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Re: Archosaur Origins (& the Clade Cemetery)

-----Original Message-----
From: Thomas R. Holtz, Jr. <tholtz@geol.umd.edu>
To: larryf@capital.net <larryf@capital.net>; Ken Kinman
<kinman@hotmail.com>; dinosaur@usc.edu <dinosaur@usc.edu>
Date: Friday, August 24, 2001 8:39 AM
Subject: RE: Archosaur Origins (& the Clade Cemetery)

>The pterosaurian ankle is apparently much less mesotarsal than typical
>considered, as related by Dave Unwin:

Which states:

" It is usually assumed that
pterosaurs have the 'derived ankle' type, but Kellner and Tomida in their
abstract for 1993 point out that in a very well preserved specimen of
Anhanguera the ankle appears to be of the crocodile-reversed type. "

Could this just be a case of reversal in this particular species? I thought
the "croc-reversed" condition was intermediate in the development of the
advanced mesotarsal from a primitive mesotarsal condition. I also assumed
that the AM condition went along fine for Padian`s bipedal stance for early
pterosaurs. (I here specify "early" because  I see the later forms as being
too heavy in the cranium and upper body to enable the upright stance, hence
the later forms being quadrupedal). If the later pterosaurs indeed became
quadrupedal, then there would not be selection for an AM hinge