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Re: Sexual Dimorphism in _Coelophysis_




I believe
there is a pretty strong case for it in _Coelophysis_ _bauri_, using neck
vs. torso length, limb ratios and skull lengths. Perhaps this type of data
could be applied to other closely related theropods (which is actually work
that I am in the process of doing right now).

Not that I necessarily agree or disagree on sexual dimorphism in _Coelophysis_, but I'm not positive that that particular population is the best suited for this kind of analysis. After all, I've worked with many fossils of _Coelophysis_, and they remain some of the most dimensionally-altered (diagenetically) fossils I've ever seen (as are most Chinle specimens -- I've even seen one phytosaur skull so twisted that the caudal half of the skull is preserved in dorsal view while the _articulated_ rostral portion is in left lateral view!) As otherwise beautifully preserved as most (but not all!) of the Ghost Ranch stuff is, it's still all heavily squished, and whatever the prevalent vector of diagenetic displacement was, it would act differently on bones oriented at different angles to that vector. I've never seen anyone attempt to quantify this degree of diagenetic alteration and correct for it when making measurements of the fossils thus affected -- it would certainly be an interesting experiment! As things stand, people simply use their own backgrounds and intuition in mentally (and for drawings) un-alter the fossils. As we all know, this can easily lead to all kinds of disagreements about the true nature of a squished fossil -- see, for example, the multiple and not necessarily complementary reconstructions over the last 100+ years of the skull of _Archaeopteryx_ (for which studies on the Solnhofen sediment have shown an ~80% diagenetic compaction, but not, as I understand it, much lateral motion).


I'm not saying that the amount of displacement of Ghost Ranch bones is huge, but it is certainly noticeable on many, many specimens, and it's conceivable that the difference between statistically significant measurement differences and statistical noise is there within the diagenetic history of the fossils...

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Jerry D. Harris
Dept of Earth & Environmental Science
University of Pennsylvania
240 S 33rd St
Philadelphia PA  19104-6316
Phone: (215) 898-5630
Fax: (215) 898-0964
E-mail: jdharris@sas.upenn.edu
and     dinogami@hotmail.com
http://www.sas.upenn.edu/~jdharris

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