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RE: dinosaur beaks and ora speeds



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

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