BBC News 21 Jun 09;
A fossil study of the extinct giant kangaroo has added weight to the theory that humans were responsible for the demise of "megafauna" 46,000 years ago.
The decline of plants through widespread fire or changes toward an arid climate have also played into the debate about the animals' demise.
But an analysis of kangaroo fossils suggested they ate saltbush, which would have thrived in those conditions.
The research is in Proceedings of the National Academy of Sciences.
There has long been dissent in the palaeontology community about the cause for extinctions worldwide after the end of the last ice age.
Central to the debate has been the demise of the Australian megafauna, including animals such as marsupial lions, hippopotamus-sized wombats and the 2m-tall giant kangaroo Procoptodon goliah .
Last year, researchers dated fossils from Tasmania with the best precision yet, finding that many species survived more than 2,000 years after the arrival of humans.
The researchers concluded that the megafauna eventually met their end due to hunting.
Dental exam
Now, researchers from Australia and the US have combined radiocarbon dating with a so-called microwear analysis of the teeth of P. goliah to determine what it ate and drank.
Different sources of water and food leave trace amounts of particular types, or isotopes, of hydrogen and carbon atoms, which are deposited in the teeth like a recorded diet.
Additionally, tiny patterns of wear give clues about the type of food a given creature chewed.
The team concluded that the giant kangaroos fed mainly on saltbush shrubs.
Because fire does not propagate well among saltbush, and because it thrives in a dry, arid climate, the case supporting two of the three potential causes for extinction was weakened.
Evidence suggests therefore that the P. goliah was hunted to extinction.
However, it is just one of many species whose disappearance fuels the debate, and there is much more work to be done before it can be considered a definitive proof.
"I'm a little hesitant to make a big conclusion," said co-author of the study, Larisa DeSantis of the University of Florida.
"What's really exciting is that this is one of the first instances where we've been able to use both isotopes and the microwear method to identify this very unique diet," she told BBC News.
Dr DeSantis said that she was pursuing a similar analysis of other megafauna fossils in other regions of Australia.
"This study neatly ties up several loose threads in the long-running extinction debate," said Richard Roberts of the University of Wollongong in Australia.
"By independently reaching the same conclusion for two very different environments - the mountainous rainforests of Tasmania and the dry rangelands of inland Australia - the mystery is no longer whether humans were ultimately responsible for the disappearance of the giant marsupials, but how they did it."
