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RE: Making Lip of It





     I only have time at the moment for a brief response, but I wanted to cover 
this at least. 

> *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.

     I have a hard time imagining this guy with lips

http://en.wikipedia.org/wiki/File:Kaprosuchus_2.jpg

     This argument also seems to ignore the fact that there were many, many 
pterosaurs flying around with exposed teeth; some of these were inland species 
such as the Istiodactylids. It seems to me that flying around through warm air 
would be a great way to dry your teeth out, yet this doesn't appear to have 
presented any kind of problem for them. Then we have (what I must assume) were 
lipless taxa such the aforementioned Kaprosuchus. There were also the various 
tusked or fanged animals throughout history we should consider. Smilodon spent 
their lives with their most important set of teeth hanging out of their mouths. 
Wild boars are a modern example with jutting tusks that they use as weapons and 
digging tools. Elephants aside, I think the question should be whether or not 
the overbite seen in dinosaurs would be sufficient as a seal for the mouth.  

Simeon Koning




----------------------------------------
> Date: Thu, 22 Sep 2011 09:56:11 +0200
> From: david.marjanovic@gmx.at
> To: dinosaur@usc.edu
> Subject: 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?