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Re: Reptilians Get Cheeky



  Waylon and David seem especially interested in this subject; I
include Pete because discussions with him have pretty much
solidified my present position on this matter (well, that and
Witmer's papers). So count this post as an addition to the last
one I wrote on cheeky dinosaurs.

----

  To clarify the actual term "chewing" applied morphologically
and mechanically, there are two actual criteria: 1) possession
of a certain kind of rocker / lateral pivot in the jaws that
allow the jaws to literally rotate, dislocate (for precision
occlusion on only _one_ side of the jaw at a time) the jaw; this
must also require a tightly bound or fused symphysis to prevent
the jaws from acting independantly (we see this in
pythonomorphs, and this leads to something as far from chewing
as you can get), and 2) the possession of molars. Yes, molars.
Chewing, as presently understood, is strictly a mammal thing
(mammaliomorphan, actually -- I think) that requires the
interdigitating cusps of the teeth both sagittally and
labiolingually to occlude.

  Therefore, no dinosaur can chew. As Pete has posted, the jaw
actions of ornithischians are unique and, for the large part,
exemplify shearing.

=====
Jaime A. Headden

  Aaaaaaaaaaaaaaaaaaaahhhhhhhhhhhhhhhhhhr-gen-ti-na
  Where the Wind Comes Sweeping Down the Pampas!!!!

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