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Re: Making Lip of It

2011/9/22 Dann Pigdon <dannj@alphalink.com.au>:
> On Thu, Sep 22nd, 2011 at 6:03 PM, David Marjanovic <david.marjanovic@gmx.at> 
> wrote:
> Some siamese cats develop super-occluded upper canines that permanently 
> protrude below the
> lips. I don't know whether it causes them any problems. It certainly makes 
> them look creepy.
> Sabretoothed cats certainly seem to have coped with permanently exposed 
> canines. As do extant
> male musk deer. Naked mole rats have forgone lips altogether - although their 
> burrows probably
> maintain a constant level of humidity, and their teeth grow and are worn down 
> at a much greater
> rate than for most mammals.
You seem to be right with sabertoothed cats and musk deer, but siamese
cats would have not bearing on the need for survival of lips covering
teeth as they were not produced by natural selection.

Besides, I think that another (rather weak, I admit) argument to say
lizard-like lips were not present in non-avian dinosaurs (accepting
their function is to keep teeth wet) may be that carnivorous dinosaurs
and some archosauriforms have teeth generally longer than most
carnivorous squamates. Thus, the lip should be generaly longer than in
a lizard. For the dinosaur to bite something, and the long teeth to
enter deeply into the flesh, the lip should be raised. This required
to raise a bigger lip, which would require more lip musculature.
Perhaps mammals can accomplish raising bigger lips which commonly
protect longer canines because the larger amount of voluntary muscle
present. Lizard teeth are commonly so short (or, when long as in
snakes and monitors, so caudally pointing) that perhaps the lip has
not to be raised too much more than passively for the teeth to mostly
penetrate prey.