Re: Making Lip of It

[Matthew Martyniuk <martyniuk@gmail.com>]

"Pterosaurs seem to have been a largely toothed but lipless group with
some non-fishing inland forms"

Again, is there any actual evidence for this assertion? AFAIK the
evidence is just as equivocal for non-beaked pterosaurs as it is for
non-beaked dinosaurs.

Matt

On Thu, Sep 22, 2011 at 10:23 PM, Sim Koning <simkoning@msn.com> wrote:
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>      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.
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>       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.
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>      I suspect the typical pattern that independently lead to beaked jaws in 
> so many archosaur lineages may have been something like this:
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> 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.
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> Simeon Koning
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