An illustration of a giant flightless bird known as Genyornis newtoni, surprised on her nest by a 1 ton, predatory lizard named Megalania prisca in Australia roughly 50,000 thousand years ago. (Illustration by Peter Trusler, Monash University) An illustration of a Genyornis surprised on her nest by a predatory lizard. (Peter Trusler/Monash University)

Tens of thousands of years ago, giant beasts roamed Australia.

Then, humans showed up.

Much of the continent's "megafauna" — large animals that populated much of the earth — has since gone extinct. And a group of researchers now says there is strong evidence suggesting that humans, rather than a changing climate, played a pivotal role in the demise of a 500-pound bird.

It appears that humans munched on the cantaloupe-sized eggs of Genyornis newtoni, a flightless bird that stood about seven feet tall and lived roughly 50,000 years ago, according to a study published Friday in the journal Nature Communications.

"We consider this the first and only secure evidence that humans were directly preying on now-extinct Australian megafauna," lead author and University of Colorado at Boulder professor Gifford Miller said in a statement.

Researchers examined eggshell fragments from more than 200 sites, many of which were found in small, 10-feet diameter clusters throughout Australia. The study's authors wrote that these patterns were likely "created by humans discarding eggshell in and around transient fires, presumably made to cook the eggs."

Gradients on eggshells burned on just one side show amino acid decomposition incompatible with the long-lasting and all-engulfing heat produced by wildfires, the researchers wrote.

"We can't come up with a scenario that a wildfire could produce those tremendous gradients in heat," Miller said. "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."

Researchers believe the eggshells are between 54,000 to 44,000 years old, which coincides with the same time frame that humans were thought to have arrived on the continent. According to the study, humans harvested Genyornis eggs, cutting down on the birds' ability to reproduce and maintain their population.

Megafauna extinction in Australia has been blamed on a mix of climate change and human intervention.

The study's authors argue that while Australia's climate did gradually become drier, the change wasn't as drastic as it was during earlier periods when the giant beasts survived. That "implies that climate change is unlikely to be the sole cause of megafaunal extinction, leaving human agency more likely to have been the decisive factor," the authors wrote.

But the lack of kill sites in Australia means there's been little archaeological proof clearly showing the role of human predators there.

"In the Americas, early human predation on the giant animals [is] clear — stone spear heads are found embedded in mammoth bones, for example," Miller said in a release. "The lack of clear evidence regarding human predation on the Australia megafauna had, until now, been used to suggest no human-megafauna interactions occurred, despite evidence that most of the giant animals still roamed Australia when humans colonized the continent."