[ExI] Humans caused Aussie megafauna extinction
thespike at satx.rr.com
Fri Jan 29 05:44:15 UTC 2010
Humans caused Aussie megafauna extinction
Friday, 29 January 2010
by Gemma Black
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
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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