RE: My opinion on dinosaur lips

["Tracy L. Ford" <dino.hunter@home.com>]

-----Original Message-----
From: owner-dinosaur@usc.edu [mailto:owner-dinosaur@usc.edu]On Behalf Of
David Marjanovic
Sent: Saturday, August 18, 2001 7:15 AM
To: The Dinosaur Mailing List
Subject: My opinion on dinosaur lips

Some points have not been addressed so far in this discussion:

The phylogenetic bracket is ambiguous: Today mammals and lepidosaurs have
lips,<<
Here is a very important thing about this debate, Mammal dentaries don't fit
inside the upper jaw. The teeth line and meet. Lizards for the most part
have teeth that interlock or meet, they don't have long overhanging teeth.
Dinosaurs on the other hand have what could be called an overbite, the lower
jaw fits inside the upper and thus have teeth that hang over the dentary.
Even spinosaurs have an overbite and the teeth do NOT interlock. Crocodiles
have the same thing, except the front teeth, in some cases do interlock.
>>crocs don't -- and turtles and birds have _beaks_ which may or may not
have evolved on lipless ancestors. <<
Turtles and birds have an over bite.
>>That crocs lost lips for whatever reason
is possible -- whales are lipless too (unlike seals and hippos).
Fig. 4-7 in PDW (p. 98) shows a cross-section through the snout of
*Dilophosaurus*; there the jaws fit quite closely and lips are shown which,
if a little longer, could have completely covered the teeth. Teeth that
extend beyond the dentary are not incompatible with lips as shown by
saber-toothed cats, elephants etc.. Keeping the teeth from desiccating is,
however, probably worth some effort: in the 19th century ivory traders
preferred forest elephants because their tusks don't have fissures.<<
>From what I understand, and I may be wrong, tusks and teeth have different
enamel.

Tracy L. Ford
P. O. Box 1171
Poway Ca  92074