lip clarifications

["David L. Martin" <dmartin@hh.gpz.org>]

This morning our aquarist came in and plopped down a newspaper with a
headline, "Dinosaurs lacked lips according to research," and
started barking at me that dinosaurs had no lips and couldn't
snarl.  I didn't try to clarify the issue with him, just like I
don't try to clarify the "all computers will collapse at the turn of
the century" issue for him.  I don't cast pearls before
swine.  But you who have ears to hear may glean something useful
here.  
As with so many issues in this group, there seems to be unnecessary
semantic confusion about something that is not at all semantically
unclear in the zoological literature.  Terrestrial vertebrates with
teeth have lips.  Period.  They protect the relatively fragile
tooth rows, contain salivary secretions, and conceal the often
conspicuous inner lining of the mouth.  Both lizards and snakes have
well-developed lips, even extremely long-toothed forms such as tree
boas.  The upper teeth slip into a pocket between the mandible and
the lower lip.  It is painfully obvious to me, having seen a number
of dinosaur skulls of various taxa, that all had well-developed
lips.
The issue of lip mobility is a completely separate one.  Complex
facial muscles and facial expressions are limited today to mammals. 
This is not to say that birds and reptiles cannot express themselves
visually with their faces.  One can even cite cases where reptiles
do seem to use their lips independently in certain contexts.  Snakes
of the genus Storeria, for example, sometimes do a "lip
curl" when handled.  The function of this behavior is not at
all clear.  I see no compelling evidence that any dinosaur could
produce facial expressions in any way comparable to what we see in
mammals.  (For that matter, many mammals are limited in this
regard.)  Nor do I see any compelling reason to believe they
couldn't.
I do find it rather absurd that there are so many restorations of
theropods with such poorly-developed lips.  Try drawing lizards
without lips and you will see what I mean.  They look
ridiculous.  I repeat that all terrestrial vertebrates with teeth,
amphibians, reptiles, or mammals, have well-developed lips.  It is
therefore for those who draw dinosaurs without them to explain why they
should be deprived of something that is so widespread and so obviously
useful.  It gives a very misleading impression of the appearance of
the animal, quite unnecessarily inaccurate in my view given the
evidence.

Best regards.

Dave