Editing Claw

{{short description|Curved, pointed appendage at the end of a digit of a mammal, bird, or reptile}}
{{other uses}}
{{redirect|Talons|other uses|Talon (disambiguation)}}

[[Image:Cat claw closeup.jpg|thumb|A domestic [[cat]]'s retractable claw in protracted position]]
[[File:The Splayed Front Paws of a Cat.jpg|alt=An orange cat stretches his front legs towards the camera. His claws are caught on a screen, which causes the paws to be spread, showing the pads and fur in between them.|thumb|An orange cat stretches his front legs showing off his feet and claws.]]
A '''claw''' is a curved, pointed appendage found at the end of a toe or finger in most [[amniote]]s ([[mammals]], [[reptiles]], [[birds]]). Some [[invertebrate]]s such as [[beetles]] and [[spiders]] have somewhat similar fine, hooked structures at the end of the leg or [[Arthropod leg|tarsus]] for gripping a surface as they walk. The pincers of [[crabs]], [[lobsters]] and [[scorpions]], more formally known as their [[chelae]], are sometimes called claws.

A true claw is made of a hard [[protein]] called [[keratin]]. Claws are used to catch and hold prey in [[carnivorous]] [[mammals]] such as [[cats]] and [[dogs]], but may also be used for such purposes as digging, climbing trees, self-defense and [[Personal grooming|grooming]], in those and other species.

Similar appendages that are flat and do not come to a sharp point are called [[nail (anatomy)|nails]] instead. Claw-like projections that do not form at the end of digits but spring from other parts of the foot are properly named [[Spur (zoology)|spur]]s.<ref>{{cite journal|last=Rand|first=A.L.|title=On the Spurs on Birds' Wings|journal=The Wilson Bulletin|year=1954|volume=66|issue=2|pages=127–134|url=http://sora.unm.edu/sites/default/files/journals/wilson/v066n02/p0127-p0134.pdf|access-date=16 November 2012}}</ref>

==Tetrapods==<!-- This section is linked from [[Pangolin]] -->
In [[tetrapod]]s, claws are made of [[keratin]] and consist of two layers. The '''unguis''' is the harder external layer, which consists of keratin fibers arranged perpendicular to the direction of growth and in layers at an oblique angle. The '''subunguis''' is the softer, flaky underside layer whose grain is parallel to the direction of growth. The claw grows outward from the '''nail matrix''' at the base of the unguis and the subunguis grows thicker while travelling across the '''nail bed'''. The unguis grows outward faster than the subunguis to produce a curve and the thinner sides of the claw wear away faster than their thicker middle, producing a more or less sharp point. Tetrapods use their claws in many ways, commonly to grasp or kill prey, to dig and to climb and hang.

===Mammals===
[[File:Katzenkralle.jpg|right|thumb|A claw sheath from a cat]]
All [[carnivora]]ns have claws, which vary considerably in length and shape. Claws grow out of the third [[Phalanx bones|phalange]]s of the paws and are made of [[keratin]]. Many [[predator]]y mammals have protractile claws that can partially hide inside the animal's [[paw]], especially the cat family, [[Felidae]], almost all of whose members have fully protractible claws. Outside of the cat family, retractable claws are found only in certain species of the [[Viverridae]] (and the extinct [[Nimravidae]]).<ref>{{Cite book |last=Turner |first=Alan |title=The Big Cats and their fossil relatives: an illustrated guide to their evolution and natural history |last2=Antón |first2=Mauricio |publisher=[[Columbia University Press]] |year=1997 |isbn=978-0-231-10228-5 |location=[[New York City]] |pages=130-133 |language=en}}</ref> A claw that is retractable is protected from wear and tear.

Most cats and dogs also have a [[dewclaw]] on the inside of the front paws. It is much less functional than the other claws but does help the cats to grasp prey. Because the dew claw does not touch the ground, it receives less wear and tends to be sharper and longer.

A [[nail (anatomy)|nail]] is [[Homology (biology)|homologous]] to a claw but is flatter and has a curved edge instead of a point. A nail that is big enough to bear weight is called a "[[hoof]]". (Nevertheless, one side of the cloven-hoof of [[Artiodactyla|artiodactyl]] [[ungulate]]s may also be called a claw). 

Every so often, the growth of claws stops and restarts, as does [[hair]]. In a hair, this results in the hair falling out and being replaced by a new one. In claws, this results in an [[abscission]] layer, and the old segment breaks off. This process takes several months for [[human]] thumbnails. [[Cat]]s are often seen working old unguis layers off on wood or on boards made for the purpose. Ungulates' hooves wear or self-trim by ground contact. Domesticated [[Equus (genus)|equids]] ([[horse]]s, [[donkey]]s and [[mule]]s) usually need regular trimming by a [[farrier]], as a consequence of reduced activity on hard ground.

====Primates====
[[Primate]] nails consist of the unguis alone, as the subunguis has disappeared. With the evolution of grasping hands and feet, claws are no longer necessary for locomotion, and instead most digits exhibit [[nail (anatomy)|nail]]s. However, claw-like nails are found in small-bodied [[callitrichids]] on all digits except the [[hallux]] or big toe. A laterally flattened [[grooming claw]], used for grooming, can be found on the second toe in living [[Strepsirrhini|strepsirrhines]], and the second and third in [[tarsiers]]. [[Aye-aye]]s have functional claws on all other digits except the hallux, including a grooming claw on the second toe.<ref name="Soligo">{{Cite journal | last1 = Soligo | first1 = C. | last2 = Müller | first2 = A. E. | doi = 10.1006/jhev.1998.0263 | title = Nails and claws in primate evolution | journal = Journal of Human Evolution | volume = 36 | issue = 1 | pages = 97–114 | year = 1999 | pmid =  9924135}}</ref> Less commonly known, a grooming claw is also found on the second pedal digit of [[night monkey]]s (''Aotus''), [[titi]]s (''Callicebus''), and possibly other [[New World monkey]]s.<ref name=Maiolino>{{Cite journal | last1 = Maiolino | first1 = S. | last2 = Boyer | first2 = D. M. | last3 = Rosenberger | first3 = A. | doi = 10.1002/ar.21498 | title = Morphological Correlates of the Grooming Claw in Distal Phalanges of Platyrrhines and Other Primates: A Preliminary Study | journal = The Anatomical Record | volume = 294 | issue = 12 | pages = 1975–1990 | year = 2011 | pmid =  22042603| doi-access =  }}</ref>

===Reptiles===

[[File:Therizinosaurus claw.jpg|thumb|At just under a meter, the claws of ''[[Therizinosaurus]]'' are among the largest recorded.]]
[[File:Grenn lizzard.jpg|thumb|right|Using its claws for anchoring, a [[Balkan green lizard|green lizard]] basks.]]

Most reptiles have well-developed claws. Most lizards have toes ending in stout claws.<ref>{{cite journal|author=Alibardi, L. |year=2008|title= Microscopic analysis of lizard claw morphogenesis and hypothesis on its evolution|journal=[[Acta Zoologica]]|doi=10.1111/j.1463-6395.2007.00312.x|volume=89|issue=2|pages=169–178}}</ref> In snakes, feet and claws are absent, but in many [[boidae|boids]] such as ''[[Boa constrictor]]'', remnants of highly reduced hind-limbs emerge with a single claw as "spurs" on each side of the anal opening.

Lizard claws are used as aids in climbing, and in holding down prey in carnivorous species.

===Birds===
[[File:Sparvhöks klor - Claws of Eurasian sparrowhawk (Accipiter nisus) - Ystad - 2024.jpg|thumb|Claws of [[Eurasian sparrowhawk]].]]
A '''talon''' is the claw of a [[bird of prey]], its primary hunting tool.<ref>{{Cite journal |last=Fowler |first=Denver W. |last2=Freedman |first2=Elizabeth A. |last3=Scannella |first3=John B. |date=2009-11-25 |editor-last=Pizzari |editor-first=Tom |title=Predatory Functional Morphology in Raptors: Interdigital Variation in Talon Size Is Related to Prey Restraint and Immobilisation Technique |url=https://dx.plos.org/10.1371/journal.pone.0007999 |journal=PLoS ONE |language=en |volume=4 |issue=11 |pages=e7999 |bibcode=2009PLoSO...4.7999F |doi=10.1371/journal.pone.0007999 |issn=1932-6203 |pmc=2776979 |pmid=19946365 |doi-access=free}}</ref> The talons are very important; without them, most birds of prey would not be able to catch their food. Some birds also use claws for defensive purposes. [[Cassowary|Cassowaries]] use claws on their inner toe (digit&nbsp;I) for defence and have been known to disembowel people.<ref>{{Cite journal |last=Lumeij |first=J. T. |date=1987 |title=Avian clinical pathology. General considerations |journal=Veterinary Quarterly |volume=9 |issue=3 |pages=249–254 |doi=10.1080/01652176.1987.9694109 |pmid=3314103|doi-access=free }}</ref><ref>{{Cite journal |last1=Cho |first1=Patricia |last2=Brown |first2=Rosanne |last3=Anderson |first3=Marilyn |date=1984-01-01 |title=Comparative gross anatomy of ratites |journal=Zoo Biology |language=en |volume=3 |issue=2 |pages=133–144 |doi=10.1002/zoo.1430030205 |issn=1098-2361}}</ref> All birds, however, have claws, which are used as general holdfasts and protection for the tip of the digits.

The [[hoatzin]] and [[turaco]] are unique among [[extant taxon|extant]] birds in having functional claws on the thumb and index finger (digits&nbsp;I and II) on the forelimbs as chicks, allowing them to climb trees until the adult plumage with flight feathers develop.<ref name=Parallel>{{cite journal |author1=Fain, Matthew G. |author2=Houde, Peter |year=2004 |title=Parallel radiations in the primary clades of birds |journal=[[Evolution (journal)|Evolution]] |volume=58 |issue=11 |pages=2558–2573 |doi=10.1554/04-235 |pmid=15612298 |s2cid=1296408 |url=http://biology-web.nmsu.edu/~houde/Parallel_radiations.pdf |access-date=2016-07-08 |archive-url=https://web.archive.org/web/20170709030601/http://biology-web.nmsu.edu/~houde/Parallel_radiations.pdf |archive-date=2017-07-09 |url-status=dead}}</ref><ref>{{cite journal |doi=10.1111/j.1096-3642.1891.tb00045.x |last=Parker |first=W. K. |year=1891 |url=https://www.biodiversitylibrary.org/page/31083330 |title=On the Morphology of a Reptilian Bird, ''Opisthocomus hoazin'' |journal=Transactions of the Zoological Society of London |volume=13 |pages=43–89 |issue=2}}</ref> However, several birds have a claw- or nail-like structure hidden under the feathers at the end of the hand digits, notably ostriches, emus, ducks, geese and kiwis.<ref>{{Cite book |last=''Sir'' Buller |first=Walter Lawry |author-link=Walter Buller |url=https://nzetc.victoria.ac.nz/tm/scholarly/tei-BulBird.html |title=A History of the Birds of New Zealand |publisher=[[Walter Buller|Sir Walter Lawry Buller]] |year=1888 |location=[[London]] |language=en |chapter=''Apteryx australis'' (South-Island Kiwi) |chapter-url=https://nzetc.victoria.ac.nz/tm/scholarly/tei-BulBird-t1-g1-t2-body-d138.html |archive-url=https://web.archive.org/web/20211020062123/https://nzetc.victoria.ac.nz/tm/scholarly/tei-BulBird.html |archive-date=2021-10-20 |via=[[New Zealand Electronic Text Collection]]}}</ref>

===Amphibians===
The only [[amphibian]]s to bear claws are the [[African clawed frog]]s. Claws evolved separately in the amphibian and [[amniote]] ([[reptiliomorph]]) line.<ref>{{cite journal|title=The anatomy and development of the claws of ''Xenopus laevis'' (Lissamphibia: Anura) reveal alternate pathways of structural evolution in the integument of tetrapods|pmid=19422431|year=2009|last1=Maddin|first1=HC|last2=Eckhart|first2=L|last3=Jaeger|first3=K|last4=Russell|first4=AP|last5=Ghannadan|first5=M|volume=214|issue=4|pages=607–19|doi=10.1111/j.1469-7580.2009.01052.x|pmc=2736125|journal=Journal of Anatomy}}</ref> However, the [[hairy frog]] has claw analogues on its feet; the frog intentionally [[Joint dislocation|dislocates]] the tips of its fingers to unsheathe the sharp points of its last [[phalanges]].

==Arthropods==
{{main|Chela (organ)}}
[[File:Beetle's claws on scanning electron microscope.jpg|thumb|A beetle's chelae under a scanning electron microscope]]
The scientifically correct term for the "claw" of an arthropod, such as a lobster or crab, is a '''[[Chelae|chela]]''' (plural ''chelae''). Legs bearing a chela are called '''[[cheliped]]s'''. Chelae are also called '''[[pincer (biology)|pincers]]'''.

==See also==
*[[Horse hoof]]
*[[Dactyly]]

==References==
{{Reflist}}

==External links==
{{Commons category}}
*[http://ratbehavior.org/claws.htm Rat Claws] ([https://web.archive.org/web/20220416103617id_/http://ratbehavior.org/claws.htm archived] from the original on {{Date|2022-04-16}}), also explains much about mammalian claws in general.

[[Category:Animal anatomy]]