Scientists and children alike have long marveled at the hammerhead shark’s peculiar head shape – also known as a “cephalofoil” – and speculated on the predator’s design. Why, you can’t help but wonder, are they shaped that way?
A study published in the Journal of Experimental Biology made headway toward answering that evolutionary question with surprising conclusions about hammerhead vision. One of the authors of the study, Michelle McComb of Florida Atlantic University, spoke to Oceana's online editor Emily Fisher about her team's discoveries.
What did you and your colleagues discover about hammerhead vision?
The popular literature is filled with claims that hammerheads have better vision, but this was never tested. Our goal was to quantify the extent of the visual fields of hammerhead sharks in contrast to more typical-shaped sharks, in order to determine if they possessed binocular vision.
What we found was a surprise – hammerhead sharks do have binocular vision, and even more surprising, the extent of binocular overlaps was greater than found in the typical-shaped sharks.
When we originally discussed this project we thought we were setting out to dispel the myth that hammerheads possessed binocular vision. We had no idea that hammerheads would have even larger binocular overlaps than normal sharks!
Why is it significant that hammerheads have binocular vision?
Binocular vision evolved to facilitate depth perception. Each eye sees a slightly different image and it’s the subtle differences within these images that are used for depth cues. So the wider separation of the eyes in hammerhead sharks enhances the stereoscopic effect and depth perception. This translates into a visual advantage for a predator like the hammerhead shark in its ability to accurately judge the distance of moving objects like prey.
As a result of your team’s research, do we have a definitive answer for why hammerhead shark heads are shaped the way they are?
Our results support the idea that vision may have played a role in the evolution of the hammerhead. However, there are several other hypotheses that remain, some of which are untested.
It is possible that several factors in combination may have led to the evolution of the head shape, including the following hypotheses:
1. The head acts as a bow plane to provide hydrodynamic lift during swimming.
2. Possible enhanced electrosensory ability due to the larger size of the head and the potential for possession of more electrosensors in the head.
3. Enhanced olfactory ability due to the wide separation of the olfactory organs and naris (nostrils) on the head.
4. The head shape may help hammerheads pin down prey items like stingrays. However, this is not strongly supported because the diet of many hammerhead species (there are 8 species of hammerhead) does not include stingrays.
Have you ever swum with sharks?
I have swum with great white sharks off the coast of South Africa, bull sharks in Australia, hammerheads in Hawaii, lemon sharks in Florida and Caribbean reef sharks in the Bahamas.
Every time I see a shark while I am in the water, I get a thrill and I feel so lucky and humbled that I am sharing space with them.