Ancient humans are to blame for the extinction of a huge 500-pound flightless bird, a new study has found.

Australian and American researchers who were analyzing the burn patterns on fragments of eggshells from a giant bird known as Genyornis newtonii which showed that the 3.5-pound, cantaloupe-sized eggs were favored by humans, who drove the bird to extinction, according to a Christian Science Monitor report.

The species lived during a time when large animals were very common, much more common than today. Australia once had a 1,000-pound kangaroo and a wombat the size of a car.

But such megafauna proved to be easy prey for ancient humans, with 85 percent of them going extinct once mankind started hunting them down for food.

For a long time now, the cause of this extinction has been hotly debated among scientists, with several theories proposed, including that climate change resulted in a mass extinction. But scientists doubt this answer because the last major climate change event didn’t seem to be severe enough to cause this big extinction, especially since megafauna survived a much more significant climate shift in the Pleistocene epoch.

There had been doubts over whether there was much predation of megafauna by humans, but the research team explroed 2,000 egg sites of Genyornis newtonii and found that in 200 of the sites, the egg shells were blackened and burned. The team ruled out wildfire as a cause for the burned egg shells, and the pattern of the burn appeared to be from cooking fires. The team ruled out a number of scenarios were natural causes could have caused the egg shells to blacken.

The findings were published in the journal Nature Communications.