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Portal:Sharks

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Introduction


Clockwise from top left: spiny dogfish, Japanese sawshark, whale shark, great white shark, horn shark, frilled shark, scalloped hammerhead and Australian angelshark representing the orders Squaliformes, Pristiophoriformes, Orectolobiformes, Lamniformes, Heterodontiformes, Hexanchiformes, Carcharhiniformes and Squatiniformes respectively.

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 rays. However, the term "shark" has also been used for extinct members of the subclass Elasmobranchii outside the Selachimorpha, such as Cladoselache and Xenacanthus, as well as other Chondrichthyes such as the holocephalid eugenedontidans.

Under this broader definition, the earliest known sharks date back to more than 420 million years ago. Acanthodians are often referred to as "spiny sharks"; though they are not part of Chondrichthyes proper, they are a paraphyletic assemblage leading to cartilaginous fish as a whole. Since then, sharks have diversified into over 500 species. They range in size from the small dwarf lanternshark (Etmopterus perryi), a deep sea species of 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. Sharks are found in all seas and are common to depths of 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 survive and 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.

Well-known species such as the great white shark, tiger shark, blue shark, mako shark, thresher shark, and hammerhead shark are apex predators—organisms at the top of their underwater food chain. Many shark populations are threatened by human activities.

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A caught crocodile shark with a ruler for size comparison
The crocodile shark, Pseudocarcharias kamoharai, is a species of shark found worldwide in tropical waters. It is the only member of the family Pseudocarcharidae. The crocodile shark is the smallest living mackerel shark, measuring only 1 m (3 ft) long, and can be distinguished by its elongated body, extremely large eyes, and relatively small fins. It is a specialized inhabitant of the open ocean, feeding on pelagic fishes and invertebrates. The size and structure of its eyes indicates that it is adapted for hunting at night. The crocodile shark is ovoviviparous and typically gives birth to litters of four. The fetuses are oophagous, meaning that they feed on eggs produced by the mother. Due to its small size, the crocodile shark is of little commercial importance. However, it is caught in substantial numbers as bycatch, leading it to be assessed as Near Threatened by the World Conservation Union. This species was responsible for damaging deep sea fiberoptic cables when the technology was first deployed in 1985.

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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
Basking shark · Blue shark · Bull shark · Great hammerhead · Great white shark · Grey reef shark · Hammerhead shark · Megalodon · Megamouth shark · Nurse shark · Oceanic whitetip shark · Requiem shark · Scalloped hammerhead · Shortfin mako shark · Swellshark · Thresher shark · Tiger shark · Whale shark


Shark biology
Ampullae of Lorenzini · Mermaid's purses · Physical characteristics of sharks · Shark teeth · Shark threat display


Shark-human interaction
Attack (drum lines, International Shark Attack File, Jersey Shore shark attacks of 1916, list of fatal, unprovoked shark attacks in the United States, shark net, shark proof cage, shark suit, Summer of the Shark· Captivity (shark tunnel· Conservation (grey nurse shark conservation, Shark Alliance, Shark Conservation Act, Shark Trust· Fishing (International Land-Based Shark Fishing Association, land-based shark fishing· Products (shark cartilage, shark finning, shark fin soup, shark liver oil)

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