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RE: Pachyrhinosaur nasal horn? (was RE: OMEISAUR CLUBS, PACHYRHIN OSAUR)



Tracy Ford wrote: 

> The keratin on the beak of birds and their feathers are formed
> differently. Don't fall into the trap of them being both keratin they 
> are exactly the same.

Not 'exactly the same' at all, I agree.  But if birds can build hard
supracranial structures out of epidermal tissue, I can't see why dinosaurs
couldn't.  For example, the casque of adult cassowaries is constructed of a
bony base or core underneath a keratinous structure.  However, the keratin
casque may *double* the height of the underlying bone, and the keratinous
structure does not necessarily conform to the shape of the bone buried
inside it.

No doubt the pachyostatic boss of pachyrhinosaurs was sheathed in horn.
What this debate boils down to is what shape this horny layer took: did it
faithfully conform to the shape of the underlying bone (mostly blunt and
rounded at the top), or was it extended dorsally into a more apical, conical
structure (mimicking the bony horn cores of other ceratopsids).  Or
something between these two extremes.

David asked why a keratinous horn would be an advantage over a bony horn.  I
can think of one possible explanation: pain.  A keratinous horn is less
painful when broken.  




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