The earlier and less-studied Australian megafaunal extinction provides a fresh start for investigating these events. It was a dramatic affair that cost the continent many large terrestrial vertebrate species like none known today, including carnivorous kangaroos, 20 foot-long monitor lizards, and a horned tortoise nearly the size of a small car. Until now, however, a fundamental obstacle has been nailing down the actual timing of the event, largely because its age pushes the limits of radiocarbon dating.

Miller's group cleared this hurdle when they documented the timing of the extinction of Genyornis newtoni, a ponderous flightless bird with thick, short legs that weighed around 200 pounds--twice as much as the modern day emu. They used a variety of alternative dating techniques (not based on radiocarbon isotopes) to analyze the birds' fossilized eggshells and set the date of Genyornis' sudden disappearance at 50,000 years. This date loosely matches the time of the Aborigines' arrival to the continent as indicated by the most reliable evidence yet available.

This was also a time of moderate climate change, making it unlikely that climate played a role in Genyornis' extinction. The authors bolstered this conclusion by comparing eggshell data (which spanned 50,000 years of Genyornis presence in ancient Australia) collected from different regions with distinct climates. It appears that the birds survived through a range of natural environmental changes with no ill effect before their sudden disappearance.

How might humans have caused Genyornis' extinction? Probably not by hunting, as many researchers have proposed. The authors conducted carbon isotope studies on the eggshell fossils to reconstruct Genyornis' diet. The bird appears to have been a
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Contact: Gabriel Paal
gpaal@aaas.org
202-326-6421
American Association for the Advancement of Science
7-Jan-1999