Australia's giant prehistoric animals, including three-meter (10-foot) -tall kangaroos, were likely wiped out by aboriginal settlers, not climate change, a researcher said Tuesday.
The question of what killed Australia's so-called megafauna — including giant kangaroos and wombat-like creatures as big as a rhinoceros — during the last Ice Age divides paleontologists.
The most popular theories are that climate change drove the giants to extinction more than 40,000 years ago or that Aborigines, who arrived in Australia as far back as 60,000 years ago, were responsible because of over hunting or burning the vegetation upon which the creatures fed.
But new fossil evidence from the Naracoorte Caves region of South Australia state ruled out climate change as the cause, according an article published in the latest edition of the Geological Society of America's monthly journal, "Geology."
The article's author, Flinders University paleontologist Gavin Prideaux, said Tuesday his research team's work in the caves indicated humans had a hand in the animals' extinction, although they found no direct evidence of human intervention.
"If it wasn't climate, then it had to be humans," Prideaux told The Associated Press.
"The real issue now is trying to resolve whether it was hunting or whether it was landscape destruction through burning ... and a bit of both is more likely," he added.
Prideaux headed an Australian research team that recorded rainfall in the Naracoorte region over 500,000 years by examining stalagmites in the caves and studying sediments.
Fossilized remains of animals that had fallen into the limestone cave system over that time _ including 20 species of extinct kangaroos, marsupial lions and hippopotamus-like marsupials _ were dated using two independent methods: optically stimulated luminescence at Australia's University of Wollongong and uranium-series dating at the University of Melbourne.
"Although populations fluctuated locally in concert with cyclical climatic changes — with larger species favored in wetter times — most, if not all of them survived even the driest times. Then humans arrived," Prideaux said in a statement.
"Our evidence show that the Naracoorte giants perished under climatic conditions similar to those under which they previously thrived, which strongly implicates humans in their extinction," he added.
The theory that the arrival of the first humans, who are known today as Aborigines, quickly wiped out Australian megafauna by over hunting was made popular by paleontologist and zoologist Tim Flannery's book "The Future Eaters" which was published in 1994 and became the basis of a television documentary series of the same title in 1998 produced by the Australian Broadcasting Corp.
Critics of the theory include Charles Darwin University forest ecology expert David Bowman, who has argued that Aborigines did not have the population density or, armed with spears and boomerangs, the technology to efficiently wipe out the massive mammals.
"It should be remembered that it becomes increasingly difficult to kill off a species as their population is reduced to low levels because of the extra hunting effort required to find the last remaining animals," Bowman said in a statement posted on the ABC Web site.
Archaeologist Judith Field said on the same Web site that she believes climate change was the main driver behind the extinctions because of fossil evidence that humans coexisted with megafauna for thousands of years.