This is more like a guideline than an actual rule. Many large cats have round pupils.
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Many "prey animals" do not have horizontal pupils at all. The horizontal pupil is mostly common in grazing animals. That said,
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There's a species of snake called the Vine snake that has horizontal pupils and it primarily eats mice.
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Mongoose are predators and also seemingly have horizontal pupils
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Cuttlefish have pupils shaped like a deranged W.
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Vertical pupils are more common in ambush predators, particularly ones that spend a lot of time low to the ground (Think: crocodiles, housecats). The pupil shape in this instance improves their depth of field, but it is also believed by some to function somewhat similar to the horizontal pupils (which allows prey to see more of the horizon), but in a vertical capacity
.
Many "prey animals" do not have horizontal pupils at all. The horizontal pupil is mostly common in grazing animals. That said,
.
There's a species of snake called the Vine snake that has horizontal pupils and it primarily eats mice.
.
Mongoose are predators and also seemingly have horizontal pupils
.
Cuttlefish have pupils shaped like a deranged W.
.
Vertical pupils are more common in ambush predators, particularly ones that spend a lot of time low to the ground (Think: crocodiles, housecats). The pupil shape in this instance improves their depth of field, but it is also believed by some to function somewhat similar to the horizontal pupils (which allows prey to see more of the horizon), but in a vertical capacity
.
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