The genus 'Diprotodon' was a group of large herbivorous marsupials that existed across most of mainland Australia from 1.6 million years ago (mya) to possibly as recently as 20,000 years ago. They were the largest marsupials to have ever lived and were an important member of Australia's extinct megafauna of the Pleistocene epoch, a period from 1.8 mya to about 11,000 years ago.
The name 'Diprotodon' refers to the two prominent forward-facing teeth in the lower jaw of these animals. The Diprotodontia are the marsupial mammals with the two enlarged lower incisor teeth, and include kangaroos, koalas, possums, wallabies, pademelons and wombats. 'Diprotodon' had a large, heavy build and a body shape similar to wombats but with long legs. The largest of these animals was 3 m long, 1.7 m tall at the shoulder and would have weighed 1.5-2.5 t. Diprotodon lived in open forest, woodlands and grasslands browsing on tree leaves, shrubs and possibly grasses. They tended to stay close to water. Wombats and koalas are their closest living relatives.
'Diprotodon' died out during a mass extinction of Australia's megafauna, which took place late in the Pleistocene epoch. This event may have been associated with the last ice age, which peaked 18,000 years ago, or it may have occurred earlier. Some of the reasons proposed for the mass extinctions include: hunting by Aboriginal people, since they had arrived on the continent towards the end of this time; habitat change as a result of the use of fire by Aboriginal groups; or climate change in the form of an ice age, which would have led to dry conditions across much of the continent. Some scientists think that probably all three factors combined to cause the massive loss of species evident in the fossil record, while others think the arrival of humans was the single most devastating cause.
This skull specimen of 'D optatum' was found in Bacchus Marsh, Victoria. It is one of the rare intact skulls of 'Diprotodon' and is now held in Museum Victoria. 'Diprotodon' skulls were relatively thin and hollow, so they were fragile and often crushed during fossilisation. It is thought the unusual internal and external structure of 'Diprotodon' skulls may have evolved to better adapt these animals to a nutrient-poor environment by reducing the weight and resources usually required of a heavier, thicker skull.
This specimen is an example of an 'unaltered' type of fossil. This fossil has undergone little or no change to the structure and composition of the bone. Younger fossils, such as this one from the Pleistocene epoch, are more likely to be found in an unaltered state than the more ancient fossils.
Fossils are the remains, moulds or traces of dead plants or animals preserved mostly in sedimentary rock such as sandstones, siltstones, shales and limestones. Fossils provide clues to invaluable information about the Earth's past, including the evolution of plants and animals, the age and formation of rocks, previous climatic and environmental conditions, and the former positions of the continents.