Crocodiles and gazelles don’t really see eye-to-eye on a number of issues—the culinary virtues of gazelle meat being the most prominent. But these animals do see the world differently, in part because of their pupils. The crocodile’s has a vertical slit, whereas the pupil of the gazelle is horizontal. The lion, lurking nearby, has a circular dot similar to humans. So why the different shapes? Researchers propose today in Science Advances that an animal’s status as predator or prey may be the determining factor. After analyzing the pupils of more than 200 land species including canines, felines, reptiles, and ungulates, the scientists found that short ambush predators such as alligators and foxes are more likely to have vertical pupils, whereas prey species—like gazelles or sheep—are more likely to have horizontal pupils. A vertical view is best for gauging distances along the ground, a useful ability when you’re lurking in the shadows and have only one shot at a mouse. A horizontal shape gives prey animals a panoramic view suited to spotting predators approaching from nearly any angle. This ability is enhanced by a feature that lets grazers rotate their eyes to keep their pupils parallel with the horizon. Circular pupils are generally found on animals that chase down their prey, such as cheetahs, or on taller ambush predators like lions and tigers. This suggests that above a certain shoulder height—about 42 cm—the functional advantages of vertical pupils are lost. The will to survive, it seems, has helped the eye of the tiger—and the fox and the horse—evolve pupils best suited to helping them do just that.
(Video credit: Science)