Scientists get to the bottom of what wiped out Australia's ancient gentle giants

Scientists get to the bottom of what wiped out Australia's ancient gentle giants - Human hunters were mainly responsible for wiping out Australia's megafauna, a study has concluded.

The reasons behind the demise of the giant animals that once roamed the continent – such as rhinoceros-sized diprotodons, towering kangaroos, marsupial lions and birds twice the size of emus – have long been hotly debated, with hunting, the human use of fire, and climate change blamed.

Chris Johnson, of the University of Tasmania, said his team had solved the extinction mystery by studying fungi that thrive in the dung of large herbivores.

The team examined two cores of sediment from Lynch's Crater, a swamp in north-east Queensland, dating back 130,000 years.

They counted the spores of these fungi and looked for pollen and charcoal in the sediments as indicators of vegetation change and fire.

Professor Johnson said the research showed megafauna numbers were stable until about 40,000 years ago, despite several periods of drying.

"This rules out climate change as a cause of extinction," he said.

The giant herbivore population crashed soon after humans arrived, with the number of spores in the sediment virtually disappearing. "So it seems that people did it."

The study, published in the journal Science, showed that after the demise of the megafauna, the vegetation changed and fire activity increased, with rainforest species disappearing and grassy eucalypt-dominated forests expanding.

But Judith Field, of the University of NSW, challenged the conclusions of the study. She said it was merely assumption that the ancient spores reflected the abundance of the giant animals.

"The only evidence we have from Queensland for megafauna indicates that they were gone before humans arrived."

There was also little archaeological evidence from any site in Australia to show humans co-existed with megafauna, and none to show they hunted them.

"The results of this paper are interesting. The interpretations drawn from it are unsubstantiated and can be explained by other mechanisms," Dr Field said.

But John Alroy, of Macquarie University, described the data as "superb and decisive".

The debate had dragged on for almost 50 years because people thought it "incredible" that stone-age hunters could have had such a big impact as to wipe out the megafauna.

Gavin Prideaux, of Flinders University, said the study was an important contribution and supported mounting evidence that climate change was not to blame.

"To test the inferences from this paper we might look at similar lake records from other regions of Australia and seek fossil deposits in the north-east that preserve bones of the giant animals themselves," Dr Prideaux said. ( smh.com.au )