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Information about Hammerhead Shark

Hammerhead Sharks

Scientific classification
Kingdom:Animalia
Phylum:Chordata
Class:Chondrichthyes
Subclass:Elasmobranchii
Order:Carcharhiniformes
Family:Sphyrnidae
Genus:Sphyrna
Rafinesque, 1810
Species
See text.


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.

Physical description

Enlarge picture
A lateral sketch of a Hammerhead Shark.
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.

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.

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.

Ecology

The hammerheads are aggressive predators, eating fish, rays, cephalopods, and crustaceans. They are found in warmer waters along coastlines and continental shelves.

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.

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.

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]

Species

Enlarge picture
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. 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]

Enlarge picture
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.

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].

References

1. ^ R. Aidan Martin. If I Had a Hammer. Rodale's Scuba Diving August 1993. Retrieved on March, 2006.
2. ^ Chapman, DD; Shivji, MS; Louis, E; Sommer, J; Fletcher, H; Prodöhl, PA (August 22, 2007). "Virgin birth in a hammerhead shark". Biology Letters 3 (4). 
3. ^ Scientist Finds 'Genetically Distinct' Shark. PhysOrg.com. Retrieved on June, 2006.
4. ^ R. Aidan Martin. Origin and Evolution of the 'Hammer'. www.elasmo-research.org. Retrieved on January, 2005.

External links

Scientific classification or biological classification is a method by which biologists group and categorize species of organisms. Scientific classification also can be called scientific taxonomy, but should be distinguished from folk taxonomy, which lacks scientific basis.
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Chordata
Bateson, 1885

Typical Classes

See below

Chordates (phylum Chordata) are a group of animals that includes the vertebrates, together with several closely related invertebrates.
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Chondrichthyes
Huxley, 1880

Subclasses and Orders

See text.

The Chondrichthyes or cartilaginous fishes are jawed fish with paired fins, paired nostrils, scales, two-chambered hearts, and skeletons made of cartilage rather than bone.
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Elasmobranchii
Bonaparte, 1838

Superorders

Batoidea (rays and skates)
Selachimorpha (sharks)

Elasmobranchii is the subclass of cartilaginous fish that includes skates, rays (batoidea), and sharks (selachii).
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Carcharhiniformes
Compagno, 1977

Families
See text.

The ground sharks, order Carcharhiniformes, are the largest order of sharks; they are also called whaler sharks.
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Sphyrna
Rafinesque, 1810

Species
See text.

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
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Constantine Samuel Rafinesque-Schmaltz, as he is known in Europe, (October 22 1783-September 18 1840) was a nineteenth-century polymath who led a chaotic life.
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genus (plural: genera) is part of the Latinized name for an organism. It is a name which reflects the classification of the organism by grouping it with other closely similar organisms.
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Sphyrna
Rafinesque, 1810

Species
See text.

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
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Eusphyra
Gill, 1862

Species: E. blochii

Binomial name
Eusphyra blochii
(Cuvier, 1816)


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Eusphyra
Gill, 1862

Species: E. blochii

Binomial name
Eusphyra blochii
(Cuvier, 1816)


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1 metre =
SI units
1000 mm 0 cm
US customary / Imperial units
0 ft 0 in
The metre or meter[1](symbol: m) is the fundamental unit of length in the International System of Units (SI).
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A hammer is a tool meant to deliver blows to an object. The most common uses are for driving nails, fitting parts, and breaking up objects. Hammers are often designed for a specific purpose, and vary widely in their shape and structure.
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Electroreception, sometimes written as electroception, is the biological ability to receive and make use of electrical impulses. It is much more common among aquatic creatures, as water is a far superior conductor than air.
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ampullae of Lorenzini are special sensing organs, forming a network of jelly-filled canals found on elasmobranchs (sharks and rays) and Chimaera. Each ampulla consists of a jelly-filled canal opening to the surface by a pore in the skin and ending blindly in a cluster of
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predation describes a biological interaction where a predator organism feeds on another living organism or organisms known as prey.[1] Predators may or may not kill their prey prior to feeding on them.
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Batoidea

Orders

Rajiformes - common rays and skates
Pristiformes - sawfishes
Torpediniformes - electric rays
See text for families.

Batoidea
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Cephalopoda
Cuvier, 1797

Orders

Subclass Nautiloidea
  • †Plectronocerida
  • †Ellesmerocerida
  • †Actinocerida
  • †Pseudorthocerida
  • †Endocerida
  • †Tarphycerida
  • †Oncocerida

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crustaceans (Crustacea) are a large group of arthropods, comprising approximately 52,000 described species [1], and are usually treated as a subphylum [2].
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continental shelf is the extended perimeter of each continent and associated coastal plain, which is covered during interglacial periods such as the current epoch by relatively shallow seas (known as shelf seas) and gulfs.
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A spermatozoon or spermatozoan (pl. spermatozoa), from the ancient Greek σπέρμα (seed) and ζῷον (living being) and more commonly known as a sperm cell
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Ova may mean:
  • Original video animation, anime that are released directly to video.
  • The plural of ovum, a female sex cell or gamete.
  • A suffix found in the surnames of Russian women; see names in Russian Empire, Soviet Union and CIS countries

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The placenta is an ephemeral (temporary) organ present in placental vertebrates, such as some mammals and sharks during gestation (pregnancy).

The placenta develops from the same sperm and egg cells that form the fetus, and functions as a fetomaternal organ with two
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In placental mammals, the umbilical cord is a tube that connects a developing embryo or fetus to the placenta. It normally contains three vessels, two arteries (Umbilical artery) and one vein (Umbilical vein), buried within Wharton's jelly, for the exchange of nutrient- and
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Boca Grande is a small residential community on Gasparilla Island, southwest Florida. Gasparilla Island is a part of both Charlotte and Lee Counties, while the actual village of Boca Grande, which is home to many seasonal and year-round residents, is entirely in the Lee County
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Parthenogenesis (from the Greek παρθένος parthenos, "virgin", + γένεσις genesis
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S. lewini

Binomial name
Sphyrna lewini
(Griffith & Hamilton Smith, 1834)

The scalloped hammerhead, Sphyrna lewini, is a hammerhead shark of the family Sphyrnidae.
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