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RE: Horner's Pachy Lumpin' - Your Thoughts?



> From: owner-DINOSAUR@usc.edu [mailto:owner-DINOSAUR@usc.edu] 
> On Behalf Of Saint Abyssal
>
> I've just read the Horner paper alleging that Dracorex and 
> Stygimoloch represent juvenile Pachycephalosaurus at 
> differing stages of development. I think he presents a 
> reasonable case, especially for Dracorex being a younger 
> Stygimoloch, but I'm not wholly convinced of the alleged 
> synonymy of all three genera. The purported erosion of the 
> Stygimoloch horns (balatant sexual display features) into the 
> more diminuitive, rounded knobs of Pachycephalosaurus upon 
> reaching maturity (right when such features should be 
> *growing*) would, if true, be a chin-scratcher.
> 
> I was just wondering if there were any DMLers who felt 
> strongly about the proposed 
> Pachycephalosaurus-Stygimoloch-Dracorex merger. I get the 
> impression there is some level of skepticism or ambivalence 
> to the proposal but haven't been actively sought out others' 
> opinions until now.

Well, the bone texture of the "Dracorex" skull has been consistent with a
non-adult status, and a lot of people were far from convinced that it was
distinct from Stygi. &/or Pachy since its initial announcement (see the DML
at the time, for instance).

The erosion of the horns would seem to be the strongest oddity in the batch.

As others have already posted, given our very small sample size it is
difficult to dismiss several alternative sources of variation (taxonomic,
geographic, stratigraphic, ontogenetic, sexual, individual, etc.)

Thomas R. Holtz, Jr.
Email: tholtz@umd.edu   Phone: 301-405-4084
Office: Centreville 1216                        
Senior Lecturer, Vertebrate Paleontology
Dept. of Geology, University of Maryland
http://www.geol.umd.edu/~tholtz/
Fax: 301-314-9661               

Faculty Director, Earth, Life & Time Program, College Park Scholars
http://www.geol.umd.edu/~jmerck/eltsite/
Faculty Director, Science & Global Change Program, College Park Scholars
http://www.geol.umd.edu/sgc
Fax: 301-314-9843

Mailing Address:        Thomas R. Holtz, Jr.
                        Department of Geology
                        Building 237, Room 1117
                        University of Maryland
                        College Park, MD 20742 USA