Re: Palpebral Bones

[chris brochu <cbrochu@fmnh.org>]

OK, like I said, I'm a systematist - not a functional morphologist.  I have no
real idea what palpebrals do in crocodylians.  But here are some thoughts on
these responses:



> On Wed, 22 Mar 2000, Matthew Bonnan wrote:
> > Chris Brochu wrote:
> > >Palpebrals in crocodylians are largest in those taxa that tend to sit still
> > >in rain forest streams.
> >
> > I guess the dumb follow up question is: could junk in the stream come
> > rushing at the crocodylians such that they would need nice, big palpebral
> > bones even when just sitting there to deflect it?

Sure, that's possible.  But none of the fish living alongside them even have
eyelids, let alone palpebrals, and they do just fine.  Ditto for salamanders,
frogs, or any other aquatic/semiaquatic vertebrate - no palpebrals, and they're
just as susceptible to having their eyes poked by a branch coming downstream.




>
> >
> > Or does there have to be a function at all?  An outgrowth of ontogeny,
> > allometric considerations, etc.?

Also a strong possibility - but if so, why the tendency toward large, compound
palpebrals in blunt-snouted forms?  In something like Paleosuchus, the 
palpebrals
literally fill the eyelid - the eyelids open like the doors of a DeLorean.




>
>

Richard W Travsky wrote:

>
> Films I;ve seen of crocs at kills show them twisting and tearing chunks
> off the prey. This can occur with other crocs doing the same thing on
> the same kill. Perhaps this feature provides some protection during
> collisions while twisting.

The blunt-snouted forms are solitary and don't feed in groups like that.  Those
that feed in groups tend to have rather small palpebrals.

Some have proposed a shading function.  Palpebrals are smallest in those taxa
with orbits facing up rather than laterally - I would expect the opposite were
shading the primary function.

chris





--
----------------------
Christopher A. Brochu
Department of Geology
Field Museum of Natural History
Roosevelt Road at Lake Shore Drive
Chicago, IL 60605

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