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 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 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 bull shark, tiger shark, great white shark, mako sharks, thresher sharks, and hammerhead sharks. (Full article...)
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This aggressive but slow-moving fish dominates feeding frenzies, and is a danger to survivors of oceanic shipwrecks and downed aircraft — it has attacked more humans than all other shark species combined. Recent studies have shown that its numbers are in steep decline as its large fins are highly valued as the chief ingredient of shark fin soup and, as with other shark species, the oceanic whitetip faces mounting pressure from fishing throughout its range.
Did you know (auto-generated)
- ... that Hixxy and Sharkey created a schism in the UK rave music scene in 1995?
- ... that Alexis Sharkey's last Instagram post before her murder documented her travels to Tulum, Mexico?
- ... that the ampullae of Lorenzini enable sharks to sense electric fields?
- ... 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 since 2018, IKEA's stuffed toy shark Blåhaj has become a popular Internet meme and an icon of the online transgender community?
- ... that "the Hurricane Shark is real"?
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Credit: Matthew Field |
More Did you know? - show different entries
- ... 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?
General images
- Image 2Clear agonistic behaviour observed in Great White Shark (from Shark agonistic display)
- Image 3A dissected view of the unique four-chambered heart of the sharkChambers: Sinus Venosus, Atrium, Ventricle, Conus Ateriosus (from Shark anatomy)
- Image 4Distribution of highly sensitive ampullae of Lorenzini across the shark's head and rostrum. (from Shark agonistic display)
- Image 5The gill slits of a whale shark flaring as it expels water from its pharyngeal cavity. (from Shark anatomy)
- Image 6BranchiostomaLanceolatum PioM (from Shark anatomy)
- Image 8Dorsal fin diagram with landmarks labeled. (from Shark anatomy)
- Image 9Sharks swimming outside shark-proof cage with people inside (from Shark cage diving)
- Image 10The 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
- Image 11Postural configuration of a Gray Reef Shark as it displays agonistic behaviour, in a sculpture (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 13In 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 14A sign at Pyramid Rock Beach in Hawaii warning about a shark sighting, 2015 (from Shark tourism)
- Image 15Lateral and cross section view of shark's red and white locomotor muscles (from Shark anatomy)
- Image 16Depiction of shark anatomy including eggs, pups, and the liver (from Shark anatomy)
- Image 17The major features of sharks (from Shark anatomy)
- Image 18This grey reef shark demonstrates countershading, with its darker dorsal surface and lighter ventral surface. (from Shark anatomy)
- Image 19Shark Anatomy (50693674756) (from Shark anatomy)
- Image 20Shark cage diving (from Shark tourism)
- Image 21Anti-cull protesters on Perth's Cottesloe Beach in Western Australia in 2014 (from Shark culling)
- Image 22Sharksucker (Echeneis naucrates) (from Shark agonistic display)
- Image 23Placoid Scale (from Shark anatomy)
- Image 24Postural elements of the agonistic display of the Gray Reef Shark (from Shark agonistic display)
- Image 25Great 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 26Great white shark cages at Isla Guadalupe, Mexico (from Shark cage diving)
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