Claw


Claw
A domestic cat's retractable claw in protracted position

A claw is a curved, pointed appendage, found at the end of a toe or finger in most mammals, birds, and some reptiles. However, the word "claw" is also often used in reference to an invertebrate. Somewhat similar fine hooked structures are found in arthropods such as beetles and spiders, at the end of the leg or tarsus for gripping a surface as the creature walks. Crabs' and lobsters' pincers, or more formally, their "chelae", are sometimes called claws.

A claw is made of 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, etc., in those and other species.

Similar appendages which are flat and do not come to a sharp point are called nails instead.

Claws of animals like tigers, lions, and bears were used in making items such as ornaments, pendants, and brooches. Tigers' and lions' claws are expensive because it is illegal to trade the parts of such protected animals.

Contents

Arthropods

The correct term for an arthropod's "claw" is a chela (plural chelae). Legs bearing a chela are called chelipeds. Chelae are also called pincers.

Tetrapods

At just under a meter, the claws of Therizinosaurus are among the largest recorded

In tetrapods, 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.

Amphibians

The only amphibians to bear claws are the African clawed frogs. Claws appear to have evolved separately in the amphibian and amniote line.[1]

Reptiles

Using its claws for anchoring, a green lizard basks

Most reptiles have toes ending in stout claws. The claws form from the last scale on the toe.[2] Most reptiles have well-developed claws. In snakes, feet and claws are absent, but in Boa constrictor, remnants of highly reduced hind-limbs emerge with a single claw as "spurs" on each side of the anal opening.

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

Birds

A talon is the claw of a bird of prey, its primary hunting tool. 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. Cassowaries use claws on their inner toe (digit II) for defence, and has been known to seriously injure people. All birds however have claws, which are used as general holdfasts and protection for the tip of the digits.

The hoatzin is unique among extant birds in having functional claws on the thumb and index finger (digit I and II) on the forelimbs as chicks, allowing them to climb trees until the adult plumage with flight feathers develop.[3] However, several birds have a claw- or nail-like structure hidden under the feathers at the end of the hand digits, notably ducks, geese and kiwis.[4]

Mammals

A nail is 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' (see also Horse hoof. However, one side of the cloven-hoof of artiodactyl ungulates may also be called a claw).

A claw sheath from a cat

Every so often, the growth of claws stops and restarts, as does hair. In 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. Cats 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 equids (horses, donkeys and mules) usually need regular trimming by a farrier, as a consequence of reduced activity on hard ground.

Many predatory mammals have protractile claws that can partially hide inside the animal's paw, especially the Felidae, where almost all of its members have fully protractible claws.

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 nails. However, claw-like nails are found in small-bodied callitrichids on all digits except the hallux or big toe, and in prosimians, which possess one or two laterally flattened toilet claws, used for grooming. These can be found on the second toe in lemurs and lorises, and the second and third in tarsiers. Aye-ayes have functional claws on all other digits except the hallux, including a toilet claw on the second toe.[5]

References

  1. ^ Maddin & al. (2009): The anatomy and development of the claws ofXenopus laevis (Lissamphibia: Anura) reveal alternate pathways of structural evolution in the integument of tetrapods. Journal of Anatomy, no 214 (4): pp 607-19 Abstract
  2. ^ Alibardi, L. (2008): Microscopic analysis of lizard claw morphogenesis and hypothesis on its evolution. Acta Zoologica: Morphology and Evolution, vol 89 (2): pp 169–178. abstract
  3. ^ Parker, W. K. (1891). "On the Morphology of a Reptilian Bird, Opisthocomus hoazin". Transactions of the Zoological Society of London 13: 43–89. doi:10.1111/j.1096-3642.1891.tb00045.x. http://biodiversitylibrary.org/page/31083330. 
  4. ^ Sir Walter Lawry Buller (1888): A History of the Birds of New Zealand. London excerpt from Zealand Electronic Text Centre collection
  5. ^ Soligo, C., Müller, A.E. (1999). "Nails and claws in primate evolution". Journal of Human Evolution 36 (1): 97–114. doi:10.1006/jhev.1998.0263. PMID 9924135. 

See also

External links


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Synonyms:
, (with the claws), , ,


Look at other dictionaries:

  • Claw — (kl[add]), v. t. [imp. & p. p. {Clawed} (kl[add]d); p. pr. & vb. n. {Clawing}.] [AS. clawan. See {Claw}, n.] 1. To pull, tear, or scratch with, or as with, claws or nails. [1913 Webster] 2. To relieve from some uneasy sensation, as by scratching; …   The Collaborative International Dictionary of English

  • claw — [klɔː ǁ klɒː] verb claw back phrasal verb 1. [transitive] claw something → back FINANCE if a company claws back shares, it takes back new shares that it had offered to its present shareholders, but they do not want to buy, and offers them to… …   Financial and business terms

  • Claw — (kl[add]), n. [AS. clawu, cl[=a], cle[ o]; akin to D. klaauw, G. klaue, Icel. kl[=o], Sw. & Dan. klo, and perh. to E. clew.] 1. A sharp, hooked nail, as of a beast or bird. [1913 Webster] 2. The whole foot of an animal armed with hooked nails;… …   The Collaborative International Dictionary of English

  • CLAW — bezeichnet: CLAW Hypothese, Hypothese über einen negativen Rückkopplungseffekt in der Klimaforschung Claw (Computerspiel) Eagle Claw Operation Eagle Claw Der Mann mit der stählernen Klaue („The Steel Claw“) …   Deutsch Wikipedia

  • Claw — Claw, v. i. To scrape, scratch, or dig with a claw, or with the hand as a claw. Clawing [in ash barrels] for bits of coal. W. D. Howells. [1913 Webster] {To claw off} (Naut.), to turn to windward and beat, to prevent falling on a lee shore. [1913 …   The Collaborative International Dictionary of English

  • Claw — Разработчик Takarajimasha Издатель Monolith Productions Дата выпуска …   Википедия

  • claw — claw; claw·less; wro·claw; de·claw; …   English syllables

  • claw — ► NOUN 1) a curved, pointed horny nail on each digit of the foot in birds, lizards, and some mammals. 2) the pincer of a crab, scorpion, or other arthropod. ► VERB 1) scratch or tear at with the claws or fingernails. 2) (claw away) try… …   English terms dictionary

  • claw — [n] nail of animal; tool shaped like nail of an animal barb, cant hook, clapperclaw, crook, fang, fingernail, grapnel, grappler, hook, manus, nail claw, nipper, paw, pincer, retractile, spur, talon, tentacle, unguis, ungula; concept 392 claw [v]… …   New thesaurus

  • claw — [klô] n. [ME claue < OE clawu < IE * g(e)l eu < base * gel , to make round, clench (as a fist) > CLING, CLAMP1, CLIMB] 1. a sharp, hooked or curved horny structure, or nail, on the foot of a bird and of many reptiles and mammals 2. a… …   English World dictionary


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