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

["Thomas R. Holtz, Jr." <tholtz@geol.umd.edu>]

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