Climate Change, Not Humans, Killed Off Megafauna

Fairfax - Bridie Smith

Tom Rich, curator for palaeontology at Museum Victoria. Photo: Jason South

It's a contentious question. Why did the giant kangaroos and rhino-sized wombats that once roamed Australia die out?
Scientists agree there are two contenders: climate change and humans. But they are fiercely divided over which caused the continent's megafauna to go extinct.
Now, fresh results of a study at a renowned Victorian fossil site in the Macedon Ranges town of Lancefield 73 kilometres north of Melbourne has provided an answer.

The diprotodon was a rhino-sized wombat that weighed about 2.8 tonnes. Photo: Peter Trusler

Lead author of the research Joe Dortch from the University of Western Australia said climate change appeared to be the culprit in the mass deaths of megafauna living in the Lancefield region 50,000 years ago. "Drought was very severe around Lancefield at that time and we are starting to see more evidence of massive climatic changes in this period in south-eastern Australia," he said.
Dr Dortch conceded the study's findings would be considered a piece of the puzzle that would add to, rather than settle the debate.

Scientist Peter White and student Jon Lushey with an excavator at the site. Photo: Joe Dortch

He said even among the six study authors, opinion was divided about the cause of megafauna extinction globally.
There was agreement that the Lancefield Swamp site represented "a drying environment" and that climate change was the major factor in the death of the megafauna that once called the area home.
Scientists say the evidence of this is that among the fossilised remains of giant kangaroos there were no juveniles or elderly animals found at the swamp, the area's last surviving waterhole.

A student working at one of the excavated bone beds at Lancefield. Photo: Joe Dortch

"That tells us that the most vulnerable members of the mob have perished somewhere else already ... and these were the healthiest and the last of the group," Dr Dortch said. "If it was a site where humans had been hunting, you would see a range of animals there."
Thousands of fossils recovered from Lancefield are housed at Museum Victoria. The museum's curator of palaeontology Tom Rich said the site was valuable to researchers internationally because it contained evidence of humans and megafauna co-existing. Key to this was the discovery of a stone artefact in 1974.
"It's a very extensive, rich site," he said. "It has drawn scientists back for decades, hoping to answer this contentious question."
Deakin University's Sanja van Huet​ didn't participate in the study, though she specialises in what happens to an organism between death and when it is discovered as a fossil.
Dr van Huet argues evidence of abrasions and weathering have been found on the fossilised bones – evidence that they were exposed to the elements at another site before being moved.
"I don't think that the animals died in the swamp, I think they died in the surrounding area," Dr van Huet said. "Heavy rainfall later washed bones into the swamp."
Overall Dr van Huet believes a combination of climate change and disease led to the extinction of Australia's megafauna. She said she was open-minded that humans could have "tipped them over the edge".
"I don't agree with 100 per cent of it but I think it's a great paper," she said.
The Lancefield Swamp fossil deposits are between 80,000 and 50,000 years old – the latter date coinciding with humans' arrival in Australia and with an extremely severe drought.
"There would have been a series of massive droughts lasting decades – perhaps over millennia," Dr Dortch said.
Discovered in 1843 by well-digger James Mayne who was searching for water, the Lancefield Swamp site has been studied by archaeologists since the 1970s.
"A carpet of fossils covers the site, which is spread over a few hectares," Dr Dortch said. The layer of bones is 10-20 centimetres deep.
The dominant animal found at the site is a giant kangaroo that would have stood up to two meters tall and weighed in at an impressive 200 kilograms. Fossilised remains of a diprotodon, a rhino-sized wombat which would have weighed about 2.8 tonnes, have also been found.
Fieldwork during the drought years of 2004-2005 uncovered a 70-centimetre-long jawbone of a diprotodon.
The findings will be published in the journal Quaternary Science Reviews in August.

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