Hunting was likely killer of giant marsupials
WOMBATS AS BIG AS a fridge, kangaroos two metres tall, a goanna that weighed over 300 kg – Australia’s ‘megafauna’ roamed the continent for nearly two million years, before vanishing by about 40,000 years ago. Exactly what caused their disappearance is hotly debated, with climate change, intensive hunting or burning of the landscape by people as the three leading contenders.
Now a team led by Gavin Prideaux at Flinders University in Adelaide thinks it has the answer. The picture is more complicated, they say, but hunting seems to be the main culprit.
Gavin and his colleagues have been studying bones from a cave in south-western Australia, aptly named the Tight Entrance Cave.
“Imagine squeezing down a narrow, seven-metre high chimney followed by a hundred metres of dusty crawling, sliding and shimmying across crevasses until you slide down a rocky slope into a large cavern,” says Gavin. “Then imagine hauling 200 15 kg bags of sediment out the same way you came in to sieve up top for small bones. Just another day at the office!”
Climate change ruled out
The cave contains bones of the massive mammals which roamed Australia for more than 100,000 years, from before people arrived in to the continent, to well beyond. “This presented us with a unique chance to do a ‘before’ and ‘after’ comparison,” says Gavin.
The team found that giant mammal populations bounced back after a sudden drying of the continent about 140,000 years ago, but then they died out before the most recent extreme dry phase, which began 30,000 years ago. They think this rules out climate change as as the main cause of the extinctions. Similarly, bushfires intensified 30,000 years before the extinctions, suggesting that they weren’t the main cause of the animals’ demise either.
The researchers found that people lived in the region at the same time as the monster mammals for at least 9,000 years. This rules out the ‘blitzkrieg’ theory that humans rapidly hunted the animals to extinction, says Gavin.
Instead, they think that long-term hunting, over 10,000 years or more, was probably the main cause of the disappearance of Australia’s megafauna, and that drier conditions, which occurred around the same time, probably made the bad situation worse. This puts paid to the commonly held idea that there is a single main reason for the loss of these species, says Gavin.
“The study firms up the view that if humans hadn’t arrived, the megafauna would have survived to the present day,” he says. “But it also shows that some role for climate change and fire cannot be ruled out.”
Palaeontology detective work
Dr John Long, a senior palaeontologist at the Natural History Museum of Los Angeles County in California, formerly of Museum Victoria in Melbourne, welcomes the work. “This is an extremely important [study]. I watched the team’s impeccable attention to detail – I would say this is one of the most detailed pieces of palaeontologial detective work accomplished in Australia,” he says.
However, not all scientists are convinced. The team doesn’t have hard data to show that early humans were implicated in the extinctions, argues Professor Mike Archer, AM, a palaeontologist at the University of New South Wales in Sydney.
Mike suggests that most of Australia’s lost species of megafauna had already become extinct before people arrived. “The steady disappearance of these larger species is more consistent with a response to climate change than anything humans were doing,” he says. And evidence from Tasmania, he adds, suggests that even when large animals were available for hunting, they were usually ignored in favour of smaller, easier-to-catch species. However, more work is needed before it’s possible to be sure about what was behind the extinctions, he says. “The argument about ultimate causation will continue until more hard evidence is gathered.”
The research is published today in the Proceedings of the National Academy of Sciences.
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