Diprotodonts are restricted to Australasia. The earliest known fossils date to the late Oligocene. However it is certain that their genesis lies earlier than this, as there are large gaps in Australia's fossil record and virtually no fossil record at all in geologically active New Guinea. The great diversity of known Oligocene diprotodonts suggests that the order began to diverge well beforehand.
Many of the largest and least athletic diprotodonts (along with a wide range of other Australian megafauna) became extinct when humans first arrived in Australia about 50,000 years ago.