Binocular vision: the secret behind hammerhead shark head shape?

Have you ever wondered why hammerheads have their eyes out on organ stops? So have countless scientists since the first hammerhead species was described over 200 years ago, but now the mystery of their bizarrely shaped head is starting to be unravelled. The hammer-shaped head, or ‘cephalofoil’, must have posed some advantage in the sharks’ particular niche in order to have evolved, with suggestions ranging from enhanced detection of prey hiding in the substrate as the cephalofoil provides a larger surface area for detecting electrical signals given off by the prey, through to benefits to navigation and manoeuvrability.

But this week a study published in the Journal of Experimental Biology has been able to demonstrate that the key advantage provided by the cephalofoil over standard conical shark heads may, somewhat surprisingly, be significantly enhanced stereoscopic vision. Stereoscopic vision is where the visual fields of the two eyes overlap, providing a three dimensional image that facilitates depth perception, which is crucial for judging distance when catching prey.

By shining lights in particular positions whilst monitoring the brain activity of different shark species, the authors of the study were able to show that sharks with a typically shaped head, such as lemon sharks, possessed only 10 degrees of overlap, whereas the eyes of scalloped hammerheads overlap by 32 degrees. The value is even greater for winghead sharks, whose cephalofoil is almost their body length, with an overlap of 48 degrees.

Dr Michelle McComb, lead author of the study, stated ‘As the hammerhead head has expanded, the degree of binocular overlap has increased with it’.

Additionally the study identified that hammerhead sharks have an astonishing 360 degree view of their surrounding environment in the vertical plane, seeing all that’s above and below, as well as an excellent stereo rear-view.

Consequently not only may the hammer-shaped head help the sharks catch their prey through improved binocular vision, but it may even help them evade potential predators by being vigilant to all that’s around them at all times.