Re: Why do some animals, like cats, snakes, and goats, have elliptical pupils?

Hi,

Interesting question.

Like so many question about anatomical features
and their probable evolutionary causes; this
topic does not seem to have been clearly 
researched.  There are a lot of "arm-chair"
Darwin's out there, however.

Since soft tissue is rarely preserved in the
fossil record, it is hard to give a solid answer.
It is clear that the elliptical pupil has developed
several times since it is found in many different
orders of animals.  This lends credeance to a 
functional interpretation.  This Web reference
can start the discussion -
 http://videoforcats.com/catvis
ion.htm

It keys on the need for speed in the pupil's
response to light and in the need for a very
wide range of response.  Another page suggests 
that a tiger has less visual acuity than a human
in broad day-light, but more than 6 times better
at night; due to the ability of its pupil to dialate
more than a round pupil. It seems obvious that
the elliptical pupil has a wider range of response.
Grab your cat and try out bright light vs. near
total darkness.  Then, after you have pried the
frighten cat off your arm, do the same with your 
dog. I have found that the speed and range of
response is clearly 'better" in the cat. 

To find the range of animals with elliptical 
pupils, I used the NorthernLight search engine
 http://www.northernlight.com

with the search string "elliptical pupils"

David