Shark skeletons are very different from those of bony fish and terrestrial vertebrates. Sharks and other cartilaginous fish (skates and rays) have skeletons made of cartilage and connective tissue.&nbsp;Cartilage is flexible and durable but is about half the normal density of bone.

Do sharks have any bones in their body?

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Sharks are a group of <a href="/wiki/Elasmobranch">elasmobranch </a><a href="/wiki/Fish">fish </a>characterized by a <a href="/wiki/Chondrichthyes#Skeleton">cartilaginous skeleton </a>, five to seven <a href="/wiki/Gill_slit">gill slits </a>on the sides of the <a href="/wiki/Head">head </a>, and <a href="/wiki/Pectoral_fin">pectoral fins </a>that are not fused to the head. Modern sharks are classified within the <a href="/wiki/Clade">clade </a>Selachimorpha (or Selachii ) and are the <a href="/wiki/Sister_group">sister group </a>to the <a href="/wiki/Batoidea">rays </a>. However, the term "shark" has also been used for extinct members of the subclass <a href="/wiki/Elasmobranchii">Elasmobranchii </a>outside the Selachimorpha, such as <a href="/wiki/Cladoselache">Cladoselache </a> and <a href="/wiki/Xenacanthus">Xenacanthus </a> , as well as other <a href="/wiki/Chondrichthyes">Chondrichthyes </a>such as the <a href="/wiki/Holocephalid">holocephalid </a><a href="/wiki/Eugeneodontida">eugenedontidans </a>.

<a href="/wiki/Carcharhiniformes">Carcharhiniformes </a> <a href="/wiki/Bullhead_shark">Heterodontiformes </a> <a href="/wiki/Hexanchiformes">Hexanchiformes </a> <a href="/wiki/Lamniformes">Lamniformes </a> <a href="/wiki/Carpet_shark">Orectolobiformes </a> <a href="/wiki/Sawshark">Pristiophoriformes </a> <a href="/wiki/Squaliformes">Squaliformes </a> <a href="/wiki/Angel_shark">Squatiniformes </a> † <a href="/wiki/Cladoselachiformes">Cladoselachiformes </a> † <a href="/wiki/Hybodontiformes">Hybodontiformes </a> † <a href="/wiki/Xenacanthida">Xenacanthida </a>(Xenacantiformes) <abbr>† </abbr><a href="/wiki/Elegestolepis">Elegestolepis </a>

Under this broader definition, the earliest known sharks date back to more than 420 million years ago.<a href="#cite_note-RQGT-3">[3] </a> <a href="/wiki/Acanthodians">Acanthodians </a>are often referred to as "spiny sharks"; though they are not part of Chondrichthyes proper, they are a paraphyletic assemblage leading to cartilaginous fish as a whole. Since then, sharks have diversified into <a href="/wiki/List_of_sharks">over 500 species </a>. They range in size from the small <a href="/wiki/Dwarf_lanternshark">dwarf lanternshark </a>(Etmopterus perryi ), a deep sea species of only 17 centimetres (6.7 in) in length, to the <a href="/wiki/Whale_shark">whale shark </a>(Rhincodon typus ), the largest fish in the world, which reaches approximately 12 metres (40 ft) in length.<a href="#cite_note-4">[4] </a> Sharks are found in all seas and are common to depths of 2,000 metres (6,600 ft). They generally do not live in freshwater although there are a few known exceptions, such as the <a href="/wiki/Bull_shark">bull shark </a>and the <a href="/wiki/River_shark">river shark </a>, which can be found in both seawater and freshwater.<a href="#cite_note-5">[5] </a> Sharks have a covering of <a href="/wiki/Dermal_denticle">dermal denticles </a>that protects their skin from damage and <a href="/wiki/Parasite">parasites </a>in addition to improving their <a href="/wiki/Fluid_dynamics">fluid dynamics </a>. They have numerous sets of replaceable teeth.<a href="#cite_note-Budker-6">[6] </a>

Well-known species such as the <a href="/wiki/Tiger_shark">tiger shark </a>, <a href="/wiki/Blue_shark">blue shark </a>, <a href="/wiki/Great_white_shark">great white shark </a>, <a href="/wiki/Isurus">mako shark </a>, <a href="/wiki/Thresher_shark">thresher shark </a>, and <a href="/wiki/Hammerhead_shark">hammerhead shark </a>are <a href="/wiki/Apex_predator">apex predators </a>—organisms at the top of their underwater <a href="/wiki/Food_chain">food chain </a>. Many shark populations are threatened by human activities. Since 1970, shark populations have been reduced by 71%, mostly from <a href="/wiki/Overfishing">overfishing </a>.<a href="#cite_note-7">[7] </a>

<ul><li><a href="#Etymology">1 Etymology </a> </li><li><a href="#Evolutionary_history">2 Evolutionary history </a><ul><li><a href="#Taxonomy">2.1 Taxonomy </a> </li> </ul> </li><li><a href="#Anatomy">3 Anatomy </a><ul><li><a href="#Teeth">3.1 Teeth </a> </li><li><a href="#Skeleton">3.2 Skeleton </a> </li><li><a href="#Jaw">3.3 Jaw </a> </li><li><a href="#Fins">3.4 Fins </a> </li><li><a href="#Dermal_denticles">3.5 Dermal denticles </a> </li><li><a href="#Tails">3.6 Tails </a> </li> </ul> </li><li><a href="#Physiology">4 Physiology </a><ul><li><a href="#Buoyancy">4.1 Buoyancy </a> </li><li><a href="#Respiration">4.2 Respiration </a> </li><li><a href="#Thermoregulation">4.3 Thermoregulation </a> </li><li><a href="#Osmoregulation">4.4 Osmoregulation </a> </li><li><a href="#Digestion">4.5 Digestion </a> </li><li><a href="#Fluoresence">4.6 Fluoresence </a> </li> </ul> </li><li><a href="#Senses">5 Senses </a><ul><li><a href="#Smell">5.1 Smell </a> </li><li><a href="#Sight">5.2 Sight </a> </li><li><a href="#Hearing">5.3 Hearing </a> </li><li><a href="#Electroreception">5.4 Electroreception </a> </li><li><a href="#Lateral_line">5.5 Lateral line </a> </li> </ul> </li><li><a href="#Life_history">6 Life history </a><ul><li><a href="#Reproduction">6.1 Reproduction </a><ul><li><a href="#Sexual">6.1.1 Sexual </a> </li><li><a href="#Asexual">6.1.2 Asexual </a> </li> </ul> </li><li><a href="#Brooding">6.2 Brooding </a><ul><li><a href="#Ovoviviparity">6.2.1 Ovoviviparity </a> </li><li><a href="#Oviparity">6.2.2 Oviparity </a> </li><li><a href="#Viviparity">6.2.3 Viviparity </a> </li> </ul> </li> </ul> </li><li><a href="#Behavior">7 Behavior </a><ul><li><a href="#Speed">7.1 Speed </a> </li><li><a href="#Intelligence">7.2 Intelligence </a> </li><li><a href="#Sleep">7.3 Sleep </a> </li> </ul> </li><li><a href="#Ecology">8 Ecology </a><ul><li><a href="#Feeding">8.1 Feeding </a> </li><li><a href="#Range_and_habitat">8.2 Range and habitat </a> </li> </ul> </li><li><a href="#Relationship_with_humans">9 Relationship with humans </a><ul><li><a href="#Attacks">9.1 Attacks </a> </li><li><a href="#In_captivity">9.2 In captivity </a> </li><li><a href="#In_culture">9.3 In culture </a><ul><li><a href="#In_Hawaii">9.3.1 In Hawaii </a> </li><li><a href="#In_American_Samoa">9.3.2 In American Samoa </a> </li><li><a href="#In_popular_culture">9.3.3 In popular culture </a> </li><li><a href="#Popular_misconceptions">9.3.4 Popular misconceptions </a> </li> </ul> </li> </ul> </li><li><a href="#Threats_to_sharks">10 Threats to sharks </a><ul><li><a href="#Fishery">10.1 Fishery </a> </li><li><a href="#Shark_culling">10.2 Shark culling </a> </li><li><a href="#Other_threats">10.3 Other threats </a> </li> </ul> </li><li><a href="#Conservation">11 Conservation </a> </li><li><a href="#See_also">12 See also </a> </li><li><a href="#References">13 References </a> </li><li><a href="#Further_reading">14 Further reading </a> </li> </ul>

Until the 16th century,<a href="#cite_note-8">[8] </a> sharks were known to mariners as "sea dogs".<a href="#cite_note-9">[9] </a> This is still evidential in several species termed "<a href="/wiki/Squalidae">dogfish </a>," or the <a href="/wiki/Porbeagle">porbeagle </a>.

The etymology of the word "shark" is uncertain, the most likely etymology states that the original sense of the word was that of "predator, one who preys on others" from the Dutch schurk , meaning "villain, scoundrel" (cf. card shark , loan shark , etc.), which was later applied to the fish due to its predatory behaviour.<a href="#cite_note-10">[10] </a>

A now disproven[<a href="/wiki/Wikipedia:No_original_research">original research? </a> ] theory is that it derives from the <a href="/wiki/Yucatec_Maya_language">Yucatec Maya </a>word xok (pronounced 'shok'), meaning "fish".<a href="#cite_note-11">[11] </a> Evidence for this etymology came from the <a href="/wiki/Oxford_English_Dictionary">Oxford English Dictionary </a>, which notes shark first came into use after Sir <a href="/wiki/John_Hawkins_(naval_commander)">John Hawkins </a>' sailors exhibited one in London in 1569 and posted "sharke " to refer to the large sharks of the <a href="/wiki/Caribbean_Sea">Caribbean Sea </a>. However, the <a href="/wiki/Middle_English_Dictionary">Middle English Dictionary </a>records an isolated occurrence of the word shark (referring to a sea fish) in a letter written by <a href="/wiki/Thomas_Beckington">Thomas Beckington </a>in 1442, which rules out a New World etymology.<a href="#cite_note-12">[12] </a> [<a href="/wiki/Wikipedia:No_original_research">original research? </a> ]

Evidence for the existence of sharks dates from the <a href="/wiki/Ordovician">Ordovician </a>period, 450–420 million years ago, before land <a href="/wiki/Vertebrates">vertebrates </a>existed and before a variety of plants had colonized the continents.<a href="#cite_note-RQGT-3">[3] </a> Only scales have been recovered from the first sharks and not all paleontologists agree that these are from true sharks, suspecting that these scales are actually those of <a href="/wiki/Thelodont">thelodont </a>agnathans.<a href="#cite_note-RQES-13">[13] </a> The oldest generally accepted shark scales are from about 420 million years ago, in the <a href="/wiki/Silurian">Silurian </a>period.<a href="#cite_note-RQES-13">[13] </a> The first sharks looked very different from modern sharks.<a href="#cite_note-RQA-14">[14] </a> At this time the most common shark tooth is the <a href="/wiki/Cladodont">cladodont </a>, a style of thin tooth with three tines like a trident, apparently to help catch fish. The majority of modern sharks can be traced back to around 100 million years ago.<a href="#cite_note-RQMS-15">[15] </a> Most fossils are of teeth, often in large numbers. Partial skeletons and even complete fossilized remains have been discovered. Estimates suggest that sharks grow tens of thousands of teeth over a lifetime, which explains the abundant fossils. The teeth consist of easily fossilized <a href="/wiki/Calcium_phosphate">calcium phosphate </a>, an <a href="/wiki/Apatite">apatite </a>. When a shark dies, the decomposing skeleton breaks up, scattering the apatite prisms. Preservation requires rapid burial in bottom sediments.

Among the most ancient and primitive sharks is <a href="/wiki/Cladoselache">Cladoselache </a> , from about 370 million years ago,<a href="#cite_note-RQA-14">[14] </a> which has been found within <a href="/wiki/Paleozoic">Paleozoic </a>strata in Ohio, Kentucky, and Tennessee. At that point in Earth's history these rocks made up the soft bottom sediments of a large, shallow ocean, which stretched across much of North America. Cladoselache was only about 1 metre (3.3 ft) long with stiff triangular fins and slender jaws.<a href="#cite_note-RQA-14">[14] </a> Its teeth had several pointed cusps, which wore down from use. From the small number of teeth found together, it is most likely that Cladoselache did not replace its teeth as regularly as modern sharks. Its caudal fins had a similar shape to the <a href="/wiki/Great_white_shark">great white sharks </a>and the pelagic <a href="/wiki/Shortfin_mako_shark">shortfin </a>and <a href="/wiki/Longfin_mako_shark">longfin makos </a>. The presence of whole fish arranged tail-first in their stomachs suggest that they were fast swimmers with great agility.

Most fossil sharks from about 300 to 150 million years ago can be assigned to one of two groups. The <a href="/wiki/Xenacanthida">Xenacanthida </a>was almost exclusive to freshwater environments.<a href="#cite_note-16">[16] </a> <a href="#cite_note-17">[17] </a> By the time this group became extinct about 220 million years ago, they had spread worldwide. The other group, the <a href="/wiki/Hybodontiformes">hybodonts </a>, appeared about 320 million years ago and lived mostly in the oceans, but also in freshwater.[<a href="/wiki/Wikipedia:Citation_needed">citation needed </a> ] The results of a 2014 study of the gill structure of an unusually well preserved 325-million-year-old fossil suggested that sharks are not "living fossils", but rather have evolved more extensively than previously thought over the hundreds of millions of years they have been around.<a href="#cite_note-18">[18] </a>

Modern sharks began to appear about 100 million years ago.<a href="#cite_note-RQMS-15">[15] </a> Fossil <a href="/wiki/Mackerel_shark">mackerel shark </a>teeth date to the <a href="/wiki/Early_Cretaceous">Early Cretaceous </a>. One of the most recently evolved families is the hammerhead shark (family Sphyrnidae), which emerged in the <a href="/wiki/Eocene">Eocene </a>.<a href="#cite_note-19">[19] </a> The oldest white shark teeth date from 60 to 66 million years ago, around the time of the <a href="/wiki/Cretaceous%E2%80%93Paleogene_extinction_event">extinction of the dinosaurs </a>. In early white shark evolution there are at least two lineages: one lineage is of white sharks with coarsely <a href="/wiki/Shark_teeth">serrated </a>teeth and it probably gave rise to the modern great white shark, and another lineage is of white sharks with finely serrated teeth. These sharks attained gigantic proportions and include the extinct megatoothed shark, <a href="/wiki/Megalodon">C. megalodon </a> . Like most extinct sharks, C. megalodon is also primarily known from its fossil teeth and vertebrae. This giant shark reached a total length (TL) of more than 16 metres (52 ft).<a href="#cite_note-20">[20] </a> <a href="#cite_note-AN-21">[21] </a> C. megalodon may have approached a maxima of 20.3 metres (67 ft) in total length and 103 <a href="/wiki/Tonne">metric tons </a>(114 <a href="/wiki/Short_ton">short tons </a>) in mass.<a href="#cite_note-bite-22">[22] </a> Paleontological evidence suggests that this shark was an active predator of large <a href="/wiki/Cetaceans">cetaceans </a>.<a href="#cite_note-bite-22">[22] </a>

Sharks belong to the <a href="/wiki/Superorder_(biology)">superorder </a>Selachimorpha in the <a href="/wiki/Subclass_(biology)">subclass </a><a href="/wiki/Elasmobranchii">Elasmobranchii </a>in the <a href="/wiki/Class_(biology)">class </a><a href="/wiki/Chondrichthyes">Chondrichthyes </a>. The Elasmobranchii also include <a href="/wiki/Batoidea">rays </a>and <a href="/wiki/Skate_(fish)">skates </a>; the Chondrichthyes also include <a href="/wiki/Chimaera">Chimaeras </a>. It was thought that the sharks form a <a href="/wiki/Polyphyly">polyphyletic </a>group: some sharks are more closely related to rays than they are to some other sharks,<a href="#cite_note-Taxonomy-23">[23] </a> but current molecular studies support monophyly of both groups of sharks and batoids.<a href="#cite_note-MolBiol2014Jan-24">[24] </a> <a href="#cite_note-MitoDNA2017Sep-25">[25] </a>

The superorder Selachimorpha is divided into Galea (or <a href="/wiki/Galeomorphii">Galeomorphii </a>), and Squalea (or <a href="/wiki/Squalomorphii">Squalomorphii </a>). The Galeans are the <a href="/wiki/Bullhead_shark">Heterodontiformes </a>, <a href="/wiki/Carpet_shark">Orectolobiformes </a>, <a href="/wiki/Lamniformes">Lamniformes </a>, and <a href="/wiki/Carcharhiniformes">Carcharhiniformes </a>. Lamnoids and Carcharhinoids are usually placed in one <a href="/wiki/Clade">clade </a>, but recent studies show the Lamnoids and Orectoloboids are a clade. Some scientists now think that Heterodontoids may be Squalean. The Squaleans are divided into <a href="/wiki/Hexanchiformes">Hexanchiformes </a>and Squalomorpha. The former includes <a href="/wiki/Cow_shark">cow shark </a>and <a href="/wiki/Frilled_shark">frilled shark </a>, though some authors propose both families to be moved to separate orders. The Squalomorpha contains the <a href="/wiki/Squaliformes">Squaliformes </a>and the Hypnosqualea. The Hypnosqualea may be invalid. It includes the <a href="/wiki/Angel_shark">Squatiniformes </a>, and the Pristorajea, which may also be invalid, but includes the <a href="/wiki/Sawshark">Pristiophoriformes </a>and the <a href="/wiki/Batoidea">Batoidea </a>.<a href="#cite_note-Taxonomy-23">[23] </a> <a href="#cite_note-CompagnoFAO-26">[26] </a>

There are more than 470 species of sharks split across twelve <a href="/wiki/Order_(biology)">orders </a>, including four orders of sharks that have gone extinct:<a href="#cite_note-CompagnoFAO-26">[26] </a>

<ul><li><a href="/wiki/Carcharhiniformes">Carcharhiniformes </a>: Commonly known as <a href="/wiki/Carcharhiniformes">ground sharks </a>, the order includes the <a href="/wiki/Blue_shark">blue </a>, <a href="/wiki/Tiger_shark">tiger </a>, <a href="/wiki/Bull_shark">bull </a>, <a href="/wiki/Grey_reef_shark">grey reef </a>, <a href="/wiki/Blacktip_reef_shark">blacktip reef </a>, <a href="/wiki/Caribbean_reef_shark">Caribbean reef </a>, <a href="/wiki/Blacktail_reef_shark">blacktail reef </a>, <a href="/wiki/Whitetip_reef_shark">whitetip reef </a>, and <a href="/wiki/Oceanic_whitetip_shark">oceanic whitetip sharks </a>(collectively called the <a href="/wiki/Requiem_shark">requiem sharks </a>) along with the <a href="/wiki/Houndshark">houndsharks </a>, <a href="/wiki/Catshark">catsharks </a>, and <a href="/wiki/Hammerhead_shark">hammerhead sharks </a>. They are distinguished by an elongated snout and a <a href="/wiki/Nictitating_membrane">nictitating membrane </a>which protects the eyes during an attack. </li><li><a href="/wiki/Bullhead_shark">Heterodontiformes </a>: They are generally referred to as the <a href="/wiki/Bullhead_shark">bullhead </a>or <a href="/wiki/Horn_shark">horn sharks </a>. </li><li><a href="/wiki/Hexanchiformes">Hexanchiformes </a>: Examples from this group include the <a href="/wiki/Cow_shark">cow sharks </a>and <a href="/wiki/Frilled_shark">frilled sharks </a>, which somewhat resembles a marine snake. </li><li><a href="/wiki/Lamniformes">Lamniformes </a>: They are commonly known as the <a href="/wiki/Lamniformes">mackerel sharks </a>. They include the <a href="/wiki/Goblin_shark">goblin shark </a>, <a href="/wiki/Basking_shark">basking shark </a>, <a href="/wiki/Megamouth_shark">megamouth shark </a>, the <a href="/wiki/Thresher_shark">thresher sharks </a>, <a href="/wiki/Shortfin_mako_shark">shortfin </a>and <a href="/wiki/Longfin_mako_shark">longfin mako sharks </a>, and <a href="/wiki/Great_white_shark">great white shark </a>. They are distinguished by their large jaws and <a href="/wiki/Ovoviviparity">ovoviviparous </a>reproduction. The Lamniformes also include the extinct <a href="/wiki/Megalodon">megalodon </a>, Carcharodon megalodon . </li><li><a href="/wiki/Carpet_shark">Orectolobiformes </a>: They are commonly referred to as the <a href="/wiki/Carpet_shark">carpet sharks </a>, including <a href="/wiki/Zebra_shark">zebra sharks </a>, <a href="/wiki/Nurse_shark">nurse sharks </a>, <a href="/wiki/Wobbegong">wobbegongs </a>, and the <a href="/wiki/Whale_shark">whale shark </a>. </li><li><a href="/wiki/Sawshark">Pristiophoriformes </a>: These are the <a href="/wiki/Sawshark">sawsharks </a>, with an elongated, toothed snout that they use for slashing their prey. </li><li><a href="/wiki/Squaliformes">Squaliformes </a>: This group includes the <a href="/wiki/Squalidae">dogfish sharks </a>and <a href="/wiki/Squalidae">roughsharks </a>. </li><li><a href="/wiki/Angel_shark">Squatiniformes </a>: Also known as <a href="/wiki/Angel_shark">angel sharks </a>, they are flattened sharks with a strong resemblance to <a href="/wiki/Stingrays">stingrays </a>and <a href="/wiki/Skate_(fish)">skates </a>. </li><li>† <a href="/wiki/Cladoselachiformes">Cladoselachiformes </a> </li><li>† <a href="/wiki/Hybodontiformes">Hybodontiformes </a> </li><li>† <a href="/wiki/Symmoriida">Symmoriida </a> </li><li>† <a href="/wiki/Xenacanthida">Xenacanthida </a>(Xenacantiformes) </li> </ul>

Shark teeth are embedded in the <a href="/wiki/Gingiva">gums </a>rather than directly affixed to the jaw, and are constantly replaced throughout life. Multiple rows of replacement teeth grow in a groove on the inside of the jaw and steadily move forward in comparison to a <a href="/wiki/Conveyor_belt">conveyor belt </a>; some sharks lose 30,000 or more teeth in their lifetime. The rate of tooth replacement varies from once every 8 to 10 days to several months. In most species, teeth are replaced one at a time as opposed to the simultaneous replacement of an entire row, which is observed in the <a href="/wiki/Isistius">cookiecutter shark </a>.<a href="#cite_note-27">[27] </a>

Tooth shape depends on the shark's diet: those that feed on <a href="/wiki/Mollusk">mollusks </a>and <a href="/wiki/Crustacean">crustaceans </a>have dense and flattened teeth used for crushing, those that feed on fish have needle-like teeth for gripping, and those that feed on larger prey such as <a href="/wiki/Mammal">mammals </a>have pointed lower teeth for gripping and triangular upper teeth with <a href="/wiki/Serration">serrated </a>edges for cutting. The teeth of plankton-feeders such as the basking shark are small and non-functional.<a href="#cite_note-Gilbertson-28">[28] </a>

Shark skeletons are very different from those of <a href="/wiki/Osteichthyes">bony fish </a>and <a href="/wiki/Tetrapod">terrestrial vertebrates </a>. Sharks and other <a href="/wiki/Chondrichthyes">cartilaginous fish </a>(<a href="/wiki/Skate_(fish)">skates </a>and <a href="/wiki/Batoidea">rays </a>) have skeletons made of <a href="/wiki/Cartilage">cartilage </a>and <a href="/wiki/Connective_tissue">connective tissue </a>. Cartilage is flexible and durable, yet is about half the normal density of bone. This reduces the skeleton's weight, saving energy.<a href="#cite_note-skeletoncorset-29">[29] </a> Because sharks do not have rib cages, they can easily be crushed under their own weight on land.<a href="#cite_note-langoni-30">[30] </a>

The <a href="/wiki/Jaw">jaws </a>of sharks, like those of rays and skates, are not attached to the <a href="/wiki/Cranium">cranium </a>. The jaw's surface (in comparison to the shark's vertebrae and gill arches) needs extra support due to its heavy exposure to physical stress and its need for strength. It has a layer of tiny hexagonal plates called "<a href="/wiki/Tesserae">tesserae </a>", which are crystal blocks of calcium salts arranged as a mosaic.<a href="#cite_note-31">[31] </a> This gives these areas much of the same strength found in the bony tissue found in other animals.

Generally sharks have only one layer of tesserae, but the jaws of large specimens, such as the bull shark, tiger shark, and the great white shark, have two to three layers or more, depending on body size. The jaws of a large great white shark may have up to five layers.<a href="#cite_note-skeletoncorset-29">[29] </a> In the <a href="/wiki/Rostrum_(anatomy)">rostrum </a>(snout), the cartilage can be spongy and flexible to absorb the power of impacts.

Fin skeletons are elongated and supported with soft and unsegmented rays named ceratotrichia, filaments of elastic protein resembling the horny keratin in hair and feathers.<a href="#cite_note-32">[32] </a> Most sharks have eight fins. Sharks can only drift away from objects directly in front of them because their fins do not allow them to move in the tail-first direction.<a href="#cite_note-langoni-30">[30] </a>

Unlike bony fish, sharks have a complex dermal corset made of flexible collagenous fibers and arranged as a helical network surrounding their body. This works as an outer skeleton, providing attachment for their swimming muscles and thus saving energy.<a href="#cite_note-Cartilagious-33">[33] </a> Their dermal teeth give them <a href="/wiki/Hydrodynamic">hydrodynamic </a>advantages as they reduce turbulence when swimming.<a href="#cite_note-SkinTeeth-34">[34] </a>

<a href="/wiki/Tail">Tails </a>provide thrust, making speed and acceleration dependent on tail shape. <a href="/wiki/Caudal_fin">Caudal fin </a>shapes vary considerably between shark species, due to their evolution in separate environments. Sharks possess a <a href="https://en.wiktionary.org/wiki/heterocercal">heterocercal </a>caudal fin in which the <a href="/wiki/Dorsum_(biology)">dorsal </a>portion is usually noticeably larger than the <a href="/wiki/Ventral">ventral </a>portion. This is because the shark's <a href="/wiki/Vertebral_column">vertebral column </a>extends into that dorsal portion, providing a greater surface area for muscle attachment. This allows more efficient <a href="/wiki/Animal_locomotion">locomotion </a>among these negatively buoyant cartilaginous fish. By contrast, most bony fish possess a <a href="https://en.wiktionary.org/wiki/homocercal">homocercal </a>caudal fin.<a href="#cite_note-35">[35] </a>

Tiger sharks have a large upper <a href="/wiki/Lobe_(anatomy)">lobe </a>, which allows for slow cruising and sudden bursts of speed. The tiger shark must be able to twist and turn in the water easily when hunting to support its varied diet, whereas the <a href="/wiki/Porbeagle">porbeagle shark </a>, which hunts schooling fish such as <a href="/wiki/Mackerel">mackerel </a>and <a href="/wiki/Herring">herring </a>, has a large lower lobe to help it keep pace with its fast-swimming prey.<a href="#cite_note-Nelson-36">[36] </a> Other tail adaptations help sharks catch prey more directly, such as the thresher shark's usage of its powerful, elongated upper lobe to stun fish and squid.

Unlike bony fish, sharks do not have gas-filled swim bladders for buoyancy. Instead, sharks rely on a large liver filled with oil that contains <a href="/wiki/Squalene">squalene </a>, and their cartilage, which is about half the normal density of bone.<a href="#cite_note-Cartilagious-33">[33] </a> Their liver constitutes up to 30% of their total body mass.<a href="#cite_note-Collins-37">[37] </a> The liver's effectiveness is limited, so sharks employ <a href="/wiki/Dynamic_lift_(fish)">dynamic lift </a>to maintain depth while swimming. <a href="/wiki/Sand_tiger_shark">Sand tiger sharks </a>store air in their stomachs, using it as a form of swim bladder. Bottom-dwelling sharks, like the <a href="/wiki/Nurse_shark">nurse shark </a>, have negative buoyancy, allowing them to rest on the ocean floor.

Some sharks, if inverted or stroked on the nose, enter a natural state of <a href="/wiki/Tonic_immobility">tonic immobility </a>. Researchers use this condition to handle sharks safely.<a href="#cite_note-ParttGruberTaniuchi-38">[38] </a>

Like other fish, sharks extract oxygen from seawater as it passes over their <a href="/wiki/Gill">gills </a>. Unlike other fish, shark gill slits are not covered, but lie in a row behind the head. A modified slit called a <a href="/wiki/Spiracle_(vertebrates)">spiracle </a>lies just behind the eye, which assists the shark with taking in water during <a href="/wiki/Aquatic_respiration">respiration </a>and plays a major role in bottom–dwelling sharks. Spiracles are reduced or missing in active <a href="/wiki/Pelagic">pelagic </a>sharks.<a href="#cite_note-Gilbertson-28">[28] </a> While the shark is moving, water passes through the mouth and over the gills in a process known as "ram ventilation". While at rest, most sharks pump water over their gills to ensure a constant supply of oxygenated water. A small number of species have lost the ability to pump water through their gills and must swim without rest. These species are obligate ram ventilators and would presumably <a href="/wiki/Asphyxiate">asphyxiate </a>if unable to move. Obligate ram ventilation is also true of some pelagic bony fish species.<a href="#cite_note-39">[39] </a> <a href="#cite_note-40">[40] </a>

The respiration and <a href="/wiki/Circulatory_system">circulation </a>process begins when deoxygenated <a href="/wiki/Blood">blood </a>travels to the shark's two-chambered <a href="/wiki/Heart">heart </a>. Here the shark pumps blood to its gills via the ventral <a href="/wiki/Aorta">aorta </a><a href="/wiki/Artery">artery </a>where it branches into <a href="https://en.wiktionary.org/wiki/afferent#Adjective">afferent </a><a href="/wiki/Arm">brachial </a>arteries. Reoxygenation takes place in the gills and the reoxygenated blood flows into the <a href="https://en.wiktionary.org/wiki/efferent#Adjective">efferent </a>brachial arteries, which come together to form the <a href="/wiki/Dorsal_aorta">dorsal aorta </a>. The blood flows from the dorsal aorta throughout the body. The deoxygenated blood from the body then flows through the <a href="/wiki/Posterior_cardinal_vein">posterior cardinal veins </a>and enters the posterior cardinal <a href="/wiki/Anal_sinuses">sinuses </a>. From there blood enters the heart <a href="/wiki/Ventricle_(heart)">ventricle </a>and the cycle repeats.<a href="#cite_note-41">[41] </a>

Most sharks are "cold-blooded" or, more precisely, <a href="/wiki/Poikilotherm">poikilothermic </a>, meaning that their internal <a href="/wiki/Thermoregulation">body temperature </a>matches that of their ambient environment. Members of the family <a href="/wiki/Lamnidae">Lamnidae </a>(such as the <a href="/wiki/Shortfin_mako_shark">shortfin mako shark </a>and the <a href="/wiki/Great_white_shark">great white shark </a>) are <a href="/wiki/Homeothermy">homeothermic </a>and maintain a higher body temperature than the surrounding water. In these sharks, a strip of <a href="/wiki/Aerobic_metabolism">aerobic </a>red muscle located near the center of the body generates the heat, which the body retains via a <a href="/wiki/Countercurrent_exchange">countercurrent exchange </a>mechanism by a system of <a href="/wiki/Blood_vessel">blood vessels </a>called the <a href="/wiki/Rete_mirabile">rete mirabile </a>("miraculous net"). The <a href="/wiki/Common_thresher">common thresher </a>and <a href="/wiki/Bigeye_thresher">bigeye thresher </a>sharks have a similar mechanism for maintaining an elevated body temperature.<a href="#cite_note-42">[42] </a>

In contrast to bony fish, with the exception of the <a href="/wiki/Coelacanth">coelacanth </a>,<a href="#cite_note-43">[43] </a> the blood and other tissue of sharks and <a href="/wiki/Chondrichthyes">Chondrichthyes </a>is generally <a href="/wiki/Isotonicity">isotonic </a>to their marine environments because of the high concentration of <a href="/wiki/Urea">urea </a>(up to 2.5%<a href="#cite_note-44">[44] </a> ) and <a href="/wiki/Trimethylamine">trimethylamine </a>N-oxide (TMAO), allowing them to be in <a href="/wiki/Osmotic">osmotic </a>balance with the seawater. This adaptation prevents most sharks from surviving in freshwater, and they are therefore confined to <a href="/wiki/Marine_(ocean)">marine </a>environments. A few exceptions exist, such as the <a href="/wiki/Bull_shark">bull shark </a>, which has developed a way to change its <a href="/wiki/Kidney">kidney </a>function to excrete large amounts of urea.<a href="#cite_note-Collins-37">[37] </a> When a shark dies, the urea is broken down to ammonia by bacteria, causing the dead body to gradually smell strongly of ammonia.<a href="#cite_note-45">[45] </a> <a href="#cite_note-46">[46] </a>

Research in 1930 by <a href="/wiki/Homer_W._Smith">Homer W. Smith </a>showed that sharks' urine doesn't contain sufficient sodium to avoid <a href="/wiki/Hypernatremia">hypernatremia </a>, and it was postulated that there must be an additional mechanism for salt secretion. In 1960 it was discovered at the <a href="/wiki/Mount_Desert_Island_Biological_Laboratory">Mount Desert Island Biological Laboratory </a>in <a href="/wiki/Salsbury_Cove,_Maine">Salsbury Cove, Maine </a>that sharks have a type of <a href="/wiki/Salt_gland">salt gland </a>located at the end of the intestine, known as the "rectal gland", whose function is the secretion of chlorides.<a href="#cite_note-47">[47] </a>

Digestion can take a long time. The food moves from the mouth to a J-shaped stomach, where it is stored and initial digestion occurs.<a href="#cite_note-Digestion-48">[48] </a> Unwanted items may never get past the stomach, and instead the shark either vomits or turns its stomachs inside out and ejects unwanted items from its mouth.<a href="#cite_note-49">[49] </a>

One of the biggest differences between the digestive systems of sharks and mammals is that sharks have much shorter intestines. This short length is achieved by the <a href="/wiki/Spiral_valve">spiral valve </a>with multiple turns within a single short section instead of a long tube-like intestine. The valve provides a long surface area, requiring food to circulate inside the short gut until fully digested, when remaining waste products pass into the <a href="/wiki/Cloaca">cloaca </a>.<a href="#cite_note-Digestion-48">[48] </a>

A few sharks appear <a href="/wiki/Fluorescent">fluorescent </a>under blue light, such as the <a href="/wiki/Swell_shark">swell shark </a>and the <a href="/wiki/Chain_catshark">chain catshark </a>, where the <a href="/wiki/Fluorophore">fluorophore </a>derives from a <a href="/wiki/Metabolite">metabolite </a>of <a href="/wiki/Kynurenic_acid">kynurenic acid </a>.<a href="#cite_note-50">[50] </a>

Sharks have keen <a href="/wiki/Olfactory">olfactory </a>senses, located in the short duct (which is not fused, unlike bony fish) between the anterior and posterior nasal openings, with some species able to detect as little as one <a href="/wiki/Parts_per_million">part per million </a>of blood in seawater.<a href="#cite_note-51">[51] </a> The size of the olfactory bulb varies across different shark species, with size dependent on how much a given species relies on smell or vision to find their prey.<a href="#cite_note-:02-52">[52] </a> In environments with low visibility, shark species generally have larger olfactory bulbs.<a href="#cite_note-:02-52">[52] </a> In reefs, where visibility is high, species of sharks from the family <a href="/wiki/Requiem_shark">Carcharhinidae </a>have smaller olfactory bulbs.<a href="#cite_note-:02-52">[52] </a> Sharks found in deeper waters also have larger olfactory bulbs.<a href="#cite_note-53">[53] </a>

Sharks have the ability to determine the direction of a given scent based on the timing of scent detection in each nostril.<a href="#cite_note-54">[54] </a> This is similar to the method mammals use to determine direction of sound.

They are more attracted to the chemicals found in the intestines of many species, and as a result often linger near or in <a href="/wiki/Sewage">sewage </a>outfalls. Some species, such as <a href="/wiki/Nurse_shark">nurse sharks </a>, have external <a href="/wiki/Barbels">barbels </a>that greatly increase their ability to sense prey.

Shark <a href="/wiki/Eye">eyes </a>are similar to the eyes of other <a href="/wiki/Vertebrates">vertebrates </a>, including similar <a href="/wiki/Lens_(anatomy)">lenses </a>, <a href="/wiki/Cornea">corneas </a>and <a href="/wiki/Retina">retinas </a>, though their eyesight is well adapted to the <a href="/wiki/Ocean">marine </a>environment with the help of a tissue called <a href="/wiki/Tapetum_lucidum">tapetum lucidum </a>. This tissue is behind the <a href="/wiki/Retina">retina </a>and reflects light back to it, thereby increasing visibility in the dark waters. The effectiveness of the tissue varies, with some sharks having stronger <a href="/wiki/Nocturnal">nocturnal </a>adaptations. Many sharks can contract and dilate their <a href="/wiki/Pupil">pupils </a>, like humans, something no <a href="/wiki/Teleost_fish">teleost fish </a>can do. Sharks have eyelids, but they do not blink because the surrounding water cleans their eyes. To protect their eyes some species have <a href="/wiki/Nictitating_membrane">nictitating membranes </a>. This membrane covers the eyes while hunting and when the shark is being attacked. However, some species, including the <a href="/wiki/Great_white_shark">great white shark </a>(Carcharodon carcharias ), do not have this membrane, but instead roll their eyes backwards to protect them when striking prey. The importance of sight in shark hunting behavior is debated. Some believe that <a href="/wiki/Electroreception">electro- </a>and <a href="/wiki/Chemoreception">chemoreception </a>are more significant, while others point to the nictating membrane as evidence that sight is important. Presumably, the shark would not protect its eyes were they unimportant. The use of sight probably varies with species and water conditions. The shark's field of vision can swap between <a href="/wiki/Monocular">monocular </a>and <a href="/wiki/Stereoscopic">stereoscopic </a>at any time.<a href="#cite_note-55">[55] </a> A <a href="/wiki/Spectrophotometry">micro-spectrophotometry </a>study of 17 species of shark found 10 had only <a href="/wiki/Rod_cell">rod photoreceptors </a>and no cone cells in their <a href="/wiki/Retina">retinas </a>giving them good night vision while making them <a href="/wiki/Colorblind">colorblind </a>. The remaining seven species had in addition to rods a single type of <a href="/wiki/Cone_cell">cone photoreceptor </a>sensitive to green and, seeing only in shades of grey and green, are believed to be effectively colorblind. The study indicates that an object's contrast against the background, rather than colour, may be more important for object detection.<a href="#cite_note-56">[56] </a> <a href="#cite_note-57">[57] </a> <a href="#cite_note-58">[58] </a>

Although it is hard to test the hearing of sharks, they may have a sharp <a href="/wiki/Hearing_(sense)">sense of hearing </a>and can possibly hear prey from many miles away.<a href="#cite_note-59">[59] </a> A small opening on each side of their heads (not the spiracle) leads directly into the <a href="/wiki/Inner_ear">inner ear </a>through a thin channel. The <a href="/wiki/Lateral_line">lateral line </a>shows a similar arrangement, and is open to the environment via a series of openings called lateral line <a href="/wiki/Canal_pore">pores </a>. This is a reminder of the common origin of these two vibration- and sound-detecting organs that are grouped together as the acoustico-lateralis system. In bony fish and <a href="/wiki/Tetrapod">tetrapods </a>the external opening into the inner ear has been lost.

The <a href="/wiki/Ampullae_of_Lorenzini">ampullae of Lorenzini </a>are the electroreceptor organs. They number in the hundreds to thousands. Sharks use the ampullae of Lorenzini to detect the <a href="/wiki/Electromagnetic_field">electromagnetic fields </a>that all living things produce.<a href="#cite_note-60">[60] </a> This helps sharks (particularly the <a href="/wiki/Hammerhead_shark">hammerhead shark </a>) find prey. The shark has the greatest electrical sensitivity of any animal. Sharks find prey hidden in sand by detecting the <a href="/wiki/Electric_field">electric fields </a>they produce. <a href="/wiki/Ocean_current">Ocean currents </a>moving in the <a href="/wiki/Earth%27s_magnetic_field">magnetic field of the Earth </a>also generate electric fields that sharks can use for orientation and possibly navigation.<a href="#cite_note-61">[61] </a>

This system is found in most fish, including sharks. It is a tactile sensory system which allows the organism to detect water speed and pressure changes near by.<a href="#cite_note-62">[62] </a> The main component of the system is the neuromast, a cell similar to <a href="/wiki/Hair_cell">hair cells </a>present in the vertebrate ear that interact with the surrounding aquatic environment. This helps sharks distinguish between the currents around them, obstacles off on their periphery, and struggling prey out of visual view. The shark can sense frequencies in the range of 25 to 50 <a href="/wiki/Hertz">Hz </a>.<a href="#cite_note-63">[63] </a>

Shark lifespans vary by species. Most live 20 to 30 years. The <a href="/wiki/Spiny_dogfish">spiny dogfish </a>has one of the longest lifespans at more than 100 years.<a href="#cite_note-64">[64] </a> <a href="/wiki/Whale_sharks">Whale sharks </a>(Rhincodon typus ) may also live over 100 years.<a href="#cite_note-65">[65] </a> Earlier estimates suggested the <a href="/wiki/Greenland_shark">Greenland shark </a>(Somniosus microcephalus ) could reach about 200 years, but a recent study found that a 5.02-metre-long (16.5 ft) specimen was 392 ± 120 years old (i.e., at least 272 years old), making it the <a href="/wiki/List_of_longest-living_organisms">longest-lived </a>vertebrate known.<a href="#cite_note-66">[66] </a> <a href="#cite_note-67">[67] </a>

Unlike most <a href="/wiki/Bony_fish">bony fish </a>, sharks are <a href="/wiki/R/K_selection_theory">K-selected </a>reproducers, meaning that they produce a small number of well-developed young as opposed to a large number of poorly developed young. <a href="/wiki/Fecundity">Fecundity </a>in sharks ranges from 2 to over 100 young per reproductive cycle.<a href="#cite_note-FAO-68">[68] </a> Sharks mature slowly relative to many other fish. For example, <a href="/wiki/Lemon_shark">lemon sharks </a>reach sexual maturity at around age 13–15.<a href="#cite_note-69">[69] </a>

Sharks practice <a href="/wiki/Internal_fertilization">internal fertilization </a>.<a href="#cite_note-Adams-70">[70] </a> The posterior part of a male shark's pelvic fins are modified into a pair of <a href="/wiki/Intromittent_organ">intromittent organs </a>called <a href="/wiki/Clasper">claspers </a>, analogous to a <a href="/wiki/Mammalian_penis">mammalian penis </a>, of which one is used to deliver <a href="/wiki/Sperm">sperm </a>into the female.<a href="#cite_note-Mating-71">[71] </a>

<a href="/wiki/Mating">Mating </a>has rarely been observed in sharks.<a href="#cite_note-72">[72] </a> The smaller <a href="/wiki/Catshark">catsharks </a>often mate with the male curling around the female. In less flexible species the two sharks swim parallel to each other while the male inserts a clasper into the female's <a href="/wiki/Oviduct">oviduct </a>. Females in many of the larger species have bite marks that appear to be a result of a male grasping them to maintain position during <a href="/wiki/Mating">mating </a>. The bite marks may also come from courtship behavior: the male may bite the female to show his interest. In some species, females have evolved thicker skin to withstand these bites.<a href="#cite_note-Mating-71">[71] </a>

There have been a number of documented cases in which a female shark who has not been in contact with a male has conceived a pup on her own through <a href="/wiki/Parthenogenesis">parthenogenesis </a>.<a href="#cite_note-73">[73] </a> <a href="#cite_note-74">[74] </a> The details of this process are not well understood, but <a href="/wiki/Genetic_fingerprinting">genetic fingerprinting </a>showed that the pups had no paternal genetic contribution, ruling out <a href="/wiki/Female_sperm_storage">sperm storage </a>. The extent of this behavior in the wild is unknown. Mammals are now the only major <a href="/wiki/Vertebrate">vertebrate </a>group in which <a href="/wiki/Asexual_reproduction">asexual reproduction </a>has not been observed.

Scientists say that asexual reproduction in the wild is rare, and probably a last-ditch effort to reproduce when a mate is not present. Asexual reproduction diminishes <a href="/wiki/Genetic_diversity">genetic diversity </a>, which helps build defenses against threats to the species. Species that rely solely on it risk extinction. Asexual reproduction may have contributed to the <a href="/wiki/Blue_shark">blue shark </a>'s decline off the <a href="/wiki/Ireland">Irish </a>coast.<a href="#cite_note-75">[75] </a>

Sharks display three ways to bear their young, varying by species, <a href="/wiki/Oviparity">oviparity </a>, <a href="/wiki/Viviparous">viviparity </a>and <a href="/wiki/Ovoviviparity">ovoviviparity </a>.<a href="#cite_note-Birth-76">[76] </a> <a href="#cite_note-77">[77] </a>

Most sharks are <a href="/wiki/Ovoviviparous">ovoviviparous </a>, meaning that the eggs hatch in the <a href="/wiki/Oviduct">oviduct </a>within the mother's body and that the egg's <a href="/wiki/Yolk">yolk </a>and fluids secreted by glands in the walls of the oviduct nourishes the embryos. The young continue to be nourished by the remnants of the yolk and the oviduct's fluids. As in viviparity, the young are born alive and fully functional. <a href="/wiki/Lamniforme">Lamniforme </a>sharks practice <a href="/wiki/Oophagy">oophagy </a> , where the first embryos to hatch eat the remaining eggs. Taking this a step further, <a href="/wiki/Sand_tiger_shark">sand tiger shark </a>pups cannibalistically consume neighboring embryos. The survival strategy for ovoviviparous species is to <a href="/wiki/Offspring">brood </a>the young to a comparatively large size before birth. The <a href="/wiki/Whale_shark">whale shark </a>is now classified as ovoviviparous rather than oviparous, because extrauterine eggs are now thought to have been aborted. Most ovoviviparous sharks give birth in sheltered areas, including bays, river mouths and shallow reefs. They choose such areas for protection from predators (mainly other sharks) and the abundance of food. <a href="/wiki/Squalidae">Dogfish </a>have the longest known <a href="/wiki/Gestation_period">gestation period </a>of any shark, at 18 to 24 months. <a href="/wiki/Basking_shark">Basking sharks </a>and <a href="/wiki/Frilled_shark">frilled sharks </a>appear to have even longer gestation periods, but accurate data are lacking.<a href="#cite_note-Birth-76">[76] </a>

Some species are <a href="/wiki/Oviparous">oviparous </a>, laying their fertilized eggs in the water. In most oviparous shark species, an <a href="/wiki/Egg_case_(Chondrichthyes)">egg case </a>with the consistency of <a href="/wiki/Leather">leather </a>protects the developing embryo(s). These cases may be corkscrewed into crevices for protection. The egg case is commonly called a <a href="/wiki/Mermaid%27s_purse">mermaid's purse </a> . Oviparous sharks include the <a href="/wiki/Horn_shark">horn shark </a>, <a href="/wiki/Catshark">catshark </a>, <a href="/wiki/Port_Jackson_shark">Port Jackson shark </a>, and <a href="/wiki/Swellshark">swellshark </a>.<a href="#cite_note-Birth-76">[76] </a> <a href="#cite_note-78">[78] </a>

Viviparity is the gestation of young without the use of a traditional egg, and results in live birth.<a href="#cite_note-:0-79">[79] </a> Viviparity in sharks can be placental or aplacental.<a href="#cite_note-:0-79">[79] </a> Young are born fully formed and self-sufficient.<a href="#cite_note-:0-79">[79] </a> Hammerheads, the <a href="/wiki/Requiem_sharks">requiem sharks </a>(such as the <a href="/wiki/Bull_shark">bull </a>and <a href="/wiki/Blue_shark">blue sharks </a>), and <a href="/wiki/Smoothhound">smoothhounds </a>are viviparous.<a href="#cite_note-FAO-68">[68] </a> <a href="#cite_note-Birth-76">[76] </a>

The classic view describes a solitary hunter, ranging the oceans in search of food. However, this applies to only a few species. Most live far more social, sedentary, <a href="/wiki/Benthic">benthic </a>lives, and appear likely to have their own distinct personalities.<a href="#cite_note-80">[80] </a> Even solitary sharks meet for breeding or at rich hunting grounds, which may lead them to cover thousands of miles in a year.<a href="#cite_note-81">[81] </a> Shark migration patterns may be even more complex than in birds, with many sharks covering entire <a href="/wiki/Ocean_basin">ocean basins </a>.

Sharks can be highly social, remaining in large schools. Sometimes more than 100 <a href="/wiki/Scalloped_hammerhead">scalloped hammerheads </a>congregate around <a href="/wiki/Seamount">seamounts </a>and islands, e.g., in the <a href="/wiki/Gulf_of_California">Gulf of California </a>.<a href="#cite_note-Collins-37">[37] </a> Cross-species social hierarchies exist. For example, <a href="/wiki/Oceanic_whitetip_shark">oceanic whitetip sharks </a>dominate <a href="/wiki/Silky_shark">silky sharks </a>of comparable size during feeding.<a href="#cite_note-FAO-68">[68] </a>

When approached too closely some sharks perform a <a href="/wiki/Shark_threat_display">threat display </a>. This usually consists of exaggerated swimming movements, and can vary in intensity according to the threat level.<a href="#cite_note-82">[82] </a>

In general, sharks swim ("cruise") at an average speed of 8 kilometres per hour (5.0 mph), but when feeding or attacking, the average shark can reach speeds upwards of 19 kilometres per hour (12 mph). The <a href="/wiki/Shortfin_mako_shark">shortfin mako shark </a>, the fastest shark and one of the fastest fish, can burst at speeds up to 50 kilometres per hour (31 mph).<a href="#cite_note-83">[83] </a> The <a href="/wiki/Great_white_shark">great white shark </a>is also capable of speed bursts. These exceptions may be due to the <a href="/wiki/Warm-blooded">warm-blooded </a>, or <a href="/wiki/Homeothermic">homeothermic </a>, nature of these sharks' physiology. Sharks can travel 70 to 80 km in a day.<a href="#cite_note-84">[84] </a>

Shark - Wikipedia

Do sharks have any bones in their body?

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