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Re: Ornithomimid beaks



On Thu, Aug 30, 2001 at 09:07:41PM +0200, David Marjanovic scripsit:
> My uncle has sent me the Nature article. There it says that the beaks were
> restricted to the premaxillae and the corresponding tips of the dentaries.
> Now what was behind this? Does it tell about me or about something else that
> I can't imagine a toothless beakless mouth over AFAIK rather sharp jaw
> margins, following a very short beak?

If the theory of theropod beak formation that has the horn butting pads,
lacrimal horns, and so on extending down the snout until close enough to
the mouth to be exapted as a cutting surface is correct, you'd expect
beaks to be initially right at the tip of the mouth.  (Although I am not
at all sure how that theory handles *lower* beaks.)

The other way to look at it is that the beak is the gripping surface of
a pair of pincers; teeth are a high metabolic cost for a
what-it-can-swallow omnivore, and that as soon as there *was* a beak
there, there was strong selection pressure against teeth.  The sharp jaw
margins may just be side effects of tooth loss.

-- 
                           graydon@dsl.ca
               To maintain the end is to uphold the means.