HONG KONG - Giant marsupials, reptiles and flightless birds that once roamed Australia became extinct about 40,000 years ago, later than had been thought and some 5,000 years after humans arrived, a new study suggests.
Controversy has long surrounded when such creatures became extinct in Australia. New equipment that can date teeth and bones has solved the puzzle, Australian researchers said in the latest issue of the journal Science.
"For a long time, we couldn't measure bone and teeth, or how old they (animals) were when they died, that is, when they went extinct," paleontologist Barry Brook at the University of Adelaide in southern Australia told Reuters by telephone.
One of the new techniques used in the latest research was uranium thorium dating, which can gauge when uranium was taken up into the animal's teeth when it was still alive.
The question as to when the last of these creatures died in Australia surfaced when other researchers began finding fossils, along with stone tools, in Cuddie Springs in New South Wales about 100 years ago and again over the past 30 years.
They analyzed surrounding sediments and found that they dated back to 30,000 years ago, contradicting evidence elsewhere in Australia which showed that the animals became extinct far earlier, or at least 40,000 years ago.
The overriding theory up to now has been that humans forced the extinction of the giant creatures. People arrived in Australia between 45,000 and 60,000 years ago.
"But now that we have new methods to date the bone itself, we can know how long ago the animals died rather than how long ago since the bones were last buried," Brook explained.
He said the bones in Cuddie Springs were probably dug up in a flood and redeposited in their final resting place, together with the stone tools, 10,000 years after the animals died.
This finding is important because it fits in with the theory that these creatures could not withstand the pressure of the encroaching humans, who arrived about 47,000 years ago.
"If they had been living together for 15,000 years, it would really undermine the idea that people had a quick, dramatic impact and wiped them out," Brooks said.
"The youngest fossil we have is 42,000 years ago and the best evidence of people spreading around Australia is 47,000 years ago, the overlap should be a maximum of 4-5,000 years."
