Man, not climate change, linked to extinctions in Australia

The disappearance roughly 40,000 years ago of dozens of large mammals in Australia — including rhinoceros-sized wombats and tapir-like marsupials — was caused by human hunting and not by climate change, according to a new study by Australian scientists. Researchers at the University of Tasmania reached that conclusion after analyzing two mud core samples dating back as far as 130,000 years.

By examining the cores for the Sporomiella fungus — which only releases its spores when in the dung of plant-eating animals — the scientists concluded that megafauna survived periods of climate change over the last 100,000 years. But when humans arrived in sizeable numbers, the presence of the spores dropped "almost to zero" around 41,000 years ago, indicating that hunting was the main reason for the extinction of these large animals, according to the paper, published in Science.

The disappearance of the big plant-eaters seems to have set the stage for fires, allowing the buildup of the dry grasses and other fine fuels that spur burning like the catastrophic wildfires still seen in Australia today. At Lynch's Crater, the disappearance of the large plant-eaters saw an increase in grasses within 300 years, then acacias, eucalyptuses and other hard-leaved plants within 400 years, and, ultimately, a rise in the pollen from forest trees some 1,600 years later.

Even today, many of the plants still extant in Australia boast features such as protective spines that would discourage grazing by megafauna or big fruit and seeds that could only be dispersed by large animals that no longer exist—a landscape shaped by ghosts. "These plants are now anachronistic," Johnson observes.

The findings seem to close the case against modern human hunters, although they remain to be confirmed at other sites throughout the continent. And, on every continent except Africa, human arrival and large animal extinctions seem to coincide, so the case may also extend globally. Drawing of Diprotodon optimum, courtesy of Melbourne Museum.



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