Asian Scientist (Jul. 4, 2013) – Researchers have ruled out climate change as the cause of extinction of most of Australia’s giant animals around 50,000 years ago.
Giant animals, also known as megafauna, used to inhabit the land mass that is Australia today. These megafauna included giant kangaroos, three meter-tall flightless birds and the Tasmanian tiger.
However, these giant animals became extinct around 50,000 years ago and there has been much debate over the cause of megafaunal extinction.
Now, a research team studying sediment cores taken from the sea bed, in the offshore canyons of the Murray River in Australia, have discovered new information about the period that rules out climate change as the cause of megafaunal extinction.
The controversy arose because the extinctions happened around the same time that humans moved into the area and also coincided with a change in the type of plant food available to the megafauna.
“These events have led to several theories of the cause of extinction, including climate change. But the timing of these events was uncertain. We didn’t know which one happened first, so we couldn’t begin to understand what could have caused the extinction,” said Professor Patrick De Deckker, who led the team.
“Sediment cores provide a record of the past. From the core we were able to reconstruct sea-surface temperature over the past 135,000 years, as well as variations in the type of vegetation in the Murray Basin, allowing us to piece together the order of these events.”
In their study, published in Nature Geoscience, the research team found that sea-surface temperature varied by only 3°C at the time of the extinction – a minor variation compared to other times in the record – indicating that the extinction did not occur in a period of major climate change.
The core also revealed a shift in vegetation type immediately after the megafaunal extinction.
“Before and during the extinction period, 70 per cent of the vegetation was typical of northern Australia today. Immediately after the extinction, this value dropped to 35 per cent,” said Professor De Deckker.
“Some people have suggested that this dramatic change in food sources might have been the cause of the megafaunal extinction, but we’ve shown that this was in fact a result of the extinction. Our idea is that with fewer herbivores around to eat them, substantial fuel remained in the landscape, which eventually led to massive fires.”
Although the researchers have ruled out climate change as a cause of megafaunal extinction, the evidence from the sediment core did not provide an explanation for the cause of the extinction.
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