Portal:Sharks

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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 bigeye thresher, Alopias superciliosus, is a species of thresher shark, family Alopiidae, found in temperate and tropical oceans worldwide. Like other thresher sharks, nearly half its total length consists of the elongated upper lobe of the tail fin. Its common name comes from its enormous eyes, which are placed in keyhole-shaped sockets that allow them to be rotated upward. This species can also be distinguished by a pair of deep grooves on the top of its head, from which its scientific name is derived.

The large eyes of the bigeye thresher are adapted for hunting in low light conditions. It is one of the few sharks that conduct a diel vertical migration, staying in deep water during the day and moving into surface waters at night to feed. To protect its sensitive brain and eyes from the temperature changes accompanying these movements, the bigeye thresher has a vascular exchange system called the rete mirabile around those organs. This species feeds mainly on fish and squid, which are stunned via whip-like strikes of the long tail. Bigeye threshers are ovoviviparous, usually bearing litters of two pups. The embryos are oophagous and feed on ova produced by the mother while inside the uterus. This shark is caught by commercial fisheries across its range; the meat is not highly regarded but the skin, fins, and liver oil are valued. It has been assessed as Vulnerable by the International Union for Conservation of Nature (IUCN).

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Did you know (auto-generated)

... 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 Hixxy and Sharkey created a schism in the UK rave music scene in 1995?
... that "the Hurricane Shark is real"?
... that the ampullae of Lorenzini enable sharks to sense electric fields?
... that Alexis Sharkey's last Instagram post before her murder documented her travels to Tulum, Mexico?
... that since 2018, IKEA's stuffed toy shark Blåhaj has become a popular Internet meme and an icon of the online transgender community?

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Credit: John Singleton Copley

Watson and the Shark, a 1778 oil-on-canvas painting by John Singleton Copley, depicts the rescue of Brook Watson from a shark attack in Havana, Cuba.

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... that the milk shark is so named because of a belief in India that eating its meat improves lactation?
... that the silky shark is the most common source of ornamental shark jaws sold to tourists in the tropics?
... that the southern African frilled shark preys mainly on smaller sharks, which it swallows whole with its greatly distensible mouth?
... that more than 90 percent of the night sharks caught off northeastern Brazil contain mercury concentrations higher than that considered safe by the local government?
... that the largetooth cookiecutter shark has the largest teeth relative to its body of any living shark?

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General images

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

Image 1Clear agonistic behaviour observed in Great White Shark (from Shark agonistic display)
Image 2A 14-foot (4.3 m), 1,200-pound (540 kg) tiger shark caught in Kāne'ohe Bay, Oahu, in 1966
Image 3White shark cage diving near Gansbaai in South Africa (2015) (from Shark cage diving)
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 5Great 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 6The gill slits of a whale shark flaring as it expels water from its pharyngeal cavity. (from Shark anatomy)
Image 7The 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 8The major features of sharks (from Shark anatomy)
Image 9Sharks swimming outside shark-proof cage with people inside (from Shark cage diving)
Image 10Anti-cull protesters on Perth's Cottesloe Beach in Western Australia in 2014 (from Shark culling)
Image 11Distribution of highly sensitive ampullae of Lorenzini across the shark's head and rostrum. (from Shark agonistic display)
Image 12A ventral dissection of a pregnant female dogshark exposing its internal gill slits and internal spiracles. (from Shark anatomy)
Image 13Placoid Scale (from Shark anatomy)
Image 14This grey reef shark demonstrates countershading, with its darker dorsal surface and lighter ventral surface. (from Shark anatomy)
Image 15A dissected view of the unique four-chambered heart of the sharkChambers: Sinus Venosus, Atrium, Ventricle, Conus Ateriosus (from Shark anatomy)
Image 16A sign at Pyramid Rock Beach in Hawaii warning about a shark sighting, 2015 (from Shark tourism)
Image 17Postural configuration of a Gray Reef Shark as it displays agonistic behaviour, in a sculpture (from Shark agonistic display)
Image 18BranchiostomaLanceolatum PioM (from Shark anatomy)
Image 19Shark Anatomy (50693674756) (from Shark anatomy)
Image 20Postural elements of the agonistic display of the Gray Reef Shark (from Shark agonistic display)
Image 21Great white shark cages at Isla Guadalupe, Mexico (from Shark cage diving)
Image 22Dorsal fin diagram with landmarks labeled. (from Shark anatomy)
Image 23Sharksucker (Echeneis naucrates) (from Shark agonistic display)
Image 24Shark cage diving (from Shark tourism)
Image 25Depiction of shark anatomy including eggs, pups, and the liver (from Shark anatomy)
Image 26Lateral and cross section view of shark's red and white locomotor muscles (from Shark anatomy)

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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