Australasian Science Magazine

By Stephen Luntz

The passionate debate about the cause of the extinction of Australia’s megafauna has taken yet another turn, with the publication in the Proceedings of the National Academy of Sciences of a paper claiming evidence that most of the giant species were gone before the first humans arrived.

Giant mammals once inhabited every continent, sometimes accompanied by huge birds and reptiles. The fact that only in Africa have many species survived may indicate that human arrival proved disastrous for animals that were not used to our presence.

However, some fossil specimen dates are thousands of years after human arrival (AS, August 2005, p.12), challenging the idea of a rapid extinction. Supporters of the human involvement theory have pushed back, questioning the dating involved for these sites.

Now A/Prof Stephen Wroe of the University of NSW has challenged human involvement from the other direction. He claims that roughly 90 species can be included in the Australian megafauna category, and of these between eight and 14 were still alive when people arrived in Australia 50,000 years ago. Many species disappear from the fossil record 130,000 years ago, around the time the world reached maximum glaciation and Australia was unprecedentedly dry.

Wroe acknowledges that humans may have eliminated the last few species but regards even this as uncertain. “There has never been any direct evidence of humans preying on extinct megafauna in Sahul [Australia joined to New Guinea] or even of a toolkit that was appropriate for big-game hunting.” Wroe says the first Aboriginal settlers were “by definition, marine people” who would have slowly spread around the coastline, taking time to adapt before venturing into the interior.

On the other hand, Wroe believes that eras of global cold would have pushed fertile zones to the continent’s margins, creating refuges too small for the largest animals, although survivors benefited from increased rainfall during the last interglacial period. If the previous glacial maximum could wipe out numerous megafauna, Wroe thinks it plausible the last one could have eliminated the surviving diprotodons and marsupial lions without human assistance.

The evidence for Wroe’s conclusion comes from redating some fossil records and observing the absence of many species at more recent sites.

Co-author Dr Scott Mooney of UNSW also challenged the idea that indigenous fire-stick farming changed Australian fire conditions to the megafauna’s detriment, suggesting that fire frequency was also driven by climate.

Disagreement is inevitable in such a controversial area, but Wroe says he so far has had “overwhelming support, surprisingly enough, including some researchers who previously argued for human-driven extinctions”.