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Re: Pre-archosaur...was : What came before Eoraptor?



-----Original Message-----
From: T. Mike Keesey <tmk@dinosauricon.com>
To: Larry Febo <larryf@capital.net>
Cc: -Dinosaur Mailing List- <dinosaur@usc.edu>
Date: Tuesday, April 11, 2000 1:11 PM
Subject: Re: Pre-archosaur...was : What came before Eoraptor?



>
>Since "lagosuchians" and dinosaurs show none of the derived traits of
>pterosaurs, flight-related or not, these two seem highly unlikely.


Unless one is argueing that the large skull openings and general
pneumatization and hence lightening of the skeleton are adaptations for
flight. As is the increasing incorporation of sacral vertebrae into the
pelvic girdle, and that the advanced mesotarsal ankle might just be an
adptation for leaping from a treetop perch.


>However, change "ancestor-descendant" relationship to "sister group"
>relationship, and the first one is likely correct (if incomplete). (Retain
>"ancestor-descendant" relationship for "lagosuchians" and dinosaurs.)
>
>Pterosaurs and avians are not very similar at all anatomically, apart from
>a handful of convergences (like keeled sterna) and of course the traits
>common to all ornithodirans. The wing structure, for one thing, is
>completely different.
>



Don`t forget the similar pneumatization, the acrocoracoid process they
share, and the fused ankle forming a double condyle...."nearly identical to
that of birds." (Padian 1983a)