These are the five weird eye pupils evolution have made possible in the animal kingdom.

Evolution has done a pretty impressive job of diversifying the world; and out of all species and how diverse our features are, we think the eye is the most bizarre of all. The eye is what enable organisms to see, and it might be the main culprit behind how most animals have different forms of eyes. Here are some weird eye forms you can find in nature, and why the pupils, in particular, are so weird.

Related media: Animals’ Pupil Shape Is Based On Whether They’re A Predator Or Prey

#1. Vertical Pupils

Niche: Ambush predators, active by day and night.

Animals: Cats, foxes, crocodiles, snakes, geckos.

The vertical-oriented pupils are a precise instrument capable of razor-sharp focusing in bright conditions. These pupils open very wide and close-up to tiny slits, and it depends on how much light it receives. These animals could determine how blurry an object is regardless of the objects distance. In comparison, vertical pupils are like portrait settings in your smartphone — which focuses on the foreground and blurs the background and clearly shows the image, in a process known as stereopsis. This is the coolest part, that orzo-shaped pupil, with its narrow points and wide center, can achieve both of these feats at once.

#2. Horizontal Pupils

Niche: Grazing prey animals.

Animals: Cattle, goats, sheep, horses, moose, white-tailed deer.

If vertical-oriented pupils are like portrait mode on your smartphone, the horizontal-oriented pupil are like panorama mode. These pupils are on each ends of the animals head, which gives it a panoramic vision that lets more light to see in front, behind, and sides. That enables them to both detect a predator, and keep an eye on it while they escape. While vertical-oriented pupils are good for precision, horizontal-oriented pupils are good for a very wide aerial view. These animals adapt: their eyes swivel clockwise to remain aligned with the ground while they graze.

#3. Crescent Pupils

Niche: Water-dwelling animals that spend a lot of time motionless.

Animals: Skates, rays, flatfishes, catfish, some whales.

Underwater animals have a different set of visual challenges since light bends differently in water than it does in air. Sea creatures have completely different pupil shapes. Crescent shapes are a perfect example. One superpower they have is a wide visual field — they can take in more information than a circular pupil with the same surface area. Their crescent-shaped pupils aren’t focused on their prey precisely. Instead, their pupils turn points of light in front of their prey into u-shapes (or crescents facing up); and points of light that are behind their prey into n-shapes (or crescents facing down). The closer the object, the larger the u-shape, and vice versa. 

#4. More Than Two Pupils

Niche: Any animal that’s not strictly active in the daytime or nighttime.

Examples: Cats, llamas, horses, geckos, skates, rays, some sharks.

It seems we’ve already mentioned some of these animals. That’s no mistake. Most animals have the ability to constrict their eyes in very bright light. For instance, goats have horizontal pupils that will constrict like a dumbbell-shape with wide openings. Vertical pupils get narrowed into slits which allow in light at both ends; so as with crescent-shaped pupils, they form a sort of “teardrop” widening at each side. There’s even more animals with weirder openings. Skates and horses have pupils with fringes that have multiple openings in bright light, while some geckos have some wiggly-shaped pupils that constrict to form even smaller pupils.

#5. Somewhat Alien Pupils

Niche: Cephalopods

Examples: Octopi, squids, cuttlefish

Cephalopods are even a weirder organism on their own. Considered the smartest invertebrates on Earth, they have the ability to communicate by changing their skin pattern, and even modify their own Deoxyribonucleic acid (DNA) — people believe they’re aliens, Google it!). Their pupils are in varying shapes: like “W,” crescent, dumbbell, oval, and whatever the heck you’d name it. Like weird! And their ability to change the skin pattern to communicate is the fact that their eyes don’t have cells for color vision. Nature would be really unfair to let them expose themselves to predators that easily. It just doesn’t make sense — that’s their sense of vision, though.

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Written by: Nana Kwadwo, Thu, May 09, 2019.

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