Re: Pleistocene/Holocene extinctions

[Dann Pigdon <dannj@alphalink.com.au>]

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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