eyes on the horizon

Horizontal pupil of a goat (flickr.com)

 Literature and lore often depict satanic or demonic animals as having hooves, horns, and elongate pupils. But my experience with goats, their delicious cheese and cute little tongues lapping up food at a petting zoo suggest otherwise. So I’m going to go ahead and make a bold statement: maybe these attributes are not markers of a demonic origin, but adaptations for predator avoidance and feeding.

You’ve probably noticed that livestock animals like horses and cows have horizontally rectangular pupils? Admittedly, this difference from our own eyes can make them seem unrelatable and a little spooky… probably interpreted as “demonic” by scribes of old. But look at the eyes of an animal, you can make inferences about where they spend most of their time, and what sort of predation they are likely to face.

Wide-angle view of ungulates, thanks to eyes being on
either side of the head and horizontally stretched pupils.

Ungulates (hoofed animals like deer, goats and sheep, bovine, horses, etc. that graze on grasses) all have the horizontal pupils, and eyes generally situated on either side of the head. This adaptation gives them an expanded range of peripheral vision. As grazers that must keep their heads down in open fields and grass plains, they have to be able to keep an eye on the horizon for Mufasa and Simba coming to eat their asses, even as they are munching on grass. Once motion is spotted, the zebra/sheep/antelope/whatever is equipped with long legs and speed that usually gets them out of hot water.

Reduced angle view that carnivores
experience.

The predators of these ungulates have vision adaptations of their own. Their eyes are situated more on the front of their head, causing the images seen by each eye to overlap. This is called binocular vision, and allows the animal keen depth perception fitting for a hunter. Of course, they trade wide-angle peripheral vision for their depth perception. But as predators and not prey, they don’t need to monitor the expansive horizons for danger as attentively. In addition, rounded pupils allow for super-tight focusing, perfect for spotting a tasty morsel off in the distance. Great depth perception + focusing power = zebra for dinner.

Can you think of any other animals with crazy eyes? Or eyes placed on the head differently than they are on yours? What do these things tell you about the animal's role in the food web?