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Re: attack on dinosaur--horrific video

On Sat, 24 Nov 2007 17:13:33 -0500, john bois <jbois@verizon.net>

> What is that quiz show where you can ask a friend to bail you out--a
> lifeline--I think? 

I never saw the show, but I think you mean "Who Wants to Be a

> I haven't been able to find a ref. that deals precisely
> with our issues.  And I am more than a little confused.  But...
> http://palaeo-electronica.org/2000_1/retinal/issue1_00.htm
> ...contains citations for the claim (hypothesis, really) that animals
> w/sclerotic rings are generally diurnal; 

First of all, you should know better than to trust obscure references
like that...

> and that secondarily sclerotic-ringless animals (crocs and mammals)
> inherited this condition due to a period of ancestral nocturnal
> life.  The above also claims that sclerotic rings are reduced in
> owls

I don't have a specific citation at that particular sentence, but I'm
pretty sure (and context suggests) that I extracted that piece of
information (reduced rings in owls) from Walls, 1942.  Apparently that
sentence didn't register completely on one of the reviewers who said
that the large sclerotic rings in owls lead him to doubt the
hypothesis.  I haven't done any detailed comparisons, so I only half
stand by the particular datum.

> --so I put two and two together: sclerotic rings interfere with
> light gathering.

Okay, I definitely never intended to suggest that.  No, my thinking
(and I haven't spent any time thinking harder about this during the
past 8 years), was that the primary function of sclerotic rings was to
maintain the shape of the eye as the animals focused.  For nocturnal
animals, acuity is sacrificed for sensitivity, so there is no benefit
to having a good focusing mechanism.  Hence, it's not that the
sclerotic rings impede nocturnal vision, it's that the benefit they
provide to diurnal animals is not there for nocturnal animals.
Consequently, mutations that would reduce any and all aspects of the
focusing apparatus (e.g., the scleral ossicles) would be neutral for
nocturnal animals and deleterious for diurnal animals.  Thus ossicles
would drift away in lineages of nocturnal animals.

Anyways, it remains a hypothesis.  I don't know as that anyone has
attempted to shoot it down over the past seven years.  I fear my
attention has been elsewhere.

So, John, I can't help you win that million dollars, but I hope you
are now less confused.

Mickey P. Rowe     (mrowe@lifesci.ucsb.edu)