The bonnethead shark or shovelhead, Sphyrna tiburo, is a member of the hammerhead shark
Hammerhead shark
The hammerhead sharks are a group of sharks in the family Sphyrnidae, so named for the unusual and distinctive structure of their heads, which are flattened and laterally extended into a "hammer" shape called a "cephalofoil". Most hammerhead species are placed in the genus Sphyrna while the...

 genus Sphyrna
Sphyrna is a genus of hammerhead sharks in the family Sphyrnidae. It currently consists of the following species:*Sphyrna corona S. Springer, 1940 *Sphyrna couardi Cadenat, 1951...

. The Greek word sphyrna translates as hammer, referring to the shape of this shark's head - tiburo is the Taino
Taíno language
Taíno, an Arawakan language, was the principal language of the Caribbean islands at the time of the Spanish Conquest, including the Bahamas, Cuba, Hispaniola, Jamaica, Puerto Rico, the Florida Keys, and the Lesser Antilles...

 word for shark.


Characterized by a broad, smooth, spade-like head, they have the smallest cephalofoil (hammerhead) of all Sphyrna. Grey-brown above and lighter on the underside, it is a timid and a harmless shark.


On average, bonnethead sharks are about 1 m (3.4 ft) long, being the smallest hammerhead shark.


This species lives in the Western Hemisphere
Western Hemisphere
The Western Hemisphere or western hemisphere is mainly used as a geographical term for the half of the Earth that lies west of the Prime Meridian and east of the Antimeridian , the other half being called the Eastern Hemisphere.In this sense, the western hemisphere consists of the western portions...

 where the water is usually warmer than 70 °F (21 °C). It ranges from New England
New England
New England is a region in the northeastern corner of the United States consisting of the six states of Maine, New Hampshire, Vermont, Massachusetts, Rhode Island, and Connecticut...

, where it is rare, to the Gulf of Mexico
Gulf of Mexico
The Gulf of Mexico is a partially landlocked ocean basin largely surrounded by the North American continent and the island of Cuba. It is bounded on the northeast, north and northwest by the Gulf Coast of the United States, on the southwest and south by Mexico, and on the southeast by Cuba. In...

 and Brazil
Brazil , officially the Federative Republic of Brazil , is the largest country in South America. It is the world's fifth largest country, both by geographical area and by population with over 192 million people...

, and from southern California
California is a state located on the West Coast of the United States. It is by far the most populous U.S. state, and the third-largest by land area...

 to Ecuador
Ecuador , officially the Republic of Ecuador is a representative democratic republic in South America, bordered by Colombia on the north, Peru on the east and south, and by the Pacific Ocean to the west. It is one of only two countries in South America, along with Chile, that do not have a border...

. During the summer it is common in the inshore waters of the Carolinas
The Carolinas
The Carolinas is a term used in the United States to refer collectively to the states of North and South Carolina. Together, the two states + have a population of 13,942,126. "Carolina" would be the fifth most populous state behind California, Texas, New York, and Florida...

 and Georgia
Georgia (U.S. state)
Georgia is a state located in the southeastern United States. It was established in 1732, the last of the original Thirteen Colonies. The state is named after King George II of Great Britain. Georgia was the fourth state to ratify the United States Constitution, on January 2, 1788...

; in spring, summer, and fall, it is found off Florida
Florida is a state in the southeastern United States, located on the nation's Atlantic and Gulf coasts. It is bordered to the west by the Gulf of Mexico, to the north by Alabama and Georgia and to the east by the Atlantic Ocean. With a population of 18,801,310 as measured by the 2010 census, it...

 and in the Gulf of Mexico
Gulf of Mexico
The Gulf of Mexico is a partially landlocked ocean basin largely surrounded by the North American continent and the island of Cuba. It is bounded on the northeast, north and northwest by the Gulf Coast of the United States, on the southwest and south by Mexico, and on the southeast by Cuba. In...

. In the winter, the bonnethead shark is found closer to the equator
An equator is the intersection of a sphere's surface with the plane perpendicular to the sphere's axis of rotation and containing the sphere's center of mass....

, where the water is warmer.


The bonnethead shark is an active tropical shark that swims in small groups of 5 to 15 individuals. Curiously however, schools of hundreds or even thousands have been reported. Bonnethead sharks move constantly following changes in water temperature and to maintain respiration. The bonnethead shark will sink if it does not keep moving since hammerhead sharks are among the most negatively buoyant of marine
Marine (ocean)
Marine is an umbrella term. As an adjective it is usually applicable to things relating to the sea or ocean, such as marine biology, marine ecology and marine geology...

Vertebrates are animals that are members of the subphylum Vertebrata . Vertebrates are the largest group of chordates, with currently about 58,000 species described. Vertebrates include the jawless fishes, bony fishes, sharks and rays, amphibians, reptiles, mammals, and birds...

s. The bonnethead shark uses a special body fluid, called "cerebrospinal fluid
Cerebrospinal fluid
Cerebrospinal fluid , Liquor cerebrospinalis, is a clear, colorless, bodily fluid, that occupies the subarachnoid space and the ventricular system around and inside the brain and spinal cord...

" or "Cl-excess", to let others know it is nearby. It also utilizes an electric-field sensing system similar to radar
Radar is an object-detection system which uses radio waves to determine the range, altitude, direction, or speed of objects. It can be used to detect aircraft, ships, spacecraft, guided missiles, motor vehicles, weather formations, and terrain. The radar dish or antenna transmits pulses of radio...

. This system allows the bonnethead shark to position itself for biting prey within a few feet where its eyes are least able to assist. This shark is not dangerous to humans.


It feeds primarily on crustacean
Crustaceans form a very large group of arthropods, usually treated as a subphylum, which includes such familiar animals as crabs, lobsters, crayfish, shrimp, krill and barnacles. The 50,000 described species range in size from Stygotantulus stocki at , to the Japanese spider crab with a leg span...

s, consisting mostly of blue crabs, but also shrimp
Shrimp are swimming, decapod crustaceans classified in the infraorder Caridea, found widely around the world in both fresh and salt water. Adult shrimp are filter feeding benthic animals living close to the bottom. They can live in schools and can swim rapidly backwards. Shrimp are an important...

, mollusks and small fish. Seagrass
Seagrasses are flowering plants from one of four plant families , all in the order Alismatales , which grow in marine, fully saline environments.-Ecology:...

es have been found in its stomach contents. Their feeding behavior involves swimming across the seafloor, moving its head in arc patterns like a metal detector, looking for minute electro-magnetic disturbances produced by crabs and other creatures hiding in the sediment. Upon discovery, they sharply turn around and bite into the sediment where the disturbance was detected. If a crab is caught, the bonnethead shark uses its teeth to grind its carapace
A carapace is a dorsal section of the exoskeleton or shell in a number of animal groups, including arthropods such as crustaceans and arachnids, as well as vertebrates such as turtles and tortoises. In turtles and tortoises, the underside is called the plastron.-Crustaceans:In crustaceans, the...

 and then uses suction in order to swallow the crab whole.

To accommodate the many types of animals that it feeds on, the bonnethead shark has small, sharp teeth in the front of the mouth (for grabbing soft prey) and flat, broad molar
Molar (tooth)
Molars are the rearmost and most complicated kind of tooth in most mammals. In many mammals they grind food; hence the Latin name mola, "millstone"....

s in the back (for crushing hard-shelled prey).


The bonnethead shark is viviparous, which means females produce eggs that are retained and nourished in the reproductive system until the young are mature enough to be released to the outside. They reach sexual maturity at about 30 inches. Four to twelve pups are born in late summer and early fall, measuring 12 to 13 inches (330.2 mm).

Researchers from Queen's University Belfast and the Southeastern University (Florida), have recently shown that a bonnethead female produced a pup by parthenogenesis
Parthenogenesis is a form of asexual reproduction found in females, where growth and development of embryos occur without fertilization by a male...

 in 2001. The birth took place at the Henry Doorly Zoo
Henry Doorly Zoo
The Omaha's Henry Doorly Zoo is a zoo in Omaha, Nebraska, located at 3701 South 10th Street.It is accredited by the Association of Zoos and Aquariums and a member of the World Association of Zoos and Aquariums. Its mission is conservation, research, recreation, and education.Omaha's Henry Doorly...

 in Nebraska and subsequent DNA analysis has shown a perfect match between mother and pup.

Sexual dimorphism

Bonnethead sharks are the only sharks known to exhibit sexual dimorphism
Sexual dimorphism
Sexual dimorphism is a phenotypic difference between males and females of the same species. Examples of such differences include differences in morphology, ornamentation, and behavior.-Examples:-Ornamentation / coloration:...

; that is, male and female adults look different from one another. In morphology, adult female bonnethead sharks have a broadly rounded head, whereas males possess a distinct bulge along the anterior margin of the cephalofoil. This bulge is formed by the elongation of the rostral cartilages of the males at the onset of sexual maturity and corresponds temporally with the elongation of the clasper cartilages.

Purpose of the hammer

The reasons for cephalofoil has caused scientific debate for more than a decade. Whatever the ultimate purpose, a wing shaped cephalofoil allows hammerhead sharks to swim on a horizontal plane and was thought to give them the ability to execute sharp turns. However, research shows that it is the vertebrae that help them execute sharp turns. The cephalofoil is responsible for better electroreception (using ampullae of Lorenzini
Ampullae of Lorenzini
The ampullae of Lorenzini are special sensing organs called electroreceptors, forming a network of jelly-filled pores. They are mostly discussed as being found in cartilaginous fishes ; however, they are also reported to be found in Chondrostei such as Reedfish and sturgeon. Lungfish have also been...

) and heightened olfactory acuity.

Pectoral fins and swimming

The pectoral fins on most fish control pitching (up-and-down motion of the body), yawing (the side-to-side motion) and rolling. Most hammerhead sharks do not yaw or roll and achieve pitch by using their cephalofoil. The smaller cephalofoil of a bonnethead shark is not as successful and they therefore have to rely on the combination of cephalofoil and their large pectoral fins for most of their motility. Compared to other hammerheads, bonnethead sharks have larger and more developed pectoral fins and are the only species of hammerhead to actively use pectoral fins for swimming.


Using data from mtDNA analysis, scientist have found that evolution of hammerhead sharks has probably begun with a taxon that had a highly pronounced cephalofoil (most likely that similar to the winghead shark
Winghead shark
The winghead shark is a species of hammerhead shark, family Sphyrnidae, named for the remarkably wide lobes on its head. It is the sole species in the genus Eusphyra...

, Eusphyra blochii), and has later been modified through selective pressures. It is thus assumed today that, judging by their smaller cephalofoil, bonnethead sharks are the more recent developments of a 25 million year evolutionary process.
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