|
-- Ralph Miller III wrote: >...With such systems in
place, it
would be very wasteful to NOT wrap cheeks around those inset teeth, thereby facilitating the material being chewed to continuously drop out of the mouth. < Why developing muscular mammalian cheeks? Skin (smaller mouth opening)
would do the job equally efficiently -preventing the food to fall out while
chewing.
>Representing the opposing view, Tracy Ford thinks that tyrannosaurs had no lips at all (just as we see in crocs today). His point was that if tyrannosaurids had a lizard-style set of lips, the upper set of teeth would inevitably bite into the lower lips. (If my characterization of Tracy Ford's hypothesis here is incorrect, I trust that I will be corrected and admonished in due time). Gregory S. Paul's _PDW_ states that the theropods would have had the lips, but the tips of some of the longer upper teeth would protrude past the lips, as in some housecats. < Monitor lizards, oras in particular have very long teeth, upper ones
reaching the lower line of jaws, yet, their teeth are completely covered
with lips. Tyrannosaurids had lips ( no reason at all to develop lipless feature
like in some fish-eating animals). Observing the skull of say, Nanotyrannus
would reveal there was no space for upper teeth to go over the lower teeth, gums
and thick scaly lower lip. Their teeth were probably completely covered with
both lips when mouth closed.
Another case are some specialized theropods, like spinosaurs - in which
tips of some of the longer upper teeth ( or all ) "would protrude
past the lips".
Unfortunately, only better fossil specimens could prove who is right
on the issue
Berislav Krzic
veselinka.stanisavac@siol.net Beri's Dinosaur World http://www.geocities.com/CapeCanaveral/Lab/1638/index.html http://members.tripod.com/~dinosaurbero/portfolio.html Dinosaur Books http://www2.siol.net/ext/zza/index.html |