Humans caused extinction of ancient giant bird, claims new studyWashington, Jan 31(AZINS) Researchers have found the first direct evidence that humans played a substantial role in the extinction of a giant bird species which inhabited Australia about 50,000 years ago.

The flightless bird, known as Genyornis newtoni, was nearly 7 feet tall and weighed 227 kilogrammes, and appears to have lived in much of Australia prior to the establishment of humans on the continent 50,000 years ago, said Gifford Miller from the University of Colorado Boulder in US. Researchers found reliable proof that humans were preying on now-extinct Australian Megafauna.

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, he said.

In analysing unburned Genyornis eggshells from more than 2,000 localities across Australia, primarily from sand dunes where the ancient birds nested, several dating methods helped researchers determine that none were younger than about 45,000 years old. Burned eggshell fragments from more than 200 of those sites, some only partially blackened, suggest pieces were exposed to a wide range of temperatures, researchers said.

Optically stimulated luminescence dating, a method used to determine when quartz grains enclosing the eggshells were last exposed to sunlight, limits the time range of burned Genyornis eggshell to between 54,000 and 44,000 years ago. Radiocarbon dating indicated the burnt eggshell was no younger than about 47,000 years old. "The blackened fragments were likely burned in transient, human fires - presumably to cook the eggs - rather than in wildfires," Miller said.

Researchers found many of the burnt Genyornis eggshell fragments in tight clusters less than 10 feet in diametre, with no other eggshell fragments nearby. Some individual fragments from the same clusters had heat gradient differences of nearly 537 degrees Celsius, conditions virtually impossible to reproduce with natural wildfires there.

"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," he added.

Another line of evidence for early human predation on Genyornis eggs is the presence of ancient, burned eggshells of emus - flightless birds weighing only about 45 kilogrammes and which still exist in Australia today - in the sand dunes. Emu eggshells exhibiting burn patterns similar to Genyornis eggshells first appeared on the landscape about 50,000 years ago, signalling they most likely were scorched after humans arrived in Australia, and are found fairly consistently to modern times, researchers said.

The findings were published in the journal Nature Communications.