RE: Rex Jaws

["Tracy Ford" <tlford@ix.netcom.com>]

-----Original Message-----
From:   owner-dinosaur@usc.edu [mailto:owner-dinosaur@usc.edu] On Behalf Of
Frank Galef
Sent:   Thursday, June 03, 1999 6:30 PM
To:     Z966341@wpo.cso.niu.edu
Cc:     dinosaur@usc.edu
Subject:        Re: Rex Jaws

So now I'll toss in my thoughts:
I have also wondered a lot about this topic.  There has been some waffling
from the lipless camp, saying that a row of scales covering the teeth are
not really lips.  Well, I don't say they have to smile or osculate, but if
it looks like a lip and it smacks like a lip, I would call it a lip.

As stated before, mammals have muscles to 'smack' their lips and 'lizards,
snakes, the tuatara doesn't.

 The
main function here is water preservation, and oral surfaces provide a lot
of area to lose moisture.  Something to cover the oral  structures seems
to be pretty prevalent in terrestrial non-beaked vertebrates, and I think
beaks seal well too, but they are not covering teeth.  Crocodilians don't
have lips, but they are mostly aquatic, and does anyone know if they have
those nutrient foraminae?

Yes, so does the terrestrial Sphenosuchians, pristichampsians (debatable by
some as to being totally terrestrial) as well as Sebecosuchians.

 I haven't seen them when I've  looked at croc
skulls, perhaps Chris Brochu has a comment?  While on the subject, what
about the exuberant gum tissue that is seen in most reptiles?  Teeth are
usually felt more than seen, even long ones.  I suspect the pink sticky
covering has something to do with continuously replacing teeth, but I
haven't been able to find anything about it in most basic reptile
references.  Any help from the experts here?   When I have looked at large
theropod skulls, the polished and worn area on the teeth seems to begin at
a distance from the bone, suggesting that gums were probably there.

Not really. It also suggest a few things, one, the tooth in the skull has
been displaced, or it's beginning to be pushed out by the incoming tooth.
Stan has it's teeth nearly falling out (some disagree, but Neil Larson
agrees) but the roots are still in the maxilla. What you do see is the
enamel of the tooth, then the root, which is huge in some cases.

IMHO theropods had crocodilian jaws, no lips but ornithischians had, well, I
need to do more research and there are a few papers coming out that will
comment on this by others which will have a great impact on this subject
(hopefully in the near future).

Tracy