Diprotodon: Australia's Giant Marsupial and Its Extinction

Diprotodon was a giant plant-eating marsupial that lived across Australia from about 1.6 million years ago until roughly 40,000 years ago. Weighing up to about 2.7 tonnes, it is the largest marsupial known to have existed. Its disappearance, after the first people reached Australia, lies at the heart of a long debate over what wiped out the continent’s Ice Age giants.

What Diprotodon was like

Diprotodon optatum belonged to the vombatiforms, the group that today includes wombats and koalas. It walked on four sturdy legs with inward-turned feet and was built rather like a very large wombat, although it was not a burrower. The name means “two forward teeth”, after the pair of large, protruding lower incisors.

Adults were about 3 to 3.8 metres long and up to about 1.8 metres tall at the shoulder. Like other marsupials, females carried their young in a pouch, which in Diprotodon is thought to have opened towards the rear. Males were considerably larger than females, a difference that once led scientists to describe the sexes as separate species.

Diprotodon ate shrubs, leaves and grasses and lived in open woodlands and grasslands across most of mainland Australia. A 2017 study of chemical signals in its teeth suggested that some animals may have moved seasonally over distances of more than 100 kilometres, which would make it the first marsupial known to migrate.

Discovery

The first Diprotodon bones known to science came from Wellington Caves in New South Wales, explored by the surveyor Thomas Mitchell in 1830. The British anatomist Richard Owen named the genus in 1838 from this early material and went on to describe the animal in more detail as more bones arrived in London.

The most spectacular finds came from Lake Callabonna, a dry salt lake in north-eastern South Australia. Bones were reported there in 1892, and in 1893 the South Australian Museum sent a team led by Edward Stirling and Amandus Zietz. They uncovered many complete skeletons, preserved where the animals had broken through the dry crust of the lake and become trapped in the soft, sticky mud beneath. The site also yielded fossils of the giant flightless bird Genyornis. Lake Callabonna is now a protected fossil reserve.

Since then, Diprotodon remains have been found at many sites across mainland Australia, from Queensland to Western Australia, often around ancient lakes, springs and creek beds where animals came to drink. Fossilised footprints have also been reported, giving clues about how the animal walked. Casts of the Callabonna skeletons were sent to museums around the world, which helped make Diprotodon the best-known symbol of Australia’s vanished megafauna outside the country as well as within it.

Extinction and the debate over its cause

Diprotodon was one of about two dozen kinds of large animals that vanished from Australia during the late Pleistocene. Others included the marsupial lion Thylacoleo, the giant kangaroo Procoptodon and Genyornis.

People reached Australia by sea at least 50,000 years ago, and some evidence points to arrival as early as about 65,000 years ago (see peopling of Australia). In 2001 a study led by Richard Roberts dated sediments at sites around the continent and concluded that much of the megafauna disappeared at about the same time, around 46,000 years ago, not long after humans arrived. Supporters of a human role argue that slow-breeding giants could not withstand even modest hunting, or that people changed vegetation through fire.

Critics point out that there is very little direct evidence of Diprotodon being killed or butchered and that Australia was becoming drier and more variable in climate over this period. Some argue that megafauna declined over a much longer span. Many researchers now favour a combination of human impact and environmental stress, with the balance still disputed. These questions form part of the wider Quaternary megafauna extinction debate.

Myths and facts

• Myth: Diprotodon was a giant wombat. It was related to wombats but belonged to a separate, extinct family, the Diprotodontidae.
• Claim: Diprotodon inspired the bunyip. Some writers have suggested that fossil bones or distant memories of megafauna influenced Aboriginal stories of the bunyip, a creature of waterholes. This is an interesting idea, but there is no firm evidence for it.
• Fact: People and Diprotodon lived at the same time. The two overlapped in Australia for thousands of years, although for how long is uncertain.

Timeline

• c. 1.6 million years ago: Diprotodon optatum is present in Australia (estimates vary).
• c. 65,000 to 50,000 years ago: The first people reach Australia.
• c. 45,000 to 40,000 years ago: Diprotodon disappears.
• 1830: Thomas Mitchell explores Wellington Caves, finding megafauna bones.
• 1838: Richard Owen names Diprotodon.
• 1893: The South Australian Museum excavates skeletons at Lake Callabonna.
• 2001: A continent-wide dating study places the main megafauna extinction around 46,000 years ago.

Why it matters

Diprotodon is the iconic giant of Ice Age Australia. Its well-preserved skeletons reveal how marsupials could evolve to elephant-like sizes on an isolated continent, and its extinction remains central to understanding how the first Australians and a changing climate reshaped the land.