Pachyrhinosaur nasal horn? (was RE: OMEISAUR CLUBS, PACHYRHINOSAU R)

["Williams, Tim" <TiJaWi@agron.iastate.edu>]

Tracy Ford wrote:

> No specimen that has a boss, not just Pachyrhinosaurus, shows ANY
> evidence of a horn. The Pipestone Creek specimens have both Concave and 
> Convex bosses. There are juveniles that have a rudimentary horn (or more
> properly, a split ridge) and at least one specimen that has both a 
> ridge and the starting of a boss. 

I'm not sure I follow this argument.  The rationale behind the possible
presence of a pachyrhinosaur nasal horn is that the boss formed the base for
a large keratinous horn on the snout - analogous to the nasal horn(s) of the
rhinoceros.  It don't see how the shape of the dorsal surface (whether it
was concave or convex) really matters.  Also, as a cornified structure, we
would not expect the horn to be fossilized as readily as the underlying
bone.  

I know Dodson (1996) does not favor this interpretation - why go to all the
trouble of transforming the nasal horn just to support a large cornified
horn when the same result (a very large horn) could be achieved by just
modifying the bony horn already there?  A good question.  However, it
doesn't mean that pachyrhinosaurs didn't do this.  Perhaps a cornified nasal
horn held certain advantages over a horn with a bony core.



Reference

Dodson, P. (1996).  The horned dinosaurs.



Tim

------------------------------------------------------------ 



Timothy J. Williams, Ph.D. 

USDA-ARS Researcher 
Agronomy Hall 
Iowa State University 
Ames IA 50014 

Phone: 515 294 9233 
Fax:   515 294 9359