Diprotodon, the Giant Wombat
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!"
Again I bring you a prehistoric beastie. This one is a Diprotodon, or Giant Wombat, Diprotodon optatum. Well, first of all it wasn't quite the same thing as the modern wombat. It was related, but in a different, now extinct, family. Still, the wombat is the closest modern equivalent of the Diprotodon. Mainly, the Diprotodon was huge. It reached a height of 2 m/6'7" at the shoulder, and a full length of over 3 m/10'. It might have weighed two tons or more. Its tail was quite short. Diprotodon had a huge head, comparable to that of a modern hippopotamus, and huge front teeth. Its scientific name indeed means 'two front teeth'. These made it look somewhat rodent-like, though as a marsupial it was about as distantly related to rodents as it's possible to be while still being a mammal. Diprotodon was the largest marsupial that, as far as we know, ever existed.
In Australian native lore there are tales of a huge, monstrous creature called the Bunyip (also given a plethora of alternative names in different Australian languages). Accounts of what the Bunyip supposedly looked like, vary greatly, but generally it was understood to be semi-aquatic, big and nasty. Diprotodon bones were on occasion identified by locals as belonging to the Bunyip. So, might Diprotodon be the Bunyip, then?
As far as we can tell, Diprotodons lived for a long time in Australia – at least from 1.6 million years ago to about 46 000 years ago. Modern humans arrived in Australia about 50 000 years ago. There was therefore a few thousand years of co-existence of humans and Diprotodons. There are a couple of depictions of a creature in the Aboriginal rock art which very much resemble Diprotodons, and there are preserved tracks, not to mention many bones, that more recent Aborigines are sure to have seen. Therefore it is quite plausible that Diprotodon might be the inspiration for the tales of the Bunyip, with many supernatural and strange elements being added to it later on.
But there are people who believe that Bunyips, and then particularly Diprotodons, still exist! Right at the outset of Diprotodon's discovery in the early Nineteenth Century, the British scientist who named and described it, Richard Owen, was so impressed with the apparent freshness of the bones, that he expected living Diprotodons to be discovered soon in the Australian interior. Back then, Australia was a world of never-before-seen wonders, and anything at all was deemed likely to turn up. There have been tales of early explorers seeing many strange things, including some that suggested living Diprotodons: huge, hippo-like bellowing beasts. Were these real accounts, or merely tall tales? After all, there is no lack of the latter in Australian folklore!
A few modern cryptozoologists – people who believe in the existence of (mostly large and spectacular) undiscovered animals – think there might still be a few Diprotodons around some of the wildest and most remote bits of the Outback. This, however, is unlikely. Diprotodons were large, slow, and certainly very conspicuous. Large mammals need large ranges and sufficient food. They can't survive as isolated individuals, they need to exist as communities of interacting and breeding individuals, they need to exist in sufficient numbers to prevent inbreeding-exacerbated diseases. It is very unlikely that such populations of an animal as large as Diprotodon might exist undetected, even in Australia. Consequently, the search for living Diprotodons is about as promising as the search for Bigfoot or the Loch Ness Monster.
Life of a Giant
During their heyday, Diprotodons lived over most of Australia. Their dentition indicates they were browsers: they used their big front teeth to nip off leaves and twigs, which they chewed with their cheek teeth. They might have eaten some grass as well. Their size and thick, strong limbs show that they were walkers, unlikely to have been able to run or gallop. Diprotodon trackways show that they walked with their toes turned inward. There are also imprints of hairs around their soles and toes, showing that, like modern wombats, they were shaggy-haired. They seem to have needed a moist climate; many fossils suggest that Diprotodons died in times of drought. There are for instance lots of bones from the bed of a dried-out lake, where Diprotodons apparently got terminally stuck in mud.
Although fossils of Diprotodons have been classified in several different species, study of their remains suggest that those are actually all the bones of just a single species, Diprotodon optatum. These fall into two types, a large one and a smaller one, just about half the size. Today we believe that these two types were the male and the female, the males being the large ones. With such a big difference in size between the male and the female, it seems clear that the Diprotodons had a society where there were dominant and aggressive males, who fought over females, the winner being able to have access to multiple females. This is supported by skeletons of large Diprotodons showing signs of injury such as males who fight with each other might incur.
Female Diprotodons had pouches like those of other marsupials in which they carried their babies. Skeletons of babies have even been found in position suggesting they had died with their mothers and become preserved while still in the pouches. Like wombats, Diprotodons had pouches facing backwards. Like all marsupials, their babies would have been born in a very undeveloped state, and then kept in the pouch and nursed for many more months before being developed enough to come out and walk around on their own.
It is pretty clear that Diprotodon did go fully extinct around 46 000 years ago. Prior to that point these beasts ranged all over Australia in numerous woodland and grassland habitats. The last known bones have been dated quite precisely. Evidence of more recent bones have turned out to be older bones re-deposited into more recent rock or soil layers.
Why did Diprotodon go extinct? These mammals had just about no natural predators. The only large predator of that time was the so-called marsupial lion or Thylacoleo. But even it, being the size of a large leopard or small lion, could have done little against an adult Diprotodon. Thylacoleo itself went extinct, leaving the largest remaining predator the Thylacine, which was the size of a large dog. The Thylacine also went extinct a bit later. Almost all of the large Australian mammals went extinct in fact, and it happened not long after the entry into Australia of a new kind of predator – humans.
Many people today do not want to believe just how destructive humans are. The recent mass extinctions of animals in Europe, Asia, the Americas and Australia, have therefore been attributed to other factors like climate change. The problem with this is that climate change happened a lot over the recent geological past. We are living right now in the midst of the Ice Ages. (I am not speaking now of the likelihood of this pattern having been disrupted by human-induced global warming.) There have been numerous cycles of warming and cooling climates over the past million years or so. During the cold periods, the ice extended as far down as southern Europe and glaciers covered about half of North America. The glaciers approached and withdrew several times, and what the animals did was merely to march southward as the glaciers spread, and back northward as they retreated. In more tropical countries, including Australia, there were no significant glaciers, but colder periods tended to be drier, so that forests retreated and grasslands and deserts spread. Still, even during cool and dry periods, there remained some warm, moist pockets of habitat which were refuges for creatures ill-adapted to the cold and drought.
So while Diprotodon survived for most of the million years or so of the Ice Ages, it died out within a few thousand years of the arrival of humans in Australia. The sad fact of the matter was that Diprotodon was defenseless against humans. Large and slow as it was, it was easy to track down, to spot, and to kill using human weapons, probably in its case thrown spears. Humans have proven everywhere that they would hunt and kill anything that they can. It is not at all implausible that they could completely eliminate an animal like the Diprotodon from an entire continent in only a few thousand years. In the absence of humans, large mammals, especially the ones with no natural predators, breed very slowly. They do this because if they didn't, they would become so numerous that they would deplete their natural resources. So without humans, they survive and maintain their numbers by having few, infrequent offspring. But those born tend to survive and live long as adults. Just a small change to this can lead from stable populations to decreasing populations. And even a small yearly rate of decrease can lead to total extinction over a period of centuries or millennia.
Today, a true megafauna – an ecology featuring numerous large mammal species – only exists in Africa. This may be because humans evolved in Africa, and the animals here have had millions of years to adapt to the pressure of their hunting exploits. (Of course today even in Africa the megafauna is in deep trouble). Regions where animals have had less experience of humans and less time to adapt to them, have been much more vulnerable and consequently have been marked by mass extinctions soon after humans arrived.
Apart from direct hunting, Diprotodons and other large Australian critters were also vulnerable to the way humans changed the landscape. Humans everywhere have used fire in numerous ways. Fire has been used as a way to drive beasts out of dense bush towards hunters. It has also been used to destroy forest and thickets to open the land for farming or to make hunting easier. In seasonally dry savannah regions, fires are also set to stimulate the growth of fresh leaves and grass. Over time, such use of fire significantly changes environments, probably too rapidly for large, slow-breeding mammals to adapt to.
Then, too, the elimination of large browsers from an environment will cause it to change. In Australia it seems to have boosted the growth of hard-leaved Eucalypts and thorny trees, which actually make use of infrequent fires in their reproduction. But these trees are not very palatable to browsing animals, and so, the large browsers go extinct even faster leading to even more rapid habitat change. But overall today it seems that human hunting was the major factor in causing the disappearance of these huge and weird beasts. And what a pity it is that they are gone! As an artist, I have to wonder just what these big things actually looked like. Their bones seem very strange, their faces most of all. In the absence of a living one or any detailed picture of a living one, all I can do is speculate.