Dicynodonts Part One
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!"
Back to ancient times we go. I'd like to introduce to you the amazing Dicynodonts! There were so many, and of such diversity, that I'll probably need to cover them over two or three separate entries, so this is merely Part One. The name of the group comes from the South African genus Dicynodon, meaning 'two dog-tooth'. Most species had a pair of long tusks in their upper jaws. Many species lacked teeth other than this, but a few did have additional cheek teeth and the most primitive ones, even some front teeth. All species had a turtle- or parrot-like, horny 'beak' lining their jaws. Dicynodonts were proto-mammals, belonging to the Anomodontia the more basal members of which I covered here earlier. They were, however, not on the main line of evolution that led to us mammals, but on a side branch. Theirs was the most vigorously growing and diverging branch among the proto-mammals, other than the branch that led to the true mammals. Many genera are known, most from South Africa. Dicynodonts varied in size from as large as a rat, to as big as a rhino. They had different lifestyles, some likely to be semi-aquatic, some that were excellent burrowers, and some which were terrestrial herbivores. They lived from the middle Permian, about 275 million years ago, to the Late Triassic, about 200 million years ago. They apparently went extinct when the dinosaurs rose to dominance. Tantalising fossils have been found which appear to be from dicynodonts, in the Cretaceous (the final period of the reign of the non-bird dinosaurs), which would extend their temporal range amazingly, if correctly identified. Personally, I'll wait for much better evidence before believing that!
As far as we know, all dicynodonts were plant-eaters. They used the horny tips of their jaws to snip off plant material; then with the jaws closed, they pulled their lower jaws back relative to their upper jaws, using a unique sliding joint at the rear of the jaw. The same joint also enabled them to 'open up' the cheek region of their jaws while keeping the front of their jaws closed, preventing the food from falling out. Being able to slide their jaws forward and backward along this joint, they could mash up plant material between their cheek teeth and/or horny ridges on their palate. Their efficient way of processing food likely helped them be so successful.
A very big question that I've encountered in my reconstruction of dicynodonts is whether they were furry. That's a fair question, seeing as they are relatives of the synapsids that evolved into true mammals, some of the advanced members of which were almost certainly furry. But the ancestors dicynodonts share with these, go back likely to early Permian times, so if dicynodonts were furry, and unless fur evolved independently more than once (a very unlikely event), the fur had to come from a mutual ancestor that lived very early. Would fur in its fullness have evolved that early already? That's what I don't know. There is no direct evidence for fur in dicynodonts – yet. But there has been traces of possible fur found from late Permian times, in the fossilized dung of predators. Dicynodonts, around at the time and as herbivores the possible prey of carnivores, seem to be good candidates as owners of the fur.
Additionally, studies have been done on the bones of dicynodonts. These show abundant blood vessels and also Haversian canals, which means their bones grew rapidly. Rapid growth likely meant a fast metabolism, which in turn might have meant endothermy, or warm-bloodedness. Fur only makes sense in a warm-blooded animal. So if they were furry, they would have been warm-blooded. But if they were warm-blooded, would they necessarily have been furry? Perhaps not. Again, the problem is pinpointing exactly when fur evolved, and which branches of the mammalian family tree shared the trait. If dicynodonts had it, then pretty much all therapsids (advanced proto-mammals) must have had it, even ones that don't seem very mammalian at all. I'm not sure if that is likely.
As a judgement call, I've decided to illustrate my dicynodonts as non-furry. The best evidence we have, shows fur very likely present in advanced cynodonts, in the mid- to late Triassic. The evidence of fur in the Permian is rather more dubious. So for now my dicynodonts go naked. They might have been covered in leathery skin, or they might have had a covering of scales, like some early proto-mammals are known to have had. If good evidence of dicynodont fur comes along, I'd be happy to devise some new reconstructions of them!
The relationships of dicynodonts, from what I've seen in my researches, is very complex, rather confusing, and perhaps due to change a lot based on newer, better studies. So for now I'm just going to show you a few representative species, without saying who is related to whom.
Our first species is Eodicynodon oosthuizeni, or 'Oosthuizen's dawn two dog-tooth'. It is the earliest/most basal dicynodont known, but already looks the part. Its jaws were not yet as fully fused as those of later dicynodonts. A small species, reaching 30-40 cm/12"-16" in overall length, it lived in the mid-Permian in South Africa.
Our next species, Diictodon feliceps ('cat-headed two weasel-tooth'), is one of the best-known of all Permian land animals. This little critter (about 45 cm/18" long) was a digger in a desert landscape. Many of their burrows were found, often with their fossils inside, endearingly snuggled up next to each other. It's possible that they died when flash-floods drenched their burrows. In shape, Diictodon was long and low-slung, with a barrel-like body and big gut to process coarse desert vegetation. It had the typical two tusk in an otherwise toothless skull. It lived in the late Permian, in South Africa.
A much larger South African dicynodont was Endothiodon. The genus gave its name to a particular fossil zone of the late Permian. It had a proportionally very large head, with small teeth in its cheek region along with the typical toothless beak at the front of its jaws. It reached about 2 m in length, but stood low with its short legs.
Our next species, Oudenodon bainii, was also from the late Permian of South Africa. Other Oudenodon species have been found, not just in South Africa but also in Zambia and Madagascar. It was a very successful genus, and a few other similar and closely-related genera are known as well. Oudenodon is characterized by a long, broad but low skull. Flaring cheekbones and a large open space in the rear of the skull made room for huge cheek muscles, for chewing. The jaws were entirely toothless, the place of the typical dicynodont tusks having been taken over by a pair of downward-pointing projections of the horny beak. Oudenodon had some strange bulges of bone above its nostrils and in front of its eyes. These might have been for display or for face-butting contests – or maybe both.
Now we meet the rock star of the ancient world, the massively famous and successful Lystrosaurus ('shovel lizard')! The amazing thing about this critter is that it survived the end-Permian mass extinction, 252 million years ago, the most disastrous extinction event known, which wiped out 90% of aquatic and more than 70% of terrestrial species. The late Permian saw a flourishing of dicynodonts and other proto-mammals, and when the disaster hit, almost all of them were wiped out. Not Lystrosaurus! It, and a tiny handful of other dicynodonts, made it through. We still have no good idea what caused the extinction. It might have been some severe environmental disturbance, perhaps causing a cooling (or a heating) of the atmosphere, perhaps causing a reduction in oxygen content. Maybe by studying Lystrosaurus we might get a clue what helped it to survive, which in turn will give us a clue as to just what happened at the end of the Permian.
From a humble, typical dicynodont living in the late Permian alongside a fauna rich in other dicynodont species, Lystrosaurus rose to become the main form of terrestrial vertebrate in the early Triassic, in some time-and-place zones constituting 95% of the fossil bones found. It lived on the entirety of Pangaea, the super-continent that in Permian times existed, all of the present continents having been joined into a single mass. Indeed, Lystrosaurus-fossils were a big piece of the puzzle suggesting that indeed the continents were differently arranged in the past. Various species of Lystrosaurus have been found in South Africa, Russia, India, China and even Antarctica!
Having colonized so much of the Earth and diverged into so many species, Lystrosaurus shows a variety of features. Its face is quite strange, its eyes being very high and right at the front of its skull. This varies, with some showing a more rounded face while others make almost a perfect right angle, the eyes protruding upward and forward almost as if on stalks. The mouth has a horny beak as well as two downward-pointing tusks. The body is long and barrel-shaped, the tail very short. The feet are broad and the limbs short but stout. Lystrosaurus varied in length from 60 cm/2' to 2.5m/8'.
In lifestyle, Lystrosaurus was apparently a good digger, living in burrows like Diictodon. It would have browsed on a variety of plants, perhaps also using its powerful front feet to dig out rhizomes or tubers. It has been reconstructed as being semi-aquatic a lot, wading into shallow water in marshes and swamps, but might equally well have lived in dry, semi-desert regions.
Actually, taking into account its world-wide abundance in the early Triassic, it must have been able to survive in a great variety of different habitats.
Our last dicynodont, for now, is the huge Kannemeyeria simocephala ('Kannemeyer's blunt-headed beast'). It also comes from a group of dicynodonts that survived the end-Permian extinction to become abundant and successful in the Triassic. It thrived from the start to the middle of that period. Originally known from South Africa, fossils of Kannemeyeria were also found in Zambia, Namibia and Russia. It reached the size of an ox, with a proportionally huge skull and the typical pair of dicynodont tusks. It and its relatives evolved into a huge variety of forms in the Triassic, good fossils showing them to flourish in Africa, South America, Russia, Poland, India, China, and North America. These large dicynodonts were the last ones of their kind, surviving right up to the end of the Triassic, but then dying out as the new, huge prosauropod and sauropod dinosaurs arrived on the scene to compete with them in the niches for large herbivores, while the large theropod dinosaurs arose to prey on them. This indeed heralded the end of the age of the proto-mammals; in the Jurassic and Cretaceous, the only remaining members of the line were the tiny mammals, and a few equally tiny advanced proto-mammals that survived, to put it simply, by being too small for the dinosaurs to bother about.
Coming soon, more dicynodonts!