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 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 "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 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 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: Matthew Field

The leopard shark is a species of houndshark found along the Pacific coast of North America from the U.S. state of Oregon to Mazatlán in Mexico.

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... that the whitefin dogfish has light-producing organs on its upper eyelids?
... that the spinner shark is named for the spinning leaps it makes out of the water as part of its feeding strategy?
...that John Singleton Copley's painting, Watson and the Shark, was based on a real-life shark attack that occurred in Havana, Cuba in 1749?
... that, like the related cookiecutter shark, the kitefin shark sometimes feeds by taking bites out of animals larger than itself?
... that the first successful artificial insemination of a shark was performed in the cloudy catshark?

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General images

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

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

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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