Re: Rex Jaws

[Frank Galef <tyra-rex2@nctimes.net>]

Matthew BONNAN wrote:

> Jordan Mallon said:
> "T.rex had quite an overbite, as most people have already mentioned
> on the
> list.  But most of the time, it's teeth were partially covered by
> it's lips."
>
> and then Dan Varner said:
> "Tracy Ford and others would disagree. As I mentioned the other day,
> Brian
> Cooley's life model of Sue's head in the Geographic is lipless. I
> don't know
> if this is the Field Museum's take or just Cooley's. Perhaps Chris
> Brochu
> could shed some light on this... In a way it would be nice if they
> were
> lipless--some of my old paintings would be correct again. Dan
> Varner."
>
> The first time I remember reading about dino lips was in Bakker's
> 1986 Dinosaur Heresies.  The idea was (if memory serves) that the
> foramina along the maxillae and dentary bones may have served as
> nutrient formina supporting lips -- i.e., that blood vessels and
> nerves passed through the openings along the jaws to support lip
> smacking.
>
> As I understand it, it turns out that many reptiles have nutrient
> foramina along their maxillae and dentaries, without having lips.
> Sorry, no reference here (but I'm sure someone out there has it).  In
> any case, the ability to snarl and move lips requires facial muscles
> in mammals, particularily the orbicularis oris (the ring-like muscle
> around your lips), the levator anguli oris, the depressor anguli oris,
> mentalis, etc.  These muscles arise from the platysma and other
> derived mammalian features.  This is not to say that we have
> definitive proof that T. rex didn't have lips and didn't snarl, but it
> suggests that the bias here is mammalian -- I am not aware at the
> moment of any reptile or bird with significant facial musculature,
> although I'm waiting to be corrected here at any minute.
>
> Shutting up (and closing my lips),
> Matt Bonnan
> NIU

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.  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?  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.
Comments from the Theropod specialists here?
Frank