Colours of Wildlife: Dinocephalians
Created | Updated Aug 26, 2018
Dinocephalians
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 in time we go yet again. These are the old terrible-headed beasts, the Dinocephalians. They, too, belong to the group of ancient ancestors of mammals, the pre-mammals or proto-mammals. Like many other groups I featured here, they're not on the main line of mammalian evolution, but constitute a strange side journey. Dinocephalians are therapsids, the more advanced members of the synapsid group. That means, compared to the more basal or 'primitive' synapsids, which were still very lizard-like, they had started to evolve more mammalian features. At least some of them had teeth differentiated into different types: incisors at the front, a pair of canine teeth in each jaw, and smaller post-canine teeth. Their front teeth or incisors locked together when they closed their mouths. In later plant-eating forms there appeared a ridge or 'heel' on the lower portion of each incisor, against which the opposite incisor could cut or crush food. (But they had not yet evolved shearing, chewing or grinding cheek teeth that fit together closely as proper mammalian teeth do.) They'd also evolved a more upright way of walking, with the belly held well off the ground. Their rear legs were almost vertical, but their front legs still splayed a bit out to the sides. Their skulls had the typical synapsid build with a single opening behind the eyes, in which cheek muscles fit. In some, this opening had enlarged significantly, to accommodate bigger muscles for a stronger bite; in others, the opening looked smaller from the outside as a result of the bones of the skull growing tremendously thick.
It is for these thickened skulls that the group gained its name. Not all species had equally overgrown skulls; Syodon and its relatives had relatively normal skulls, while Tapinocephalus and its kin had very thick skull bones indeed. Some, like Keratocephalus, Styracocephalus and especially Estemmenosuchus had additional bony outgrowths on their heads. While looking very fearsome, most of them were plant eaters, though a few such as Anteosaurus were likely predators. With legs rather small for their bodies, they were unlikely to have been fast runners. Then again, neither was their prey, back in those days. Land animals had barely begun to walk, so running was not yet much on the cards.
 |  |  |
 |  |  |
 |  |  |
 |  |  |
So when were 'those days', exactly? Dinocephalians first appeared on the scene in the Middle Permian period, about 270 million years ago. (For comparison, good old Tyrannosaurus rex lived a mere 65 million years ago!) The Permian was the last period of the Palaeozoic, or the age of Ancient Life. It ended in a mass extinction that almost wiped out all 'higher' life forms on our planet – but in the event, a few survived, and the stage was set for a whole new diversification of forms in the Mesozoic, the age of 'Middle' Life. The strange thing is that life in the middle to late Permian was actually already quite sophisticated. In spite of much of the 'primitiveness' in most of the land-living creatures, there was a high diversity and a great variety of forms, and they were starting to experiment with new body features and tricks of the metabolism. The Permian likely saw the first warm-blooded and furry critters. Indeed by the end of the period, some were already looking very mammalian. The extinction event set back these proto-mammals, and cleared the stage; for a while as the Mesozoic started it looked as if the mammal ancestors might recover, but then unexpectedly a new group surged onto the scene – the archosaurs or ruling reptiles, from the ranks of which sprang the dinosaurs. Mammalian evolution was interrupted by this, and for about 140 million years the mammals were small creatures skulking by night, scurrying about the feet of the dinosaurs; only when the big dinosaurs became extinct and the Mesozoic ended, could mammalian evolution go mainstream again, to characterize the Cenozoic, the age of Recent Life, our own present era.
In the Middle Permian, there was yet no sign of the extinction to come. Earth appeared still largely in the form of a single landmass, Pangaea, surrounded by a single vast ocean, Panthalassa. The climate was recovering from an ice age in the Carboniferous; glaciers were retreating in the southern portion of Pangaea, called Gondwana. The land was initially barren as the ice cleared, but soon got populated by plants and animals. Moist regions were forested, with the old Carboniferous coal-swamp plants still present, but more modern ones, primarily the ancestors of conifers and cycads, making an appearance. Dry regions were more sparsely vegetated. There was yet nothing like grass, but there might have been open 'savannahs' clothed in low, hardy ferns, interspersed with shrubs and trees. The drier conditions likely spurred the evolution of reptiles and proto-mammals with tougher, more watertight skins and egg shells, and physiological adaptations to conserve water. More open landscapes likely became populated with the first herds of large, plant-eating animals.
Excellently preserved series of middle-Permian rocks are known in Russia. It is in these that we find one of the oldest (and as it happens, strangest) of dinocephalians - Estemmenosuchus mirabilis ('wonderful crowned crocodile'). Two kinds are known, the one pictured here with almost antler-like outgrowths of its skull and face. This one is usually called Estemmenosuchus mirabilis. A second type, usually called Estemmenosuchus uralensis, has shorter and more subdued outgrowths. These might indeed be different species, but some scientists have considered them to be the males and females of a single species. Amazingly, not only were excellently preserved skulls and skeletons found of these animals, but also some skin impressions left in mud that later petrified. These provide interesting clues about the nature of proto-mammal skins. A big question has always been when and where fur first evolved. Well, the impressions of the skins of the Estemmenosuchus show no trace of fur, but do show evidence of glands. These are a feature of modern mammalian skins, such as milk glands, sweat glands and scent glands. We still don't know the exact nature of dinocephalian skin glands, but it's intriguing to think that they were already there. Fur, in turn, perhaps only showed up in the Late Permian, in some more advanced therapsids.
These dinocephalians reached a length of 3 m, of which their short, stubby tails made up just a small portion. Most of it was their big, barrel-like bodies, and giant heads, their skulls, at 65 cm/26" length, being as large as those of hippos. They probably weighed a ton or more. They had very big fangs in their mouths, but even so, were likely vegetarians. Along with the rather tank-like Pareiasaurs, a group perhaps more closely related to modern turtles than to mammals, they were the first large herbivores of their times. The only animals that might have threatened them, were the carnivorous Gorgonopsians or gorgon-faces, another group of proto-mammals that I'll feature here soon. Even these, however, were unlikely to take on an adult, male Estemmenosuchus.
Also from the mid-Permian of Russia comes Syodon biarmicum or 'pig-tooth from Bjaramland'. It was named for its large, curving canine teeth, like the tusks of a pig. These animals were much smaller and graceful, reaching an overall length (with a fairly long tail included) of about 1.2 m/4'. That is to say, if they were indeed adults and not the youngsters of animals that became much larger.
Different growth stages being given different names is found in our next critter, also from Russia, Titanophoneus potens ('powerful Titan-killer'). What is now recognized as an adult Titanophoneus was earlier given a different name, Doliosauriscus. There were significant differences between the adult form and juveniles. Youngsters had a longer, more slender snout, and little to no thickening of the skull bones. Adults had skulls of up to 80 cm/32" length, and very thick bones just above the eyes. The muzzle was proportionally not as long, but deeper and wider. Titanophoneus was clearly a ferocious predator.
A related predator was Deuterosaurus jubilaei. It had a proportionally shorter, stouter skull, nevertheless up to 80 cm in length. The animal in full might have been over 5 m long!
Our final Russian dinocephalian is Ulemosaurus svijagensis. This one had very thick skull bones, the roof being 10 cm/4" thick in places. What was the function of this? There weren't any predators around which killed their prey with knocks to the head, so they might likely have been giving each other the knocks themselves. They might have used head-butting as a kind of interpersonal contest, perhaps to decide the possession of territory or access to females – though there's no sign of males and females having different thicknesses of skulls. It was similar in size to Estemmenosuchus, though it lived a few million years later.
Aside from that, Ulemosaurus was likely a herbivore. It had teeth of similar shape throughout its jaw, although they were larger in front and became smaller towards the rear of the jaw. Some scientists think these teeth would have been suitable for cutting meat. It might have been an omnivore, eating both meat and plants.
The other place where extensive mid-Permian rocks have been found is my own country, South Africa! And here we find the most amazing menagerie of weird old dinocephalians. One of the earliest known is Styracocephalus platyrhynchus, 'flat-snouted spike-head'. It was named for the rearward protrusions of its skull. It also had flaring cheekbones. In ways it was similar to Estemmenosuchus, but somewhat less frightful. Its skull was about 40 cm/16" in length, and its body reached a length of 1.8 m/6'.
Soon, South African dinocephalians differentiated into plant-eating and meat-eating forms. The largest predators of the time were the Anteosaurs. Syodon and Titanophoneus both belonged to the group. In South Africa its main representative was Anteosaurus itself. It was named for Antaeus, the mythological Greek giant who drew his strength from the Earth and was only defeated by Hercules, who lifted him off the ground and crushed him. Anteosaurus magnificus ('magnificent Antaeus-lizard') had a huge skull with enormous thick bosses over its eyes, cheekbones and the rear of the skull. It also had big, sharp canines, and a primitive feature for a proto-mammal, teeth on its palate. It reached a full length of 5-6 m/17'-20' and a weight of 500-600 kg/1100-1300 lbs. It had strangely small legs for the size of its body.
But it was the plant-eating contingent of dinocephalians that reached the greatest diversity and success in South Africa. One of the large early forms was Jonkeria truculenta ('Jonker's truculent critter'), with a skull of about 55 cm and a body perhaps reaching a length of 5 m/17". It had a long, flat snout, and large canine teeth.
A similar, more specialized form was Struthiocephalus whaitsi ('Whaits's ostrich-head'). If you've seen an ostrich's face up close, you'll know that it has a flat bill, but Struthiocephalus could even be called a duck-bill. Its skull, aside from the broad, flat snout, had a bump between and above the eyes that has been interpreted as the base of a long, unicorn-like horn. Or it might have just been a big bump on its skull, used for head-butting of shoving matches. A plant-eater, the teeth in its skull were small, peg-like and all about the same size. It might have fed on soft marsh plants.
Keratocephalus moloch, 'demonic horn-head', had a variably-long and flat snout, and a horn-like bump on its forehead. It is known from several skulls as well as good skeletal material.
Tapinocaninus pamelae ('Pamela's humble-canine') was the most basal member of the main thick-skulled forms, the tapinocephalians. It still had a canine tooth that was significantly larger than its other teeth, but its other teeth were similar to the peg-like teeth of the plant-eating tapinocephalians.
Tapinocephalus ('humble-head') itself is known from skulls and skeletons found in the Karoo region of South Africa, to the point where its fossils give the name for an entire specific layer of mid-Permian rocks. It had one of the biggest, thickest heads in the group. It also had massive limbs held in place by huge pectoral and pelvic girdles. One of the biggest of the group, it might have reached a weight of two tons. It's been speculated to have been semi-aquatic like a hippo, but with its powerful limbs might well have been fully terrestrial.
The best-known of all dinocephalians is Moschops capensis, 'calf-face from the Cape'. There was even a children's TV show called 'Moschops' in the eighties, featuring one of these as main character in addition to some dinosaurs and an ichthyosaur. The real thing was very similar to the Russian Ulemosaurus though living a bit later. Its skull was very thick, deep and wide. It might have been used for head-butting; some scientists have suggested Moschops was semi-aquatic and its heavy head helped it to dive head-down to reach plants growing on the bottom of lakes. But its heavy limbs would have functioned well enough to carry it on dry land. Moschops reached an overall length of about 3 m.
One of the most specialized of the thick-heads was Criocephalosaurus vanderbyli, 'Van der Byl's ram-headed lizard'. This one is not well-known, but had a very thick and high skull. Fossils attributed to the genus were found in South Africa as well as Zimbabwe. It's not known from any other parts of the skeleton, but was likely similarly built to Moschops. Here I show the possible head-butting behaviour.
Apart from Russia and Southern Africa, dinocephalians have also been found in Tanzania, Brazil and China.
Inexplicably, after flourishing and reaching a high diversity over a few million years, dinocephalians went extinct, worldwide! They didn't make it into the Late Permian; they were quite vanished already, when the mass extinction at the end of the period wiped out almost everything else. Why the dinocephalians disappeared when they did is one of the big unsolved mysteries of palaeontology.
