Palaeoecosystem collapse - evidence in the egg shells

A report in Science suggests that the arrival of humans on Australia altered the continent's ecosystem, changing it to the desert scrub we see today.

Chemical analysis on hundreds of fragments of fossilised eggshells suggested that the change in diet could be due to the alteration of the birds' natural habitats by humans burning the grassland for hunting, clearing or even for signalling other bands.

The resultant scrubland vegetation forced the birds to change their diet, in turn causing a change in the chemical composition of the eggshells. Birds such as Genyornis newtoni, a prehistoric bird the size of an ostrich, failed to adapt and died out.

There is a belief that the arrival of modern humans on other continents led to mass extinctions. In Australia, more than 85% of Australia's megafauna went extinct after human arrived. But others believe that megafaunal "extinctions were not caused by any single event, but reflect compounding factors."

In an earlier post, Siva highlighted an article that revealed that Australia megafauna coexisted with humans for as much as 15,000 years.

"'Fires wiped out' ancient mammals." By Helen Briggs. BBC News, 08 Jul 2005. See also Science Daily, 10 Jul 2005 and related articles listed therein.

Original article: Miller, GH, ML Fogel, JW Magee, MK Gagan, SJ Clarke & BJ Johnson, 2005. Ecosystem Collapse in Pleistocene Australia and a Human Role in Megafaunal Extinction. Science, 309 (5732): 287-290. 8 July 2005. DOI: 10.1126/science.1111288.

Abstract - Most of Australia's largest mammals became extinct 50,000 to 45,000 years ago, shortly after humans colonized the continent. Without exceptional climate change at that time, a human cause is inferred, but a mechanism remains elusive. A 140,000-year record of dietary 13C documents a permanent reduction in food sources available to the Australian emu, beginning about the time of human colonization; a change replicated at three widely separated sites and in the marsupial wombat. We speculate that human firing of landscapes rapidly converted a drought-adapted mosaic of trees, shrubs, and nutritious grasslands to the modern fire-adapted desert scrub. Animals that could adapt survived; those that could not, became extinct.