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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
amniote Amniotes (from Greek ἀμνίον ''amnion'', "membrane surrounding the fetus", earlier "bowl in which the blood of sacrificed animals was caught", from ἀμνός ''amnos'', "lamb") are a clade of tetrapod vertebrates comprising reptiles (c ...
s (
mammals Mammals (from Latin , 'breast') are a group of vertebrate animals constituting the class Mammalia (), and characterized by the presence of mammary glands which in females produce milk for feeding (nursing) their young, a neocortex (a region ...
,
reptiles Reptiles are tetrapod animals in the class or clade Reptilia . As a class in Linnean taxonomy, Reptilia refers to a paraphyletic grouping comprising all amniotes (vertebrates which encase their embryos in a series of protective sacs) except syn ...

reptiles
,
birds Birds are a group of warm-blooded vertebrates constituting the class Aves , characterised by feathers, toothless beaked jaws, the laying of hard-shelled eggs, a high metabolic rate, a four-chambered heart, and a strong yet lightweight skele ...

birds
). Some
invertebrate Invertebrates are animals that neither possess nor develop a vertebral column (commonly known as a ''backbone'' or ''spine''), derived from the notochord. This includes all animals apart from the subphylum Vertebrata. Familiar examples of inverte ...
s such as
beetles Beetles are a group of insects that form the order Coleoptera (), in the superorder Endopterygota. Their front pair of wings are hardened into wing-cases, elytra, distinguishing them from most other insects. The Coleoptera, with about 400,000 ...
and
spiders Spiders (order Araneae) are air-breathing arthropods that have eight legs, chelicerae with fangs generally able to inject venom, and spinnerets that extrude silk. They are the largest order of arachnids and rank seventh in total species diversi ...

spiders
have somewhat similar fine, hooked structures at the end of the leg or tarsus for gripping a surface as they walk. The pincers of
crabs Crabs are decapod crustaceans of the infraorder Brachyura, which typically have a very short projecting "tail" (abdomen) ( el, βραχύς , translit=brachys = short, / = tail), usually hidden entirely under the thorax. They live in all the world ...
,
lobsters Lobsters are a family (Nephropidae, sometimes also ''Homeridae'') of large marine crustaceans. Lobsters have long bodies with muscular tails, and live in crevices or burrows on the sea floor. Three of their five pairs of legs have claws, incl ...

lobsters
and
scorpions Scorpions are predatory arachnids of the order Scorpiones. They have eight legs, and are easily recognized by a pair of grasping pincers and a narrow, segmented tail, often carried in a characteristic forward curve over the back and always endin ...
, more formally known as their
chelae A chela (), also named claw, nipper, or pincer, is a pincer-like organ at the end of certain limbs of some arthropods. The name comes from Greek () through New Latin ('). The plural form is chelae. Legs bearing a chela are called chelipeds. Anoth ...
, are sometimes called claws. A true claw is made of a hard
protein Proteins are large biomolecules or macromolecules that are comprised of one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, respo ...
called
keratin Keratin () is one of a family of fibrous structural proteins known as scleroproteins. ''α-Keratin'' is a type of keratin found in vertebrates. It is the key structural material making up scales, hair, nails, feathers, horns, claws, hooves, callu ...

keratin
. Claws are used to catch and hold prey in
carnivorous A carnivore , meaning "meat eater" (Latin, ''caro'', genitive ''carnis'', meaning "meat" or "flesh" and ''vorare'' meaning "to devour"), is an animal whose food and energy requirements derive solely from animal tissue or meat, whether through hu ...
mammals Mammals (from Latin , 'breast') are a group of vertebrate animals constituting the class Mammalia (), and characterized by the presence of mammary glands which in females produce milk for feeding (nursing) their young, a neocortex (a region ...
such as
cats The cat (''Felis catus'') is a domestic species of small carnivorous mammal. It is the only domesticated species in the family Felidae and is often referred to as the domestic cat to distinguish it from the wild members of the family. A cat ...
and
dogs The domestic dog (''Canis familiaris'' or ''Canis lupus familiaris'') is a domesticated form of wolf. The dog descended from an ancient, extinct wolf, with the modern grey wolf being the dog's nearest living relative. The dog was the first sp ...
but may also be used for such purposes as digging, climbing trees, self-defense and grooming, in those and other species. Similar appendages that are flat and do not come to a sharp point are called 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 A spur is a metal tool designed to be worn in pairs on the heels of riding boots for the purpose of directing a horse or other animal to move forward or laterally while riding. It is usually used to refine the riding aids (commands) and to back ...
s.


Tetrapods

In
tetrapod Tetrapods (; from Greek 'four' and 'foot') are four-limbed animals constituting the superclass Tetrapoda . It includes extant and extinct amphibians, reptiles (including dinosaurs and therefore birds), and synapsids (including mammals). Tetra ...
s, claws are made of
keratin Keratin () is one of a family of fibrous structural proteins known as scleroproteins. ''α-Keratin'' is a type of keratin found in vertebrates. It is the key structural material making up scales, hair, nails, feathers, horns, claws, hooves, callu ...

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

All
carnivora Carnivora is an order of placental mammals that have specialized in primarily eating flesh. Its members are formally referred to as carnivorans, though some species are omnivorous, such as raccoons and bears, and quite a few species such as pand ...
ns have claws, which vary considerably in length and shape. Claws grow out of the third
phalange The phalanges (singular: ''phalanx'' ) are digital bones in the hands and feet of most vertebrates. In primates, the thumbs and big toes have two phalanges while the other digits have three phalanges. The phalanges are classed as long bones. St ...
s of the paws and are made of
keratin Keratin () is one of a family of fibrous structural proteins known as scleroproteins. ''α-Keratin'' is a type of keratin found in vertebrates. It is the key structural material making up scales, hair, nails, feathers, horns, claws, hooves, callu ...

keratin
. Many
predator Predation is a biological interaction where one organism, the predator, kills and eats another organism, its prey. It is one of a family of common feeding behaviours that includes parasitism and micropredation (which usually do not kill the hos ...
y mammals have protractile claws that can partially hide inside the animal's
paw A paw is the soft foot-like part of a mammal, generally a quadruped, that has claws. Common characteristics The paw is characterised by thin, pigmented, keratinised, hairless epidermis covering subcutaneous collagenous and adipose tissue, which ...
, especially the cat family,
Felidae Felidae () is a family of mammals in the order Carnivora, colloquially referred to as cats, and constitutes a clade. A member of this family is also called a felid (). The term "cat" refers both to felids in general and specifically to the dome ...
, 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 Viverridae is a family of small to medium-sized mammals, the viverrids (), comprising 14 genera, which are subdivided into 33 species. This family was named and first described by John Edward Gray in 1821. Viverrids occur all over Africa, southern ...
(and the extinct
Nimravidae Nimravidae is an extinct family of carnivorans, sometimes known as false saber-toothed cats, whose fossils are found in North America and Eurasia. Not considered to belong to the true cats (family Felidae), the nimravids are generally considered c ...
). A claw that is retractable is protected from wear and tear. Most cats and dogs also have a
dewclaw of a dog: A. Claw, B. Digital pads, C. Metacarpal pad, D. Dewclaw, E. Carpal pad A dewclaw is a Digit (anatomy), digit – vestigial in some animals – on the foot of many mammals, birds, and reptiles (including some extinct orders, like certain ...
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 Nail or Nails may refer to: In biology * Nail (anatomy), toughened protective protein-keratin (known as alpha-keratin, also found in hair) at the end of an animal digit * Nail (beak), a plate of hard horny tissue at the tip of some bird beaks O ...
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 "
hoofCloven hooves of roe deer (''Capreolus capreolus''), with prominent dewclaws A hoof ( or ), plural hooves ( or ) or hoofs , is the tip of a toe of an ungulate mammal, strengthened by a thick and horny keratin covering. Artiodactyls are even-toed un ...
". (Nevertheless, one side of the cloven-hoof of
artiodactyl The even-toed ungulates (Artiodactyla , ) are ungulates—hoofed animals—which bear weight equally on two (an even number) of their five toes: the third and fourth. The other three toes are either present, absent, vestigial, or pointing posteri ...
ungulate Ungulates (pronounced ) are members of a diverse clade of primarily large mammals with hooves. These include odd-toed ungulates such as horses, rhinoceroses and tapirs, and even-toed ungulates such as cattle, pigs, giraffes, camels, sheep, deer, ...
s may also be called a claw). Every so often, the growth of claws stops and restarts, as does
hair Hair is a protein filament that grows from follicles found in the dermis. Hair is one of the defining characteristics of mammals. The human body, apart from areas of glabrous skin, is covered in follicles which produce thick terminal and fin ...
. In a hair, this results in the hair falling out and being replaced by a new one. In claws, this results in an
abscission Abscission (from Latin ''ab'', "away", and ''scindere'', "to cut'") is the shedding of various parts of an organism, such as a plant dropping a leaf, fruit, flower, or seed. In zoology, abscission is the intentional shedding of a body part, such a ...
layer, and the old segment breaks off. This process takes several months for
human Humans (''Homo sapiens'') are the most populous and widespread species of primates, characterized by bipedality, opposable thumbs, hairlessness, and intelligence allowing the use of culture, language and tools. They are the only extant members ...

human
thumbnails.
Cat The cat (''Felis catus'') is a domestic species of small carnivorous mammal. It is the only domesticated species in the family Felidae and is often referred to as the domestic cat to distinguish it from the wild members of the family. A 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
equids Equidae (sometimes known as the horse family) is the taxonomic family of horses and related animals, including the extant horses, donkeys, and zebras, and many other species known only from fossils. All extant species are in the genus ''Equus'', w ...
(
horse The horse (''Equus ferus caballus'') is a domesticated odd-toed ungulate mammal. It belongs to the taxonomic family Equidae and is one of two extant subspecies of ''Equus ferus''. The horse has evolved over the past 45 to 55 million years fr ...

horse
s,
donkey The donkey or ass (''Equus africanus asinus'') is a domesticated member of the horse family, Equidae. The wild ancestor of the donkey is the African wild ass, ''E. africanus''. The donkey has been used as a working animal for at least 5000 yea ...
s and
mule A mule is the offspring of a male donkey (jack) and a female horse (mare). Horses and donkeys are different species, with different numbers of chromosomes. Of the two first-generation hybrids between these two species, a mule is easier to obtai ...
s) usually need regular trimming by a
farrier : ''The Farrier'' Image:Panamanian_farrier_at_work.jpg, Rasping the Horse hoof, hoof A farrier is a specialist in equine hoof care, including the trimming and balancing of horses' hooves and the placing of shoes on their hooves, if necess ...
, as a consequence of reduced activity on hard ground.


Primates

Primate A primate ( ) (from Latin , from 'prime, first rank') is a eutherian mammal constituting the taxonomic order Primates (). Primates arose 85–55 million years ago first from small terrestrial mammals, which adapted to living in the trees ...
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 Nail or Nails may refer to: In biology * Nail (anatomy), toughened protective protein-keratin (known as alpha-keratin, also found in hair) at the end of an animal digit * Nail (beak), a plate of hard horny tissue at the tip of some bird beaks O ...
s. However, claw-like nails are found in small-bodied callitrichids on all digits except the
hallux Toes are the digits (fingers) of the foot of a tetrapod. Animal species such as cats that walk on their toes are described as being ''digitigrade''. Humans, and other animals that walk on the soles of their feet, are described as being ''plantigr ...
or big toe. A laterally flattened
grooming claw Close-up of a ruffed lemur's foot, showing the toilet-claw on the second toe and nails on all other toes A grooming claw (or toilet claw) is the specialized claw or nail on the foot of certain primates, used for personal grooming. All prosimians ha ...
, used for grooming, can be found on the second toe in living
strepsirrhines Strepsirrhini or Strepsirhini (; ) is a suborder of primates that includes the lemuriform primates, which consist of the lemurs of Madagascar, galagos ("bushbabies") and pottos from Africa, and the lorises from India and southeast Asia. Collectiv ...
, and the second and third in
tarsiers Tarsiers are haplorrhine primates of the family Tarsiidae, which is itself the lone extant family within the infraorder Tarsiiformes. Although the group was once more widespread, all of its species living today are found in the islands of Southeas ...
.
Aye-aye The aye-aye (''Daubentonia madagascariensis'') is a long-fingered lemur, a strepsirrhine primate native to Madagascar with rodent-like teeth that perpetually grow and a special thin middle finger. It is the world's largest nocturnal primate. ...
s have functional claws on all other digits except the hallux, including a grooming claw on the second toe. Less commonly known, a grooming claw is also found on the second pedal digit of
night monkey Night monkeys, also known as owl monkeys or douroucoulis (), are nocturnal New World monkeys of the genus ''Aotus'', the only member of the family Aotidae (). The genus comprises eleven species which are found across Panama and much of South Amer ...
s (''Aotus''),
titi The titis, or titi monkeys, are the New World monkeys of the subfamily Callicebinae, which contains three extant genera, ''Cheracebus'', ''Callicebus'', and ''Plecturocebus.'' This subfamily also contains the extinct genera ''Xenothrix, Antilloth ...
s (''Callicebus''), and possibly other
New World monkey New World monkeys are the five families of primates that are found in the tropical regions of Mexico, Central and South America: Callitrichidae, Cebidae, Aotidae, Pitheciidae, and Atelidae. The five families are ranked together as the Ceboidea , t ...
s.


Reptiles

Most reptiles have well-developed claws. Most lizards have toes ending in stout claws. In snakes, feet and claws are absent, but in many
boids Boids is an artificial life program, developed by Craig Reynolds in 1986, which simulates the flocking behaviour of birds. His paper on this topic was published in 1987 in the proceedings of the ACM SIGGRAPH conference. The name "boid" correspon ...
such as ''
Boa constrictor#REDIRECT Boa constrictor#REDIRECT Boa constrictor {{R from miscapitalisation ...
{{R from miscapitalisation ...
'', 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

A talon is the claw of a
bird of prey Birds of prey, also known as raptors, include species of bird that primarily hunt and feed on vertebrates that are large relative to the hunter. Additionally, they have keen eyesight for detecting food at a distance or during flight, strong feet ...
, 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 ''Casuarius'' is a genus of birds in the order Casuariiformes, whose members are the cassowaries. It is classified as a ratite (flightless bird without a keel on its sternum bone) and is native to the tropical forests of New Guinea (Papua New Gu ...

Cassowaries
use claws on their inner toe (digit II) for defence, and have been known to disembowel people. All birds however have claws, which are used as general holdfasts and protection for the tip of the digits. The
hoatzin The hoatzin (, ''Opisthocomus hoazin''), also known as the reptile bird, skunk bird, stinkbird, or Canje pheasant, is a species of tropical bird found in swamps, riparian forests, and mangroves of the Amazon and the Orinoco basins in South America ...
and
turaco The turacos make up the bird family Musophagidae ( "banana-eaters"), which includes plantain-eaters and go-away-birds. In southern Africa both turacos and go-away-birds are commonly known as loeries. They are semi-zygodactylous: the fourth (oute ...
are unique among
extant Extant is the opposite of the word extinct. It may refer to: * Extant hereditary titles * Extant literature, surviving literature, such as ''Beowulf'', the oldest extant manuscript written in English * Extant taxon, a taxon which is not extinct, s ...
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. 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.


Amphibians

The only
amphibian Amphibians are ectothermic, tetrapod vertebrates of the class Amphibia. All living amphibians belong to the group Lissamphibia. They inhabit a wide variety of habitats, with most species living within terrestrial, fossorial, arboreal or fresh ...
s to bear claws are the
African clawed frog The African clawed frog (''Xenopus laevis'', also known as the xenopus, African clawed toad, African claw-toed frog or the ''platanna'') is a species of African aquatic frog of the family Pipidae. Its name is derived from the three short claws on ...
s. Claws appear to have evolved separately in the amphibian and
amniote Amniotes (from Greek ἀμνίον ''amnion'', "membrane surrounding the fetus", earlier "bowl in which the blood of sacrificed animals was caught", from ἀμνός ''amnos'', "lamb") are a clade of tetrapod vertebrates comprising reptiles (c ...
line.


Arthropods

The scientifically correct term for the "claw" of an arthropod, such as a lobster or crab, is a chela (plural ''chelae''). Legs bearing a chela are called
cheliped A chela (), also named claw, nipper, or pincer, is a pincer-like organ at the end of certain limbs of some arthropods. The name comes from Greek () through New Latin ('). The plural form is chelae. Legs bearing a chela are called chelipeds. Anoth ...
s. Chelae are also called pincers.


See also

*
Horse hoof A horse hoof is a structure surrounding the distal phalanx of the 3rd digit (digit III of the basic pentadactyl limb of vertebrates, evolved into a single weight-bearing digit in equids) of each of the four limbs of ''Equus'' species, which is cov ...
*
Dactyly In biology, dactyly is the arrangement of digits (fingers and toes) on the hands, feet, or sometimes wings of a tetrapod animal. It comes from the Greek word δακτυλος (''dáktylos'') = "finger". Sometimes the ending "-dactylia" is used. ...


References


External links

{{Commons category, Claws
Rat's Claws
also explains much about mammalian claws in general. Animal anatomy