Diprotodon optatum

Diprotodon is the largest known marsupial. Its fossilized bones come from Australian quaternary formations and particularly from ancient lake deposits and cave fills. Callabona Lake yielded a considerable quantity of fossil Diprotodon remains, from hundreds of individuals who were trapped in the lake mud as it was drying out.

The first diprotodontids appeared at the end of the Oligocene, around 25 million years ago. They are iconic elements of the native marsupial fauna of Australia. The wombat, an herbivorous animal of medium size, is the closest modern marsupial relative of the Diprotodon.

Diprotodon owes its name to the two large, forward-pointing, lower incisors, a characteristic of the group. It was a massively-built herbivore: measuring up to 3.8 metres long and 1.7 metres high at the shoulder and weighing slightly less than 3 tons. Its body was supported by inward-facing legs, with toes that are small for its size. On the back feet, a rudimentary thumb, reduced to a metatarsal, splays at a 90-degree angle to the other toes, and appears to indicate that the ancestors of this animal had an opposable thumb and were tree-dwellers. 

For nearly 20,000 years, Diprotodon lived alongside the Australian aborigines before becoming extinct. It lived in savannas, semi-arid plains and open environments. It displays significant sexual dimorphism.

Reconstructed at the South Australian Museum of Adelaide with bones from Lake Callabonna, Southern Australia