#stem-mammals

[a-dinosaur-a-day]

I personally call Dimetrodon and early synapsids like that "mammaloids" to differentiate them from the diapsid lineage (which I call reptiles for the sake of convenience). This linguistically makes sense to me because if humans are humanoid, then mammals are mammaloid.

Ooh I like that. I usually go with stem-mammals in most situations, but mammaloid is a great word

[synapsidgirl]

I did a thing.

Compression completely screwed up the background, but other than that, I pretty happy with it. It’s still a WIP, with placeholder eyes and tusks, and of course he’s missing his claws, because I completely forgot to retopo them, and couldn’t be bothered to do it yesterday.

I’m also going to have to add more resolution on a tail, and check what exactly is going on with the back legs and the head - you can’t see it in the video, but there’s some strange deformation going on in those at some points.

I’ll probably have to manually assign what’s supposed to be deformed with what instead of relying on automatic weights, but, again... to lazy to do this just now.

I also modeled him in a way that allows to animate his mouth opening and closing, but I’d have to make new armature to do this, and it’d be the first time I’d be animating mouth on anything, so it’ll probably be a while before I do this. I’m not even sure the mesh in and around the mouth is done correctly for this. I’m guessing it’ll take quite a bit of trial and error to get something I’ll be happy with.

Also, this isn’t supposed to be realistic walk cycle. I just had a thought of: “but what if... a cheerful Diictodon?” and that’s what this is.

And despite the long litany of shouls-be’s and I’ll-have-to’s I’m seriously really pleased with this little guy.

[alphynix]

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.

———

Nix Illustration | Tumblr | Pillowfort | Twitter | Patreon

[alphynix]

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.

Tumblr | Pillowfort | Twitter | Patreon

[alphynix]

Dicynodonts were a group of herbivorous animals with toothless beaks and protruding tusks, part of the synapsid lineage and much closer related to mammals than to reptiles. They were some of the most successful and widespread land vertebrates from the Late Permian to the Middle Triassic, with one genus even briefly taking over the world in the aftermath of the End-Permian mass extinction event.

And it turns out some of them got very big.

Fossils of a surprisingly large dicynodont were first reported in 2008, but it wasn’t until just recently in late 2018 that this giant creature was finally given an official name -- Lisowicia bojani.

Close in size to a modern elephant, at around 2.6m tall (8′6″) and 4.5m long (14′9″), it was by far the largest known example of its kind to have ever lived. And while most other dicynodonts had upright hindlimbs and sprawling forelimbs, Lisowicia seems to have developed a fully upright posture much more similar to that of quadrupedal dinosaurs and modern mammals.

It was also one of the very last of its kind, living during the Late Triassic of Poland, about 208 million years ago (although there was a possible later survivor in Australia). This was around the same time that early sauropod dinosaurs were likewise first starting to experiment with gigantism, suggesting that both groups were convergently evolving to exploit newly-available ecological niches.

[alphynix]

Procynosuchus delaharpeae, a synapsid from the Late Permian (~259-252 mya). Measuring about 60cm long (2′), it was one of the earliest members of the cynodonts, the lineage that would eventually lead to mammals.

Its fossils are mostly known from southern Africa, but similar remains have also been found in Europe and Russia, suggesting it was actually quite widespread across the supercontinent of Pangaea that existed at the time.

It had a long vertically-flattened tail, strong leg muscles, and paddle-like feet -- all adaptations that suggest it was a semi-aquatic otter-like animal capable of agile swimming. It also had forward-facing eyes, giving it good binocular vision and depth perception while pursuing fish underwater.

[alphynix]

Who’s that synapsid?

It’s Bulbasaurus phylloxyron!

This creature was a member of the dicynodonts, a group of herbivorous mammal-relatives with beaks and protruding tusks. Its fossils are known from the Late Permian of South Africa, about 259-254 million years ago, and it would have been roughly the size of a cat, around 60cm long (2′).

It wasn’t officially named after the pokémon character Bulbasaur, but instead in reference to the bulbous bosses on its snout. But combined with how the species name “phylloxyron” means “leaf razor”, it doesn’t seem to entirely be a coincidence.

[alphynix]

The recently-described Ascendonanus nestleri from the Early Permian of Germany (~290 mya). This 40cm long (1′4″) animal was a member of a group called varanopids -- which may have been an early branch of the synapsid lineage and distantly related to modern mammals*.

Known from several near-complete fossils that include rare soft tissue impressions, it’s the first varanopid to show preserved skin details -- revealing a pattern of very lizard-like rectangular scales. If it is a synapsid this is a pretty big deal, since early synapsids were previously thought to have had scale-less leathery skin.

It also had unusual mosaic-like patches of tiny osteoderms above its eyes, a feature previously known only in some temnospondyl amphibians. Whether this was the result of convergent evolution or the trait actually being ancestral to most tetrapods is unclear.

Its slender body, long digits, and highly curved claws indicate it was an agile climber. It probably mainly lived up in the treetops, feeding on insects, making it one of the earliest known tetrapods specialized for an arboreal lifestyle.

(*Maybe. There's apparently an upcoming study that suggests varanopids might actually be sauropsids instead.)