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RE: Making Lip of It

     To reiterate my point about pterosaurs: there were insectivorous and 
toothed inland species (some Istiodactylids) that probably weren't making a 
regular habit of dunking their heads into water. Even the species that were 
fishing would have been doing so in saltwater, something that tends to rapidly 
desiccate tissues. Plus I doubt they spent their *entire* day soaking their 
heads in sea water, as I'm sure they would have needed to roost at some point. 
Kaprosuchus was most likely a terrestrial croc with what was apparently a 
largely terrestrial ancestry, and it almost certainly didn't have lips. Then 
there are the numerous mammalian examples with exposed teeth despite the fact 
that they are not easily replaced. I really don't think tooth dessication was 
that much of a problem at all for most animals with exposed teeth. Nor is a dry 
mouth for that matter: parrots have very dry mouths as they spend most of the 
time with their mouths partly open, and they are *dinosaurs*. In fact, if a 
parrot has a wet tongue it is usually a sign of illness. I really see no 
barrier to a dinosaur evolving a largely dry mouth, or exposed teeth, or both.


      What can phylogenetic bracketing tell us? If we look at terrestrial 
crocodylopmorphs such as Sebecus and Kaprosuchus, we see jaw morphology with 
interlocking teeth that would not have left much room for lizard like lips. 
Pterosaurs seem to have been a largely toothed but lipless group with some 
non-fishing inland forms. modern birds have beaks as did many dinosaurs, many 
of which seem to have evolved independently. Kaprosuchus seems to have had a 
keratinous 'bumper' of some sort on the tip of the snout. Perhaps this is how 
the typical archosaurian beak started out? I can see the advantage in having a 
hard covering on the parts of the the mouth that were most prone to abrasion 
and injury. All this suggests to me that 'liplessness' was the basal condition 
for most of Archosauria. Perhaps a lack of fleshy lips allowed for the rather 
large sharp teeth we see in so many predatory archosaurs. Lizard like lips may 
very well have been more trouble than they were worth for a great many 
archosaurs. This is something I have yet to see addressed. The assumption often 
seems to be that lips would have been beneficial for predatory archosaurs, and 
so no good reason can be found for why they would be lacking. If you look at 
the open mouth of a lizard such as Komodo dragon, you will notice that their 
teeth are not even visible despite their large size. If a dinosaur such as 
Deinonychus had lips of this sort, it would have looked toothless when it 
opened its mouth. The reality is that the sharp teeth of Varanids actually tend 
to lacerate the tissue surrounding them. I suspect that this would have been a 
problem for many theropods, not an advantage. 

     I suspect the typical pattern that independently lead to beaked jaws in so 
many archosaur lineages may have been something like this:

1. Lizard lips with interlocking teeth > 2. Lizard lips covering jaws with an 
overbite > 3. Reduced lips with an overbite > 4. No lips with exposed teeth 
(most of Archosauria) > 5. Exposed teeth with a hard scaly covering on the 
skull > 6. Teeth with a rostral 'proto-beak' > 7. A reduction in size and/or 
number of teeth > 8. A toothless beak.    

Simeon Koning