Small species back-up giant marsupial climate change extinction claim

05/27/05

Thinking small in a time when everything was big has helped Queensland researchers to unearth new evidence that climate change, instead of humans, was responsible for wiping out Australian giant marsupials or megafauna 40,000 years ago.

Instead of only excavating '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 south-eastern Queensland.

Reported in the journal Memoirs of the Queensland Museum tomorrow (Tuesday 31 May) they found smaller species, dependent on a wetter environment, had also disappeared.

By systematically analysing a 10 metre 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.

The results suggest that the extinction of Darling Downs megafauna was caused by a massive shift in climate rather than by the arrival of humans who over hunted animals or destroyed habitats by burning the landscape.

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.

PhD researcher Gilbert Price, of QUT's School of Natural Resource Science who led the study, says:

"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.

"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."

Megafauna roamed the globe in the Pleistocene epoch, between 1.8 million and 10,000 years ago.

In the northern hemisphere species such as the woolly mammoth and sabretooth tiger dominated the landscape, while in Australia - which evolved for 40 million years in isolation - giant marsupials ruled.

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 are still not clear what impact it had on fauna.

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

Closer examination revealed a bias in sample collection in favour of larger animals and 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 Mr 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."

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 carbon dating was performed on samples. And further work, due to be published later in the year, on other sites in the region confirm the stratification of fossils in the creek bed.

The dig also failed to unearth evidence of human activity, suggesting they didn't inhabit the region at the same time as megafauna.

Queensland Museum Assistant Curator in Geosciences, Scott Hocknull added:

"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."

Source: Eurekalert & others

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