Thirty thousand years ago, however, the continent wasn't like that. Rainfall was high, temperatures were mild, the land was verdant. There were extensive grasslands and game was plentiful. It was the aboriginal "dream time".
In those days Australia, like Africa today, had its own megafauna.
But ours were marsupials, as distinct from the placentalmammals of the Old and New Worlds. Nevertheless, the view across Australian plains would have looked remarkably like the famous Serengetti Game Reserve today, only with different actors.
But then, between 25,000 and 18,000 years ago, the climate changed. As the ice age neared its climax, mile high ice sheets scoured northern Europe and North America down to bedrock. Sea levels fell by 200 metres, right to the edge of the continental shelf. In the southern hemisphere, the climate cooled, rainfall diminished. The Australian continent suffered cold and extreme aridification. The deserts moved coastwards and dunes dominated the landscape of western Victoria. Rivers dried out out and springs that had watered lush grasslands were left as oases in a barren desert. At Lancefield, megafauna drawn to perhaps the last remaining waterhole in the district became mired and perished, leaving their bones to be found by latter day palaeontologists.
The great dying in Australia appears to have coincided with the dramatic desiccation that occurred at the height of the Ice Age. When the ice at last relented, 10,000 years ago, the megafauna of Australia were almost all gone. Animals who survived were generally reduced in size compared with their Pleistocene forebears. Consequently, Australian marsupial fauna today is but a pale shadow of what it once was.
Evolution in Australia spawned equivalent marsupials to fill the same ecological niches that were available elsewhere to placental mammals. Where there were no herds of fast moving zebras or antelopes, there appeared kangaroos. Where there were no large grazers like rhinos and elephants, there arose Diprotodontines and Zygomaturines.
And where there were no lions or leopards, there appeared marsupial predators. Most notable among these was Thylacoleo carnifex, the Australian "Marsupial Lion". It was a large animal, ranging up to the size of an African lion.
This reconstruction of T. carnifex is by artist Peter Schouten("Prehistoric Animals of Australia", ed. S. Quirk & M. Archer, Australian Museum, Sydney, 1983".)
Its cat-like appearance owes something to the theory that T. carnifex was descended from the Burryamids, or Pygmy Possums, which are native to the mountains of S.E. Australia. Hence an arboreal reconstruction with leopard-like appearance is presented. An alternative interpretation has thylacoleonids arising from Vombatid stock. In this case they would have been more closely related to modern day wombats than to possums. That ancestry would, presumably, leave them looking not quite so feline in appearance. The reader should consult the reference material for further exposition on the question of Thylacoleo's ancestry.
dentition of this animal was unique. It had no canine teeth as do placental
predators like wolves or lions. Instead it was equipped with very large
incisors and extremely specialised carnassial teeth. These had become blade-like
cutting edges, two pairs only being positioned on the upper and lower jaws.
It has been asserted that T. carnifex's dentition represents the most extreme specialisation of any known mammalian carnivore. The reader is directed particularly to references #2 & #3 for a detailed discussion.
The front paws of T. carnifex were equipped with a partly opposable thumb. The terminal phalanx of the thumb sported an impressively large, curved claw, while the other digits had smaller claws. The rear feet were equipped with similarly opposable thumbs. It's probably true to say that this was an animal equipped with four hands, rather than paws, and that it almost certainly was primarily an arboreal hunter. However, fossil specimens have been unearthed in areas which were open plains when the animal lived. So it appears to have been resourceful enough to make a living with or without a forest habitat.
Variation in the size of fossil remains are usually interpreted to mean that males of the species were bigger than females. Sexual dimorphism is common in many mammalian species, for instance kangaroos, lions and seals. It generally indicates a breeding system where males must defeat and dispossess other more dominant males for access to females. In such species, mature males are often fewer in number than breeding-age females.
Generally speaking, fossil T. carnifex presents as a large animal which exhibited a wide range in body size. Fossil evidence suggests that an average individual would have weighed about 45 kg (Ref #2). The largest specimens, which were just a shade smaller than the African lioness, Panthera leo, appear to have lived in south-eastern Australia.
If indeed our mystery animal exists
and it turns out to be Thylacoleo carnifex, we may have on our hands
yet another example of convergent evolution. The most outstanding case
of this phenomenon is the Thylacine, the famous marsupial wolf.
It's an animal which bears an astonishing physical resemblance to placental
wolves. Yet, as a marsupial, it's about as far removed from them as a gazelle
is from a kangaroo. One of the many oddities thrown up by Darwinian Selection
in Australia is that examples of convergent evolution appear to be restricted
to carnivorous animals. For obscure reasons, Australian herbivores don't
seem to exhibit the phenomenon.
|T. carnifex disappears from the fossil record about 20,000 years ago. Are there any representations of Thylacoleo available in aboriginal rock art from so long ago? Surprisingly, the answer is a tentative 'yes'. This image is taken from The Dreamtime Animals: extinct megafauna in Arnhem Land rock art, P.Murray & G. Chaloupka, Archaeol. Oceania 19 (1984) 105-116.The authors cautiously rate it a possible image of Thylacoleo.|