Portal:Sharks

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Sharks are a group of elasmobranch cartilaginous fishes characterized by a ribless endoskeleton, dermal denticles, five to seven gill slits on each side, and pectoral fins that are not fused to the head. Modern sharks are classified within the division Selachii and are the sister group to the Batomorphi (rays and skates). 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 earliest confirmed modern sharks (Selachii) are known from the Early Jurassic around 200 million years ago, with the oldest known member being Agaleus, 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) to 18.8 metres (62 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 sharks, which can be found in both seawater and freshwater, and the Ganges shark, which lives only in freshwater. Sharks have a covering of placoid scales (denticles) that protects the skin from damage and parasites in addition to improving their fluid dynamics. They have numerous sets of replaceable teeth.

Several shark species are apex predators, which are organisms that are at the top of their food chain with select examples including the bull shark, tiger shark, great white shark, mako sharks, thresher sharks, greenland sharks and hammerhead sharks. Some sharks are filter-feeding planktivores, such as the whale shark and basking shark, which are among the largest fish that ever lived. (Full article...)

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The smooth hammerhead, Sphyrna zygaena, is a species of hammerhead shark, family Sphyrnidae, so named because of the distinctive shape of the head, which is flattened and laterally extended into a hammer shape (called the "cephalofoil"), without an indentation in the middle of the front margin (hence "smooth"). Unlike other hammerheads, this species prefers temperate waters and occurs worldwide at medium latitudes. In the summer, these sharks migrate towards the poles following cool water masses, sometimes forming schools numbering in the hundreds to thousands.

The second-largest hammerhead shark, the smooth hammerhead can measure up to 5 m (16 ft) long. It is an active predator that takes a wide variety of bony fishes and invertebrates, with larger individuals also feeding on sharks and rays. As in the rest of its family, this shark is viviparous and gives birth to litters of 20–40 pups. A relatively common shark, it is captured, intentionally or otherwise, by many commercial fisheries throughout its range; its fins are extremely valuable for use in shark fin soup. This shark is potentially dangerous and has likely been responsible for a few attacks on humans, though it is less likely to encounter swimmers than other large hammerhead species due to its temperate habitat.

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Did you know (auto-generated)

... that Shark Tank was adapted from a Japanese show that aimed to encourage entrepreneurship during a lengthy period of economic stagnation in the Japanese economy?
... that, during Real Madrid's 1927 tour of the Americas, José María Muñagorri nearly jumped into shark-infested waters to rescue a teammate?
... that a shark cost a competitor a silver medal in the spearfishing event at the 2014 Micronesian Games?
... that shark fin is one of the "four sea delicacies", a quartet of luxury seafoods in Chinese cuisine?
... that the shark god Kāneikokala, according to Hawaiian tradition, rescued shipwrecked sailors and returned them to their home islands?
... that the parasitic copepod Driocephalus cerebrinoxius burrows into the brains of sharks through their noses?

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Credit: Didier Descouens

The jaw of a shortfin mako shark. The species feeds mainly upon cephalopods, bony fishes including mackerel, tuna, bonito, and swordfish, but it may also eat other sharks, porpoises, sea turtles, and seabirds.

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... that no more than 250 mature northern river sharks are estimated to live in the wild?
... that the closure of the Tethys Sea 10–14 million years ago led to the sicklefin lemon shark and the lemon shark becoming separate species?
... that the spined pygmy shark, dwarf lanternshark and pygmy ribbontail catshark are candidates for being the smallest shark in the world, all maturing at under 20 cm (8 in) long?
... that most attacks on humans by the blacktip reef shark consist of people being bitten on their legs or feet while wading in shallow water?
... that the egg capsule of the crested bullhead shark has paired tendrils extending up to 2 m (6.6 ft), greater than the length of the adult shark?

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General images

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

Image 1Distribution of highly sensitive ampullae of Lorenzini across the shark's head and rostrum. (from Shark agonistic display)
Image 2Placoid Scale (from Shark anatomy)
Image 3A sign at Pyramid Rock Beach in Hawaii warning about a shark sighting, 2015 (from Shark tourism)
Image 4Shark cage diving (from Shark tourism)
Image 5Depiction of shark anatomy including eggs, pups, and the liver (from Shark anatomy)
Image 6The major features of sharks (from Shark anatomy)
Image 7Postural elements of the agonistic display of the Gray Reef Shark (from Shark agonistic display)
Image 8A 14-foot (4.3 m), 1,200-pound (540 kg) tiger shark caught in Kāne'ohe Bay, Oahu, in 1966
Image 9In this drawing, there is a diagram of the placement of shark organs. From this model, we can see and distinguish the placement of organs compared with other species. EX. The testes of a shark are located on the ventral plane, near the fins, while a human's testes are located further down, near the bladder. (from Shark anatomy)
Image 10Anti-cull protesters on Perth's Cottesloe Beach in Western Australia in 2014 (from Shark culling)
Image 11The gill slits of a whale shark flaring as it expels water from its pharyngeal cavity. (from Shark anatomy)
Image 12A ventral dissection of a pregnant female dogshark exposing its internal gill slits and internal spiracles. (from Shark anatomy)
Image 13Great white shark cages at Isla Guadalupe, Mexico (from Shark cage diving)
Image 14Sharksucker (Echeneis naucrates) (from Shark agonistic display)
Image 15In 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 16Shark Anatomy (50693674756) (from Shark anatomy)
Image 17Clear agonistic behaviour observed in Great White Shark (from Shark agonistic display)
Image 18White shark cage diving near Gansbaai in South Africa (2015) (from Shark cage diving)
Image 19The 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 20Branchiostoma lanceolatum (from Shark anatomy)
Image 21Postural configuration of a Gray Reef Shark as it displays agonistic behaviour, in a sculpture (from Shark agonistic display)
Image 22Dorsal fin diagram with landmarks labeled. (from Shark anatomy)
Image 23Lateral and cross section view of shark's red and white locomotor muscles (from Shark anatomy)
Image 24Great 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 25This grey reef shark demonstrates countershading, with its darker dorsal surface and lighter ventral surface. (from Shark anatomy)
Image 26Sharks swimming outside shark-proof cage with people inside (from Shark cage diving)
Image 27A dissected view of the unique four-chambered heart of the sharkChambers: Sinus Venosus, Atrium, Ventricle, Conus Ateriosus (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