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Noses and Lips



Title: The following is an excerpt of some of my thoughts ( about my diplodocus restorations for Larry Witmer and observations concer

The following is an excerpt of some of my thoughts ( about my diplodocus restorations for Larry Witmer and observations concerning theropod lips) from a running dialogue I've been having with Tracy Ford, with some additional comments...

 

 

Concerning the size of the "external nose" for instance, there are a
few examples of skulls with a definitive prong originating from the backside
of the nasal opening ( look at the skull drawing in the 3 step lateral
drawing I did) that points at an acute angle "upwards" from the nasal
opening, instead of across it, towards the nasals.  I don't just recall at
the moment if the prong is formed by the frontals invading the nasal space
or which elements it's formed from.  The interesting thing, is that in many of the Diplodocus skulls it appears to be "worn down" and not as
prominent as in other specimens.  The point is that the orientation of the
prong is not not a preservational distortion, it really does point somewhat
outward, away from the general contour along the top of the skull.  The way
it sits suggests that it may be supporting a mass of soft tissue,  I
wouldn't be surprised if it continued in a cartilaginous arch to attach onto
the nasals. A more "flattened" form of the bony bridge delineating the nasal
arch in the camarasaurid, brachiosaurid sort of model.  It could be part of
an anchor for a nasal septum as well.  Whatever it is, it doesn't seem to
allow the current shape of the diplodocid skull to remain as it has been
accepted up to now.  There's much more as well, but you can read the rest in
Larry's paper.

 

Theropod Lips.  I have always supported the general premise of
no lips / exposed teeth in theropods.  I've had long term dialogues on this
subject with Phil Currie and he initially was convinced that theropod teeth must be contained within lips to prevent moisture loss which could effect the enamel on
exposed teeth. I cited crocs as a good example of exposed teeth to which
Phil countered that they lived in an aquatic environment which would
alleviate the problem. What about sabertooths?  He said the makeup of these
sorts of mammalian teeth differed from the reptilian model.  My argument had
the same basis yours does, and initially stemmed from a painting of a
tyrannosaur I wanted to do with the animal's mouth shut.  Obviously the tips
of the maxillary crowns passed beyond the ventral margin of the dentary ( as
is evident in a variety of tyrannosaur specimens).  He had a daspletosaur
skull lying on it's side in his office one day and I had noticed a sort of
waffling inside the maxillas that I thought might be resting "stops" for the
dentary teeth.  Since theropod dentition doesn't allow for occlusion, what
else would stop the jaw adductors from driving the dentary teeth up into the
palate when taking a bite out of prey?  The sculpturing inside the
maxillary's seemed to show the extent of excursion by the dentaries into the
upper jaw cavity.  If this was the case and we accept the fact that the
maxillary crowns extend beyond the lower margin of the dentaries and we also
know that the skin in reptiles is usually closely appressed to the skull,
the possibility of a lower lip arrangement capable of  receiving a set of
large maxillary crowns ( which would have to be akin to mammalian "jowls")
seems an unacceptable variation on the common reptilian model. I feel pretty
confident that the lower jaws fit nicely into the uppers *.  Are the
premaxillary arcade and maxillary teeth exposed?  To a degree certainly.
Are they completely exposed?   I'm not so sure... If the teeth are affected
by the degree of moisture, perhaps there is a partial upper lip in
association with (salivary?) glands keeping the crowns from drying out.  It
seems at least a possibility.  Conversely, what's the condition in
sauropods?, a similar dilemma. 

 

*One last point to ponder.  Go stand directly below a tyrannosaurus mount
and look up at the bottom of the head ( I've done this at the Tyrrell that
has the AMNH skull on a composite skeleton. What I notice is the lower jaws
form a "V" shape meeting at the symphysis formed by the bottom of the "V".
Overtop is the outline of the skull in which premaxillas / maxillas form a
"U" shape.  If this is the natural morphology of the skull and you consider
the "V" lower jaws, fitting into the "U" upper jaws, there would seem to be
a sizeable gap (side to side) between the upper and lower tooth rows when
the mouth is shut.  If this is real, then shouldn't there be a "fleshy"
component (lower lips?) to seal the mouth between tooth rows, when closed?

In consideration of some of the more recent posts on these subject to the list, I would like to add that Mark Hallett brings up a valid point concerning parasitic invaders and oral “hygiene”within the mouths of dinosaurs. Larry and I had discussed at one point broaching the subject of sauropod lips but have not gotten to it yet.  In my opinion, Mark’s treatment of lips as evidenced in his recent Rapetosaurus rendering is a very compelling and naturalistic approach and considers the importance of protection in sauropod dentition.

In theropods, I don’t think a crocodilian model can be supported and that some variation of an upper lip should exist.

 

Mike Skrepnick