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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. :)

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Dann Pigdon
GIS / Archaeologist              geo cities.com/dannsdinosaurs
Melbourne, Australia             heretichides.soffiles.com
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