Re: Rex Jaws

["Matthew BONNAN" <Z966341@wpo.cso.niu.edu>]

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