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Megafauna mystery

By Pat, 12 July 2013 News

Marsupial lion skeleton. It casts its shadow on the back wall.

Marsupial lions are an example of Australia’s extinct megafauna.
Image: Karora/Wikimedia Commons

Giant wombats, short-faced kangaroos and the largest land lizard to ever have lived are just some of Australia’s megafauna. These large animals have mostly gone extinct. However, the cause of their extinction is still a matter of debate.

The term megafauna means ‘large animal’ and refers to a number of species, including mammals, birds and fish. There is no strict definition to determine if species are megafauna, although mass is the main factor considered.

Australian megafauna are generally smaller than those found on other continents. A mass of 45 kilograms or more is used as a threshold. This is not the only definition in use, and other criteria may be taken into account.

Today, there are very few Australian animal species that can be classified as megafauna. The saltwater crocodile, red kangaroo and cassowary are some examples considered to be megafauna.

There used to be more megafauna in Australia. Diprotodon, a rhino-sized relative of the wombat, was the largest mammal species. Megalania, a giant lizard, was the largest predator. There were also larger species of kangaroos, echidnas and flightless birds. They didn’t all live at the same time. Some survived until around 40 000 years ago.

What caused the most recent megafauna extinctions is not clear. Some paleontologists claim the arrival of humans and related hunting and changes to ecosystems were the cause. Others claim climate change and other environmental factors were to blame.

Each hypothesis has evidence in support of its claim. For example, those who blame humans point out these extinctions happened rapidly and coincided with the arrival of humans in Australia. However, evidence from some ice cores and lake sediments indicate that, at the time of extinction, temperatures were increasing and rainfall decreasing, leading to Australia becoming drier. This supports the climate change theory.

There have been papers published recently that support one or the other theory. While most megafauna are long gone, this scientific debate certainly isn’t!

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