People joke about asking horses, “Why the long face?” We should redirect this question to hammerhead sharks. Their famous head extensions, called cephalofoils, can measure 3 feet from eye to eye. And scientists are still trying to nail down exactly what purposes they serve.
A study published in Scientific Reports explored how the sharks’ strangely shaped craniums affect how they swim. Although the cephalofoil helped with maneuverability, the researchers found, it did not seem to generate lift. In fact, it added a lot of drag — so much that some hammerheads may need to use roughly 10 times as much force as other sharks just to get through the water, said Glenn R. Parsons, a biological oceanographer and shark specialist at the University of Mississippi and one of the new paper’s authors.
There are some benefits to having a hammer for a head. Most experts agree that the widely-spaced eyes, nostrils and electroreceptors enabled by the cephalofoil’s shape allow the hunters to better pinpoint their prey. The heads can also serve as weapons — biologists have observed a female great hammerhead use her noggin to bludgeon a stingray.
But you have to wonder what it’s like to swim around with that thing.
To investigate, Parsons and his colleagues turned to computational fluid dynamics. There are at least eight hammerhead species. The researchers included all eight species in their study, laser-scanning the heads of preserved museum specimens to “capture the physical shape in minute detail,” Parsons said. Each digitized head was then placed in a virtual underwater environment, allowing the researchers to measure water pressure, drag and flow. They then did the same for a few shark species with more typical pointy heads.
When a hammerhead’s cephalofoil was level — as is typical when they are swimming — it did not generate lift, the researchers found.
But as soon as the cephalofoil was tilted up or down, the force quickly came into play, enabling a rapid ascent or descent. This helps to explain why hammerheads are “much more maneuverable than a typical shark,” said Parsons, who thinks the skill may help them snap up food from the sea floor.
The researchers also measured how much drag the cephalofoils produced. The winghead shark, which has the largest hammer, appears to be dealing with “20 to 40 times the amount of drag” as a typical fish, Parsons said.