The
are a group of sharks that form the family Sphyrnidae, so named for the unusual and distinctive structure of their heads, which are flattened and laterally extended into a "hammer" shape called a cephalofoil.The known species range from 0.9 to 6.0 m (2 ft 11 in to 19 ft 8 in) in length and weigh from 3 to 580 kg (6.6 to 1,278.7 lb). They are usually light gray and have a greenish tint. Their bellies are white, which allows them to blend into the background when viewed from below, and sneak up on their prey. Hammerheads have disproportionately small mouths compared to other shark species. They are also known to form schools during the day, sometimes in groups over 100. In the evening, like other sharks, they become solitary hunters. National Geographic explains that hammerheads can be found in warm, tropical waters, but during the summer, they participate in a mass migration to search for cooler waters.