Colours of Wildlife: Biarmosuchians
Created | Updated Aug 12, 2018
Biarmosuchians
Willem is a wildlife artist based in South Africa. He says "My aim is simply to express the beauty and wonder that is in Nature, and to heighten people's appreciation of plants, animals and the wilderness. Not everything I paint is African! Though I've never been there, I'm also fascinated by Asia and I've done paintings of Asian rhinos and birds as well. I may in future do some of European, Australian and American species too. I'm fascinated by wild things from all over the world! I mainly paint in watercolours. . . but actually many media including 'digital' paintings with the computer!"
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On we go with the prehistoric beasties! I'm working on the pre-mammals, still … there's still a good bit of road to go. These ones you see here are called Biarmosuchians. They are what we would call basal therapsids. Let's look at the terminology and at the relationships.
Biarmosuchians are called so after one of the first members of the group, Biarmosuchus which means 'crocodile from Bjarmaland (a region in Russia)'. It's not a crocodile, though. It looks a bit like a dog crossed with a monitor lizard. The very first members of the group to which mammals belong, the synapsids, were very lizard-like. Initially they were quite small, but soon there were animals like Dimetrodon and Edaphosaurus which reached lengths of over 3 m. But they still had the reptile shape: long, heavy tail, short legs, rather sprawling posture. But whereas the first ones had teeth that were all similar in size and shape, by the time of Dimetrodon the teeth were starting to diversify: some were small, some much larger. A pair of teeth in each jaw were larger than the others, but not yet completely differentiated from them. This early pre-mammal stage is called the Pelycosaurs, and from this group (we don't know from exactly which species, but it was likely from a sphenacodont – a sail-less animal similar to Dimetrodon) that the first Biarmosuchians evolved. Biarmosuchus itself must be quite close to what the very first one looked like.
Compared to the sphenacodont pelycosaurs, the Biarmosuchians were another few steps closer to the later mammalian condition. All synapsids have the single opening on each side of the skull, behind the opening for the eyes. The opening in the pelycosaurs was rather small; in the Biarmosuchians, it enlarged. This hollow in the side of the skull was filled by muscle tissue; this means the Biarmosuchians had bigger jaw-closing muscles and thus a stronger bite. In Biarmosuchians, the canine teeth became completely differentiated from the other teeth (except in Nikkasaurus, a small and apparently very primitive species). Also the Biarmosuchians developed comparatively longer legs, and a more upright walking posture. Their leg orientation was intermediate between sprawling sideways, like modern lizards and crocodiles, and upright, like modern mammals such as dogs. Their feet faced forwards as they walked, and their toes were shorter, with fewer toe-bones in them compared to the long, lizard-like toes of the sphenacodonts. Their tails also were not quite as long and dragging as those of the earlier pre-mammals.
For these reasons, the Biarmosuchians are considered as heralding a new division in the pre-mammal classification – they're considered the most basal of the therapsids, the group that went on to produce the true mammals. Indeed, there were quite a few more steps to complete so as to yield the full mammalian condition. From these basal therapsids, the next group, the theriodonts (beast-toothed) evolved, from which the cynodonts (dog-toothed) evolved, the most advanced ones of which became the mammaliaforms (mammal-formed) and finally the true mammals. In my book, all these steps will be made clear, but I'm not concerned only with the line that lead to the true mammals, but also with all the side journeys along the way. The Burnetiamorphs, which I discussed in the previous article, was one such a side journey, not leading to the mammals but interesting in its own right. Burnetiamorphs were actually specialized Biarmosuchians. So in this article we're actually looking at the less specialized ones. But these less-specialized ones gave rise to the next two, more mammalian-like, groups, the Therocephalians, and the Gorgonopsians, a group I'll cover here in the future.
All of this was happening in the Permian period, the final one of the Palaeozoic or the Age of Ancient Life. Indeed, in this age the groundwork for modern life was being laid. It saw the diversification of the proper reptiles – the first lizard-like and turtle-like things were coming into existence. The end of the period saw the first archosaurs or 'ruling reptiles', from which crocodiles and dinosaurs (and from them later the birds) evolved. The ancestors of the mammals, especially, came into their own. They were indeed the most diverse and dominant group of land-living animals in the Permian. A vast amount of pre-mammalian diversity was lost at the end of the Permian, when a mass extinction wiped out as much as 90-95% of all ocean-living species and about 70% of all species living on land. Fortunately for us, a few pre-mammals pulled through, and rediversified to gave rise to yet new and interesting species.
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Biarmosuchus tener itself lived in Russia about 267 million years ago. It is known from many preserved skeletons, though there are a few bits of it we're not yet quite sure of. It was the size of a typical dog, with a skull of up to 20 cm/8" in length, and an overall body length of up to 1.5 m/5'. Its proportions indicate an animal that probably was fast and agile. It had the enlarged canine teeth typical of the group; the teeth in front and behind the canine teeth were much smaller, but also sharply pointed like the canines itself; it was still too soon for the highly evolved grinding and shearing teeth such as (most) true mammals possess. It's reasonable to conclude that Biarmosuchus was a hunter of small and quick animals – smaller synapsids as well as lizard-like reptiles, – and amphibians, with which the rivers and swamps abounded.
Also in Russia, skulls and skeletal parts of animals similar to Biarmosuchus were found – only, they were much larger. Eotitanosuchus olsonii ('Olson's dawn titan crocodile') could reach a length of 2.5 m/over 8", and Ivantosaurus ensifer ('Ivan's sword-bearing lizard') was larger still. In these two species, the opening in the skull was bigger, and the canine tooth had increased in size to the extent of becoming a 'sabre-tooth' such as those possessed (over 250 million years later) by certain cats now sadly extinct. These must have been fearsome top-predators in their days – maybe semi-aquatic like crocodiles, ambushing their prey at drinking sites. Some scientists think that Eotitanosuchus and Ivantosaurus were actually the adults and Biarmosuchus the juveniles of a single species. But others say that the differences between the forms of the skulls suggest that they are all different species, indeed.
Nikkasaurus tatarinovi (also from Russia) is very different. It is a very small, lizard-like creature, and its skull has numerous, small, lizard-like teeth, without the enlarged canines. But it is still a synapsid, having a single opening at the rear of the skull. It had very large eye sockets. These suggest it might have been a juvenile, but also opens the possibility that it was nocturnal. Many later pre-mammals explored the nocturnal lifestyle, and this feature indeed is what enabled the first mammals to survive and hold on amidst the giant dinosaurs. Nikkasaurus was likely an insect eater.
Also very small, but more typical of the group, was Ictidorhinus martinsi ('Martins' weasel-snout') from South Africa. Again it has very large eyes, meaning possibly a juvenile, or a nocturnal or partly nocturnal animal. It seems to be very close to the ancestor of the Burnetiamorphs.
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Moving on, we have Hipposaurus boonstrai, 'Boonstra's horse 'lizard'. This is actually one of South Africa's best known pre-mammals despite there only being two specimens. It was again the size of an average dog, about 1.2m/4' in overall length. A nice model of it is in the Museum in Cape Town, but showing it with scaly skin instead of the more likely smooth, glandular skin known for early pre-mammals. It was lightly built, running with body held well above the ground. It looks like an ideal ancestor of later pre-mammals like the Gorgonopsians.
Finally, Herpetoskylax hopsoni ('Hopson's creeping puppy') was, along with Ictidorhinus, close to the ancestry of the Burnetiamorphs. It didn't have the bumpy skull typical of that group, instead having a sleek head with a long muzzle and long, sharp canines. I show it hunting one of the huge dragonflies that flew in the ancient skies. It was similar in size to Hipposaurus. Living in the Late Permian, 259-254 million years ago, it was one of the last members of the group.
Next, we're going to take a detour and look at the strange Dinocephalians, or 'terrible-headed beasts'. These, too, likely evolved from a Biarmosuchian-grade synapsid, but from the outset went into bizarre directions.
