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Re: Query: Evolution of Pterosaurs



>1) Why would little thecodonts becomes arboreal in the first place?  To fill
>in an unoccupied niche?  Escape from ground-dwelling predators?  

Either would do, IF it happened.  A safe nesting site is another possible
reason.

>
>2) Did the skin membrane even evolve as a gliding adaptation?  (Must have...)

As we have no intermediate fossils, who knows?  But I have also heard
thermoregulation and display suggested as possible uses.
>
>3) How did evolution go from thecodonts to actual genuine pterosaurs?  Isn't
>there a large gap in the fossil record where the transition took place?

Yes.  As far as I know there is no such thing as a half-pterosaur (we have
the same problem, BTW, with bats - the earliest fossil bat is a perfectly
good, volant bat.

>
>4) If in fact thecodonts evolved skin membranes as gliding adaptions in the
>trees, how did they go from membranes to actual wings?  They did achieve
>powered flight, correct?  And they must have had a reason for powered flight,
>since they sure didn't need it in the trees...

I have often wondered about the glide to flight adaptive path.  There is
simply no evidence that it happened; I am more inclined to think that
gliders evolve, not into fliers, but into better gliders (eg the modern colugo).

>
>5) The pterosaurs seemed to be fish-eaters from the very beginning.  How did
>they go from arboreal thecodonts to sea-going ichthyovores?

If they actually did.  And could this be an artifact of fossilization?  It
may be that there were lots of insectivorous arborial pterosaurs that we
don't know about (what about Anurognathus, for example?).

Your other questions are good ones and are, in fact, the hotly debated
topics that I (as a layman) seem to see going on in the pterosaur world.
But for starters - you MUST get and read Wellnhofer's "Illustrated
Encyclopedia of Pterosaurs".  I know of nothing remotely as thorough for the
general reader, and I think, given your questions, you will find it
un-put-downable.
--
Ronald I. Orenstein                           Phone: (905) 820-7886 (home)
International Wildlife Coalition              Fax/Modem: (905) 569-0116 (home)
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