Fwd: re: pygostyle

["John R. Hutchinson" <jrhutch@socrates.berkeley.edu>]

>X-Originating-IP: [137.99.54.38]
>From: "Timothy Williams" <twilliams_alpha@hotmail.com>
>To: dinosaur@usc.edu, jrhutch@socrates.berkeley.edu
>Subject: re: pygostyle
>Date: Wed, 03 Nov 1999 13:59:59 EST
>Mime-Version: 1.0
>
>John R. Hutchinson wrote:
>
>>
>>Whoa, hold on here.  That is incorrect.  As Chiappe (1996; Munchner
>>Geowissenschaftliche Abhandlungen Reihe A 30:215) noted, "Contrary to
>>Alvarenga & Bonaparte (1992), it is not known whether there was a
>>pygostyle."  I have examined all of the known specimens and I concur; you
>>cannot tell.  There are 5 or more free caudals; that's all you can say
>>about the tail,...
>
>The rather tall caudal neural spines, though, suggests that _Patagopteryx_'s
>tail might be long rather than short.

I strongly disagree that they suggest anything remarkable.  I don't see any
strong, general correlation between neural spine length and tail length in
vertebrates, especially archosaurs.  I also don't see how you could
distinguish between such a putative correlation and other factors, such as
proximal stiffening of the tail and/or soft tissue attachments.  Given that
the distal tail is not preserved, I see any statements about its morphology
as dubious unless concrete evidence is cited.

However, one might infer that a pygostyle was present because all proximate
outgroups (Confuciusornithidae, Enantiornithes, and Ornithurae) have a
pygostyle.  Lacking contrary evidence, the least speculative assumption
would be that a pygostyle was present in Patagopteryx.  Nonetheless, that
hypothesis, like any alternative, cannot be tested until there is empirical
evidence.

==================
John R. Hutchinson
Department of Integrative Biology               Phone:  (510) 643-2109
3060 Valley Life Sciences Bldg.                 Fax:    (510) 642-1822
University of California
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http://www.ucmp.berkeley.edu/people/jrh/homepage.html