#caseasauria

Angelosaurus dolani was an early synapsid, part of the caseid family and closely related to the more well-known Cotylorhynchus.

Living in what is now Texas, USA during the mid-Permian, about 270 million years ago, it's only known from partial skeletal remains but was probably around 3m long (~10').

Like other large herbivorous caseids it would have had a tiny head with proportionally big nostrils, a short neck, a large barrel-shaped body accommodating a voluminous gut, a long tail, and strong sprawling limbs. But compared to its relatives Angelosaurus was particularly bulky, with shorter thicker heavily-muscled limbs and stubbier digits ending in broad hoof-like claws.

In closely related caseids the presence of teeth on the roof of the mouth and a well-developed hyoid apparatus suggests these animals had big tough tongues, which may have been used to mash mouthfuls of plant matter against the palatal teeth to partially break it up before swallowing.

Based on skin impressions from other early synapsids, Angelosaurus probably had crocodilian-like scutes on some parts of its body – likely on its underside and tail, and maybe also on the top of the head as indicated by the pitted bone texture of caseid skulls – but whether the rest of its skin was scaly or naked and glandular is currently unknown.

In recent years there have also been some proposals that large caseids may have had a semiaquatic hippo-like ecology, but this idea is controversial.

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Rain Frog inspired Caseid

Lineart & Speedpaint.

The Synapsid kids are going to kill me for the comparison.

Weird Heads Month #02: Tiny Heads

Sometimes the really weird thing about a head isn't any sort of ridiculous ornamentation.

Sometimes it's just the wrong size.

That's what was going on with Cotylorhynchus romeri from the early Permian of North America, living about 280-272 million years ago. Despite looking like a big fat lizard this creature was actually a very early synapsid, closer related to modern mammals than to reptiles, and it was a distant cousin of other stem-mammals like the famous Dimetrodon.

Around 3.5m long (11'6"), it was one of the largest herbivores of the early Permian, with a very wide barrel-shaped body, chunky limbs, and a comically small head. Such a tiny head isn't necessarily unique – another synapsid Edaphosaurus also had a fairly small skull compared to its body, and dinosaurs like stegosaurs, sauropods, and moa had heads even more disproportional. But something about Cotylorhynchus in particular just looks… incredibly odd.

It also had some surprisingly sizeable nostril openings in that little skull, and it had may have had a very good sense of smell or perhaps some sort of specialized breathing system like the modern saiga's "air conditioning" nose.

Although usually depicted as a fully terrestrial animal, the structure of Cotylorhynchus' bones and its flattened paddle-like hands and feet have recently been used to suggest that it may have been semi-aquatic, more of a Permian hippo than a cow. But such a lifestyle would have required it to have a much more efficient method of breathing than previously thought – suggesting it had a mammal-like diaphragm, and possibly also explaining that weird nose.

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