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The eyes with vertical pupils of small cats and some reptiles are very good at seeing better in the dark and avoiding being blinded thanks to their ability to regulate the amount of light that enters the eyes very well. They are also very sensitive to movement within a limited range. The drawbacks they have; they can see within a very limited range of colors and do not see very well either from very close or from far away.

Hawks' eyes, on the other hand, have one of the best eyesights in the animal world, capable of distinguishing details in small objects more than a kilometer away, they can see in more colors than humans and some can even see in the ultraviolet spectrum, etc. The downside of these eyes is that they are fixed to the hawks eyesockets, they cannot move them and they are very sensitive to sudden changes in light.

I have in mind a class of shape-shifting magicians (werewolves / other animals) most of whom undergo a significant change in the shape of their eyes; they acquire eyes with vertical pupils. (I like their aesthetically)

Is it biologically plausible the existence of vertical pupils with their capabilities added to the capabilities of the eyes of a hawk and without any of their disadvantages? Doesn't one thing rule out the other?

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Colour vision is not related to pupil shape, so yes, your scenario is plausible.

Colour vision is a matter of retinal receptor cells (cone cells). UV vision is at least in part a function of the lens (in humans, the lens filters out UV, some wavelengths of which we can otherwise see). Visual acuity is a function of focusing light through the lens and onto the retina.

Low light vision is a matter of retinal receptor cells (rod cells). Cats have a lot of these, but fewer cones. Their colour vision sucks; their low light vision is awesome. Hawks have a lot of cone cells, but fewer rods. Colour vision is awesome; but their low light vision sucks.

Basic trade-off there.

Pupil shape seems to be correlated with ecological niche. Your progenitor animals will thus likely be some kind of ambush predator, who hunts exclusively in the day time and may begin its approach from a great distance, possibly from a high place.

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  • $\begingroup$ Is it always a trade off? A pair of eyes can't have a lor of rod cells and a lot of cone cells at the same time? Having one takes the space the other needs to develop, or something like that? $\endgroup$ – Mike May 1 '20 at 8:32
  • $\begingroup$ Pretty much. There's only so much space, particularly in the central retina, where a hunter would want its best vision. $\endgroup$ – elemtilas May 1 '20 at 9:39

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