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Re: comparative color vision

At 12:10 PM -0500 5/21/99, Mickey P. Rowe wrote:
>Nevertheless comparative molecular
>biology indicates that the most recent common ancestor of
>Crossopterygian and Actinopterygian fish had four cone classes (i.e.
>potentially tetrachromatic vision).  That split predates the evolution
>of Tetrapoda (which derive from the Crossopterygia), so it encompasses
>almost all extant fish.  Mammals lost two of those cone classes.
>Primates re-evolved a third.  We've thus almost caught up to our
>ancestors...  Many fish are known to have retained all four cone
>classes, and very few are known to have fewer than three.
Very interesting. So the primitive dinosaurian ancestor had four cone
classes. Where did rods evolve (and with them, presumably, night vision)?
Is there any evidence when multiple cone classes first appeared? -- Jeff