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Re: Crylophosaurus and Australia



Phil Hore wrote-

> All good points, but do you not also think that Australia has a nasty
habit of doing exactly that!

I think you are generalizing too many characteristics of the recent
geographic/ecologic Australian situation as being fundamental to Australia
itself.

> Look at Australia compared to Africa. Africa has several carnivores that
fill each niche.
> Large carnivores you have lions, leopards, hyenas etc
> Medium sized carnivores you have cheetahs, jackals etc and so on. (this is
only a rough guide) but in
> Australia you only seem to have one animal in each roll. Large-thylacoleo,
medium thylacine, small quolls-
> devils. Introduce a new species and you seem to lose one. 50 000 years
ago, man enters as the large
> carnivore, goodbye Thylacoleo. 3000 years ago dingos arrive and mainland
thylacines go..200 years later > we introduce dogs and the dingos are all
but gone (though probably breed away then anything else). Cats > and foxes
are now well on their way to taking over the small carnivore roll.( I have
left out snakes and crocs > as we seem to match each other here)
> Everything also seems to be closely related as well. You really only have
a handful of species, and most of > these are still reasonably related.
Certainly we have never had the interspecies mingling that other
> continents have had, and in no way am I trying to compare modern Australia
to prehistoric Australia
> (environment etc), I'm just trying to point out that some environments do
indeed do exactly that- they do
> produce vast, continent filling numbers of animals from a very small
original stock.

Recent Australia may have low diversity of large carnivores (there are
several species of medium-sized dasyurids, and many small ones), but was
this true of Australia in the past?  I doubt it.  Could it be due in part to
the restricted forested habitat of recent Australia?  I think so, and I
don't think the climate has been the same since the Mesozoic.  Is a "large"
carnivorous mammal really analogous to a large carnivorous dinosaur,
considering the differences in size, gait, reproduction, etc.?  I doubt it,
so such comparisons are of very limited use.  Is the ease at which
introduced taxa replace old ones due to the fact these new taxa are
placentals, with different metabolisms, reproductive strategies and
intelligence?  I think so, thus it doesn't support the "low possible maximum
diversity of Australian predators" theory.  Try introducing many types of
carnivorans to Australia.  I think multiple species would survive just fine.
The Australian mammals are closely related to each other because of recent
isolation of the continent.  Up to the Late Jurassic, at least, Australia
was still attached to Gondwana, which had all sorts of theropods-
ceratosaurs, carnosaurs, basal coelurosaurs, alvarezsaurids,
oviraptorosaurs, dromaeosaurs, etc..  And this diversity is just what we see
in Cretaceous Australia.

> Now let me ask you, is it not more then likely that two fossils, found in
locations that would have been
> reasonably close at the time (though separated by a gulf in time), that
seem to be similar (with what little is
> now for the oz polar allosaur) are more likely to be somehow related then
not? Or should we, like the first
> Europeans to arrive in Australia, try and link our animals to those that
are already known rather then find
> our own, and more exciting evolution heritage? Should we not look for more
plausible reasons for how our
> animals came to appear here?

No, it's not more than likely.  Just how is "Allosaurus" "robustus" more
similar to Cryolophosaurus than it is to any other Early Jurassic theropod?
It's a medium-sized (though we don't know if either specimen was adult),
probably post-coelophysoid (but not if Cryolophosaurus is a dilophosaur),
and probably non-coelurosaurian (but not if "Allosaurus" "robustus" is a
basal coelurosaur).  If you can find evidence for a more "exciting"
evolutionary heritage among Australian theropods, be my guest.  But I see no
reason that possibility should be more likely than any other.

Mickey Mortimer