Major General James G. Blunt

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Sharks are a group of elasmobranch fish characterized by a cartilaginous skeleton, five to seven gill slits on the sides of the head, and pectoral fins that are not fused to the head. Modern sharks are classified within the clade Selachimorpha (or Selachii) and are the sister group to the Batoidea (rays and kin). Some sources extend the term "shark" as an informal category including extinct members of Chondrichthyes (cartilaginous fish) with a shark-like morphology, such as hybodonts. Shark-like chondrichthyans such as Cladoselache and Doliodus first appeared in the Devonian Period (419–359 million years), though some fossilized chondrichthyan-like scales are as old as the Late Ordovician (458–444 million years ago). The oldest confirmed modern sharks (selachimorphs) are known from the Early Jurassic, about 200 million years ago, though records of true sharks may extend back as far as the Permian.

Sharks range in size from the small dwarf lanternshark (Etmopterus perryi), a deep sea species that is only 17 centimetres (6.7 in) in length, to the whale shark (Rhincodon typus), the largest fish in the world, which reaches approximately 12 metres (40 ft) in length. They are found in all seas and are common to depths up to 2,000 metres (6,600 ft). They generally do not live in freshwater, although there are a few known exceptions, such as the bull shark and the river shark, which can be found in both seawater and freshwater. Sharks have a covering of dermal denticles that protects their skin from damage and parasites in addition to improving their fluid dynamics. They have numerous sets of replaceable teeth.

Several species are apex predators, which are organisms that are at the top of their food chain. Select examples include the tiger shark, blue shark, great white shark, mako shark, thresher shark, and hammerhead shark. (Full article...)

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The great hammerhead, Sphyrna mokarran, is the largest of the hammerhead sharks (family Sphyrnidae), attaining a maximum length of 6.1 m (20 ft). It is found in tropical and warm temperate waters worldwide, inhabiting coastal areas and the continental shelf. The great hammerhead can be distinguished from other hammerheads by the shape of its "hammer" (called the "cephalofoil"), which is wide with an almost straight front margin, and by its tall, sickle-shaped first dorsal fin. A solitary, strong-swimming apex predator, the great hammerhead feeds on a wide variety of prey ranging from crustaceans and cephalopods, to bony fishes, to smaller sharks. Observations of this species in the wild suggest that the cephalofoil functions to immobilize stingrays, a favored prey. This species has a viviparous mode of reproduction, bearing litters of up to 55 pups every two years.

Although potentially dangerous, the great hammerhead rarely attacks humans. It sometimes behaves inquisitively toward divers and should be treated with respect. This shark is heavily fished for its large fins, which are extremely valuable on the Asian market as the main ingredient of shark fin soup. As a result, great hammerhead populations are declining substantially worldwide, and it has been assessed as Endangered by the World Conservation Union.

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Did you know (auto-generated)

... that since 2018, IKEA's stuffed toy shark Blåhaj has become a popular Internet meme and an icon of the online transgender community?
... that the ampullae of Lorenzini enable sharks to sense electric fields?
... that Timo Meier became the first player in San Jose Sharks franchise history to score five goals in one game when he was 25?
... that "the Hurricane Shark is real"?
... that Alexis Sharkey's last Instagram post before her murder documented her travels to Tulum, Mexico?
... that Hixxy and Sharkey created a schism in the UK rave music scene in 1995?

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WikiProjects

WikiProjects related to sharks:

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Credit: Luc Viatour

The blacktip reef shark is a species of requiem shark, family Carcharhinidae, easily identified by the prominent black tips on its fins. It is among the most abundant sharks inhabiting the tropical coral reefs of the Indian and Pacific Oceans, and prefers shallow, inshore waters.

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... that the spadenose shark exhibits the most advanced form of placental reproduction in fishes?
... that the dark, puffadder, brown, and Natal shysharks of South Africa are so named because they curl into a ring when threatened and "shyly" cover their eyes with their tails?
... that the daggernose shark can adjust the timing of events in its reproductive cycle by several months?
... that the lollipop catshark is shaped like a tadpole and has an almost gelatinous body?
... that the Australian swellshark can survive out of water for more than a day?

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General images

The following are images from various shark-related articles on Wikipedia.

Image 1Great white shark cages at Isla Guadalupe, Mexico (from Shark cage diving)
Image 2Lateral and cross section view of shark's red and white locomotor muscles (from Shark anatomy)
Image 3Distribution of highly sensitive ampullae of Lorenzini across the shark's head and rostrum. (from Shark agonistic display)
Image 4In a milestone decision in 2013, CITES prohibited international trade in the fins of the scalloped hammerhead (pictured) and four other shark species. (from List of threatened sharks)
Image 5A 14-foot (4.3 m), 1,200-pound (540 kg) tiger shark caught in Kāne'ohe Bay, Oahu, in 1966
Image 6Anti-cull protesters on Perth's Cottesloe Beach in Western Australia in 2014 (from Shark culling)
Image 7Shark cage diving (from Shark tourism)
Image 8The major features of sharks (from Shark anatomy)
Image 9A ventral dissection of a pregnant female dogshark exposing its internal gill slits and internal spiracles. (from Shark anatomy)
Image 10Placoid Scale (from Shark anatomy)
Image 11BranchiostomaLanceolatum PioM (from Shark anatomy)
Image 12White shark cage diving near Gansbaai in South Africa (2015) (from Shark cage diving)
Image 13This grey reef shark demonstrates countershading, with its darker dorsal surface and lighter ventral surface. (from Shark anatomy)
Image 14Great white shark at Isla Guadalupe, Mexico, August 2006. Animal estimated at 11–12 feet (3.3 to 3.6 m) in length, age unknown. (from Shark tourism)
Image 15The whale shark, the world's largest fish, is classified as Endangered.

Binding legislation and harvest management strategies... are urgently needed to address the disproportionate impact of fisheries on cartilaginous fishes.

– IUCN global study 2010

(from List of threatened sharks)
Image 16Sharksucker (Echeneis naucrates) (from Shark agonistic display)
Image 17Dorsal fin diagram with landmarks labeled. (from Shark anatomy)
Image 18Postural elements of the agonistic display of the Gray Reef Shark (from Shark agonistic display)
Image 19A dissected view of the unique four-chambered heart of the sharkChambers: Sinus Venosus, Atrium, Ventricle, Conus Ateriosus (from Shark anatomy)
Image 20Clear agonistic behaviour observed in Great White Shark (from Shark agonistic display)
Image 21Sharks swimming outside shark-proof cage with people inside (from Shark cage diving)
Image 22A sign at Pyramid Rock Beach in Hawaii warning about a shark sighting, 2015 (from Shark tourism)
Image 23Depiction of shark anatomy including eggs, pups, and the liver (from Shark anatomy)
Image 24Postural configuration of a Gray Reef Shark as it displays agonistic behaviour, in a sculpture (from Shark agonistic display)
Image 25Shark Anatomy (50693674756) (from Shark anatomy)
Image 26The gill slits of a whale shark flaring as it expels water from its pharyngeal cavity. (from Shark anatomy)

Topics

Shark · Outline of sharks

Shark orders

Carcharhiniformes (groundsharks) · Cladoselachiformes (extinct) · Eugeneodontida (extinct) · Heterodontiformes (bullhead sharks) · Hexanchiformes (most primitive sharks) · Hybodontiformes (extinct) · Iniopterygia (extinct) · Lamniformes (mackerel sharks) · Orectolobiformes (carpet sharks and relatives) · Pristiophoriformes (sawsharks and relatives) · Squaliformes (gulper sharks, bramble sharks, lantern sharks, rough sharks, sleeper sharks, dogfish sharks and relatives) · Squatiniformes (angel sharks) · Symmoriida (extinct) · Xenacanthida (also known as Xenacantiformes, extinct)

Major species