Hammerhead sharks occur worldwide; the most prominent species include the great hammerhead (S. mokarran), the smooth hammerhead (S. zygaena), the scalloped hammerhead (S. lewini), and the bonnethead shark (see).
Hammerheads are easy for even a novice to identify, with eyes located at the ends of two thin lobes and the overall structure resembling a hammer. One possible reason why the head takes on a hammer shape may be that the shape is ideal for turning and locating odors, making the best use of the electroreceptors present in all sharks, which in turn makes detecting food an easier chore.
The largest species is the great hammerhead, which can reach a length of 20 feet and a weight of 1,000 pounds. This shark prefers warm waters and is rarely found outside tropical areas.
The most widely distributed hammerhead is likely the smooth hammerhead, which grows to 14 feet. The front edge of its head is rounded and unnotched at the center, or smooth, and it inhabits shallow, calm coastal waters of bays and harbors.
The scalloped hammerhead is a gray-brown to olive shark that generally grows 5 to 7 feet, usually smaller than the smooth hammerhead but sometimes reaching 15 feet. The front edge of its head is rounded and notched, or scalloped. Both smooth and scalloped hammerheads occasionally school in large numbers.
Stingrays are thought to be the favored food of many hammerheads, and all species are viviparous and prolific, giving birth to many live young at a time. These sharks are exceptionally strong and can make fast, long surface and midwater runs when hooked, fighting hard and thrashing about with a great deal of excitement.