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Re: Making Lip of It



 [...] I'm leaning more and more to the lipless side of this debate.
 Though I do have problems with some of the arguments being put
 forward by both sides. For example, in old post on this list Tracy
 Ford argues that the presence of an overbite strongly suggests a
 lipless morphology, since lizards tend to have interlocking teeth and
 no overbite. However, from what I can tell, geckos have an overbite
 rather similar to that of some dinosaurs.


http://digimorph.org/library/pop.htm?/specimens/Gekko_gecko//specimenlarge.jpg

I don't see why an overbite should mean there can't be lips. Part of the function of lips is to protect the teeth from drying out, and that still applies to the upper teeth in an animal with an overbite.

The ivory from forest elephants is said to be much better than that from savanna elephants because the tusks of savanna elephants are exposed to much drier air.

 Arguments that revolve around foramina don't seem to help much. If
 they are diagnostic of anything, it seems to be degrees of
 sensitivity and vascularity of the skin around the jaws. The nutrient
 foramina found around the jaws of spinosaurids follow a single
 channel until they reach the tip of the snout, where they begin
 spread out or form several rows. This suggests to me that the
 foramina had more to do with sensitivity of the mouth than to the
 presence of lips. Deinonychus has a double row of foramina on the
 maxilla while they seem (to me) to be lacking on the rostrum. So
 perhaps they lacked lips altogether and possessed a keritanous
 proto-beak? I know you do not like this idea, but splitting the lip
 tendon/ligament seems only to be a problem if you assume they had
 lips in the first place.


http://digimorph.org/library/pop.htm?/specimens/Osteolaemus_tetraspis//specimenlarge.jpg

Foramina can mean plenty of different things. Squamates have foramina for squamate-only slime and (in some cases) poison glands. Crown-group crocodiles have foramina all over their snouts for water pressure receptors. Mammals, and maybe other theropsids, have foramina for nerves associated with whiskers, and so on...

 If you look at the jaws of a dwarf crocodile, you will notice that
 they are practically covered in foramina. I know some have argued
 that the liplessness of crocs is probably due to their aquatic
 nature, but then I have to ask why this did not present a problem for
 terrestrial crocs such as Kaprosuchus or Simosuchus, both of which
 were fully terrestrial, with one likely an herbivore.

 http://en.wikipedia.org/wiki/File:Simosuchus_clarki_skull.jpg

*Kaprosuchus* and *Simosuchus* do not belong to the freshwater clade of crocodyliforms, which contains the crown-group, nor to the marine clade (which may or may not be the sister-group of the freshwater clade). Their terrestriality is inherited straight from the ancestral archosaur and beyond. I'm not going to speculate on whether they had lips, except to note that their teeth may have benefited from protection against drying out.

 In the case of Simosuchus, the placement of foramina does not seem to
 differ greatly from what we see in some dinosaurs such as
 Deinonychus. You may notice that there is a cluster of foramen
 located on the maxilla, while they are lacking on the rostrum.
 Perhaps the tip of the snout was covered with a hard keritanous
 covering, perhaps a sort of proto-beak?

Why?