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Humans were preying on now-extinct Australian Megafauna: Study

Humans were preying on now-extinct Australian Megafauna: Study

University of Colorado Boulder-led team has discovered the first direct evidence that humans played a substantial role in the extinction of the huge, wondrous beasts inhabiting Australia some 50,000 years ago. The team refers to a 500-pound bird. In the past 100,000 years, many of the largest animals on Earth became extinct.

The reasons remain contentious. In recent years, some scientists have argued that habitat loss through climate change or fire was the killer blow. The flightless bird, known as Genyornis Newtoni, 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, said CU-Boulder Professor Gifford Miller.

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. We consider this the first and only secure evidence that humans were directly preying on now-extinct Australian megafauna, said 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.

A paper on the subject appears online Jan. 29, in Nature Communications.

In analyzing unburned Genyornis eggshells from more than 2,000 localities across Australia, researchers determine that none were younger than about 45,000 years old. 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. Amino acids -- the building blocks of proteins -decompose in a predictable fashion inside eggshells over time. In eggshell fragments burned at one end but not the other, there is a tell-tale gradient from total amino acid decomposition to minimal amino acid decomposition, he said. Such a gradient could only be produced by a localized heat source. Miller's team used radiocarbon dating as well as amino acid racemisation, a technique that involves studying changes in amino acids over time and which can provide an accurate time clock.

Professor Miller and his colleagues found eggs from both birds in the same places, suggesting that the two species co-existed and nested close to one another. That is until 50,000 years ago, give or take five thousand years. At this point there is an abrupt lack of genyornis egg shells but the emu egg shells remain. Because Professor Miller found emu egg shells dating to the present day, he thinks the results are not due to a sudden paucity of egg shells - rather, at that time genyornis became extinct. Miller also said 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 individual 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. 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 100 pounds and which still exist in Australia today -- in the sand dunes.

The Genyornis eggs are thought to have been roughly the size of a cantaloupe and weighed about 3.5 pounds, Miller said. Evidence of Australia megafauna hunting is very difficult to find, in part because the megafauna there are so much older than New World megafauna and in part because fossil bones are easily destroyed by the chemistry of Australian soils, said Miller.

Humans were preying on now-extinct Australian Megafauna: Study