Climate Change Caused Extinction of Australia's Giant Animals

BRISBANE, Australia, June 1, 2005 (ENS) - Queensland researchers have unearthed new evidence that climate change, rather than human activity, was responsible for wiping out Australia's giant marsupials thousands of years ago. The giant marsupials that carried their young in pouches are related to the kangaroos and wombats of today.

Instead of excavating only trophy specimens such as giant kangaroos and wombats, the researchers from Queensland University of Technology (QUT) and Queensland Museum performed the first systematic analysis of a site in the fossil rich Darling Downs region of southeastern Queensland.

By systematically analyzing a 10 meter (32 foot) deep section of creek bed, the team uncovered 44 species, ranging from land snails, frogs, lizards and small mammals to giant wombats and kangaroos, including many species previously unknown to have occurred in the Darling Downs fossil record.

They knew that the giant marsupials had vanished, but they discovered that smaller species, dependent on a wetter environment, had also disappeared.

The results suggest that the extinction of the giant animals whose remains are found at Darling Downs was caused by a massive shift in climate rather than by the arrival of humans who overhunted animals or destroyed habitats by burning the landscape.

Price

Lead researcher Gilbert Price examines a giant marsupial fossil. (Photo courtesy Queensland University of Technology (QUT))
Gilbert Price, PhD, of Queensland University of Technology's School of Natural Resource Science, led the study. "Unravelling the cause of the late Ice Age extinction has occupied scientists for centuries. It is essential to know if the risks faced by species and ecosystems today are the same as those in the past," he said.

"If we can document past environmental change and its influence on the extinction of species, it might have predictive value in estimating the effects of possible future climate changes and its impacts on modern species," said Price.

The findings, which were unearthed with the help of amateur fossil hunter, Ian Sobbe, are of particular significance because the Darling Downs fossil deposits are among the youngest Australian megafauna deposits - laid down on the cusp of the extinction event.

Megafauna - giant mammals, birds and reptiles - roamed the globe in the Pleistocene epoch, between 1.8 million and 10,000 years ago. The woolly mammoth, sabre-toothed tiger and giant deer roamed the Northern Hemisphere.

In Australia - which evolved for 40 million years in isolation - giant marsupials ruled.

Most of the megafauna species became extinct late in the Pleistocene Epoch, perhaps 20,000 years ago. The Aborigines arrived in Australia at least 60,000 years ago, and so shared the continent with many megafauna species for thousands of years.

Some scientists have theorized that Aboriginal hunting, or their use of fire, which led to an increase in grasslands and dry forests, may have been partly responsible for the extinction of Australia's megafauna. But the Darling Downs research indicates that climate change, not human activity was the deciding factor.

Dipro

Gilbert Price superimposed next to the megafauna Diprotodon (Photo courtesy QUT)
The largest marsupial ever discovered, Diprotodon optatum, evolved about a million years ago and may have become extinct as recently as 15,000 years ago. A plant eater, it was the size of a rhinoceros - three meters (10 feet) long, almost two meters (over six feet) high at the shoulder, and weighing as much as two tons.

Diprotodon optatum was quite widespread throughout inland Australia prior to the last glacial peak about 18,000 years ago. Inland Australia was somewhat less arid at that time, and supported extensive grasslands.

The last Ice Age brought increasingly dry conditions to the inland, and this may have caused the extinction of Diprotodon soon after. Fossils of Diprotodon and other animals are plentiful in the dry inland lakes of South Australia, and may be evidence that the last of the Diprotodons retreated into the lakes as they dried up.

Procoptodon goliah was the largest kangaroo ever. It belonged to the sthenurine family, which had shortened flat faces and forward-looking eyes.

Current theories suggest that between 50,000 and 20,000 years ago, increasing aridity in Australia led to cooler and drier conditions that decreased wooded habitats and expanded deserts and grasslands, but researchers have not clearly understood what impact it had on the giant animals.

The Darling Downs contain some of the most extensive and significant Pleistocene megafauna deposits in Australia but because it has been excavated since the 1840s it was assumed that the palaeoenvironment record was well established.

megafauna

Price with life-size models of megafauna at Queensland Museum (Photo courtesy QUT)
Closer examination by Price and his team revealed a bias in sample collection in favor of larger animals and the fact that there had been few attempts to document ecological and sediment data.

"Our samples show that species dependent on habitats such as woodlands and vine thickets dominate the lowest section of the trench, which dates to around 45,000 years ago," says Price.

"Other younger sections have a mixture of both large and small species that are habitat generalists or are species found in open areas, suggesting the landscape was evolving towards open grassland.

"By the latest Pleistocene species dependent on wetter conditions disappear from the fossil record while animals such as long-nosed bandicoots that aren't habitat specific remain" Price explained.

Analysis of sediment and ecological data shows that it became increasingly arid during the late Pleistocene, which led to the disappearance of woodland and scrubland and expansion of grassland.

To verify their results, Price and his team had carbon dating performed on the samples. Further work on other sites in the region, due to be published later in the year, confirm the stratification of fossils in the creek bed.

The Darling Downs dig failed to unearth evidence of human activity, suggesting Aborigines did not inhabit the region at the same time as the megafauna.

Scott Hocknull, Queensland Museum assistant curator in geosciences, said, "We're not just digging up a pile of old bones. These amazing fossil deposits are providing us with the key to understanding Australia's past, something integral when developing long term strategies for a sustainable future."