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!"

If you've been reading my recent articles about the unique prehistoric animals of South America during the time it was an 'island continent' (occasionally along with Antarctica) following the extinction of the non-avian dinosaurs, you'll have noted that I mention a group called the Sparassodonts. These were carnivorous mammals unique to South America, with no close modern relatives. The name 'sparassodont' means 'rending/tearing tooth'. So today let us look at a representative sparassodont, Borhyaena tuberata. Despite the name, it wasn't related or actually much like modern-day hyenas. It was a vaguely dog- or foxlike predator, reaching 2.2 m/7'2" in overall length and a bodyweight of perhaps 60 kg/130 lbs. It was long-bodied, fairly short-legged, with a heavy skull and a rather stout tail. It lived in the early Miocene, 17.5-15.5 million years ago. Its fossils were found in Argentina and Chile, and it was named by Florentino Ameghino in 1887.

The Marsupialoid Sparassodonts

For long, the sparassodonts were considered to be marsupials. Marsupials are the mammals that deliver their babies at a very early and underdeveloped stage, with (most species) then nursing them in pouches for weeks to months longer. Today they occur only in South America and Australia, but in ancient times were more widespread. All indications are that the sparassodonts also had such pouches and also birthed their young very early. However, the sparassodonts now appear not to be proper marsupials, but instead what is called a 'sister group' to the modern marsupials. It is likely that several ancient groups of mammals had pouches and gave birth to relatively undeveloped young, with only a single group, the placentals, which now dominate the world's mammalian fauna, having developed a way to carry their babies for a long period in their wombs.

Because marsupials also occur in the Americas, it seemed natural to think that sparassodonts were also marsupials, and they're often reconstructed looking similar to Australian marsupial predators, like the now sadly extinct Thylacine or Tasmanian Wolf/Tiger, and the Tasmanian Devil. Logically, however, it would make more sense to consider sparassodonts to be closer to the Opossums, which are the marsupials dominating South America, with one species in North America. But now it appears that they were outside of the group that contains both the American and the Australian marsupials of the present day. The earliest ones are known from the Palaeocene, the first period of life following the extinction of the dinosaurs, and it is likely that their evolution had diverged from that of other marsupial-like mammals even earlier. They've so far only been found in South America.

Sparassodonts were quite diverse, although it appears they were all carnivorous, though some species appear to also have been able to eat plant foods. They range from small weasel- or mongoose-like animals weighing only about 1 kg/2lbs to predators the size of a leopard or jaguar. Most seem to have been adapted to climbing and living in forests. Some of the larger kinds were mainly terrestrial, living in more open habitats such as dry woodlands or savannahs. There were wolverine-like and bear-like forms, fox-like forms, and even one that had huge sabre-like canine teeth like the sabretooth cats of other continents. This is an amazing example of convergent evolution, where animals not at all closely related develop similar appearances because of leading similar lifestyles. This is indeed a feature of all the sparassodonts, seeing as they all indeed showed resemblances to mammalian carnivores that occupied similar ecological niches.

Borhyaena itself, and a few other sparassodonts, show hyena-like adaptations in their strong neck muscles, jaws and teeth. Though borhyaena looks like it would have been able to crack bones, it is nevertheless believed to be an active hunter rather than a scavenger. Some skulls show wounds to the face suggesting that they actually fought with and bit each other, aggressive behaviour similar to that of the modern Tasmanian devil. Its relatively short legs mean that it was likely not one to catch its prey on the run, instead probably an ambush hunter, hiding and then suddenly pouncing on its intended victim. A relative, Australohyaena antiqua, was much more strongly adapted to bone-cracking and looks like it might truly have been called a hyena-equivalent.

During the long period of South America's isolation, the sparassodonts shared duties as predators with the Terror Birds. The largest of the terror birds were bigger than the biggest sparassodonts, and they were therefore the apex predators, the only ones that could kill and prey on the largest of the South American herbivores. The terror birds with their long, strong legs were fast runners and thus likely to dominate the open plains, while the sparassodonts lived more in forests, woodlands and scrub. The heyday of the sparassodonts was the Miocene Period, but a few kinds hung on into the Pliocene. It seems the last of them died out around 3 million years ago in the late Pliocene. We don't know just why they died out. In the Pliocene, a land bridge, at first a chain of islands, started to form between North and South America, allowing 'modern' placental predators to enter the southern continent. The first group to do so, where the procyonids, relatives of the raccoons. But they did not seem to have offered much competition to the sparassodonts, since they were mostly small with specialized ecological niches. Nevertheless, the sparassodonts declined and by the late Pliocene when the land bridge was completed and big placental predators such as wolves, bears, jaguars and sabretooth cats, could enter South America, the sparassodonts were all gone. The most likely reason for their demise might be climate change, with South America becoming cooler and drier towards the onset of the Ice Ages, but this is not entirely satisfying as even in the coolest times, much of South America still enjoyed a warm, tropical to subtropical climate.

Willem

27.04.20 Front Page

Back Issue Page