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!"

I've discussed over 100 kinds of proto-mammals by now in this article series. I worked roughly chronologically, starting with the earlier ones and ending with the most recent ones, but I did make a few jumps, and left out some of the very early ones that deserved proper treatment. I sort of privileged the South African kinds in my writings, but there were also some important and fascinating ones that were found in America. Today I offer you three very ancient American ones that somehow got left out until now.

First, let us look at Sphenacodon ferox. The name means 'fierce wedge-point tooth'. Like many fossil species, it was originally named for distinctive features of its teeth, in this case the sharp, compressed crowns of its rear teeth. The very first find was just a piece of its lower jaw, so there wasn't much else but teeth to go by. Soon more complete fossils were found and today we know it from most of its skeleton. Sphenacodon was a big and powerful hunter of its time. It had a comparatively large skull that was deeper than wide. Its sharp teeth were differentiated into small, pointed front teeth, large stabbing teeth in the middle, and slicing teeth at the back. As in its close relative Dimetrodon, the famous sail-backed proto-mammal (that many people confuse for a dinosaur), this represented the beginning of the tooth differentiation in the mammalian line. Sphenacodon had a big body and a long tail, with comparatively short limbs, but likely already started walking with its feet brought in underneath its body and its belly and even tail held well off the ground. (This detail comes from fossilized trackways, unique glimpses into the life of creatures, being marks they made while still living.) It had on its back a low ridge formed by tall vertebral spines. Nowhere near as tall as the sail on the back of Dimetrodon, it likely only had value as a display feature. Sphenacodon reached about 2.5 m in overall length in the largest species. The fossils of Sphenacodon were found in western North America, in New Mexico, Arizona and Utah. They date from the Late Carboniferous and early Permian periods, 300-280 million years ago. Back then the region had a warm and moist climate, and was covered in the Earth's first great forests from which so much of our planet's coal reserves were formed. In these ancient coal forests Sphenacodon was a hunter of the other four-legged things that had but recently crawled out of the rivers and lakes: the early amphibianoids, para-reptiles, synapsids or proto-mammals, and diapsids, the group from which present-day reptiles as well as crocodiles, dinosaurs and birds evolved. Back then these were all still fairly similar, all looking rather lizard-like.

Our next critter is Secodontosaurus obtusidens ('blunt-toothed cutting-toothed lizard'). Once again its name refers to its teeth; it, too was first named and described from pieces of the upper and lower jaws. It was not a lizard; it was also an ancient proto-mammal, a synapsid, and in fact was also a pelycosaur like Sphenacodon. It was a close relative and similar to Dimetrodon in having a tall sail supported by spines on its back. We don't know quite as much about its skeleton as we do about Dimetrodon, so we don't know if it, too, had the tips of its sail spines exposed; I reconstructed it as if it didn't. But mainly its difference from Dimetrodon was that it had a longer, lower skull, more like that of a crocodile. Its teeth were also not as differentiated, all being rather similar in size and shape. Maverick palaeontologist Robert Bakker has dubbed it the 'Fox-Faced Finback'. It is not clear how it used its long face. It might have snatched fish from the water, as I show in my reconstruction. Another possibility is that it used its long, thin jaws to probe and pull small critters out of burrows and crevices. It was fairly large, reaching an overall length of 2.7 m. It lived in what is today Texas, in the early Permian, 285-272 million years ago.

Our last critter is a bit of an enigma. Tetraceratops insignis ('emblematic four-horned face') might also be a pelycosaur like Sphenacodon and Secodontosaurus. It is quite different-looking thought. Cat-sized, it had a skull less than 10 cm/4" in length. It was distinguished not just by four, but actually six facial protuberances. There were low ridges over its nostrils and eyes, and a projection at the corner of its lower jaw. These might have been covered in a horny tissue in life. It also had differentiated teeth: there were to unusually long teeth at the front of its jaw, and also two even longer teeth in the position the canine teeth occupied in more advanced proto-mammals. As it is, it is either an advanced pelycosaur, or actually the first therapsid, the group of advanced proto-mammals that later evolved into many kinds including the direct ancestors of the true mammals. The small Tetraceratops would not have been very mammalian-looking, though. Only its skull was found and its body was likely still lizard-like, although it most probably also had the more mammalian high-walk as described for Sphenacodon. It lived in the Early Permian, about 275 million years ago, also in Texas.

I hope you enjoyed these three ancient faces. A few more holes remain to be patched up where the proto-mammals are concerned; then I hope to start talking of the subsequent evolution of the mammals proper. Oh, and I hope in between to find time to talk more of our wonderful present-day wildlife as well!

Colours of Wildlife Archive

Willem

29.04.19 Front Page

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