The menu for the earliest inhabitants of the Australian Outback some 50,000 years ago may have included some very big omelets.
A new study led by CU-Boulder now shows the first direct evidence that humans played a substantial role in the extinction of a 500-pound, flightless bird known as Genyornis newtoni on that continent by collecting and cooking its eggs. It’s simple math: Less eggs means less reproductive success by the birds.
Genyornis was nearly 7 feet tall and appears to have lived in much of Australia prior to the establishment of humans on the continent 50,000 years ago, says Professor Gifford Miller, who led the study. Its eggs were about the size of cantaloupes and likely weighed more than three pounds each, he believes.
The evidence consists of diagnostic burn patterns on Genyornis eggshell fragments that indicate humans were collecting and cooking its eggs -- thereby reducing the birds’ reproductive success – rather than burn marks on the shells caused by wildfires.
“We consider this the first and only secure evidence that humans were directly preying on now-extinct Australian megafauna,” says Miller, associate director of CU-Boulder’s Institute of Arctic and Alpine Research. “We have documented these characteristically burned Genyornis eggshells at more than 200 sites across the continent.”
Genyornis roamed Australia with an astonishing menagerie of other now-extinct megafauna that included a 1,000-pound kangaroo, a 2-ton wombat, a 25-foot-long-lizard, a 300-pound marsupial lion and a Volkswagen-sized tortoise. More than 85 percent of Australia’s mammals, birds and reptiles weighing over 100 pounds went extinct shortly after the arrival of the first humans.
The team used several dating methods to look at unburned Genyornis eggshells from more than 2,000 localities across Australia, all at least 45,000 years old.
Miller notes the researchers found many of the burnt Genyornis eggshell fragments in tight clusters less than 10 feet in diameter, with no other eggshell fragments nearby. Some partially burned fragments from the same clusters had heat gradient differences of nearly 1,000 degrees Fahrenheit, conditions virtually impossible to reproduce with natural wildfires there, he said.
“We can’t come up with a scenario that a wildfire could produce those tremendous gradients in heat,” says Miller. “We instead argue that the conditions are consistent with early humans harvesting Genyornis eggs, cooking them over fires, and then randomly discarding the eggshell fragments in and around their cooking fires.”
Another line of evidence for early human predation on Genyornis eggs in Australia is the presence of ancient, burned eggshells of emus -- flightless birds weighing only about 100 pounds and which still exist in Australia today. Emu eggshells exhibiting burn patterns similar to Genyornis eggshells first appear on the landscape about 50,000 years ago, signaling they most likely were scorched after humans arrived in Australia, and are found fairly consistently to modern times, he explains.
The demise of the ancient megafauna in Australia has been hotly debated for more than a century, swaying between human predation, climate change and a combination of both, explains Miller. Some some still hold fast to the climate change scenario -- specifically the continental drying in Australia from about 60,000 to 40,000 years ago.
But according to Miller neither the rate nor magnitude of that change was as severe as earlier climate shifts in Australia during the Pleistocene epoch, which lacked the punch required to knock off the megafauna.
Miller and others suspect Australia’s first inhabitants traveled to the northern coast of the continent on rafts launched from Indonesian islands several hundred miles away. “We will never know the exact time window humans arrived on the continent,” he said. “But there is reliable evidence they were widely dispersed across the continent before 47,000 years ago.”
A paper on the subject appeared in Nature Communications.