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Re: Pleistocene/Holocene extinctions
Brandon Pilcher writes:
What is the most widely accepted and/or likely theory for the mass extinctions in Eurasia, the Americas, and Australia at the Pleistocene/Holocene boundary?
As has been pointed out, mass extinctions happened in Australia well before
the Holocene. They also happened tens of thousands of years *after* humans
entered the continent.
Australian megafaunal extinction seems to have been a combination of
climatic change (a general trend towards drier conditions) and evironmental
change - the latter due in no small part to the way humans were managing the
land. So called 'fire-stick farming' (burning off large areas of land to
encourage fresh growth for grazing prey animals) changed the vegetation
regime across most of Australia, selecting for fire-tolerant species. Since
Australians no doubt hunted megafauna for tens of thousands of years before
the mass extinctions, hunting alone was probably not the main cause. However
indirect human actions that changed vegetation regimes would have had a much
greater impact on megafauna (especially if many of the largest herbivores
were browsers rather than grazers). Any one of these factors (hunting,
deliberate burning, climate change) might not have caused extinctions by
itself, but in combination may have proven too much for megafaunal species
to adapt to.
Of course it's not all bad news. Grazing macropods ('roos and wallabies) did
very well, as did koalas. Before humans arrived in Australia, the koala
appears to have been an extremely rare animal (at least by fossil
standards). Deliberate human burning eventually killed off the less
fire-tolerant trees that had out-competed eucalypts for millions of years.
Once eucalypts began to take over, the continent became koala heaven. Modern
land clearing practices have also resulted in kangaroo population
explosions. Grey and red kangaroos are probably more numerous now than
they've even been in Australia.
What we have to remember about any sort of climatic or environmental change
is that although some species may be driven to extinction, other species
that prefer the new conditions may do better than ever. After all, if it
wasn't for the K/Pg extinctions, us mammals would probably still be way down
on the food chain. :)
GIS / Archaeologist geo cities.com/dannsdinosaurs
Melbourne, Australia heretichides.soffiles.com