Portal:Sharks

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Sharks are a group of elasmobranch cartilaginous fish 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 (or Selachimorpha) and are the sister group to the Batoidea (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 (selachimorphs) 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) 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 and hammerhead sharks. Some sharks are filter-feeding planktivores, such as the whale shark and basking shark, which are among the largest fish ever lived. (Full article...)

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The megalodon (/ˈmɛɡələdɒn/ MEG-ə-lə-don; from Greek: μέγας ὀδούς, "big tooth"), Carcharodon megalodon or Carcharocles megalodon (in dispute), was a giant shark that lived in prehistoric times. The oldest remains of this species found are about 18 million years old and C. megalodon became extinct in the Pleistocene epoch probably about 1.5 million years ago. It was the apex predator of its time and is the largest carnivorous fish known to have existed.

C. megalodon could grow more than 18 metres (59 ft) long and is also quite possibly the largest shark ever to exist. From scrutiny of its remains, scientists conclude that C. megalodon belongs to the order Lamniformes. However, scientists are still debating which genus would be most appropriate for C. megalodon from the two proposed. Fossil evidence has revealed that megalodon fed upon large marine animals.

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Credit: Citron

The frilled shark (Chlamydoselachus anguineus) is one of two extant species of shark in the family Chlamydoselachidae, with a wide but patchy distribution in the Atlantic and Pacific Oceans.

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... that the velvet belly lantern shark has proteins in its liver that can detoxify heavy metals such as cadmium, copper, mercury, and zinc?
... that at night, the Pacific angelshark may use bioluminescent plankton to target its prey?
... that the Galapagos shark is often the most abundant shark around oceanic islands?
... that the blotched catshark exhibits fluorescence, with spots that glow yellow under blue light?
... that the grey reef shark is the first shark species known to perform a threat display to warn off divers who are too close?

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General images

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

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