Re: The Eternal Question: Lips or Skin?

[JAMES ARONIS <Apollo@MLink.net>]

Birds don't possess any dentition that would trap and accumulate matter 
eventually
leading to desiccation. Dogs OTOH, have lips and spend a large portion of their 
lives
with their mouths open as part of their cooling-down process (panting). They do 
have
problems with soft tissue and dental rot. This is NOT to say that dogs are 
prone to
dental rot because they open their mouths often. Nor, am I stating that lips are
anatomical features specifically designed to prevent desiccation. I'm just 
playing
the devil's advocate here. The evolution of lips in mammals must have had 
another
purpose besides the added advantage of covering and protecting teeth. This
"advantage" may have been incidental. If indeed teeth required this form of
protection in the first place.

I don't know if anyone mentioned in this "lips debate" that theropods evolved a
strategy to defeat dental rot. Their ability to continuously replace old worn 
teeth
with new ones in the same fashion as sharks do today, would have incidentally 
been
useful at replacing rotting teeth as well. This very fact alone may have 
negated the
need for a "dentition-protection" tissue covering.


Danvarner@aol.com wrote:

>
> >Quoting Mark Hallett:
> >
> >"Crocs (excluding
> >extinct terrestrial forms) don't have to deal with the potential dessication
> >of lip and mouth mucosa that other tetrapods do, since they're either in the
> >water or close to it.
>
>        About dessication. Today, any bird that shows up on my 100+ degree(F)
> porch has its mouth wide open. That's one way you can tell it's hot. I wonder
> if Tyrannosaurus did the same thing on a particularly blistering day. It
> certainly isn't a problem for George, our Red-winged Lipless Blackbird. DV