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Solving the Mysteries of the Australian Megafauna

Credit: Aaron Camens, Flinders University

A skeleton of Diprotodon, Australia’s largest ever living land mammal, exposed at Lake Callabonna in South Australia. Credit: Aaron Camens, Flinders University

Two new papers have narrowed the date of Australia’s megafauna extinctions as well as the cause of their demise.

The many kinds of bizarre large land animals that inhabited Australia until around the past 50,000 years are known as the megafauna. These included the largest marsupials, lizards and birds to ever walk the Earth. Diprotodon is the iconic poster boy of the brigade, a wombat -shaped beast the size of a rhino weighing up to 2.7 tonnes that lived right across the mainland. The biggest birds that ever lived were the dromornithids, emu-like flightless bird around 450 kg in weight and 3 metres high, but more closely related to ducks and geese. The king of the post-dinosaurian reptiles was our ancient killer goanna, Varanus (Megalania) prisca, which as perhaps up to 6 metres long and whose closest living kin is the Komodo dragon of Indonesia.

For some time there has been an ongoing debate about what caused the extinction of these marvellous beasts. One theory says it was entirely brought on by climate change, particularly the aridity associated with ice ages. Another theory argues it was the arrival of humans into the country, which resulted in hunting of the animals and changing of their habitat through fire stick farming. A third camp thinks it was a complex scenario that probably involved factors from both sides. In the past couple of months two significant new works have added interesting new information that affects the way we think about the megafauna’s demise.

While it can be shown that many of the big, common megafaunal animals went extinct around 50–45,000 years ago, many of the rarer species of megafauna, which are known from few remains, cannot be tied to a similar tight dateline for their extinction. This is not to say they didn’t exist up to this point in Australia, just that we don’t have fossils in the right deposit to date their final days. Climate advocates use this as evidence that the megafauna could have gone extinct in stages, stepwise, over the past 150,000 years.

Yet absence of evidence is not evidence for absence. Indeed some archaeologist are more reserved in their opinions, holding the view that unless we find a megafauna skeleton with a human bone or artefact associated with it, we cannot ever say that humans interacted with these beasts.

A new paper led by PhD student Fred Saltré of the University of Adelaide changes this by using a mathematically rigorous statistical reappraisal of the 659 known reliable dates for megafauna in Australia. Published in Nature Communications (www.tinyurl.com/j54ofms), it showed there was a broadly synchronous extinction of the megafauna within the first 13,500 years of their overlap with the first humans. People arrived in the country about 55,000 years ago, based on a modelled age estimate from actual stone tools dated at 48,000 years old.

The data also show that the extinctions were independent of climate aridity and variability at this time. In other words it cuts out the climate change argument entirely from the discussion.

The second paper, led by Dr Gerald Grellet-Tinner and colleagues at Flinders University, smashed a long-held belief about the giant flightless bird Genyornis. A series of papers led by American scientist Gifford Miller, who dated fossil eggshell thought to belong to Genyornis, was able to show that the megafauna died out about 45,000–50,000 years ago. The new paper has cast doubt on the identity of these egg fragments, as structural analysis shows the eggs were identical to those of living megapodes (mound-builders like the Australian brush turkey). The dated eggshell fragments probably belonged to an extinct large megapode and not Genyornis. This implies we actually know a lot less about Genyornis than we thought, but still supports the evidence that a major extinction event took place 45–50,000 years ago, and this included large extinct species of megapodes.

John Long is Strategic Professor in Palaeontology at Flinders University, and current President of the Society of Vertebrate Paleontology.