why marsupials only in australia? - why not in any other continent? (Jun/14/2008 )
Geographic isolation is the answer, it just happened that Aus separated from the rest of the world before eutherian mammals became dominant. It also helps that the marsupium is a low energy consuming equivalent to the womb. Australia is a low energy environment due to the stability of the continental crust in the region and the paucity of the soils (really they should stop growing grass and farming in a western style over there, it is ruining the country), which means that energy saving adaptions are a must... check out Koala on wikipedia, especially the bit about the brain!
Also - Aus did have large predators (marsupial lion, amongst others), and still has 7 of the 10 most toxic snake species in the world, as well as goannas and saltwater crocodiles, all of which are pretty dangerous customers.
I think the koala's biggest problem is the high toxicity of eucalypt oils, which means it has to spend most of its time detoxifying its food, and why it has the largest liver per kg boy weight!
Only 7 of the top 10 snakes? I thought it was 19 of the top 20, or as Bill Bryson put it, 19 of the top 19 most toxic snakes....
Hmm..top-level predator such as a virus!
human... the top-level predator who like kangaroo meat.
Just kidding...
Hey, kangaroo meat is very good. It goes well with an emu burger! I bet there aren't too many other countries that eat their coats of arms!!!!!
Hmm..top-level predator such as a virus!
true...
Hmm..top-level predator such as a virus!
true...
The Tasmanian devil may become finally a victim of this "predator" if I remember right. This abscesses or tumours in the face. I love these grumpy fellows.
The big number of snakes is perhaps a result of the species number of small mammals (rodents (and bats) were there and spreading before humans came and imported new species) and marsupials (most species are small).
In South America exist various small marsupial species (not only the opossum, though this is the most successful and also expanded to North America successful). My book says 70 species live in South America. All are of "rat-type" and size and often living on trees, i.e. a hidden way of live, nocturnal and not very numerous.
aren't there some pretty dangerous snakes in Africa too? just read that snakes evolved something like 150 Ma either from a lizard or had an aquatic origin (which to me says nothing) during the cretaceous period. during the cretaceous the earth was something like this:
and mammals were a minority of the existing animals. so we could speculate lots of things. that snakes are more poisonous in australia because they had a selective pressure due to the lack of preys, also the climate could have affected their metabolism or whatever you want to imagine...
Just thought I'd restart this one.
South America has plenty of extinct marsupial species, again from its Gondwana-time.