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Re: Ozzy Emu omlettes at Lake Eyre? Eye-eye!



To fill in a bit on the Australian megafaunal extinctions (I talked with
the authors for a short article for New Scientist):

The dating is based on eggshell, which allows carbon dating to go back
further than carbon dating of bone, because of chemical differences between
the two. Genyornis eggs vanish at the same point as bones of the other
megafauna, but can be dated accurately. There's no evidence of extensive
climate change at this time; the main known disruption at the time is the
arrival of people, who could have spread across the continent in a few
thousand years, according to population models. Paleontological evidence
suggests Genyornis was a browser that would have been vulnerable if fires
wiped out small shrubs that it had fed on, but human predation could have
contributed as well.

The situation was different in the Americas, where the Pleistocene
megafauna vanished at a time when two things were happening, people were
leaving evidence of their presence across the continent, and the ice age
was ending.

The basic lesson, as John Bois says, is
>different extinctions may be caused by different things, and most
>extinctions are caused by many things--both physical and biological, and
>that it is usually foolish to identify first causes, this study may have
>implications for other extinctions, particularly the K/T.  At the very
>least, it should give pause to those who are content with simplistic
>causes explaining _patterns_ in extinctions.

My feeling is that it's very rare when any single factor is responsible for
an extinction. Instead, there's an itnereaction of biological factors,
climatic events, geography (allowing invasions of competing species), and
the odd catastrophe (e.g. asteroid impact). -- Jeff Hecht

Jeff Hecht     Boston Correspondent    New Scientist magazine
525 Auburn St.,          Auburndale, MA 02466             USA
tel 617-965-3834 fax 617-332-4760 e-mail jhecht@world.std.com
URL: http://www.sff.net/people/Jeff.Hecht/
see New Scientist on the Web: http://www.newscientist.com/