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I would like to start out by saying that ornithischians in general and
ornithopods specifically were by far NOT boring dinosaurs.  That distinction
is placed squarely on basal coelurosaurs, by far the most boring of all
dinosaurs... or perhaps ducks, they're kind boring too.

Anyway.... :-) Although Witmer is certainly correct in his use of the EPB to
demonstrate that ornithischians did not have mammalian buccinators, this is
something I think no one ever thought anyway.  He is also correct in stating
that all the osteological features previously touted as being indicative of
cheeks aren't.

He's wrong though.  Orntihischian dinosaurs evolved ways of chewing and or
slicing food two different ways in two different lineages.  Ornithopods
crushed their food with some mild cranial kenesis that had the maxillae bulge
out over the dentary, and the processed food fall to the outside of the oral
cavity.  Marginocephalians (well, ceratopians really) sliced food in a
similar manner, where the processed food would fall to the outside of the
oral cavity.

The problem here, is a very derived oral cavity where food is processed in a
way totally unique among the Reptilia, yet, without cheeks (or some sort of
barrier) they would have been less efficient at processing food, as
everything that was processed would fall out on the ground.

In other words... why bother with chewing, when there are other large
dinosaurs that ate plants and didn't have complicated oral cavities like that
(sauropods, therizinosaurs, etc), and they did just fine.

So, at least within the Cerapoda, ornithischians probably had some sort of
cheeky barrier, if not all over Ornithischia.

Lastly, I would like to point out that EVERYONE DRAWS ORNITHISCHIAN FACES
WRONG (including myself).  They cheeks were not puffy, and were probably not
congruent with the surrounding skin, were probably thin and possibly not even
muscular.  Additionally, that deepened facial excavation that all
ornithischians had in life... the supposed cheek anchor would probably have
been pretty visible in life.

Pete Buchholz

"They're gonna be put to death." <smirk>
----'President' George W Bush