Pictures and Profiles of Therapsids

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Meet the Mammal-Like Reptiles of the Paleozoic Era

Therapsids, also known as mammal-like reptiles, evolved during the middle Permian period and went on to live alongside the earliest dinosaurs. On the following slides, you'll find pictures and detailed profiles of over three dozen therapsid reptiles, ranging from Anteosaurus to Ulemosaurus.

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Anteosaurus

Name:

Anteosaurus (Greek for "early lizard"); pronounced ANN-tee-oh-SORE-us

Habitat:

Swamps of southern Africa

Historical Period:

Late Permian (265-260 million years ago)

Size and Weight:

About 20 feet long and one ton

Diet:

Probably meat

Distinguishing Characteristics:

Large size; long, crocodile-like tail; weak limbs

Anteosaurus looked remarkably like a dinosaur caught halfway between evolving into a crocodile: this huge therapsid (a member of the family of mammal-like reptiles that preceded the dinosaurs) had a streamlined, crocodilian body with a huge snout, and its puny-looking limbs lead paleontologists to believe that it spent most of its life in water. As with many therapsids, the feature of Anteosaurus that gets experts' hearts pounding is its teeth, a melange of canines, molars and incisors that could have been used to rip into everything from overgrown ferns to the small, quivering reptiles of the late Permian period.

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Arctognathus

Name:

Arctognathus (Greek for "bear jaw"); pronounced ark-TOG-nath-us

Habitat:

Plains of southern Africa

Historical Period:

Late Permian (250 million years ago)

Size and Weight:

About three feet long and 20-25 pounds

Diet:

Meat

Distinguishing Characteristics:

Long legs; canine-like build

The Karoo Basin in South Africa has proven to be a rich source of some of the world's strangest prehistoric animals: the therapsids, or "mammal-like reptiles." A close relative of Gorgonops and the similarly named Arctops ("bear face"), Arctognathus was a disturbingly canine-looking reptile, equipped with long legs, a short tail, a vaguely crocodilian snout, and (as far as paleontologists can tell) a mammal-like coat of fur. At three feet long, Arctognathus was smaller than most of its contemporaries, meaning it probably preyed on skittering amphibians and lizards much lower down on the Permian food chain.

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Arctops

Name:

Arctops (Greek for "bear face"); pronounced ARK-tops

Habitat:

Plains of southern Africa

Historical Period:

Late Permian (250 million years ago)

Size and Weight:

About six feet long and 100 pounds

Diet:

Meat

Distinguishing Characteristics:

Moderate size; long legs; crocodile-like snout

Some of the therapsids, or "mammal-like reptiles," of the Permian period were very mammal-like indeed. A good example is Arctops, the "bear face," an uncannily canine-looking reptile equipped with long legs, a short tail, and a crocodile-like snout with two prominent fangs (Arctops presumably possessed fur as well, though this feature hasn't been preserved in the fossil record, and probably a warm-blooded metabolism.) Just one of numerous therapsids of late Permian southern Africa, Arctops was closely related to the even more impressively named Gorgonops, the "Gorgon face."

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Biarmosuchus

Name:

Biarmosuchus (Greek for "Biarmia crocodile"); pronounced bee-ARM-oh-SOO-cuss

Habitat:

Woodlands of central Asia

Historical Period:

Late Permian (255 million year ago)

Size and Weight:

About four feet long and 50 pounds

Diet:

Meat

Distinguishing Characteristics:

Large head; slender legs

An otherwise unremarkable therapsid — the family of "mammal-like reptiles" that preceded the dinosaurs and spawned the earliest mammals — Biarmosuchus is notable for being (as far as paleontologists can tell) a relatively primitive example of the breed, dating all the way back to the late Permian period. This dog-sized reptile had slender legs, a large head, and sharp canines and incisors that indicate a carnivorous lifestyle; as with all therapsids, it's possible that Biarmosuchus was also blessed with a warm-blooded metabolism and a doglike coat of fur, though we may never know for sure.

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Chiniquodon

Name:

Chiniquodon (Greek for "Chiniqua tooth"); pronounced chin-ICK-woe-don

Habitat:

Woodlands of South America

Historical Period:

Middle Triassic (240-230 million years ago)

Size and Weight:

About two feet long and 5-10 pounds

Diet:

Meat

Distinguishing Characteristics:

Large head; quadrupedal posture; vaguely feline appearance

Today, Chiniquodon is the generally accepted name for what had previously been classified as three separate therapsid genera: Chiniquodon, Belosodon and Probelosodon. Essentially, this mammal-like reptile looked like a scaled-down jaguar, with its unusually elongated head, coat of insulating fur and (presumably) warm-blooded metabolism. The middle Triassic Chiniqudon also possessed more rear teeth than other therapsids of its time — ten each in its upper and lower jaws — which means it likely crushed its prey's bones to get to the tasty marrow inside.

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Cynognathus

Cynognathus possessed many "modern" features normally associated with mammals (which evolved tens of millions of years later). Paleontologists believe this therapsid sported hair, and may even have given birth to live young rather than laying eggs.

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Deuterosaurus

Name:

Deuterosaurus (Greek for "second lizard"); pronounced DOO-teh-roe-SORE-us

Habitat:

Woodlands of Siberia

Historical Period:

Middle Permian (280 million years ago)

Size and Weight:

About 18 feet long and one ton

Diet:

Probably omnivorous

Distinguishing Characteristics:

Large size; thick skull; quadrupedal posture

Deuterosaurus is a good example of the family of therapsids (mammal-like reptiles) known as anteosaurs, after the poster genus Anteosaurus. This large, landbound reptile had a thick trunk, sprawling legs, and a relatively blunt, thick skull with sharp canines in the upper jaws. As is the case with many large therapsids of the Permian period, it's unclear if Deuterosaurus was a herbivore or a carnivore; some experts think it may have been omnivorous, a bit like a modern grizzly bear. Unlike other therapsids, it was probably covered with scaly, reptilian skin rather than fur.

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Dicynodon

Name:

Dicynodon (Greek for "two dog toothed"); pronounced die-SIGH-no-don

Habitat:

Woodlands of the southern hemisphere

Historical Period:

Late Permian (250 million years ago)

Size and Weight:

About four feet long and 25-50 pounds

Diet:

Plants

Distinguishing Characteristics:

Narrow build; beaked skull with two large canines

Dicynodon ("two dog toothed") was a relatively plain-vanilla prehistoric reptile that has given its name to an entire family of therapsids, the dicynodonts. The most notable feature of this slender, inoffensive plant-eater was its skull, which had a horny beak and lacked any teeth save for two large canines protruding from the upper jaw (hence its name). Dicynodon was one of the most common therapsids (mammal-like reptiles) of the late Permian period; its fossils have been unearthed all over the southern hemisphere, including Africa, India and even Antarctica, prompting its waggish description as the Permian equivalent of a rabbit.

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Diictodon

Name:

Diictodon (Greek for "two weasel toothed"); pronounced die-ICK-toe-don

Habitat:

Woodlands of southern Africa

Historical Period:

Late Permian (250 million years ago)

Size and Weight:

About 18 inches long and a few pounds

Diet:

Plants

Distinguishing Characteristics:

Narrow body; quadrupedal posture; oversized head with two shark tusks

As you might have guessed from its name, Diictodon ("two weasel toothed") was closely related to another early therapsid, Dicynodon ("two dog toothed"). Unlike its more famous contemporary, though, Diictodon made its living by burrowing into the ground, both to regulate its body temperature and to hide from larger predators, a behavior shared by yet another Permian therapsid, Cistecephalus. Judging by its numerous fossil remains, some paleontologists think only male Diictodons had tusks, though this matter has yet to be conclusively settled.

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Dinodontosaurus

Name:

Dinodontosaurus (Greek for "terrible toothed lizard"); pronounced DIE-no-DON-toe-SORE-us

Habitat:

Woodlands of South America

Historical Period:

Middle Triassic (240-230 million years ago)

Size and Weight:

About eight feet long and a few hundred pounds

Diet:

Probably omnivorous

Distinguishing Characteristics:

Stocky build; tusks in upper jaw

The dicynodont ("two-dog-toothed) reptiles of the Permian period were relatively small, inoffensive creatures, but not so their Triassic descendants like Dinodontosaurus. This dicynodont therapsid ("mammal-like reptile") was one of the largest terrestrial animals of Triassic South America, and judging by the remains of ten juveniles found jumbled together, it boasted some fairly advanced parenting skills for its time. The "terrible tooth" part of this reptile's long name refers to its impressive tusks, which may or may not have been used to slash at live prey.

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Dinogorgon

Name:

Dinogorgon (Greek for "terrible gorgon"); pronounced DIE-no-GORE-gone

Habitat:

Woodlands of southern Africa

Historical Period:

Late Permian (250 million years ago)

Size and Weight:

About 10 feet long and 200-300 pounds

Diet:

Meat

Distinguishing Characteristics:

Large skull; cat-like build

One of the most fearsomely named of all the therapsids — the mammal-like reptiles that preceded and lived alongside the dinosaurs, and gave rise to the earliest mammals during the Triassic period — Dinogorgon occupied the same niche in its African environment as a modern big cat, preying on its fellow reptiles. Its closest relatives seem to have been two other predatory South American therapsids, Lycaenops ("wolf face") and Gorgonops ("gorgon face"). This reptile was named after the Gorgon, the monster from Greek myth who could turn men into stone with a single gaze from her penetrating eyes.

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Estemmenosuchus

Name:

Estemmenosuchus (Greek for "crowned crocodile"); pronounced ESS-teh-MEN-oh-SOO-kuss

Habitat:

Woodlands of eastern Europe

Historical Period:

Late Permian (255 million years ago)

Size and Weight:

About 13 feet long and 500 pounds

Diet:

Probably omnivorous

Distinguishing Characteristics:

Large size; sprawling legs; blunt horns on skull

Despite its name, which means "crowned crocodile," Estemmenosuchus was actually a therapsid, the family of reptiles ancestral to the earliest mammals. With its large skull, sprawled, stumpy legs and squat, cow-like body, Estemmenosuchus wouldn't have been the speediest land animal of its time and place, but fortunately super-agile predators had yet to evolve in the late Permian period. As with other large therapsids, experts aren't quite sure what Estemmnosuchus ate; the safest bet is that it was an opportunistic omnivore.

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Exaeretodon

Name:

Exaeretodon (Greek derivation uncertain); pronounced EX-eye-RET-oh-don

Habitat:

Swamps of South America and southern Asia

Historical Period:

Late Triassic (230 million years ago)

Size and Weight:

About 5-6 feet long and 100-200 pounds

Diet:

Plants

Distinguishing Characteristics:

Large size; grinding teeth in jaws

As mammal-like reptiles go, Exaeretodon seems to have been comparable in its habits (if not in its size and appearance) to a modern sheep. This plant-eating therapsid was equipped with grinding teeth in its jaws — a distinctly mammalian trait — and its young were born without the ability to chew, which presumably necessitated a high level of postnatal parental care. Perhaps most remarkably, females of the species gave birth to only one or two young at a time, as evidenced by fossil specimens discovered by the famous South American paleontologist Jose F. Bonaparte.

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Gorgonops

Name:

Gorgonops (Greek for "Gorgon face"); pronounced GORE-gone-ops

Habitat:

Plains of South Africa

Historical Period:

Late Permian (255-250 million years ago)

Size and Weight:

About 10 feet long and 500-1,000 pounds

Diet:

Meat

Distinguishing Characteristics:

Long, flat head with canine teeth; possible bipedal posture

Not much is known about Gorgonops, a genus of therapsid (the "mammal-like reptiles" that preceded the dinosaurs and gave rise to the earliest mammals) that's represented by a handful of species. What we do know is that Gorgonops was one of the largest predators of its day, attaining a respectable lengths of about 10 feet and weights of 500 to 1,000 pounds (not much to brag about compared to later dinosaurs, but fearsome enough for the late Permian period). As with other therapsids, it's possible that Gorgonops may have been warm-blooded and/or sported a coat of fur, but pending further fossil discoveries we may never know for sure.

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Hipposaurus

Name:

Hipposaurus (Greek for "horse lizard"); pronounced HIP-oh-SORE-us

Habitat:

Woodlands of southern Africa

Historical Period:

Late Permian (255 million years ago)

Size and Weight:

About four feet long and 100 pounds

Diet:

Probably omnivorous

Distinguishing Characteristics:

Squat trunk; quadrupedal posture; weak jaws

The most notable thing about Hipposaurus, the "horse lizard," is how little it resembled a horse — though presumably the famous paleontologist Robert Broom couldn't have known that when he named this genus back in 1940. Based on an analysis of its skull, this mid-sized therapsid (mammal-like reptile) of the late Permian period appears to have had very weak jaws, meaning it would have been restricted in its diet to small, easily chewed plants and animals. And in case you were wondering, it wasn't even close to being horse-sized, only weighing about 100 pounds.

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Inostrancevia

Name:

Inostrancevia (after Russian geologist Alexander Inostrantsev); pronounced EE-noh-stran-SAY-vee-ah

Habitat:

Woodlands of Eurasia

Historical Period:

Late Permian (250 million years ago)

Size and Weight:

About 10 feet long and 500-1,000 pounds

Diet:

Small animals

Distinguishing Characteristics:

Large size; sharp teeth

Inostrancevia's claim to fame is that it's the largest "gorgonopsid" therapsid yet discovered, a 10-foot-long Permian reptile that looked ahead to the large dinosaurs of the Mesozoic Era, which was just around the corner, geologically speaking. As well-adapted as it must have been to its Siberian environment, though, Inostrancevia and its fellow gorgonopsids (such as Gorgonops and Lycaenops) didn't make it past the Permian-Triassic boundary, though the smaller therapsids to which it was related went on to spawn the first mammals.

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Jonkeria

Name:

Jonkeria (Greek for "from Jonkers"); pronounced yon-KEH-ree-ah

Habitat:

Woodlands of southern Africa

Historical Period:

Middle Permian (270 million years ago)

Size and Weight:

About 16 feet long and 500 pounds

Diet:

Unknown

Distinguishing Characteristics:

Large size; pig-like build; quadrupedal posture

Jonkeria was very similar to its south African relative Titanosuchus, although slightly bigger and with shorter, stouter legs. This therapsid (mammal-like reptile) is represented by numerous species, a sure sign that some of these species may eventually be "downgraded," eliminated, or assigned to other genera. The most controversial thing about Jonkeria is what it ate — paleontologists can't decide if this Permian creature hunted the large, slow-moving pelycosaurs and archosaurs of its day, subsisted on plants, or perhaps enjoyed an omnivorous diet.

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Kannemeyeria

Name:

Kannemeyeria ("Kannemeyer's lizard"); pronounced CAN-eh-my-AIR-ee-ah

Habitat:

Woodlands of Africa, Asia, South America and India

Historical Period:

Early Triassic (245-240 million years ago)

Size and Weight:

About 10 feet long and 500 pounds

Diet:

Plants

Distinguishing Characteristics:

Large head; squat trunk; quadrupedal posture with splayed legs

One of the most widespread of all the therapsids (mammal-like reptiles) of the early Triassic period, species of Kannemeyeria have been unearthed as far afield as Africa, India and South America. This large, ungainly-looking reptile seems to have led a cowlike existence, munching mindlessly on vegetation whilst evading attack by smaller, nimbler, predatory therapsids and archosaurs (however, it belonged to a different therapsid branch than the one that actually evolved into mammals!). A related genus, the Chinese Sinokannemeyeria, may yet prove to be a species of Kannemeyeria.

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Keratocephalus

Name:

Keratocephalus (Greek for "horned head"); pronounced KEH-rat-oh-SEFF-ah-luss

Habitat:

Swamps of southern Africa

Historical Period:

Middle Permian (265-260 million years ago)

Size and Weight:

About nine feet long and one ton

Diet:

Probably meat

Distinguishing Characteristics:

Stocky build; blunt snout; short horn on nose

Since it was discovered in the Tapinocephalus Assemblage Beds in South Africa, you may not be surprised to learn that Keratocephalus was a close relative of Tapinocephalus, another plus-sized therapsid of the middle Permian period. The interesting thing about Keratocephalus is that it's represented in the fossil record by a variety of differently shaped skulls — some long-snouted, some short-snouted — which may be a sign of sexual differentiation or (alternately) a hint that its genus was comprised of several different species.

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Lycaenops

Name:

Lycaenops (Greek for "wolf face"); pronounced LIE-can-ops

Habitat:

Woodlands of southern Africa

Historical Period:

Middle Permian (280 million years ago)

Size and Weight:

About three feet long and 20-30 pounds

Diet:

Meat

Distinguishing Characteristics:

Small size; fanged jaws; quadrupedal posture

One of the more mammalian of the therapsids, or "mammal-like reptiles," Lycaenops resembled a scaled-down wolf, with a slender build, narrow, fanged jaws and (probably) fur. Even more importantly for a Permian predator, Lycaenop's legs were relatively long, straight and narrow, compared to the splayed posture of its fellow reptiles (though not as long and straight as the legs of much later dinosaurs, which were characterized by their upright posture). There's no way to know for sure, but it's possible that Lycaenops hunted in packs to take down the larger therapsids of southern Africa like Titanosuchus.

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Lystrosaurus

Judging by the numerous fossil remains of Lystrosaurus that have been discovered as far afield as India, South Africa and even Antarctica, this mammal-like reptile of the late Permian period was impressively widespread for its time. See an in-depth profile of Lystrosaurus

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Moschops

It may seem hard to believe, but the huge Permian therapsid Moschops was the star of a short-lived kids' TV show back in 1983--though it's unclear whether the producers knew that it wasn't technically a dinosaur.

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Phthinosuchus

Name:

Phthinosuchus (Greek for "withered crocodile"); pronouced FTHIE-no-SOO-kuss

Habitat:

Woodlands of western Europe

Historical Period:

Middle-Late Permian (270-260 million years ago)

Size and Weight:

About five feet long and 100-200 pounds

Diet:

Probably meat

Distinguishing Characteristics:

Narrow skull with blunt snout; quadrupedal posture

Phthinosuchus is as mysterious as its name is unpronounceable: this "withered crocodile" was clearly a type of therapsid (aka mammal-like reptile), but it possessed many anatomical characteristics in common with the pelycosaurs, another branch of ancient reptiles that preceded the first dinosaurs and went extinct by the end of the Permian period. Because so little is known about Phthinosuchus, it lies on the fringes of therapsid classification, a situation that may change as more fossil specimens come to light.

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Placerias

Name:

Placerias; pronounced plah-SEE-ree-ahs

Habitat:

Plains of western North America

Historical Period:

Late Triassic (220-215 million years ago)

Size and Weight:

About 10 feet long and 1 ton

Diet:

Plants

Distinguishing Characteristics:

Squat body with quadrupedal posture; beak on snout; two small tusks

Placerias was one of the last of the dicynodont ("two-dog toothed") therapsids, the family of mammal-like reptiles that spawned the first true mammals. To draw a mammalian comparison, the squat, stocky-legged, one-ton Placerias bore an uncanny resemblance to a hippopotamus: it's even possible that this reptile spent much of its time in water, the way modern hippopatomuses do. Like other dicynodonts, Placerias was rendered extinct by the wave of better-adapted dinosaurs that appeared during the late Triassic period.

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Pristerognathus

Name:

Pristerognathus (Greek derivation uncertain); pronounced PRISS-teh-ROG-nah-thuss

Habitat:

Woodlands of southern Africa

Historical Period:

Late Permian (250 million years ago)

Size and Weight:

About six feet long and 100-200 pounds

Diet:

Meat

Distinguishing Characteristics:

Slender build; quadrupedal posture; large tusks in upper jaw

Pristerognathus was one of the many sleek, carnivorous therapsids (aka mammal-like reptiles) of late Permian South Africa; this genus was notable for its exceptionally large tusks, which it presumably used to inflict lethal wounds on the slower-moving reptiles of its ecosystem. It's possible that Pristerognathus hunted in packs, though as yet there's no evidence for this; in any event, the therapsids went extinct by the end of the Triassic period, though not before spawning the earliest mammals.

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Procynosuchus

Name:

Procynosuchus (Greek for "before the dog crocodile"); pronounced PRO-sigh-no-SOO-kuss

Habitat:

Woodlands of southern Africa

Historical Period:

Late Permian (255 million years ago)

Size and Weight:

About two feet long and 5-10 pounds

Diet:

Fish

Distinguishing Characteristics:

Narrow snout; paddle-like hind feet; quadrupedal posture

Procynosuchus was an early example of the "dog-toothed" therapsids, or "mammal-like reptiles," known as cynodonts (as opposed to dicynodonts, the "two-dog-toothed" therapsids; don't be too worried if all this jargon seems confusing!). Based on its anatomy, paleontologists believe Procynosuchus was an accomplished swimmer, diving into the lakes and rivers of its southern African habitat to nab small fish. This Permian creature had very mammal-like teeth, but its other anatomical features (such as its stiff spine) were decidedly reptilian.

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Raranimus

Name:

Raranimus (Greek for "rare spirit"); pronounced rah-RAN-ih-muss

Habitat:

Woodlands of Asia

Historical Period:

Early Permian (270 million years ago)

Size and Weight:

About two feet long and 5-10 pounds

Diet:

Probably omnivorous

Distinguishing Characteristics:

Small size; quadrupedal posture; canines in upper jaw

"Diagnosed" in 2009 on the basis of a single, partial skull, Raranimus may prove to be the earliest therapsid (mammal-like reptile) yet discovered — and since therapsids were directly ancestral to the first mammals, this tiny beast may inhabit a place near the root of the human evolutionary tree. The discovery of Raranimus in China hints that therapsids may have originated in Asia during the middle Permian period, then radiated out to other territories (notably southern Africa, where many therapsid genera dating to the late Permian have been found).

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Sinokannemeyeria

Name:

Sinokannemeyeria ("Kannemeyer's Chinese reptile"); pronounced SIGH-no-CAN-eh-my-AIR-ee-ah

Habitat:

Woodlands of Asia

Historical Period:

Middle Triassic (235 million years ago)

Size and Weight:

About six feet long and 500-1,000 pounds

Diet:

Plants

Distinguishing Characteristics:

Horny beak; short legs; barrel-shaped body

Like the widespread Lystrosaurus — of which it may have been a direct descendant — Sinokannemeyeria was a dicynodont, a subgroup of the therapsids, or mammal-like reptiles, that preceded the dinosaurs and eventually evolved into the first mammals of the late Triassic period. This herbivore cut an ungainly figure, with its thick, beaked head, toothless jaws, two short tusks, and pig-like profile; it probably subsisted on extremely tough vegetation, which it ground up with its massive jaws. Sinokannemeyeria may yet wind up being assigned as a species of its marginally more pronounceable cousin, Kannemeyeria.

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Styracocephalus

Name:

Styracocephalus (Greek for "spiked head"); pronounced STY-rack-oh-SEFF-ah-luss

Habitat:

Woodlands of southern Africa

Historical Period:

Late Permian (265-260 million years ago)

Size and Weight:

About 15 feet long and one ton

Diet:

Plants

Distinguishing Characteristics:

Large size; crest on head

In appearance, Styracocephalus looked ahead to the hadrosaurs, or duck-billed dinosaurs, of the late Cretaceous period: this was a large, quadrupedal, herbivorous therapsid ("mammal-like reptile") that sported a distinctive crest on its head, which may have varied in size and shape between males and females. Some paleontologists believe Styracocephalus spent part of its time in the water (like a modern hippopotamus), but as yet there's no firm evidence to support this conclusion. By the way, Styracocephalus was an entirely different creature from the later Styracosaurus, a ceratopsian dinosaur.

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Tetraceratops

Name:

Tetraceratops (Greek for "four-horned face"); pronounced TET-rah-SEH-rah-tops

Habitat:

Woodlands of North America

Historical Period:

Early Permian (290 million years ago)

Size and Weight:

About three feet long and 20-25 pounds

Diet:

Small animals

Distinguishing Characteristics:

Horns on face; lizard-like posture

Despite its name, Tetraceratops was an entirely different animal from Triceratops, a ceratopsian dinosaur that lived hundreds of millions of years later. In fact, this small lizard wasn't even a true dinosaur, but a therapsid ("mammal-like reptile"), by some accounts the earliest one yet discovered and closely related to the pelycosaurs (most famous example: Dimetrodon) that preceded it. All we know about Tetraceratops is based on a single skull found in Texas in 1908, which paleontologists continue to study as they puzzle out the evolutionary relationships among the earliest non-dinosaur reptiles.

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Theriognathus

Name:

Theriognathus (Greek for "mammal jaw"); pronounced THEH-ree-OG-nah-thuss

Habitat:

Woodlands of southern Africa

Historical Period:

Late Permian (250 million years ago)

Size and Weight:

About three feet long and 20-30 pounds

Diet:

Meat

Distinguishing Characteristics:

Narrow snout; slender build; possibly fur

If you happened across an adult Theriognathus 250 million years ago, during the late Permian period, you might be forgiven for mistaking it for a modern-day hyena or weasel — there's a good chance that this therapsid (mammal-like reptile) was covered with fur, and it certainly had the sleek profile of a mammalian predator. It's even conceivable that Theriognathus possessed a warm-blooded metabolism, though it's possible to take the mammalian analogies too far: for example, this ancient creature retained a distinctly reptilian jaw. For the record, the therapsids spawned the first true mammals of the late Triassic period, so maybe all those mammalian accoutrements wouldn't have been out of the question!

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Thrinaxodon

Paleontologists believe that Thrinaxodon may have been covered in fur, and also may have had a moist, cat-like nose. Completing the resemblance to modern tabbies, it's possible that the therapsid sported whiskers as well (and for all we know, orange and black stripes).

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Tiarajudens

Name:

Tiarajudens (Greek for "Tiaraju teeth"); pronounced tee-AH-rah-HOO-dens

Habitat:

Swamps of South America

Historical Period:

Late Permian (260 million years ago)

Size and Weight:

About four feet long and 75 pounds

Diet:

Plants

Distinguishing Characteristics:

Moderate size; large, saber-like canines

Prominent, saber-like canines are usually associated with megafauna mammals like the saber-tooth tiger (which used its dental equipment to inflict deep stab wounds on its unfortunate prey). That's what makes Tiarajudens so unusual: this dog-sized therapsid, or "mammal-like reptile," was clearly a devoted vegetarian, yet it possessed a pair of oversized canines on a par with anything sported by Smilodon. Clearly, Tiarajudens didn't evolve these canines to intimidate giant ferns; rather, they were most likely a sexually selected characteristic, meaning males with bigger choppers had the opportunity to mate with more females. There's also the chance that Tiarajudens used its teeth to keep the larger, carnivorous therapsids of the late Permian period at bay.

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Titanophoneus

Name:

Titanophoneus (Greek for "titanic murderer"); pronounced tie-TAN-oh-PHONE-ee-us

Habitat:

Woodlands of central Asia

Historical Period:

Late Permian (255-250 million years ago)

Size and Weight:

About eight feet long and 200 pounds

Diet:

Meat

Distinguishing Characteristics:

Long tail and head; short, sprawling legs

As therapsids, or mammal-like reptiles, go, Titanophoneus has been a bit oversold by paleontologists. True, this "titanic murderer" was probably dangerous to other therapsids of the late Permian period, but it must have been positively harmless compared to the bigger raptors and tyrannosaurs that lived almost 200 million years later. Probably the most advanced feature of Titanophoneus was its teeth: two dagger-like canines in front, accompanied by sharp incisors and flat molars in back for grinding up flesh. As with other mammal-like reptiles — which went on to spawn the first true mammals of the late Triassic period — it's possible that Titanophoneus was covered in fur and had a warm-blooded metabolism, though we may never know for sure.

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Titanosuchus

Name:

Titanosuchus (Greek for "giant crocodile"); pronounced tie-TAN-oh-SOO-kuss

Habitat:

Swamps of south Africa

Historical Period:

Late Permian (255 million years ago)

Size and Weight:

About six feet long and a few hundred pounds

Diet:

Probably fish and small animals

Distinguishing Characteristics:

Crocodile-like head and body

The impressively named Titanosuchus (Greek for "giant crocodile") is a bit of a cheat: this reptile wasn't a crocodile at all, but a therapsid (mammal-like reptile), and while it was fairly big by Permian standards it wasn't anywhere close to being a giant. As far as paleontologists can tell, Titanosuchus tilted decisively toward the reptile end of the "mammal-like reptile" spectrum, almost certainly having smooth, reptilian skin and lacking the presumed warm-blooded metabolism of later, furry therapsids. It was closely related to another early reptile with a deceptive name, the mostly harmless Titanophoneus ("giant murderer").

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Trirachodon

Name:

Trirachodon; pronounced try-RACK-oh-don

Habitat:

Woodlands of southern Africa

Historical Period:

Early Triassic (240 million years ago)

Size and Weight:

About one foot long and a few pounds

Diet:

Insects

Distinguishing Characteristics:

Small size; narrow snout; quadrupedal posture

Trirachodon represents one of the more spectacular fossil finds of recent years: a highway excavation crew near Johannesburg, in South Africa, uncovered a complete burrow containing 20 more-or-less complete Trirachodon specimens, ranging from juveniles to adults. Clearly, this small therapsid (mammal-like reptile) not only burrowed underground, but lived in social communities, an astonishingly advanced feature for a 240-million-year-old reptile. Previously, this type of behavior was thought to have begun with the earliest mammals of the Triassic period, which evolved millions of years later.

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Ulemosaurus

Name:

Ulemosaurus (Greek for "Ulema River lizard"); pronounced oo-LAY-moe-SORE-us

Habitat:

Woodlands of central Asia

Historical Period:

Late Permian (250 million years ago)

Size and Weight:

About 13 feet long and 1,000 pounds

Diet:

Probably omnivorous

Distinguishing Characteristics:

Dense skull; large, squat body

Like other large therapsids ("mammal-like reptiles") of the late Permian period, Ulemosaurus was a squat, splay-footed, extremely slow reptile that went completely unthreatened by the more agile predators that only evolved tens of millions of years later. This bull-sized creature was distinguished by its extremely thick skull, a sign that males may have head-butted one another for dominance within the herd. While its bulky body points to a herbivorous diet, some paleontologists believe Ulemosaurus (and other large therapsids) may have been opportunistically omnivorous, basically eating anything it could hope to digest.

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Strauss, Bob. "Pictures and Profiles of Therapsids." ThoughtCo, Feb. 16, 2021, thoughtco.com/therapsid-mammal-like-reptile-4043336. Strauss, Bob. (2021, February 16). Pictures and Profiles of Therapsids. Retrieved from https://www.thoughtco.com/therapsid-mammal-like-reptile-4043336 Strauss, Bob. "Pictures and Profiles of Therapsids." ThoughtCo. https://www.thoughtco.com/therapsid-mammal-like-reptile-4043336 (accessed April 7, 2025).