Eggshell cracks open debate on extinction of giant bird

An eggshell of a giant bird is the first direct evidence implicating First Australians in the bird’s extinction.

Artwork - drawing sketch of large flightless elephant bird "Genyornis newtoni" by F Knight from boo...

The recent discovery of burnt fragments of eggshell of the giant flightless bird Genyornis newtoni is the first direct evidence implicating the First Australians in the bird’s extinction about 47,000 years ago.

The fragments, found on the shores opposite Western Australia’s Ningaloo Reef and at other sites across Australia, will reignite debate over the role of humans in the mass extinction of the Australian megafauna.

The megafauna was a group of animals including the 2m-tall, 200kg genyornis and marsupials such as giant kangaroos, the two-tonne wombat-like Diprotodon, and the “marsupial lion”.

A team led by geologists Giffor­d Miller, of the University of Colorado, Boulder, and John Magee, of the Australian National University, analysed burnt Genyornis eggshell recovered from more than 200 sites in Western and South Australia, and NSW.

Their results, published in the latest edition of the British journal Nature Communications, weaken the case made by other academics that global climate change, not people, caused the extinctions.

Researchers have long argued about why virtually every species weighing more than 45kg went extinct soon after humans colonised Australia. Some have blamed ice-age aridity. Others have blamed people for enacting a hunting “blitzkrieg”.

Professor Miller, who is also affilia­ted with Perth’s Curtin University, and Dr Magee have previously ­argued that the mechanism was a “slow burn” — ecosystem collapse caused by human-lit fires to manage the landscape.

However, the sparse Australian archeological record has lacked “kill” sites until now.

It is generally agreed that the ancestral Aborigines learned to manage an environment impoverished by the demise of the megafauna, and did so until the arrival of Europeans, who caused their own cascade of extinctions.

The Miller-Magee team measured the concentration of amino acids across wholly and partially burnt eggshell. They wanted to find a way to discriminate between eggshell burned in natural wildfires and eggshell burned in campfires after people baked the eggs and ate them.

The scientists found that the partial blackening of eggshell fragments could only be ­explained by the irregular heating of a campfire, when part of a discarded­ eggshell touched an ember. They used three methods to date the eggshell.

Professor Miller said more research was needed to discriminate between the two models of human-caused extinction — a hunting blitzkrieg or a slow burn.

The problem lies in the dating of human colonisation and megafaunal extinctions.

“We now have human predation on megafauna firmly ­established,” Professor Miller told The Australian.

“That would have been one factor putting pressure on large animals, but we also have firm evidence supporting abrupt ecosystem restructuring across at least the arid zone at the same time. That would weigh equally to predation as the cause of megafauna extinction, and the slowly drying climate wouldn’t have helped.”