The Hammerhead shark (of the Genus “Sphyrna”) is one of the most physically unique of the world’s ocean-dwelling creatures. A highly evolved carnivore, it is also an excellent hunter usually found in the world’s coastal tropical waters.
== Body and Head ==
The solitary Great Hammerhead (Sphyrna mokarran) is the second largest predatory fish, following the infamous Great White shark. These hammerheads are grayish-brown or olive green on top, with an off-white belly. They have serrated teeth and sport extremely tall dorsal fins that are instantly recognizable.
The almost flat, mallet-shaped head acts as a wing, providing better hydrodynamics while swimming, but hammerheads are also strong enough to pin their preferred food, stingrays, to the ocean floor. Hammerheads also eat squid, octopi, crustaceans, smaller fish, and sometimes other sharks.
A group of sensory organs, called Ampullae of Lorenzini, is situated on a shark’s snout and allows better detection of prey by identifying electrical fields. In the hammerhead, these electro-receptors are stretched along the front of the head, and it is believed that this increases the hammerhead’s ability to find prey along the sea floor.
The eyes on either side of the head provide a large vision range, which helps give hammerheads a great advantage over other sharks when hunting. The nostrils are also located at the ends of these projections, except on the Winghead shark, where they stretch along the front.
== Evolution ==
How did the hammerhead get this way? Three hypotheses for this highly successful adaptation come from findings at the Elasmobranch Research Laboratory at Florida Atlantic University in 2003. They seem to support a combination of successful mutations that allow the hammerhead to become the great hunter that it is: Electro-sensory reception (the ability to discern minor electric fields), olfactory acuity (the ability to “smell” odors directionally), and hydrodynamics (the ability to maneuver easily).
According to the ReefQuest Center for Shark Research, Geneticist Andrew Martin found that the large hammer appeared relatively suddenly (evolutionarily speaking) in the Winghead shark first, with narrower hammers emerging in other species later.
== Other Hammerheads ==
Not all hammerheads are the same, as nine different species exist, most being rather small and harmless to humans. Many of these smaller species school together, some in the hundreds. Even so, they avoid the Great Hammerhead and other large predators.
The hammerhead that most people think of is the Great Hammerhead, which is the largest and most fearsome. The average size is about 11.5 feet (3.5m) and 500 pounds (230kg), but it can grow as big as 20 feet (6m) long and can weigh 1,000 pounds (450 kg).
Other species include: Bonnethead (a.k.a. Shovelhead; has the narrowest hammer), Scalloped Bonnethead, Scalloped Hammerhead (a.k.a. Bronze Hammerhead or Kidney-headed; A variation of this shark was discovered off the coast of South Carolina in 2006), Scoophead, Smalleye Hammerhead (a.k.a. Golden Hammerhead), Smooth Hammerhead (a.k.a. Black Hammerhead), Whitefin Hammerhead, and the Winghead (of the Genus Eusphyra, with the widest hammer size).