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, or 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.
It’s always about survival
UC Berkeley and Durham University researchers were also intrigued by these somewhat atypical shape. Being scientists, they decided to investigate and analyzed pupil shapes of no fewer than 214 land species.
What they eventually found was that pupil shape is 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, making it easier to pounce on prey. Meanwhile, herbivores — which are the target of carnivores — have rectangular slit pupils as a line of defense, offering them a broader field of vision.
As a herbivore, apart from some antlers and hooves, there’s not that much you can do to fend back a predator. The best thing they can do is run away, which is why many herbivores are also fast. Before you can run, though, 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. This way, even when they’re grazing, goats can always keep a good eye on the world and lurking predators.
Rectangular pupils are typically employed by equines and ruminants, such as sheep, deer, and horses.
Tibi is a science journalist and co-founder of ZME Science. He writes mainly about emerging tech, physics, climate, and space. In his spare time, Tibi likes to make weird music on his computer and groom felines.