Dicynodonts Part 2
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 continue with the dicynodonts; please see the previous article on them for details about the group itself. They were proto-mammals, not the ones which directly preceded the true mammals, but a second group that was extremely successful for a time but then died out with no descendants. The dicynodonts, and also the cynodonts which were the ancestors of the true mammals, flourished in the Triassic period. The dicynodonts however did not survive past the Triassic, unless some highly intriguing fossils from the Cretaceous do prove to belong to them.
But we'll be looking at some well-known species from the Permian and the Triassic. The ones you'll see today, do a good job of illustrating just how diverse the group was. Since they differ so much from each other, how can we even say they're all dicynodonts? Features of the bones tell the tale, showing them all to be descendants of a single ancestor, that despite many modifications, retained some very specific characteristics. While most dicynodonts, true to the name of the group which means 'two dog-tooth', had two enlarged canine teeth in their upper jaws, some lacked these. But all of them had a horny, toothless 'beak' at the front of their jaws. All of them also have specialized sliding hinges at the back of their jaws, which helped them chew their food a certain way. All of them had rather long, barrel-like bodies, with short limbs and tails. As far as we can tell, all of them were herbivores. But within those shared characteristics, they varied greatly.
Starting alphabetically, we have Aulacephalodon bainii ('Bain's furrow-headed tooth'), a large dicynodont from late Permian times. It is named for Andrew Geddes Bain, a Scottish geologist who discovered many other prehistoric critters in the nineteenth century. First found as early as 1844, is known from South Africa and also from Zambia in central Africa. One of the larger dicynodonts, it had a skull up to 40 cm/16" in length, and an overall length of about 1.5 m/5'. It had strange bumps on its nose and above its eyes. These were also found in some other dicynodont species, and might have been display features, or indications that they face-butted each other for some reason. Fossilized footprints have been discovered that were likely made by this or a related species; they show that the legs were rather wide-splayed and the stride short; it was a heavy, slow and rather waddling animal. The place and time was one in which much of the region was a dry semi-desert, but this species might have lived on floodplains next to rivers where plant growth was more luxurious.
Our next dicynodont, Cistecephalus microrhinus ('small-nosed box-head') demonstrates just how adaptable dicynodonts were. It is amazingly similar to a mole, and is the first well-adapted digging vertebrate in the known fossil record. It was small, reaching a maximum length of 60 cm/2' but usually much less. It had a long body with short limbs, the front feet being spade-like and powerfully muscled, and the shoulder joint directed sideways. Its skull was unlike those of other dicynodonts, being flattened above with a very short snout region, but there was still the toothless beak at the front. The rear part of the skull was very broad. The eyes faced partly forward, which would have given it binocular vision. So even despite it being a digger in dark tunnels, it still would have used its eyesight. Perhaps like other digging animals it used its tunnelling mainly to escape predators by day, coming out by night to forage on the surface. Cistecephalus is quite well-known, giving its name to a characteristic fossil zone of the Late Permian period of South Africa. It was first named from fossils sent to Britain from South Africa, by the paleontologist Richard Owen, in 1876. Similar critters have been found in India.
The next species, Dinodontosaurus turpior ('ugly terrible-toothed lizard') is from South America, for a change. Note that despite the name it was not a dinosaur, a lizard, or a typical reptile, but a proto-mammal like the other dicynodonts. It is one of the latest-living species, from the Middle to Late Triassic period, 242 to 235 million years ago. Like Kannemeyeria featured in the previous entry, it was a very large species reaching close to 3 m in length. What's amazing about Dinodontosaurus is that we have fossils of its babies or puppies; ten found together strongly suggest that the young ones stayed in a group and were cared for by the adults. This species likely lived in herds, and was very common in its time. Its fossils are found in Brazil and Argentina.
Our next critter, Emydops arctatus ('box-shaped turtle-face'), is a more typical dicynodont. It's still fairly closely related to Cistecephalus, and was discovered in 1912. It was quite small, with a skull reaching 8 cm/just over 3" in length, and an overall body length of 30-40 cm/12"-16". It was proportionally large-headed and short-limbed. It had a few small teeth in its cheeks, apart from the tortoise-like horny beak. It was a small and unspecialized plant eater that lived in the late Permian in South Africa.
Our final dicynodont is little Robertia broomiana, 'Robert Broom's critter'. (Robert Broom was a palaeontologist who discovered many dicynodonts and other proto-mammals in South Africa.) This to me ranks as one of the cutest of all prehistoric animals. It was a mere 20 cm/8" in length, making it one of the smallest known dicynodonts. It had a proportionally large skull, with the eyes large and situated to the front of the head. It had a pair of large upper tusks, and a few other tiny teeth in its jaws. Related to Emydops and Cistecephalus, it was likely a good digger, but not living permanently in tunnels. It might have dug for roots, rhizomes and tubers of plants. The seasonal, semi-arid climate of the time may have meant that active plant growth was restricted to only part of the year. Like Aulacephalodon, Robertia might also have been found mainly on the floodplains. ('The Permian dicynodonts in South Africa stayed mainly on the plain' would have been a bit of a mouthful for Eliza Doolittle to say, so they went with a simpler sentence.)
Just a little afterword. Dmitri mentioned recently how hard it is to believe these things really existed. It does seem incredible that life existed here so long ago and in such strange forms. I've mentioned before that my love for the proto-mammals really exploded into being when I was about seven or eight years old and stumbled upon an exhibition of proto-mammal fossils in the Transvaal Museum in Pretoria. I think the specimens were on loan for just a short time since I've never seen them again at that museum; they probably now reside in the museum in Cape Town (to which I'm going to have to make a pilgrimage sooner or later). I remember the experience vividly. On the walls there were paintings of ancient proto-mammals like the Permian Struthiocephalus, (probably inaccurately) depicted with a long, sharp, unicorn-like horn, as well as some of the earliest dinosaurs, specifically Massospondylus, which co-occurred with many proto-mammals in the South African Triassic. But what really delighted me were the fossils themselves. They were displayed in cabinets behind glass, and I think some of them were accompanied by clarifying sketches and printed text telling a bit more about them. They were incredible, extremely delicate and exquisite. Most of the proto-mammals were quite small, so their skulls were less than the length of my hand. From the skulls you could get an idea of their faces, which were very dog-like and yet also very different from a dog or any living thing – they were like dream-puppies. And they were undeniably real! I was looking at bits of rock that, incomprehensibly long periods ago, were parts of the bodies of living creatures, who went about their little lives, then died and left these signs for us. At the museum store they sold a little book (mostly) about these proto-mammals and I promptly asked my dad to buy it for me. I still have and cherish it, it's lying right beside me even now (I used it as a reference for writing this article).
But that book, great as it is, barely scratches the surface. It only depicts fourteen species of South African proto-mammal, and in the text discusses only a few more. From what I learned in the subsequent years, there are so many more species than those. The total number of genera of proto-mammals alone must number a couple of hundred at least; while most of them are known from very fragmentary remains, at least half have good enough bone evidence to base solid reconstructions on. But most of them have only ever been studiously depicted in technical papers that are hard to even find. Most have never been featured in a proper book printed for the public. There are these days illustrations of them to be found online, but most of those aren't very good.
What's worse is the utter, utter ignorance here in South Africa about what is in fact a treasure of the world right here in our own country. Our fossil record of proto-mammals is the best and most diverse in the world, and it covers the incredible period of evolution from lizard-like crawlers to fully mammalian animals, in amazing detail. This is our very own history! I often wonder just why it is that our people have no idea about this. Perhaps it is because Christianity is so strong; most people today here do not believe in evolution and don't want to know about anything that challenges this (dis)belief. And so, discoveries and studies of even more amazing things don't get mentioned in newspapers. But in the scientific world itself, discovery follows discovery. These days they're examining the bones with scans showing their inner structure; a big thing as far as I'm concerned is that we're now looking at the evolution of the nerves in the skulls, which gives us info not only on the likely way their faces looked and worked, but also about the way their brains and senses developed. We can now scan rocks without having to break them open, showing the little critters petrified inside, in position. These new studies are vital, because in old days the fossils were not treated with much respect, and lots of information consequently got lost. We need info especially on the post-cranial skeletons, and we need evidence for the evolution of crucial mammalian features like fur, warm-bloodedness, parental care and milk glands. Aside from the 'main line' of evolution that led to us mammals, the many, many side roads that evolution took along the way, even if they led to dead ends, are still fascinating in their own right. And we also need to consider that these 'dead ends' were not necessarily due to poor adaptation or a lack of evolutionary potential, but many were just due to bad luck. If, for instance, the Permian Extinction hadn't promptly wiped out about 70% of all land-living species, some of these evolutionary roads might not have been dead ends at all, but might have become amazing highways to totally new destinations.
It is with a view to remedying the poor state of information about proto-mammals that I'm writing these prehistory features. Indeed, I want to discuss much more than just the proto-mammals, but I am starting with them, for the reasons given. I hope to have enough soon for a little book – that will nevertheless be more complete than anything else yet published. I will need another article or two to finish with the dicynodonts; then, I'll talk about the gorgonopsians, and finally get to the real meat of the matter, the cynodonts, which ultimately led to the first true mammals.