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Re: Quo vadis, T. rex?



In a message dated 96-02-02 02:05:57 EST, pharrinj@PLU.edu (Nicholas J.
Pharris) writes:

>On Thu, 1 Feb 1996 Dinogeorge@aol.com wrote:
>
>> In a message dated 96-02-01 20:37:01 EST, pharrinj@PLU.edu (Nicholas J.
>> Pharris) writes:
>> 
>> >What I do not agree with is the linking of tyrannosaurs with the much 
>> >more primitive (ornitholestid-grade) _Compsognathus_ purely on the 
>> >occurrence of the didactyl condition in these two taxa (or that the 
>> >arctomet foot evolved in tyrannosaurs from scratch, i.e. from a 
>> >completely uncompressed foot like that of _Compsognathus_).
>> 
>> Actually, take a look at the pelvic bones of _Compsognathus_ and see how
>> closely they resemble miniature versions of tyrannosaurid pelvic bones.
>Grow
>> a bit of pubic boot, lose a bit of distal ischial enlargement, and
"Voila,"
>a
>> tyrannosaurid pelvis.
>
>Or take an ornithomimid pelvis, scale it up, and "Voila`," a 
>tyrannosaurid pelvis in one easy step.

Not quite that easy, I'm afraid. There's still a distal ischial expansion in
the ornithomimid pelvis that needs to be taken care of, and of course the
pubic boot has to enlarge also. Also, the ornithomimid ischium has a
differently shaped and positioned obturator process from that of
tyrannosaurids and is more downcurved. It's easier to get to the
tyrannosaurid pelvis from _Compsognathus_ than from an ornithomimid.