London, January 25 (ANI): A new research has suggested that humans, not climate change, may have caused the mass extinction of Australia's giant animals, tens of thousands of years ago.
Scientists have long argued over what killed off about 50 species of animals weighing more than 45 kilograms, including the gigantic kangaroo, Procoptodon, and the two-tonne wombat-like marsupial Diprotodon, late in the Pleistocene epoch, which stretched from 2.6 million until about 12,000 years ago.
Some have proposed that the ancestors of Australian Aborigines, who reached the continent between 60,000 and 45,000 years ago, rapidly hunted the animals to extinction.
Evidence for a human cause has been mounting over the past decade.
One study dated the extinction of the 2-metre-tall, 200-kilogram flightless bird Genyornis to about 50,000 years ago, soon after human colonization, and at a time when the climate was benign.
However, one site, Cuddie Springs in New South Wales, has been held up as evidence for a long overlap between humans and megafauna, seemingly clearing people of being the main agents of the extinction of the animals.
It is the only site with megafauna remains and Aboriginal artefacts in the same sedimentary layers.
Those layers had been dated by radiocarbon and luminescence methods to between about 40,000 and 30,000 years old.
But some researchers doubted the results, which dated the megafauna only indirectly, through charcoal and sand grains in the layers bearing the fossils and stone tools.
They said the site had been disturbed, with megafauna fossils from older deposits working their way into younger deposits.
Lacking the protein collagen, the bones could not be dated directly by the radiocarbon method.
Now, according to a report in Nature News, a team led by Rainer Grun, a geochronologist at the Australian National University in Canberra, has used electron spin resonance (ESR) and uranium-series techniques to date the megafauna teeth directly.
All of the specimens of extinct species are at least 50,000 years old, some much older.
The results debunked claims of the late survival of the giant animals and a long period of coexistence between them and people.
The findings weaken arguments for climate change as the main cause of the demise of the megafauna.
According to Richard Roberts, a geochronologist at the University of Wollongong, Australia, and biologist Barry Brook, of the University of Adelaide, Australia, "human impact was likely the decisive factor", possibly through hunting of young megafauna. (ANI)