A head start when it comes to eyesight

Why do hammerhead sharks have such a famously strange-shaped head?

One hypothesis is that having eyes on either side of such a wide 'hammer' allows the sharks to see better.

But even this idea divides scientific opinion, as researchers argue over whether the hammerhead design makes it more or less difficult to see.

The mystery may now be solved by a study showing that a hammerhead gives sharks outstanding binocular vision and an ability to see through 360 degrees.

The finding is published in the Journal of Experimental Biology.


This question has persisted since hammerheads were first described over 200 years ago

Dr Michelle McComb
Florida Atlantic University, Boca Raton, US.

Debate over why hammerheads are shaped as they are goes back centuries, and arguments over their visual capabilities goes back decades, says Dr Michelle McComb from Florida Atlantic University in Boca Raton, Florida, US.

For example, in 1948, zoologist Gordon Walls, a leading authority on vertebrate eye evolution, suggested that the position of a hammerhead shark's eye precluded it from having binocular vision.

Yet in 1984, leading shark expert Leonard Campagno countered by suggesting that the distance between a hammerhead's eyes would actually give it excellent binocular vision.

Binocular vision occurs when the fields of two eyes overlap, allowing the accurate perception of depth and distance. It is especially important for predators which need to judge the distance to their prey.

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