Hammerhead sharks of the genus Sphyrna are members of the family Sphyrnidae. The only other genus of Sphyrnidae, Eusphyra, contains only one species, Eusphyra blochii, the winghead shark. Image File history File linksMetadata Greyreefsharksmall2. ... For other uses, see Genus (disambiguation). ... Genera Eusphyra Sphyrna Sphyrnidae is a family of hammerhead sharks containing only two genera, one of which, Eusphyra, contains only one species. ... Binomial name Eusphyra blochii (Cuvier, 1816) Range of winghead shark The winghead shark, Eusphyra blochii, is a species of oceanic shark, so named because it has a wing-shaped head. ... The winghead shark is a species commonly found in oceans. ...

Physical description

The nine known species of hammerhead range from 0.9 to 6 m long (3 to 20 feet). All the species have a projection on each side of the head that gives it a resemblance to a flattened hammer. The shark's eyes and nostrils are at the tips of the extensions. This article is about the unit of length. ... A claw hammer For other uses, see Hammer (disambiguation). ...

The hammer shape of the head was once thought to help sharks get food, aiding in close-quarters maneuverability and allowing the shark to turn sharply without losing stability. However, it was found that the special design of its vertebrae allowed it to make the turns correctly, more than its head. But as a wing the hammer would also provide lift; hammerheads are one of the most negatively buoyant of sharks. Like all sharks, hammerhead have electrolocation sensory pores called ampullae of Lorenzini. By distributing the receptors over a wider area, hammerheads can sweep for prey more effectively.^[1] These sharks have been able to detect an electrical signal of half a billionth of a volt. The hammer-shaped head also gives these sharks larger nasal tracts, increasing the chance of finding a particle in the water by at least 10 times as against the ability of other 'classical' sharks. Electroreception, sometimes written as electroception, is the biological ability to receive and make use of electrical impulses. ... The ampullae of Lorenzini are special sensing organs, forming a network of jelly-filled canals found on elasmobranchs (sharks and rays) and Chimaera. ...

Wider spacing between sensory organs better enables an organisms to detect gradients and therefore the location of a gradient source such as food or a mate. The peculiar head of this shark can be thought of as analogous to the antennae of an insect.

A lateral sketch of a hammerhead shark.

The hammerheads are aggressive predators, eating fish, rays, cephalopods, and crustaceans. They are found in warmer waters along coastlines and continental shelves. Image File history File links No higher resolution available. ... Image File history File links No higher resolution available. ... Predator and Prey redirect here. ... For other uses, see Fish (disambiguation). ... Orders Rajiformes - common rays and skates Pristiformes - sawfishes Torpediniformes - electric rays See text for families. ... Orders Subclass Nautiloidea †Plectronocerida †Ellesmerocerida †Actinocerida †Pseudorthocerida †Endocerida †Tarphycerida †Oncocerida †Discosorida Nautilida †Orthocerida †Ascocerida †Bactritida Subclass †Ammonoidea †Goniatitida †Ceratitida †Ammonitida Subclass Coleoidea †Belemnoidea †Aulacocerida †Belemnitida †Hematitida †Phragmoteuthida Neocoleoidea (most living cephalopods) ?†Boletzkyida Sepiida Sepiolida Spirulida Teuthida Octopoda Vampyromorphida The cephalopods (Greek plural (kephalópoda); head-foot) are the mollusc class... For the Dutch band, see Crustacean (band). ... The continental shelf is an area of relatively shallow sea water that is found on the edge of each continent. ...

Hammerheads have disproportionately small mouths and seem to do a lot of bottom-hunting. They are also known to form schools during the day, sometimes in groups of over 100. In the evening, like other sharks, they become solitary hunters.

Hammerheads are notably the only creature in the animal kingdom besides humans to acquire a tan from prolonged exposure to sunlight. Tanning occurs when a hammerhead is in shallow water or close to the surface for long periods.

It's also noted that in recent studies that when large groups of hammerheads gather, they usully communicate with other individuals by creating pressure waves by thrashing their heads more sharply than usual, causing pressure waves that other individuals pick up and respond to.^{[citation needed]}

Reproduction

Reproduction in the hammerhead shark occurs once a year with each litter containing 20 to 40 pups. Hammerhead shark mating courtship is a violent affair. The male will bite the female until she acquiesces, allowing mating to occur. Unlike many other shark species, the hammerhead shark has internal fertilization which creates a safe environment for the sperm to unite with the egg. The embryo develops within the female inside a placenta and is fed through an umbilical cord, similar to mammals. The gestation period is 10 to 12 months. Once the pups are born the parents do not stay with them and they are left to fend for themselves. A world-record 1,280 pound (580 kg) pregnant female hammerhead shark was caught off Boca Grande, Florida on May 23, 2006. The shark was carrying 55 pups, which suggests scientists had previously underestimated the number of pups per gestation. A spermatozoon or spermatozoan ( spermatozoa), from the ancient Greek σπέρμα (seed) and (living being) and more commonly known as a sperm cell, is the haploid cell that is the male gamete. ... A human ovum An ovum (loosely, egg or egg cell) is a female sex cell or gamete. ... The placenta is a sack of fat present in placental vertebrates, such as some mammals and sharks during gestation (pregnancy). ... In placental mammals, the umbilical cord is a tube that connects a developing embryo or fetus to the placenta. ... This page is about the community in Florida. ...

In May 2007 scientists discovered that Hammerhead sharks can reproduce asexually through a rare method known as parthenogenesis, as they have the ability to fertilize their own eggs. At first the announcement was considered skeptically, due to the fact that a female shark can store sperm inside her for months, even years, but it was confirmed through DNA testing that the pup lacked any paternal DNA. This is the first documented case of any shark doing this.^[2] For the religious belief, see Virgin Birth of Jesus. ... The structure of part of a DNA double helix Deoxyribonucleic acid, or DNA, is a nucleic acid molecule that contains the genetic instructions used in the development and functioning of all known living organisms. ...

Species

School of scalloped hammerheads, Wolf Island, Galapagos Islands

Of the nine known species of hammerhead, three can be dangerous to humans: the scalloped, great, and smooth hammerheads. Image File history File links No higher resolution available. ... Image File history File links No higher resolution available. ... NASA Satellite photo of the Galápagos archipelago. ...

• Genus Sphyrna
  • Subgenus Sphyrna
    • Scalloped hammerhead, Sphyrna (Sphyrna) lewini (Griffith & Smith, 1834)
      • "Cryptic scalloped hammerhead" - Scalloped hammerheads turn out to be divided into two separate species, which have not been officially reclassified with separate names.
    • Great hammerhead, Sphyrna (Sphyrna) mokarran (Rüppell, 1837)
    • Smooth hammerhead, Sphyrna (Sphyrna) zygaena (Linnaeus, 1758)
    • Whitefin hammerhead, Sphyrna (Sphyrna) couardi Cadenat, 1951
  • Subgenus Mesozygaena
    • Scalloped bonnethead, Sphyrna (Mesozygaena) corona Springer, 1940
    • Squarehead shark Sphyrna (Mesozygaena) sp. listed on elasmo-research's list
  • Subgenus Platysqualus
    • Scoophead, Sphyrna (Platysqualus) media Springer, 1940
    • Bonnethead or shovelhead, Sphyrna (Platysqualus) tiburo (Linnaeus, 1758)
    • Smalleye hammerhead, Sphyrna (Platysqualus) tudes (Valenciennes, 1822)

Announcements in June, 2006 reported the discovery of a possible new species of hammerhead off the shores of South Carolina. The possible new species is referred to simply as a cryptic species until it receives an official designation. This is prolonged, in part, because the discovery is really that the "scalloped hammerhead" is possibly two different species, not that a new species has been sighted, in the normal way. The discovery that scalloped hammerheads are possibly two species is purely a result of genetic testing, not identification of physical differences. ^[3] Binomial name Sphyrna lewini The Scalloped Hammerhead is a member of the hammerhead family originally called Zygaena lewini, but was later renamed to its current name, Sphyrna lewini. ... Binomial name Sphyrna lewini (Griffith & Hamilton Smith, 1834) School of scalloped hammerheads, Wolf Island, Galapagos Islands. ... Binomial name Sphyrna mokarran (Rüppell, 1837) The great hammerhead shark, Sphyrna mokarran, is the largest species of hammerhead sharks. ... Binomial name Sphyrna mokarran (Rüppell, 1837) The great hammerhead, Sphyrna mokarran, is the largest species of hammerhead shark. ... Binomial name Sphyrna zygaena The smooth hammerhead is the only species of hammerhead shark found in the Galapagos Islands, approximately 1 000 km West of the South American Pacific Coastline. ... Binomial name Sphyrna zygaena (Linnaeus, 1758) The smooth hammerhead, Sphyrna zygaena, is a large hammerhead shark living in temperate and tropical seas. ... A painting of Carolus Linnaeus Carl Linnaeus, also known after his ennoblement as Carl von Linné, and who wrote under the Latinized name Carolus Linnaeus (May 23, 1707 – January 10, 1778), was a Swedish scientist who laid the foundations for the modern scheme of taxonomy. ... Binomial name Sphyrna couardi Cadenat, 1951 The whitefin hammerhead, Sphyrna couardi, is a shark of the family Carcharhinidae, found in tropical waters of the eastern Atlantic Ocean oceans between latitudes 34° N and 6° S. Its length is up to about 3 m. ... Binomial name Sphyrna couardi Cadenat, 1951 The whitefin hammerhead, Sphyrna couardi, is a shark of the family Carcharhinidae, found in tropical waters of the eastern Atlantic Ocean oceans between latitudes 34° N and 6° S. Its length is up to about 3 m. ... Binomial name Sphyrna corona Springer, 1940 The scalloped bonnethead, Sphyrna corona, is a shark of the family Carcharhinidae, found in tropical waters of the eastern Pacific Ocean between latitudes 30° N and 18° S. Its length is up to about 92 cm. ... Binomial name Sphyrna corona Springer, 1940 The scalloped bonnethead, Sphyrna corona, is a shark of the family Carcharhinidae, found in tropical waters of the eastern Pacific Ocean between latitudes 30° N and 18° S. Its length is up to about 92 cm. ... Binomial name Sphyrna media Springer, 1940 The scoophead, Sphyrna media, is a hammerhead shark of the family Carcharhinidae, found in tropical waters of the western Atlantic Ocean between latitudes 31° N and 34° S. Its length is up to about 1. ... Binomial name Sphyrna media Springer, 1940 The scoophead, Sphyrna media, is a hammerhead shark of the family Carcharhinidae, found in tropical waters of the western Atlantic Ocean between latitudes 31° N and 34° S. Its length is up to about 1. ... Binomial name Sphyrna tiburo (Rüppell, 1837) Bonnethead shark (Sphyrna tiburo) is a member of the hammerhead shark family (Sphyrna). ... Binomial name Sphyrna tiburo (Linnaeus, 1758) Range of bonnethead shark The bonnethead shark or shovelhead, Sphyrna tiburo, is a member of the hammerhead shark genus Sphyrna. ... Binomial name Sphyrna tiburo (Linnaeus, 1758) Range of bonnethead shark The bonnethead shark or shovelhead, Sphyrna tiburo, is a member of the hammerhead shark family Sphyrna. ... A painting of Carolus Linnaeus Carl Linnaeus, also known after his ennoblement as Carl von Linné, and who wrote under the Latinized name Carolus Linnaeus (May 23, 1707 – January 10, 1778), was a Swedish scientist who laid the foundations for the modern scheme of taxonomy. ... Binomial name Sphyrna tudes The smalleye hammerhead or golden hammerhead Sphyrna tudes is a small subtropical hammerhead shark found in the southwest Atlantic from Venezuela to Uruguay, in the Mediterranean Sea and in the eastern Pacific. ... Binomial name Sphyrna tudes Valenciennes, 1822 The smalleye hammerhead or golden hammerhead Sphyrna tudes is a small subtropical hammerhead shark found in the southwest Atlantic from Venezuela to Uruguay, in the Mediterranean Sea and in the eastern Pacific. ... Valenciennes (Dutch: Valencijn, Latin: Valentianae) is a town and commune in northern France in the Nord département on the Escaut river. ... Official language(s) English Capital Columbia Largest city Columbia Largest metro area Columbia Area  Ranked 40th  - Total 34,726 sq mi (82,965 km²)  - Width 200 miles (320 km)  - Length 260 miles (420 km)  - % water 6  - Latitude 32° 2′ N to 35° 13′ N  - Longitude 78° 32′ W to 83... In biology, a cryptic species complex is a group of species that satisfy the scientific definition of species — that is, they are reproductively isolated from each other — but which are anatomically indistinguishable. ...

A hammerhead shark at Atlantis Paradise Island.

Since sharks do not have mineralized bones and rarely fossilize, it is their teeth alone that are commonly found as fossils. The hammerheads seem closely related to the carcharhinid sharks that evolved during the mid-Tertiary Period. Because the teeth of hammerheads resemble those of some carcharhinids, it has been difficult to determine when hammerheads first appeared. It is probable that the hammerheads evolved during the late Eocene, Oligocene or early Miocene. Image File history File linksMetadata Size of this preview: 800 × 413 pixelsFull resolution (2432 × 1256 pixel, file size: 1. ... Image File history File linksMetadata Size of this preview: 800 × 413 pixelsFull resolution (2432 × 1256 pixel, file size: 1. ... The Royal Towers joined by the Bridge. ... For other uses, see Fossil (disambiguation). ... Species 31 species; see text. ... Tertiary geological time interval covers roughly the time span between the demise of the non-avian dinosaurs and beginning of the most recent Ice Age, approximately 65 million to 1. ... hfajhfiudshfas == == == --24. ... The Oligocene epoch is a geologic period of time that extends from about 34 million to 23 million years before the present. ... The Miocene Epoch is a period of time that extends from about 23. ...

Geneticist Andrew Martin used DNA to study all of the hammerhead species and he concluded that the first hammer appeared on the winghead shark, which has the largest hammer, and the rest of the hammerhead sharks evolved one at a time from the original winghead shark each with a smaller hammer ^[4]. The structure of part of a DNA double helix Deoxyribonucleic acid, or DNA, is a nucleic acid molecule that contains the genetic instructions used in the development and functioning of all known living organisms. ... The winghead shark is a species commonly found in oceans. ...

References

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External links

• Video of divers with Hammerhead sharks in the Red Sea
• Animal Diversity Web Genus Sphyrna with species sub-pages
• Hammerhead Shark! web directory, with pictures
• Hammerhead Shark Facts fact sheet, general info, shark diving info
• Scaloped Hammerhead Shark Fact Sheet Scaloped Hammerhead Shark Fact Sheet
• Hammerhead Photos and Profile
• "Electroreception in juvenile scalloped hammerhead and sandbar sharks" by Stephen M. Kajiura and Kim N. Holland, The Journal of Experimental Biology (2002). Attempts to explain the "hammer" shape.
• MarineBio: Great hammerhead shark, Sphyrna mokarran
• BBC News announcement of new Hammerhead species
• Video of Hammerhead attacking Tarpon