Among the 65 frontal-eyed, ambush predators in this study, 44 had vertical pupils, and 82 percent of them had shoulder heights that were less than 42 centimeters (16.5 inches). Vertical pupils appear to maximize the ability of small animals to judge distances of prey.
The authors explained this by calculating that depth-of-field cues based upon blur are more effective for estimating distances for short animals than tall ones.
"We are learning all the time just how remarkable the eye and vision are," said Love. "This work is another piece in the jigsaw puzzle of understanding how eyes work."
The authors noted that this research focused on terrestrial species. They expect to examine associations of aquatic, aerial and arboreal life on eye position and pupil shape in future studies.