Editing Shark (section)

==Anatomy==
{{Main|Shark anatomy}}
[[File:Parts of a shark.svg|thumb|upright=1.5|General anatomical features of sharks|alt=Drawing of a shark labeling major anatomical features, including mouth, snout, nostril, eye, spiracle, dorsal fin spine, caudal keel, clasper, labial furrows, gill openings, precaudal pit and fins: first and second dorsal, anal, pectoral, caudal and pelvic]]

===Teeth===
{{Main|Shark tooth}}
[[File:Tiger shark teeth.jpg|thumb|The teeth of [[tiger shark]]s are oblique and serrated to saw through flesh|alt=The serrated teeth of a [[tiger shark]], used for sawing through flesh]]

Shark teeth are embedded in the [[Gingiva|gums]] 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 [[conveyor belt]]; 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 [[Isistius|cookiecutter shark]].<ref>{{cite web
| url = http://www.elasmo-research.org/education/white_shark/teeth.htm
| title = Teeth of the Skin
| first = R. Aidan
| last = Martin
| access-date = 2007-08-28
| archive-url = https://web.archive.org/web/20071012160555/http://elasmo-research.org/education/white_shark/teeth.htm
| archive-date = 2007-10-12
| url-status = live
}}</ref>

Tooth shape depends on the shark's diet: those that feed on [[mollusk]]s and [[crustacean]]s 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 [[mammal]]s have pointed lower teeth for gripping and triangular upper teeth with [[serration|serrated]] edges for cutting. The teeth of plankton-feeders such as the basking shark are small and non-functional.<ref name="Gilbertson" />

===Skeleton===
Shark skeletons are very different from those of [[Osteichthyes|bony fish]] and [[tetrapod|terrestrial vertebrates]]. Sharks and other [[chondrichthyes|cartilaginous fish]] ([[Skate (fish)|skate]]s and [[batoidea|rays]]) have skeletons made of [[cartilage]] and [[connective tissue]]. Cartilage is flexible and durable, yet is about half the normal density of bone. This reduces the skeleton's weight, saving energy.<ref name="skeletoncorset">{{cite web
|url=http://www.elasmo-research.org/education/white_shark/skeleton.htm
|title=Skeleton in the Corset
|last=Martin
|first=R. Aidan
|publisher=ReefQuest Centre for Shark Research
|access-date=2009-08-21
|archive-url=https://web.archive.org/web/20091125073318/http://www.elasmo-research.org/education/white_shark/skeleton.htm
|archive-date=2009-11-25
|url-status=live
}}</ref> Because sharks do not have rib cages, they can easily be crushed under their own weight on land.<ref name=langoni>{{cite web|archive-url=https://web.archive.org/web/20100805003021/http://langonigraphix.com/skeleton.html|archive-date=August 5, 2010 |url=http://langonigraphix.com/skeleton.html
|title=A Shark's Skeleton & Organs
|access-date=August 14, 2009
}}</ref>

===Jaw===
The [[jaw]]s of sharks, like those of rays and skates, are not attached to the [[cranium]]. 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 "[[tesserae]]", which are crystal blocks of calcium salts arranged as a mosaic.<ref>{{cite book
| last = Hamlett
| first = W. C.
| title = Sharks, Skates and Rays: The Biology of Elasmobranch Fishes
| publisher = Johns Hopkins University Press
| year = 1999f
|isbn= 978-0-8018-6048-5
| oclc = 39217534}}</ref> 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.<ref name="skeletoncorset"/> In the [[rostrum (anatomy)|rostrum]] (snout), the cartilage can be spongy and flexible to absorb the power of impacts.{{cn|date=November 2024}}

===Fins===
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.<ref>{{cite book|last=Hamlett|first=William C.|title=Sharks, skates, and rays: the biology of elasmobranch fishes |publisher=The Johns Hopkins University Press |date=April 23, 1999|edition=1st|page=56 |isbn=978-0-8018-6048-5|url=https://books.google.com/books?id=ON-sPP5rowwC&q=shark%20fin%20%20ceratotrichia%20supported&pg=PA56}}</ref> 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.<ref name=langoni/>

===Dermal denticles===
{{Further|Fish scale#Placoid scales}}
[[File:Denticules cutanés du requin citron Negaprion brevirostris vus au microscope électronique à balayage.jpg|thumb|The dermal denticles of a [[lemon shark]], viewed through a [[scanning electron microscope]] |alt=The dermal denticles of a lemon shark]]

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.<ref name=Cartilagious>{{cite web|url=http://www.elasmo-research.org/education/topics/p_cartilage.htm|title=The Importance of Being Cartilaginous|last=Martin|first=R. Aidan|publisher=ReefQuest Centre for Shark Research|access-date=2009-08-29|archive-url=https://web.archive.org/web/20090227013312/http://www.elasmo-research.org/education/topics/p_cartilage.htm|archive-date=2009-02-27|url-status=live}}</ref> Their dermal teeth give them [[hydrodynamic]] advantages as they reduce turbulence when swimming.<ref name="SkinTeeth">{{cite web
| url = http://www.elasmo-research.org/education/white_shark/scales.htm
| title = Skin of the Teeth
| first = R. Aidan
| last = Martin
| access-date = 2007-08-28
| archive-url = https://archive.today/20120801074741/http://www.elasmo-research.org/education/white_shark/scales.htm
| archive-date = 2012-08-01
| url-status = dead
}}</ref> Some species of shark have pigmented denticles that form complex patterns like spots (e.g. [[Zebra shark]]) and stripes (e.g. [[Tiger shark]]). These markings are important for [[camouflage]] and help sharks blend in with their environment, as well as making them difficult for prey to detect.<ref name="Camouflage">{{cite web | url = https://www.nationalgeographic.com/animals/article/camouflage-explained | archive-url = https://web.archive.org/web/20210301165710/https://www.nationalgeographic.com/animals/article/camouflage-explained | url-status = dead | archive-date = March 1, 2021 | title = Camouflage facts | website = [[National Geographic Society]] | date = 4 January 2019 | access-date = 2021-11-25}}</ref> For some species, dermal patterning returns to healed denticles even after they have been removed by injury.<ref>{{Cite journal|last1=Womersley|first1=Freya|last2=Hancock|first2=James|last3=Perry|first3=Cameron T.|last4=Rowat|first4=David|date=February 2021|title=Wound-healing capabilities of whale sharks (Rhincodon typus) and implications for conservation management|journal=Conservation Physiology|volume=9|issue=1|pages=coaa120|doi=10.1093/conphys/coaa120|pmc=7859907|pmid=33569175}}</ref>

===Tails===
[[Tail]]s provide thrust, making speed and acceleration dependent on tail shape. [[Caudal fin]] shapes vary considerably between shark species, due to their evolution in separate environments. Sharks possess a [[wiktionary:heterocercal|heterocercal]] caudal fin in which the [[Dorsum (biology)|dorsal]] portion is usually noticeably larger than the [[ventral]] portion. This is because the shark's [[vertebral column]] extends into that dorsal portion, providing a greater surface area for muscle attachment. This allows more efficient [[Animal locomotion|locomotion]] among these negatively buoyant cartilaginous fish. By contrast, most bony fish possess a [[wiktionary:homocercal|homocercal]] caudal fin.<ref>{{cite web|url=http://www.fathom.com/course/21701777/session1.html|title=Jaws: The Natural History of Sharks|last=Michael|first=Bright|publisher=Columbia University|access-date=2009-08-29|url-status=dead|archive-url=https://web.archive.org/web/20090511000030/http://www.fathom.com/course/21701777/session1.html|archive-date=2009-05-11}}</ref>

Tiger sharks have a large upper [[lobe (anatomy)|lobe]], 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 [[Porbeagle|porbeagle shark]], which hunts schooling fish such as [[mackerel]] and [[herring]], has a large lower lobe to help it keep pace with its fast-swimming prey.<ref name="Nelson">{{cite book
| last=Nelson
| first=Joseph S.
| title= Fishes of the World
| publisher=John Wiley and Sons
|location=New York
| year= 1994
|isbn= 978-0-471-54713-6
| oclc=28965588| title-link=Fishes of the World
}}</ref> 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.