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Re: I don't think this made it onto the list: Androgynous Rex

I tend to view this conundrum as a Late Cretaceous version of  Saturday
Night Live's "Pat".


On Mon, 19 Jun 2006 15:56:11 -0400 "Thomas R. Holtz, Jr."
<tholtz@geol.umd.edu> writes:
> Erickson, G.M., A.K. Lappin, and P. Larson. 2005. Androgynous rex ? 
> The utility of chevrons for determining the sex of crocodilians
> and non-avian dinosaurs. Zoology 108: 277-286.
> Abstract
> The sex of non-avian dinosaurs has been inferred on numerous 
> occasions using a variety of anatomical criteria, but the efficacy 
> of
> none has been proven. Nearly 50 years ago Romer suggested that the 
> cranial-most or first chevron in the tails of some reptiles,
> including crocodilians, is sexually dimorphic. Recent work on this 
> subject purportedly substantiated that the female first chevron
> articulates in a more caudal position than in males. Furthermore, it 
> was concluded that this element is shorter in females. These
> phenotypic attributes theoretically provide a broader cloacal 
> passageway for eggs by ovipositing females and a greater attachment
> area for male "penile retractor muscles". Because theropod dinosaurs 
> such as Tyrannosaurus rex presumably show similar variation in
> chevron anatomy, the same criteria has been advocated for sexing 
> dinosaurs. We tested the neontological model for the chevron sexual
> dimorphism hypothesis using a skeletonized growth series of American 
> alligators (Alligator mississippiensis) of known sex. No
> statistical support for the hypothesis was found. Furthermore, 
> analysis of a diversity of crocodilian taxa from museum collections
> revealed similar findings suggesting the alligator results are not 
> taxon specific. Study of well-preserved tyrannosaurid dinosaurs
> in museum collections showed nearly invariant chevron positioning 
> like that seen in crocodilians. This suggests the usefulness of
> chevron anatomy for sexing dinosaurs is tenuous.
>               Thomas R. Holtz, Jr.
>       Senior Lecturer, Vertebrate Paleontology
> Department of Geology         Director, Earth, Life & Time 
> Program
> University of Maryland                College Park Scholars
>       Mailing Address:
>               Building 237, Room 1117
>               College Park, MD  20742
> http://www.geol.umd.edu/~tholtz/
> http://www.geol.umd.edu/~jmerck/eltsite
> Phone:        301-405-4084    Email:  tholtz@geol.umd.edu
> Fax (Geol):  301-314-9661     Fax (CPS-ELT): 301-405-0796