Marsupial Lions and Monster Kangaroos: Australia's Vanished Fauna

At the end of the Pleistocene, Australia was still home to an extraordinary range of marsupial megafauna. These animals evolved independently from the rest of the placental world for millions of years, which is why it is so fascinating to see both how diverse and unusual they became and how similar some of them appear to placental mammals in both physiology and ecology.

 Thylacoleo, also known as the marsupial lion, was one of the largest predators in the Australian continent at up to 130 kg. Pound for pound, it had the strongest bite of any mammal, living or extinct. With retractable claws like a cat, semi-opposable thumbs and a stiff kangaroo-like tail, not to mention massive carnassial cheek teeth for tearing flesh, it would have made a fearsome predator, and were it still alive would probably make our trip to Tasmania a lot more dangerous.

Diprotodon was the largest marsupial of all time, weighing in at a massive 2800 pounds, the size of a rhinoceros. Related to both wombats and koalas, Diprotodon probably behaved more similarly to a rhino or hippo, living in forests, woodlands, and grassland, grazing on vegetation and possibly staying close to waters. Diprotodon has been claimed as the basis behind the legendary bunyip of Aboriginal myth, and cave paintings exist that may depict both Diprotodon and Thylacoleo. 

Kangaroos were not immune to gigantism. Procoptodon reached 6.6 feet in height, and probably walked rather than hopped. Kangaroos also took on some niches we might have trouble imagining: the earlier (Pliocene) Propleopus oscillans had large shearing teeth which indicate it might have eaten meat.

Artist's recreation of Thylacoleo attacking Diprotodon. 

Finally, amidst all these marsupials there is one reptile that deserves our attention. We might know of the Komodo Dragon as the largest lizard in the world, but when the first Aborigines arrived in Australia, they had to deal with Megalania. At up to 20 feet in length Megalania was the largest lizard of all time, and undoubtedly the top predator anywhere it lived.

These are all examples of island gigantism and convergent evolution. Without big cats or ungulates, marsupials and reptiles evolved to huge sizes to fill these niches.

http://en.wikipedia.org/wiki/Megalania
http://en.wikipedia.org/wiki/Thylacoleo
http://en.wikipedia.org/wiki/Diprotodon