An analysis of 214 species of land animals shows that a creature's ecological niche is a strong predictor of pupil shape. Species with pupils that are vertical slits are more likely to be ambush predators that are active both day and night. In contrast, those with horizontally elongated pupils are extremely likely to be plant-eating prey species with eyes on the sides of their heads. Circular pupils were linked to "active foragers," or animals that chase down their prey.