Tag: therapsid

Rechnisaurus

Rechnisaurus cristarhynchus here was a member of the dicynodonts, a group of stocky herbivorous beaky-jawed synapsids that were distantly related to modern mammals. Living in what is now eastern India during the Middle Triassic, about 247-242 million years ago, it’s only known from a single fossil skull – but based on the body proportions of better-known close relatives like Kannemeyeria it was probably somewhere around 1.2m long (~4′).

It had a raised bony crest running down the middle of its snout, with deep bowl-like depressions on either side that probably served to make the crest seem visually larger it already was. (They probably didn’t house any weird soft-tissue structures, however, since these type of dicynodonts tended to have very extensive keratinous coverings over their snouts.)

It also had raised bony areas around its parietal eye, and extensive bony flanges covering most of its tusks giving its face a sort of jowly appearance. All these features were probably for visual display and may have been brightly colored in life.

And, while I usually like to reconstruct dicynodonts as extensively fluffy… recently some fossil specimens of Lystrosaurus have been found showing bumpy leathery skin impressions. This doesn’t necessarily mean that all dicynodonts were hairless (especially since there are still those Permian coprolites), but since kannemeyeriiformes like Rechnisaurus were quite closely related to Lystrosaurus, I’ve gone with no fuzz at all on this one.

Ericiolacerta

The synapsids were an incredibly successful and diverse group during the Permian period, but after the devastating “Great Dying” mass extinction event 252 million years ago only three lineages survived into the Triassic – the cynodonts (close relatives and ancestors of modern mammals), the dicynodonts (beaked tusked weirdos who briefly took over the world), and the therocephalians.

Therocephalians were close relatives of cynodonts, and convergently evolved several very mammal-like anatomical features in their skulls, teeth, and limbs. But unlike their cousins this lineage never fully recovered in the Triassic, and they ultimately disappeared completely around 242 million years ago.

Ericiolacerta parva was one of these short-lived Mesozoic therocephalians, known from the early Triassic (~252-247 million years ago) of South Africa and Antarctica, in regions that were connected at the time as part of the supercontinent of Pangaea. It was a fairly small animal, about 20cm long (~8″), with small sharp teeth that indicate it mainly fed on insects, and semi-opposable thumbs and inner toes that suggest it was also a capable climber.

Holes in the bones of its snout would have carried numerous nerves and blood vessels, which may be evidence of sensitive fleshy lips and possibly whiskers. And while there’s no direct evidence of fur in therocephalians, they do appear to have been active warm-blooded animals – and possible fossilized synapsid hair from the Permian period suggests fuzziness might have been ancestral to all of the “protomammal” lineages that survived into the Triassic.

Perplexisaurus

If there’s any equivalent to carcinization in mammals, it’s turning into an otter-beaver-like semi-aquatic form.

Because it just keeps happening.

Modern examples alone include otters, beavers, muskrats, giant otter shrews, desmans, aquatic genets, yapoks, lutrine opossums, and platypuses – and in the fossil record there were early pinnipeds, remingtonocetids, pantolestids, stagodontids, and Liaoconodon going as far back as the early Cretaceous. Even outside of the true mammals there were also Castorocauda, Haldanodon, and Kayentatherium during the Jurassic, and much further back in the late Permian there was the early cynodont Procynosuchus.

So a non-cynodont synapsid doing the exact same thing really isn’t all that surprising.

Perplexisaurus foveatus was a member of the therocephalians, a group of synapsids that were close evolutionary “cousins” of the cynodonts-and-true-mammals lineage. Similar in size to a modern rat, about 20cm long (8″), it lived in Western Russia during the Late Permian about 268-265 million years ago.

At the time this region was a river plain with a tropical climate, experiencing seasonal floods that turned the whole area into what’s known as “viesses” (a name based on the abbreviation “V.S.S.” standing for “very shallow sea”), vast shallow lake-seas that persisted for weeks or months at a time.

So this little animal has been interpreted as being semi-aquatic, swimming around and feeding on aquatic invertebrates and tiny fish and amphibians. Its skull had numerous pits around the front of its face, suggesting that it had a highly sensitive snout – probably whiskery, allowing it to hunt entirely by touch in dark murky water, but it’s also been proposed to have possibly had an electroreceptive sense similar to modern platypuses.

Smilesaurus

Despite having a genus name that sounds more like it should belong to a cartoon dinosaur mascot for dental hygiene, Smilesaurus ferox was actually a real gorgonopsian, a predatory synapsid distantly related to modern mammals.

Living in South Africa during the Late Permian, around 259-254 million years ago, Smilesaurus was comparable to a medium-sized dog at around 1m long (3’3″). It had some of the longest sabre-like canine teeth of any known gorgonopsian, proportionally comparable to those of sabertoothed cats – and it may have hunted in a similar manner, using powerful grasping limbs to pin down struggling prey and then dispatching it with slashing bites.

…And it also turns out that when you don’t horribly shrink-wrap a gorgonopsian, you end up with something that looks rather like a bear-hippo.

(For some similarly chonky gorgonopsians, check out Tas’ @i-draws-dinosaurs reconstructions here. Bullet Man was definitely a bit of an inspiration in this.)

Haldanodon

The docodonts were a group of mammaliaformes (close relatives of the earliest true mammals) which lived across North America, Europe, and Asia from the Middle Jurassic to the Early Cretaceous. Originally only known from teeth and jaw fragments they were traditionally thought to be fairly generic shrew-like insectivores, but more recent discoveries of better fossils have revealed they were actually much more diverse, occupying ecological niches ranging from squirrel-like tree-climbers to mole-like diggers to beaver-otter-like swimmers.

Most of the more complete fossil material of these animals comes from the mid-Jurassic of China, but one species from elsewhere is also known from a partial skeleton.

Haldanodon exspectatus here lived in central Portugal during the Late Jurassic, about 155 million years ago. Around 15-20cm long (6-8″), it had small eyes and short chunky well-muscled limbs with the front paws adapted for digging. Since it inhabited a very swampy environment it probably wasn’t a pure mole-like burrower – extensive tunnels would have constantly flooded – but it may have instead been a similar sort of semi-aquatic animal to modern platypuses and desmans, foraging for invertebrates in the water and excavating burrows in the banks.

Roughened areas of bone on its snout may also have supported a patch of tough keratinous skin, which would have helped protect its face while digging.

Diictodon

Even before Lystrosaurus briefly took over the world, the dicynodont synapsids were a highly successful group. These herbivorous beaked-and-tusked mammal-cousins were abundant all over the supercontinent of Pangaea during the Late Permian and occupied a wide variety of ecological niches, ranging from rat-sized to almost bear-sized. (And later during the Triassic some got even bigger.)

Towards the smaller end of that size range were species like Diictodon. Living around 259-254 million years ago in Southern Africa (but with fossils also found in northern China, suggesting a much larger geographic range) this dicynodont grew up to about 45cm long (1’6″) and was a gopher-like creature adapted for digging, with a tubular body and short muscular limbs.

It was a very common animal, making up around half of all vertebrate fossils in some locations. Numerous preserved spiral-shaped burrows have been found concentrated in small areas, going down as much as 1.5m (5′) into the ground.

Several different species have been named within the Diictodon genus, but currently they’ve all been lumped together under the single name of Diictodon feliceps. There’s a lot of anatomical variation between specimens, though, with some notably being smaller and lacking the distinctive tusks seen in others – which may be evidence of sexual dimorphism, with the tuskless individuals possibly being females. (Although differences in inner ear anatomy may also indicate they were a separate species entirely, in which case female D. feliceps might instead be represented by fossils showing smaller tusks.)

I’ve illustrated one of the tuskless forms here, since they don’t generally get as much attention as the tusked ones. It’s also speculatively fluffy and iridescent similar to modern golden moles.

Weird Heads Month #30: Lumpy-Faced Synapsids

Among the synapsids (“proto-mammals”), head ornamentation evolved multiple times in the therapsids, from basal members of the group like Tetraceratops, burnetiamorphs, and dinocephalians to later lineages like dicynodonts and gorgonopsids.

But these sorts of structures don’t seem to have really ever developed in one of the lineages most closely related to the ancestors of modern mammals, a group known as therocephalians.

…With the exception of Choerosaurus dejageri.

Living in South Africa during the late Permian, around 259-254 million years ago, this small synapsid was only about 35cm long (1’2″) but sported some large bulging bony bosses on the sides of both its snout and lower jaw.

The bosses would have been covered by tough skin in life, similar to modern giraffid ossicones.

A study of Choerosaurus‘ skull found that its head was rather delicately built, and the bosses were relatively fragile and lacked the sort of reinforcement needed to resist impacts, suggesting that these structures weren’t used as weapons for fighting each other but were probably more for display – so they may even have been brightly colored.

The upper jaw bosses were also well-supplied with nerves and blood vessels, and would have been quite sensitive to touch.

Weird Heads Month #10: Permian Crowns

The tiny-headed Cotylorhynchus we saw earlier in this series wasn’t the only synapsid with a weird head.

A little more closely related to modern mammals, the dinocephalians were a a diverse group that were found across Pangaea during the middle of the Permian period. Many of them had thickened skulls that may have been used for headbutting each other, and some also developed bony horn-like projections around their faces.

And Estemmenosuchus mirabilis here was particularly elaborately ornamented, earning it a name meaning “wondrous crowned crocodile”. It lived in the Perm region of Russia during the mid Permian, about 268-265 million years ago, and was one of the largest dinocephalians, reaching at least 3m long (9’10”).

It had two big antler-like structures on its head, two wide cheek flanges, and a small nose horn, almost looking like the synapsid version of a ceratopsid dinosaur – and with its big bulky body, fairly erect-legged posture, and herbivorous-or-omnivorous diet it may have been a fairly close ecological equivalent to them, too.

But it’s also possible it was semi-aquatic, and it certainly does have a very hippo-like appearance when reconstructed with a decent amount of soft tissue.

One specimen of Estemmenosuchus even preserved skin impressions around its face, which were described in Russian in the early 1980s. They show scaleless glandular skin with a slightly bumpy texture, similar to that of hairless mammals or some amphibians. Since it occupied a point in the synapsid family tree close to where hair may have originated (somewhere in the Permian therapsids), it’s not clear if it was entirely hairless or if it had just secondarily lost some of it.

Tiarajudens

Synapsids just keep evolving saber teeth.

Both proto-mammals and true mammals have independently evolved oversized fangs quite a few different times in a lot of different lineages over the last few hundred million years (even in some modern ones), and one of the first to experiment with such a feature was Tiarajudens eccentricus.

Living in southern Brazil towards the end of the Permian period, about 265-260 million years ago, Tiarujudens was an early member of a group of known as anomodonts. These chunky herbivorous synapsids weren’t directly ancestral to modern mammals, but were instead evolutionary cousins, and their lineage eventually included tusked dicynodonts like the world-conquering Lystrosaurus.

Tiarajudens was around 1-1.2m long (3’3″-3’11”) and sported a pair of very long blade-like canine teeth in its upper jaw. Since the rest of its teeth were clearly adapted for eating plants – with one of the the earliest known examples of flat grinding molars that would have allowed it to chew up tough vegetation – these fangs probably served more of a display or defensive function.

The saber teeth may even have been a sexually dimorphic feature like in modern musk deer. Another anomodont from South Africa, Anomocephalus africanus, is incredibly similar to Tiarajudens except for a lack of fangs – and since South America and Africa were connected as part of Pangaea at the time, it’s possible that these two actually represent males and females of the same species.

Without finding a larger number of fossils we can’t know for certain, but it’s an interesting possibility at least.

Diademodon

Modern mammals are the only surviving members of a much larger evolutionary group known as the synapsids – which back in the Permian period were the dominant land vertebrates.

But much like all other life on Earth at the time, the synapsids were absolutely devastated in the “Great Dying” mass extinction at the end of the Permian, 252 million years ago. Only three lineages survived into the Triassic: the dicynodonts (who briefly took over the world), the therocephalians (who went extinct not long afterwards), and the cynodonts (who eventually gave rise to early mammals).

Diademodon tetragonus here lived right in the wake of the extinction during the Early and Middle Triassic, about 251-242 million years ago. Around 2m long (6′6″), it was one of the largest known cynodonts, and it must have been a fairly successful species since it ranged across a large chunk of Pangaea, known from modern southern Africa, South America and Antarctica.

It had pig-like cheekbones and enormous jaw muscles, along with sharp incisors and canine teeth at the front of its jaws and grinding molars at the back. This arrangement suggests that much like modern pigs it may have been an opportunistic omnivore, occasionally snacking on smaller animals and carrion – although an isotope analysis of its teeth indicates the vast majority of its diet was probably still vegetation in shady damp environments.