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Re: Extinction Question and a Thank You!



Dinosaur World wrote:
> 
> What I am not clear on is why there are so many modern animals that have
> retained the same basic design as their Permian and Cretaceous counterparts?
> If early Crocodiles, Alligators, Sharks, Insects etc. were subjected to
> global environmental changes that were long enough and strong enough to wipe
> out other species, why then do they still resemble their modern
> counterparts?

As a great American philosopher once said: "If it aint broke, don't fix
it".

Or in other (less flippant) words, if a creature's general body form is
already supremely well adapted for that organisms way of life, then
there will be very little impetus for change. Evolution is not change
for change's sake. There has to be an adaptive advantage in order for
changes to be selected for.

Hence why ichthyosaurs, dolphins and sharks all share roughly similar
body forms, despite no close relationships with each other. There comes
a point where general body form just can't be refined any further. 

Of course, non-fossilisable (a new word?) aspects like internal organs
or blood chemistry may well be very different in modern
sharks/insects/etc than in their distant ancestors, so evolution may
have been making radical changes all along - just not in general body
shape.

-- 
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Dann Pigdon
GIS / Archaeologist         http://www.geocities.com/dannsdinosaurs
Melbourne, Australia        http://heretichides.ravencommunity.net/
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