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Hammerhead sharks are one of the strangest animals in the ocean. These creatures can have heads that are almost 50% as wide as their entire body length. The shark's eyes are located on the sides of their wide heads. Some researchers argued that the hammerhead shark would not have good depth perception because there would be no overlap between the visual fields of each eye; other researchers argued that the wide separation between the eyes would improve depth perception. But no one had tested the shark's eyes until researchers at Florida Atlantic University and the University of Hawaii caught a few sharks.
In experiments published in The Journal of Experimental Biology, the researchers measured the electro-retinogram (ERG) from the eyes of several species of hammerhead shark. The ERG measures the response of the photoreceptors in the eye. The visual field of one hammerhead shark eye (monocular visual field) is about 180 degrees. Surprisingly, the researchers found a significant overlap of the visual fields from each eye. In fact, for the winghead shark, the binocular overlap was 48 degrees! Because of this overlap, it is likely that hammerhead sharks have excellent depth perception.
The hammerhead shark also makes eye and head movements as it swims to provide even better binocular vision and depth perception. These characteristics give the hammerhead shark an exceptional view of its undersea world.
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