Colours of Wildlife: Astrapotheres

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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!"

Astraponotus by Willem

Forgive me for shoving you into the virtual time machine again, but I really feel we can learn a lot about present-day life on this planet by pondering past life on this planet. I also think we are enlarging our mental horizons a bit by realizing that life has been continuing and changing and evolving but maintaining huge diversity over millions and even billions of years. So today we're going back some millions of years to the continent of South America. Today, it is connected by the Isthmus of Panama to the continent of North America. But this isthmus wasn't always there. It has formed over the past five million years or so; previous to that, for many millions of years, South America was disconnected from North America by a wide seaway. But strangely enough, for much of that time it remained in contact with Antarctica. For some time, Antarctica hosted a kind of life similar to what was on South America … but when it finally drifted to its present position at the South Pole, and when the global climate cooled down significantly, ice sheets covered it and it lost almost all of its land life.

But South America, during the time of its isolation, abounded in life. Disconnected from North America and the other continents, its life evolved separately into a whole slew of unique forms. I hope eventually to cover all of them, but for now let us look at just one group – the Astrapotheres.

Today we have fossils of several kinds of Astrapotheres, going back to the Palaeocene Period, shortly after the non-avian dinosaurs became extinct, and continuing to the Middle Miocene, about 11.8 million years ago. This is a good reign, but it came to an end before the link between North and South America was established. Astrapotheres were therefore exclusively South American and Antarctican.

Astrapotheres show no clear relationship with any modern mammal group, though they were indeed hoofed mammals, perhaps distantly related to Perissodactyls – horses, rhinos and tapirs. They had many unique features. They started out rather small, sheep-sized or so, but were already some of the biggest mammals of their time (remember when the dinosaurs reigned, mammals were mostly rat- or at most cat-sized). They soon became much bigger. The big ones had long bodies supported on short, stout limbs. Their hind feet were 'flat', treading on the whole sole (this is called 'plantigrade') but their front feet trod with just the tips of the toes on the ground; the rest of the sole was supported on a high 'cushion' similar to the feet of elephants. They had big heads, and the large kinds developed long 'tusks'. These looked in some cases similar to the tusks of elephants, but had different origins. Elephant tusks are the incisor or front teeth, but Astrapothere tusks were the canine or eye teeth. The upper canines moved past and ground against the lower ones, sharpening both. They had incisor teeth only in their lower jaws, if at all.

Not only did they have elephant-like tusks, many of the big ones show signs of having had elephant-like trunks as well. Now trunks, being soft tissue, doesn't show up in the fossils. But we can infer a trunk from the design of the skull. The nasal bones are very short and high, in fact ending just above and/or in front of the eyes. This is typical for animals that have trunks or elongated snouts and lips, such as the present-day Tapirs and Dik-Dik antelopes. Just looking at where the lower front teeth go, they would have needed to close against some tissue well ahead of where the upper skull bones end, so there had to be substantial face-flesh in front. Some species also had tusks protruding so far forward, that these would have hindered them in eating unless they had a trunk that could gather in food from beyond the tusks. These inferred 'trunks' would have made them look very much like tapirs, or even elephants.

Also reminiscent of elephants was their size. The largest kinds, though rarely more than 2 m/6'7" at the shoulder, reached bodyweights of three tonnes or more. This made them some of the largest mammals ever alive in South America. Today, the largest native South and Central American mammal is Baird's Tapir, reaching a bodyweight of three to four hundred kilograms, or only about a tenth of the mass of the big astrapotheres.

Because of their size, the big astrapotheres were sometimes thought to be semi-aquatic like hippos, in that water would have helped support the weight of their bodies. But hippos are quite able to walk and run easily on land. Similar-sized astrapotheres therefore likely could sustain a life mostly on land. They might still have enjoyed wallowing, as rhinos and elephants do. We don't know much else about their lifestyles. They most likely were vegetarians, using their tusks mainly to strip leaves, twigs and bark from trees.

Our first species is Astraponotus assymetrum. This one lived in the Eocene, 37.2-33.9 million years ago. Its fossils were found in Argentina. It was about the size of a tapir, and had an unusually high and narrow skull, with very highly situated nasal bones indicating the likelihood of a short proboscis.

Astrapotherium by Willem

Next is Astrapotherium magnum itself. Its name means 'great lightning beast'. It lived in the Miocene, 21-15.7 million years ago, also in what is today Argentina. This was a fairly typical big astrapothere. It stood perhaps 1.3 m/4'4" at the shoulder, with a length of about 2.5 m/8'2", and a weight of a ton or slightly more. (A larger species, Astrapotherium burmeisteri, might have exceeded two and a half tonnes.) I'm portraying it here with a relatively smooth skin (or at most with short hairs) like a rhino or a hippo, since animals of that size have more of an issue keeping cool than keeping warm. Modern-day tapirs are covered in short hairs.

Hilarcotherium by WillemGranastrapotherium by Willem

The next two species flourished a bit later, and somewhat further to the north. Fossils of both were found in Colombia. They belong to a branch of the family called the Uruguatheriinae or the 'Uruguay Beast' subfamily. Granastrapotherium snorki ('Large lightning beast with a snorkel') had the longest tusks so far known in an astrapothere, making it look very much like the gompotheres, ancient elephants that often had four forward-pointing tusks. The upper tusks, in the male, reached a metre/yard in length, while those of the female were about half as long. It must have had a long trunk to enable it to gather and eat food, for which it received its species name. It was very large, to boot, reaching an estimated 3.5 tonnes in weight. It lived from 13.8 to 11.8 million years ago. Hilarcotherium castanedaii ('Castaneda's beast from Hilarco village') had a longer reign, from 15.5 to 11.8 million years ago. Its upper tusks were much shorter. It might therefore also have had a shorter 'trunk'. The main species was estimated at weighing between 1 200 and 1 400 kg (between about 2 600 and 3 000 lbs). Another species, Hilarcotherium miyou ('large beast from Hilarco village'), known from fragmentary fossil material, was perhaps much bigger, being estimated at 6.5 tonnes in bodyweight – as much as a big bull African bush elephant! This makes it a rival for the much later mammoths, that entered South America in the Pliocene and Pleistocene, as the heaviest South American mammal.

Astrapotheres were strange mammalian 'experiments', that, while reminiscent of our modern-day tapirs and elephants, nevertheless were quite different, with unique features of their own, and today, with no living close relatives for comparison, we can but guess as to many features of their appearance and lifestyles. My reconstructions are likely 'conservative' in too much resembling modern mammals; what I would give for a real time machine to go back and see what they were really like!

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