Ever took a moment to stare a goat in the eyes? If you have, you might have noticed something really weird: their pupils are horizontal rectangular. It’s one of those things that baffles the mind once it hits you because we’re so used to circular pupils or even vertical slit ones, on account of cats or snakes.
UC Berkeley and Durham University researchers were also intrigued by these somewhat atypical shape. Being scientists, they decided to investigate and look at the pupil shapes of no fewer than 214 land species.
What they eventually found was that pupil shape is directly linked to the ecological niche or role of the animal. The general pattern is predators have vertical slit pupils because these help them judge distance better, so it’s easier to pounce on prey. Herbivores that are often the target of carnivores, however, have rectangular slit pupils as a line of defense.
As a herbivore, apart from some antlers and hooves, there’s not that much you can do to fend back against a predator that’s adapted to stealth and razor sharp munching weaponry. The best thing they can do is run away, which is why many herbivores are also fast. Before you can run, you need to know when it’s time to make an exit which is where the goat’s rectangular eyes come in. These enable a panoramic vision which can detect intruders approaching from various directions.
The horizontal pupils also enhance the image quality of objects directly ahead of the animal. This clear front-image helps guide rapid locomotion over a potentially rough terrain, the researchers noted in Science Advances.
Grazing animals like goats also rotate their eyes when they bow their heads down so their eye slits are parallel to the ground at all times. They can rotate more than 50 degrees per eyes or 10 times more than the human eye. Even when its ‘lunch time’, grazers can always keep a good eye on the world and lurking predators.