GENYORNIS EXTINCTION VERSUS EMU SURVIVAL: SOLVING THE PROBLEM OF MEGAFAUNAL EXTINCTION IN AUSTRALIA

For more than 150 years debate has raged about the timing, cause and process of the extinction of the Australian megafauna, focussed initially on climate change versus human predation and extending to human-induced environmental change in the 1960’s. The debate has been bedevilled throughout by poor numerical chronology but two recent studies, using non-radiocarbon chronologies and direct dating of megafaunal remains or rigorous criteria to exclude faunal reworking have determined extinction dates of 50±5 ka for the giant flightless bird Genyornis and 46.4±2.5 ka for a number of marsupial megafaunal species.

An extinction date coeval across climatic zones and for a variety of taxa at 46-50±5ka, soon after the likely date of human arrival on the continent (55±5 ka), implicates a human role in the extinction but says nothing of the process. It is unlikely that the archaeological record will ever provide more than proof of human-megafauna overlap. To finally resolve the extinction debate we need to obtain an unequivocal extinction chronology for a wide variety of taxa across a wide transect of climatic zones and to determine whether extinction was selective for dietary preference from an improved eco-physiological understanding of the animals and palaeodietary analyses. Before its extinction, Genyornis coexisted with emus at least across the arid and semi-arid zones where eggshells of both species occur relatively abundantly in aeolian sediments. While both are large flightless birds, they are taxonomically distant and are probably best regarded as convergent evolution within the bird lineage, with significant behavioural and physiological differences which resulted in Genyornis extinction and emu survival. In addition to being the most commonly occurring bio-mineral fossil, eggshell is far superior to bone for the preservation of its original chemistry, allowing excellent opportunities for chronology and isotopic palaeodietary studies. We believe that a comparison between Genyornis and emu characteristics across an environmental and climatic gradient coupled with an examination of the timing and environmental context of Genyornis extinction offers the best prospects for unravelling the cause and process of megafaunal extinction.