RE: dinosaur beaks and ora speeds

["Tim Williams" <twilliams_alpha@hotmail.com>]

Thomas R. Holtz, Jr. wrote:

> Well, I would add that in living beaked reptiles (turtles, birds), as well 
> as extinct forms generally accepted as beaked (ornithomimosaurs, for 
> instance) there is a relatively sharp edge between the lateral and ventral 
> surfaces of the maxillae.  In contrast, in _Alioramus_ and _Carch._ there 
> is a curved surface grading the lateral into the ventral surface.

If I understand you correctly, in ornithomimosaurs the cornified 
rhamphotheca provides the cutting edge to the upper (and lower) jaw, as in 
the beaks of turtles and birds.  IMHO, _Alioramus_, _Carcharodontosaurus_, 
_Majungatholus_ and other non-maniraptorans, by contrast, were not "beaked", 
but nevertheless had a cornified zone expressed on the dorsal rostrum 
(perhaps continuous with any pre- or postorbital ornamentation).  Thus, in 
these forms this sheath was not trophic in function, but decorative or 
(?)thermoregulatory and did not extend to the oral cavity.



Tim

_________________________________________________________________
Tired of spam? Get advanced junk mail protection with MSN 8. 
http://join.msn.com/?page=features/junkmail