG-ah-LAN-coe-SORE-us Habitat: Woodlands of southern Europe Historical Period: Late Triassic (230-210 million years ago) Size and Weight: About seven inches long and less than a pound Diet: Insects Distinguishing Characteristics: Bird-like skull; opposing digits on hind feet Known informally as a "monkey lizard," Megalancosaurus was a tiny ancestral reptile of the Triassic period that seems to have spent its entire life high up in trees, and thus evolved some features reminiscent of both birds and arboreal monkeys. For example, the males of this genus were equipped with opposing digits on their hind feet, which presumably allowed them to hang on tight during the act of mating, and Megalancosaurus also possessed a bird-like skull and pair of distinctly avian forelimbs. As far as we can tell, however, Megalancosaurus did not have feathers, and despite the speculation of some paleontologists it was almost certainly not ancestral to modern birds. 25 of 37 Mesosaurus Mesosaurus. Wikimedia Commons The early Permian Mesosaurus was one of the first reptiles to return to a partially aquatic lifestyle, a throwback to the ancestral amphibians that preceded it by tens of millions of years. See an in-depth profile of Mesosaurus 26 of 37 Milleretta Milleretta. Nobu Tamura Name: Milleretta ("Miller's little one"); pronounced MILL-eh-RET-ah Habitat: Swamps of southern Africa Historical Period: Late Permian (250 million years ago) Size and Weight: About two feet long and 5-10 pounds Diet: Insects Distinguishing Characteristics: Relatively large size; lizard-like appearance Despite its name--"Miller's little one," after the paleontologist who discovered it--the two-foot-long Milleretta was a comparatively large prehistoric reptile for its time and place, late Permian South Africa. Although it looked like a modern lizard, Milleretta occupied an obscure side branch of reptile evolution, the anapsids (named for the lack of characteristic holes in their skulls), the only living descendants of which are turtles and tortoises. To judge by its relatively long legs and sleek build, Milleretta was capable of skittering at high speeds in pursuit of its insect prey. 27 of 37 Obamadon Obamadon. Carl Buell The only prehistoric reptile ever to be named after a sitting president, Obamadon was a fairly unremarkable animal: a foot-long, insect-eating lizard that disappeared at the end of the Cretaceous period along with its dinosaur cousins. See an in-depth profile of Obamadon 28 of 37 Orobates Orobates. Nobu Tamura Name Orobates; pronounced ORE-oh-BAH-teez Habitat Swamps of western Europe Historical Period Late Permian (260 million years ago) Size and Weight Undisclosed Diet Plants Distinguishing Characteristics Long body; short legs and skull There wasn't a single "aha!" moment when the most advanced prehistoric amphibians evolved into the first true reptiles. That's why it's so hard to describe Orobates; this late Permian creature was technically a "diadectid," a line of reptile-like tetrapods characterized by the much better-known Diadectes. The importance of the small, slender, stubby-legged Orobates is that it's one of the most primitive diadectids yet identified, for example, whereas Diadectes was capable of foraging far inland for food, Orobates seems to have been restricted to a marine habitat. Further complicating matters, Orobates lived a full 40 million years after Diadectes, a lesson in how evolution doesn't always take a straight path! 29 of 37 Owenetta Owenetta. Wikimedia Commons Name: Owenetta ("Owen's little one"); pronounced OH-wen-ET-ah Habitat: Swamps of southern Africa Historical Period: Late Permian (260-250 million years ago) Size and Weight: About one foot long and one pound Diet: Probably insects Distinguishing Characteristics: Large head; lizard-like body The thickets of paleontology become densely tangled when experts deal with obscure prehistoric reptiles that never made it out of the Permian period, and left no major living descendants. A case in point is Owenetta, which (after decades of disagreement) has tentatively been classified as a "procolophonian parareptile," a phrase that requires some unpacking. Procolophonians (including the eponymous genus Procolophon) are believed to have been distantly ancestral to modern turtles and tortoises, while the word "parareptile" applies to various branches of anapsid reptiles that went extinct hundreds of millions of years ago. The issue still isn't settled; the exact taxonomic position of Owenetta in the reptile family tree is being constantly reassessed. 30 of 37 Pareiasaurus Pareiasaurus (Nobu Tamura). Name Pareiasaurus (Greek for "helmet cheeked lizard"); pronounced PAH-ray-ah-SORE-us Habitat Floodplains of southern Africa Historical Period Late Permian (250 million years ago) Size and Weight About eight feet long and 1,000-2,000 pounds Diet Plants Distinguishing Characteristics Thick-set body with light armor plating; blunt snout During the Permian period, pelycosaurs and therapsids occupied the mainstream of reptile evolution--but there were also plenty of bizarre "one-offs," chief among them the creatures known as pareiasaurs. The eponymous member of this group, Pareiasaurus, was an anapsid reptile that looked like a grey, skinless buffalo on steroids, mottled with various warts and odd protrusions that likely served some armoring function. As is often the case with animals that give their names to broader families, less is known about Pareiasurus than about a better-known pareiasaur of Permian southern Africa, Scutosaurus. (Some paleontologists speculate that pareiasaurs may have lain at the root of turtle evolution, but not everyone is convinced!) 31 of 37 Petrolacosaurus Petrolacosaurus. BBC Name: Petrolacosaurus; pronounced PET-roe-LACK-oh-SORE-us Habitat: Swamps of North America Historical Period: Late Carboniferous (300 million years ago) Size and Weight: About 16 inches long and less than a pound Diet: Probably insects Distinguishing Characteristics: Small size; splayed limbs; long tail Probably the unlikeliest creature ever to be portrayed on the popular BBC series Walking with Beasts, Petrolacosaurus was a tiny, lizard-like reptile of the Carboniferous period that's famous for being the earliest known diapsid (a family of reptiles, comprising archosaurs, dinosaurs and crocodiles, that had two characteristic holes in their skulls). However, the BBC committed a boo-boo when it posited Petrolacosaurus as a plain-vanilla reptile ancestral to both synapsids (which comprise therapsids, the "mammal-like reptiles," as well as true mammals) and diapsids; since it was already a diapsid, Petrolacosaurus couldn't have been directly ancestral to synapsids! 32 of 37 Philydrosauras Philydrosauras. Chuang Zhao Name Philydrosauras (Greek derivation uncertain); pronounced FIE-lih-droe-SORE-us Habitat Shallow waters of Asia Historical Period Middle Jurassic (175 million years ago) Size and Weight Less than a foot long and a few ounces Diet Probably fish and insects Distinguishing Characteristics Small size; long tail; lizard-like body Normally, a creature like Philydrosauras would be relegated to the fringes of paleontology: it was small and inoffensive, and occupied an obscure branch of the reptile evolutionary tree (the "choristoderans," a family of semi-aquatic diapsid lizards). However, what makes this particular choristoderan stands out is than an adult specimen was fossilized in the company of its six offspring--the only reasonable explanation being that Philydrosauras cared for its young (at least briefly) after they were born. While it's likely that at least some reptiles of the earlier Mesozoic Era cared for their young as well, the discovery of Philydrosaurus gives us conclusive, fossilized proof of this behavior! 33 of 37 Procolophon Procolophon. Nobu Tamura Name: Procolophon (Greek for "before the end"); pronounced pro-KAH-low-fon Habitat: Deserts of Africa, South America and Antarctica Historical Period: Early Triassic (250-245 million years ago) Size and Weight: About one foot long and a few pounds Diet: Plants Distinguishing Characteristics: Small size; sharp beak; lightly armored head Like its fellow vegetarian, Hypsognathus, Procolophon was one of the few anapsid reptiles to survive beyond the Permian-Triassic boundary 250 million years ago (anapsid reptiles are distinguished by the characteristic lack of holes in their skulls, and are represented today only by modern turtles and tortoises). To judge from its sharp beak, oddly shaped teeth and relatively strong forelimbs, Procolophon evaded both predators and the daytime heat by burrowing underground, and may have subsisted on roots and tubers rather than above-ground vegetation. 34 of 37 Scleromochlus Scleromochlus. Vladimir Nikolov Name: Scleromochlus (Greek for "hardened lever"); pronounces SKLEH-roe-MOE-kluss Habitat: Swamps of western Europe Historical Period: Late Triassic (210 million years ago) Size and Weight: About 4-5 inches long and a few ounces Diet: Probably insects Distinguishing Characteristics: Small size; long legs and tail Every now and then, the vagaries of fossilization throw a bony wrench into the carefully laid plans of paleontologists. A good example is the tiny Scleromochlus, a skittering, long-limbed, late Triassic reptile that (as far as experts can tell) was either ancestral to the first pterosaurs or occupied a poorly understood "dead end" in reptilian evolution. Some paleontologists assign Scleromochlus to the controversial family of archosaurs known as "ornithodirans," a group which may or may not even turn out to make sense from a taxonomic standpoint. Confused yet? 35 of 37 Scutosaurus Scutosaurus. Wikimedia Commons Name: Scutosaurus (Greek for "shield lizard"); pronounced SKOO-toe-SORE-us Habitat: Riverbanks of Eurasia Historical Period: Late Permian (250 million years ago) Size and Weight: About six feet long and 500-1,000 pounds Diet: Plants Distinguishing Characteristics: Short, straight legs; thick body; short tail Scutosaurus appears to have been a relatively evolved anapsid reptile that was, however, far removed from the mainstream of reptile evolution (the anapsids weren't nearly as important, historically speaking, as contemporary therapsids, archosaurs and pelycosaurs). This buffalo-sized herbivore had rudimentary armor plating, which covered its thick skeleton and well-muscled torso; it clearly needed some form of defense, since it must have been an exceptionally slow and lumbering creature. Some paleontologists speculate that Scutosaurus may have roamed the floodplains of the late Permian period in large herds, signaling to one another with loud bellows--a supposition supported by an analysis of this prehistoric reptile's unusually large cheeks. 36 of 37 Spinoaequalis Spinoaequalis. Nobu Tamura Name Spinoaequalis (Greek for "symmetrical spine"); pronounced SPY-no-ay-KWAL-iss Habitat Swamps of North America Historical Period Late Carboniferous (300 million years ago) Size and Weight About one foot long and less than a pound Diet Marine organisms Distinguishing Characteristics Slender body; long, flat tail Spinoaequalis is an important evolutionary "first" in two different ways: 1) it was one of the first true reptiles to "de-evolve" to a semi-aquatic lifestyle, not long after ancestral reptiles like Hylonomus had themselves evolved from amphibian ancestors, and 2) it was one of the first diapsid reptiles, meaning it possessed two characteristic holes on the sides of its skull (a trait Spinoaequalis shared with its rough contemporary, Petrolacosaurus). The "type fossil" of this late Carboniferous reptile was discovered in Kansas, and its proximity to the remains of saltwater fish are a hint that it may have occasionally migrated from its freshwater habitat into the ocean, possibly for mating purposes. 37 of 37 Tseajaia Tseajaia. Nobu Tamura Name Tseajaia (Navajo for "rock heart"); pronounced SAY-ah-HI-yah Habitat Swamps of North America Historical Period Early Permian (300 million years ago) Size and Weight About three feet long and a few pounds Diet Probably plants Distinguishing Characteristics Small size; long tail Over 300 million years ago, during the Carboniferous period, the most advanced amphibians began to evolve into the first true reptiles--but the first stop was the appearance of "amniotes," reptile-like amphibians that laid their eggs on dry land. As amniotes go, Tseajaia was relatively undifferentiated (read "plaid vanilla") but also extremely derived, since it actually dates to the beginning of the Permian period, tens of millions of years after the first true reptiles appeared. It has been classified as belonging to a "sister group" of the diadectids (typified by Diadectes), and was closely related to Tetraceratops.