29 January 2010

Humans caused Aussie megafauna extinction

Cosmos Online
The key anomaly in the Australian megafauna debate has been resolved, and "if people hadn't arrived in Australia, we'd still have the giants of yesteryear to admire," the lead researcher said.

An artist's reconstruction of the half-tonne Palorchestes azael, an extinct Australian giant marsupial that was similar to a ground sloth.
Credit: Image courtesy of Peter Schouten

SYDNEY: The key anomaly in the Australian megafauna debate has been resolved, and “if people hadn’t arrived in Australia, we’d still have the giants of yesteryear to admire,” researchers report.

Giant Australian marsupials, reptiles and flightless birds went extinct between 45,000 and 60,000 years ago. The reason behind the extinction of Australian megafauna has been the subject of debate for decades, said the lead author of the study, Richard Roberts from the University of Wollongong near Sydney, Australia.

One theory is that Australian megafauna, including three-metre-high kangaroos and flightless birds weighing half a tonne, was driven to extinction at around the same time that humans arrived.

The other theory is that the onset of the latest ice age, which peaked around 21,000 years ago, caused the extinction of the megafauna.

Cuddie Springs anomaly

While several archaeological sites support the first theory, one site at Cuddie Springs stood out as an anomaly. The study, published in the journal Science, showed that the supposedly undisturbed fossils had actually been moved, resolving the anomaly.

Cuddie Springs, in western New South Wales, has long been promoted as a site containing both megafauna fossils and stone tools in the same sedimentary layer.

By dating the surrounding sediments researchers found that the fossils and tools could be as young as 30,000 years – suggesting that humans and megafauna co-inhabited the continent for an extensive period of time.

However, a geologist from the Australian National University, Rainer Grun, recently dated the fossils directly, using a combination of electron spin resonance (ESR) and uranium-series (U-series) dating.

Cuddie Springs deposits had moved

The results, published online in the journal Quaternary Science Reviews, showed that some of the supposedly undisturbed fossils in the sedimentary layer were actually more than 450,000 years old, suggesting that they had been reworked from much older deposits.

“It seems that none of the fossils in the archaeological levels at Cuddie Springs are younger than the extinction window between 51,000 and 40,000 years ago,” said Richard. “This pulls Cuddie back into line with all other sites on the continent, and removes its ‘anomaly tag’,” he said.

“Rainer Grun leads the world in ESR/U-series dating, so his findings for Cuddie Springs deserve serious consideration,” Richard said.

Extinction is complicated, experts warn

However, Danielle Clode, a zoologist from the University of Melbourne, and author of Prehistoric Giants: the Megafauna of Australia, thinks it might be misguided to suggest that there was just one cause behind the extinction of Australian megafauna.

“I know how incredibly difficult it is to understand what exactly is driving species extinction today, even when we can watch and study the process directly,” she said.

“I think it is very unlikely that the decline of the megafauna was caused by a single factor, and even less likely that we are ever going to be able to work out what did drive their extinctions, in anything other than the most general terms.”

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