"Representative Trantis"  wrote in news:b8h3qs$165d$1
{at}darwin.ediacara.org:

> Marsupials survived in Australia because there are no predators.
> 
> Is this statement true? If so, would they have not been able to survive
> elsewhere?, is the lack of predators the only reason they survived?
>


This is obviously not true, as there are predators which are marsupials. I 
think the argument you are referring to is that marsupials survived in 
Australia because there are no _placentals_. The other evidence in favor of 
this argument is that few South American marsupials survived the invasion 
by North American placentals after the formation of the Central American 
land bridge.  

There is probably more to the story than this, however. A number of large 
terrestrial reptiles also survived in Australia in competition with 
marsupial mammals, even though large terrestrial reptiles did not compete 
successfully with marsupial mammals in South America. The explanation may 
also have something to do with climate variability and lack of nutrient 
availability, which might tend to favor reptiles and marsupials.


Yours,

Bill Morse
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