hammerhead shark, active, surface-living shark, genus Sphyrina. Its curious head has lateral projections resembling the crossbar of a T, and its eyes and ears are located in the outer tips of the projections. This arrangement apparently gives the shark excellent binocular vision, and helps them see above, below, and behind as well as in front. It has been suggested that the extension of the head in the plane of the pectoral fins may give the fish increased lift, but there is no evidence that hammerheads are better swimmers than other sharks. Found in inshore, brackish water, hammerheads are both predators and scavengers. They feed on a variety of fishes including skates, rays, and other hammerheads, and large hammerheads have been known to attack and eat humans without provocation. The largest species is the widely distributed great hammerhead, S. mokarran, which typically reaches 15 ft (4.6 m) in length; the distance between its eyes may be as much as 3 ft (90 cm). The common hammerhead, S. zygaena, is found in all tropical waters, summering as far N as Newfoundland. It may reach a length of 12 ft (3.7 m). The bonnethead, or shovelhead, shark, S. tiburo, is a small, harmless hammerhead found in the W Atlantic from Brazil to Massachusetts. It reaches a length of 5 ft (150 cm) and its lateral lobes are much shorter than in other species, giving the head a rounded appearance. It is notable for eating seagrass as well as crustaceans and other prey. There are several other species distributed throughout tropical and temperate oceans. Hammerhead sharks are classified in the phylum Chordata, subphylum Vertebrata, class Chondrichthyes, order Selachii, family Sphyrnidae.
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