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Re: Bird lips and dinosaur jaws

From: Matti Aumala <mjaumala@nettilinja.fi>
> The corners of theropod mouths are usually restored with a stretch
> skin that covers the jaw muscles and folds between the jaws when
> are closed, basically like in most modern reptiles. Birds however
> to have sort of lips and skin covering the jaw muscles that remains
> top of the jaws at all times, and is often covered with feathers.
> when and how did this change from reptilian mouths with fold-away
> to avian mouths with lips happen?
> Some dinosaurs, most notably oviraptorids, actually look very
> with the classic reptilian mouths, but seem much more "ordinary"
> restored with avian mouths. I've seen some maniraptorans
> with avian-like mouths, as well as birds with reptilian mouths (most
> notably G.S.Paul's Phorusrhacids in Predatory Dinosaurs of the
> Can you tell for sure what the corners of a bird's/theropod's mouth
> was like from the skull, or is it mostly based on speculation?

I managed to get my scanner to work long enough to scan (with rather
low quality) the sketch I made to illustrate this question. You can
find it from this URL:
[The above head is a typical example of the reptilian mouth and the
one below has avian mouth with birdlike "cheeks".]

I know Jaime A. Headden already covered the subject of
oviraptorosaurian jaws quite thoroughly (though I have to admit that
as at best an amateur at dinosaur anatomy I'm not exactly sure if I
understood half of how it was connected to my question :-) but I'm
most interested about the changes that took place in dromaeosaurs and
truly avian dinosauria.

Matti Aumala