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No. 65: Sep-Oct 1989

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Why the hammer head?

Hammerhead shark
You probably thought, as we did, that the function of the hammerhead shark's weirdly shaped head was to separate the eyes and thus improve binocular vision. This is not the case. The visual fields of the hammerhead's eyes do not overlap at all. Each eye presents the brain with a separate, completely different image to integrate. What, then, could be the purpose of the hammer head? No one really knows, but three suggestions are as follows:

  1. The head acts as a hydrofoil and gives the heavier-than-water, swimbladderless shark better swimming control.

  2. Grooves on the hammer head channel water toward the nostrils, providing "stereoscopic sniffing."

  3. The head is a platform for electromagnetic sensors that help locate prey. Stingrays are a favorite food of the hammerhead, and the shark may de-tect them electromagnetically, as surmised by the author of this article in the following encounters:

    "I have observed great hammerheads swimming close to the bottom, swinging their heads in wide arcs (a motion common, in a lesser degree, to all large sharks) as if using the increased electroreceptive area of their hammer like the sensor plate of a metal detector. Sometimes, these animals would doubleback to scoop up one of several stingrays hiding in the bottom silt. The minute electrical pulse that keeps the stingray's heart and spiracles operating betrays their presence to a hungry hammerhead."

(Martin, Richard; "Why the Hammer Head?" Sea Frontiers, 35:142, 1989.)

From Science Frontiers #65, SEP-OCT 1989. � 1989-2000 William R. Corliss