The fossilised teeth of kangaroos and other extinct marsupials reveal southeastern Queensland three million years ago was a mosaic of tropical forests, wetlands and grasslands, and much less arid than previously thought.
Researchers say the study, published today in the journal PLOS ONE, may provide clues about how modern animals will respond to the most recent round of climate change.
Using new dating techniques, the researchers examined the bones and teeth of three different species of kangaroos and a giant, wombat-like marsupial in the Chinchilla region of southeastern Queensland, to reconstruct their diets.
“Everyone knows the saying ‘you are what you eat’ – and that really is true,” said study co-author Gilbert Price, paleoecology researcher at the University of Queensland.
The researchers found the extinct kangaroo ate plants similar to those consumed by modern kangaroos in wet regions, rather than the arid plants that now grow in the region.
The data showed a lot of variation in the animals’ diet 2.5 to 5 million years ago, suggesting the animals lived in a mixed forest environment.
“It’s certainly not like that today – we don’t have crocodiles or tree kangaroos or anything like that living there today,” Dr Price said.
“So there has been some significant climatic changes that have driven some major habitat changes over that period of time.”
Dr Gilbert said the study provided a useful snapshot of what life was like when the prehistoric level of carbon in the atmosphere was almost similar to today’s levels.
“We still don’t know how the animals we have around us today have even responded to the most recent episode of climatic change,” he said.
“Part of the problem is there’s been such a lack of ecological monitoring of the populations we have around us.”
Mike Archer, from the University of New South Wales’ Evolution of Earth & Life Systems Research Group, said the research was an important confirmation of what many researchers already suspected.
“The results make sense in terms of what we have also begun to understand about much of the rest of inland Australia – that grasslands don’t make an appearance until very late …,” he said.
“Hence the 44% of Australia that is technically arid today may have been a relatively very recent development.”
Prior to this, there was a brief “greenhouse” phase about five million years ago, Professor Archer said, when rainforest emerged in places such as western Victoria.
“But this was a brief interruption of a general drying trend that began about 15 million years ago,” he said.
Christopher Johnson, Professor of Wildlife Conservation at University of Tasmania, said the paper was a “very good piece of research” but the most interesting result of the study was that “the changes have not been all that big”.
“The description given here for the environments around Chinchilla all those years ago is not that different to subtropical southeast Queensland, a hundred km or so to the east, in the present day,” he said.
“In other words, these extinct animals were living in an environment that would be very familiar to us today. This makes it hard to imagine that environmental change explains why species like them are no longer with us.”