H is for Hammerhead

Sharks may date back 450 million years, but the first hammerheads didn't appear until about 20 million years ago.

There are nine hammerhead shark species, and they are found in oceans around the world. Most are small, at least as sharks go, but the great hammerhead can grow up to 20 feet and weigh a whopping 1,000 pounds.

Like unraveling the mystery of the narwhal's tusk, researchers went digging to understand why the hammerhead shark has a hammer-shaped head. And it turns out there may be more than one explanation.

Some evidence suggests that the long, dorso-ventrally flattened head (which scientists have termed the cephalofoil) helps hammerheads make sharp turns more swiftly than their pointy-nosed peers.

The shark's wide-set eyes and nostrils may provide better depth perception and improved accuracy when identifying and navigating toward a new scent. Additionally, scientists believe that hammerheads may have a heightened ability to sense electromagnetic fields, compared to other sharks.

Though all sharks possess the necessary sensory organs, called ampullae of Lorenzini, the hammerhead's are distributed along its wide head allowing it to scan the environment with greater accuracy.

As you may have guessed, hammerheads can also employ their cephalofoil during a hunt. Some have been spotted pinning stingrays to the seafloor to prevent their escape. Hammerheads typically hunt alone, but during migrations they sometimes school by the hundreds.

Unfortunately, that tradition makes them extremely vulnerable to overfishing. The great, scalloped and slender hammerheads are listed as endangered by the IUCN. The smooth and smalleye hammerheads are also listed as vulnerable.