Re: Selective Extinction

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

Peter Von Sholly wrote:
> 
> An old and often asked question about the final dinosaur extinction is why
> certain animals went and others didn't.  I read somewhere recently about an
> impact theory wherein a wave of hot gasses swept across the land destroying
> most everything in its path.  I wonder if there could be anything in the
> idea that creatures who lay low to the ground (crocodiles, lizards,
> turtles, snakes, frogs, small mammals, many insects etc) would have been
> spared in such a scenario (even some birds and flyers high up in the air
> might have been missed by the main devastation).  But bigger animals that
> stood with higher profiles made better targets and were simply mowed down.
> This is obviously not the whole picture but it does seem that the animals
> who survived were closer to the ground that those who did not.

        Then again, there were a lot of small species of dinos that
seem to have been wiped out too, although birds seem to have made it
through fine and presumably they were in a similar size group to
small non-avian dinos. Perhaps the larger species were too specialized
to withstand environmental stress, with the smaller generalists
being better able to survive (as is thought to be the case with
any extinction). However this still does not explain the bird / small
dino distinction, unless the ability to fly gave birds the edge to
be able to forage over larger areas for what resources remained. But
in this case, why did pterosaurs become extinct?
        I doubt anyone will come up with a definitive answer for
the Late Cretaceous extinctions. One problem I have with the whole
global acid rain scenario (either from volcanism or impact) is that
amphibians seem to have survived, and today they are considered
sensitive indicators of air or water-born pollution. I've only
recently read an article (Science? Nature? The source escapes me)
about the proposed giant dust cloud theory, and non-ionized
hydrogen invading the atmosphere sucking up oxygen, with that ever
popular Oort cloud thrown in for good measure. It has to rate as
one of the most complex and imaginitive theories yet. Hats off to
the authors I say. Whether it was close to the truth or not it
made for an entertaining read.
-- 
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        Dann Pigdon
        Melbourne, Australia

        Dinosaur Reconstructions:
        http://www.geocities.com/capecanaveral/4459/
        Australian Dinosaurs:
        http://www.alphalink.com.au/~dannj
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