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.
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.
I'm a firm supporter of the 6th Mass Extinction (somewhat misnamed) being largely anthropogenic. It's a post in the works, but it'll be months before it gets to see the light of the blogosphere.
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