Humans 'wiped out' mega beasts
Sydney - It was not climate change that wiped out Australia's giant animals 40 000 years ago, but the spears and clubs of the first settlers, researchers said on Friday.
What did for the megafauna - rhino-sized wombats, birds twice as big as emus, claw-footed kangaroos and massive marsupial lions - has been fiercely debated for almost 100 years.
But now blame for the disappearance of the 2.5-ton diprotodon and around 50 other megafauna species has been laid at the door of the first humans who arrived on the continent from Asia, in a scientific finding that will be unpalatable to some.
The University of Tasmania's Chris Johnson led a team that analysed fungal spores dating back 130 000 years taken from sediment cores drilled out of a swamp at Lynch's Crater in the Atherton Tablelands in north Queensland.
They found that spores of the fungi that thrive in the dung of large herbivores like the diprotodon were widespread until around 41 000 years ago, with samples younger than that showing no traces of the spores.
Their study provides the best evidence yet that the megafauna were doing fine when the humans arrived, around that time, but died out not long after.
"People hunted them in big numbers and made them go extinct," Professor Johnson said.
He and his colleagues hope that their discoveries, published in the magazine Science, will finally put to bed the notion that a change in climate caused the extinction.
But University of Melbourne researcher Matt Cupper, a specialist in carbon dating, said the jury was still out on whether the megafauna were wiped out through hunting.
"We've not ever found the smoking gun," he said. "A combination of factors could be involved, with climate change weakening the animals and making them more susceptible to extinction."
For others in the field, like botanist Matt McGlone from the New Zealand government's Landcare Research outfit, Johnson's paper is definitive and the debate is now over.
"That's the message to the world: When humans arrive on a landscape on a new country they put enormous pressure on animals heavier than 10kg and a lot of them go extinct. It may have taken a short time or a longish time in Australia but it happened and it would have happened without any other intervention in the way of climate, disease, fire, whatever," he said.
Johnson's research team found sediment samples spanning back over 80 000 years that, through carbon dating, showed two climate changes in the glacial cycle but the megafauna weathering both.
Those who blame the country's first human inhabitants have sometimes been accused of racism. And some have argued that it is incomprehensible that small bands of hunters with nothing more than sticks and stones could have wiped out so many massive beasts.
Johnson notes that some took that fallacious view of whaling: How could small bands of whalers affect numbers in the planet's vast oceans?
"But those whale populations are replacing themselves very slowly," Johnson said. "Even if you go out and harvest 2% of them, they'll soon become extinct."
The fresh research is less definitive about that other great controversy in Australia's environmental history: Whether it was fire or the extinctions that led to mixed rainforest giving way to the grassy eucalypt-dominated savannah that now covers much of the country.
It could be that the absence of the giant herbivores caused more grass to grow and the increase in the fuel load led to more and bigger fires.
McGlone may agree with Johnson's theory of the cause of the megafauna extinction, but he is not convinced that was the cause of the changes to the landscape. "I think it was human fire," he said.
Based on that scenario, not only did humans change the fauna, McGlone said, they changed the flora too.