Re: Making Lip of It

[David Marjanovic <david.marjanovic@gmx.at>]

>  [...] 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?