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Re: Pygostyle



-----Original Message-----
From: dbensen <dbensen@gotnet.net>
To: Dinogeorge@aol.com <Dinogeorge@aol.com>
Cc: ornstn@home.com <ornstn@home.com>; dinosaur@usc.edu <dinosaur@usc.edu>
Date: Monday, November 01, 1999 10:53 PM
Subject: Re: Pygostyle


>>>
>It has been my experience that everything can be used to argue anything in
>this field, and therefore nothing has any meaning. Pygostyle schmygostyle.
>Think whatever you like; it makes no difference.<<
>
>I disagree here.  Things like that DO mean something because it seems that
>ONLY ADVANCED BIRDS have pygostyles.  If the oviraptor was taken alone,
then
>that would work out; the oviraptor is a flightless bird that hasn't lost a
>feature of its ancestors.  However, less advanced (more basal, whatever)
>oviraptors than this one DO NOT have pygostyles, and so we know that the
>feature is not  something from its ancestors.  This fossil has very far
>reaching effects as I see it.  Either
>a) GS Paul (and other's) hypothesis that the oviraptors are flightless
birds
>is wrong (I certainly hope it isn't), or
>b) the pygostiles are convergent (is such a feature useful enough to be
>evolved independently?  Do regular pygostiles and the oviraptor's share
enough
>features that we know they are actually the same, not just superficially
>similar structures?)
>c) Caudipteryx and all the other dinosaurs we consider more basal than this
>unnamed one are actually more derived and have lost this pygostyle
(doubtful,
>since they were earlier than the unnamed one and we more primitive in many
>respects)
>e) This thing isn't an oviraptor at all (I don't think so, but how much do
we
>REALLY KNOW about this creature.  "So mister Oviraptor, if that _is_ your
real
>name . . .":)
>f)The pygostyle was glued on by a Chinese farmer or a graduate student (You
>know those farmers:)
>
>As I look at this list, I think that a or b is the most probable solution
>(given Occam's razor, a is the best), but I really like Dr. Paul's theory
>about flightless birds and it makes sense in every other instance.  I hope
>that there is just a simple answer that I haven't thought of.
>
>Dan
>
>

I choose from column "b". I think pygostyles are convergent. They seem to
occur in the later "stages" in vertebrate flight development. I think there
may be a "trend" towards this morphology as both birds and pterosaurs seem
to have hit on it independently (and convergently). (YES,...you heard me
mention it in the SAME sentence!....birds, pterosaurs and convergence...IN
THIS ASPECT ONLY!)  I really try to use convergence as sparingly as
possible, but in this instance it seems rather obvious.