Why do Animal Eyes have Pupils of Different Shapes? (Data Files)

There is a striking correlation between terrestrial species' pupil shape and ecological niche (i.e., foraging mode and time of day they are active). Species with vertically elongated pupils are very likely to be ambush predators and active day and night. Species with horizontally elongated pupils are very likely to be prey and to have laterally placed eyes. Vertically elongated pupils create astigmatic depth of field such that images of vertical contours nearer or farther than the distance to which the eye is focused are sharp while images of horizontal contours at different distances are blurred. This is advantageous for ambush predators to use stereopsis to estimate distances of vertical contours and defocus blur to estimate distances of horizontal contours. Horizontally elongated pupils create sharp images of horizontal contours ahead and behind creating a horizontally panoramic view that facilitates detection of predators from various directions and forward locomotion across uneven terrain