In most amniotes (mammals, reptiles, birds), a claw is a curved, pointed appendage present at the end of a toe or finger. Some invertebrates, such as beetles and spiders, have fine, hooked projections at the end of their legs or tarsus that allow them to grip a surface while walking. Crabs, lobsters, and scorpions have pincers termed chelae, which are more technically known as claws.
A real claw is formed of keratin, a hard protein. Claws are used by carnivorous mammals such as cats and dogs to catch and hold prey, but they can also be used for digging, climbing trees, self-defense, and grooming in those and other species. Nails are similar flat appendages that do not develop to a sharp tip. Spurs are claw-like extensions that arise from various areas of the foot rather than the end of the digits.
Tetrapods
Claws of tetrapods are formed of keratin and have two layers. The unguis is the tougher outer layer, made up of keratin fibres that are organized perpendicular to the development direction and in layers at an oblique angle. The subunguis is a softer, flaky bottom layer with a grain that runs parallel to the development direction. While traveling across the nail bed, the claw extends outward from the nail matrix at the base of the unguis, and the subunguis thickens. The unguis develops outward quicker than the subunguis, resulting in curvature, while the claw’s thinner sides wear away quicker than the thicker centre, resulting in a more or less sharp point. Tetrapods use their claws for a variety of purposes, including grasping or killing prey, digging, climbing, and hanging.
Mammals
Claws are found on all carnivores and vary in length and shape. Claws are comprised of keratin and grow from the third phalanges of the paws. Many predatory mammals have protractile claws that can partially hide inside the animal’s paw, particularly members of the Felidae family, which has nearly all members with completely protractible claws. Retractable claws are exclusively found in select Viverridae species outside of the cat family (and the extinct Nimravidae). A retractable claw is more resistant to wear and strain.
On the inside of the front paws of most cats and dogs is a dewclaw. It is less functional than the other claws, but it does assist cats in catching prey. Because the dewclaw does not come into contact with the ground, it experiences less wear and is sharper, and lasts longer.
A nail resembles a claw, except it is flatter and has a curving edge rather than a point. A “hoof” is a nail that is large enough to support the weight. (However, one side of the cloven-hoof of artiodactyl ungulates’ cloven-hoof may also be referred to as a claw.)
Claws, like hair, stop and start growing every now and again. This causes the hair to fall out and be replaced by a new one in the hair. This causes an abscission layer in claws, and the old segment falls off. For human thumbnails, this procedure takes several months. Cats are frequently seen removing old unguis layers from wood or specially designed boards. Ground contact wears or self-trims the hooves of ungulates. Because of their limited activity on hard ground, domesticated equids (horses, donkeys, and mules) require frequent farrier trimming.
Primates
Because the subunguis has vanished, primates’ nails are only made up of the unguis. Claws are no longer required for mobility, thanks to the evolution of grasping hands and feet, and most digits now have nails. Claw-like nails are seen on all digits except the hallux or big toe in small-bodied callitrichids. The second toe of living strepsirrhines and the second and third toes of tarsiers have a laterally flattened grooming claw that is used for grooming. Except for the hallux, aye-ayes have functional claws on all other digits, including a grooming claw on the second toe. A grooming claw can also be seen on the second pedal digit of night monkeys (Aotus), titis (Callicebus), and possibly other New World monkeys, which is less well-known.
Reptiles
Claws are strongly developed in most reptiles. The toes of most lizards finish in robust claws. Feet and claws are missing in snakes, although remains of very reduced hind-limbs emerge with a single claw as “spurs” on each side of the anal orifice in several boids, such as the Boa constrictor. Claws of lizards are employed as climbing aids and to hold down food in carnivorous species.
Birds
A talon is a bird of prey’s primary hunting gear, its claw. The talons are vital to most birds of prey; without them, they would be unable to catch their prey. Claws are also used by some birds to defend themselves. Cassowaries have been known to disembowel individuals using their claws on their inner toe (digit II). Claws, on the other hand, are present in all birds and serve as general holdfasts and protection for the tips of the digits.
As chicks, the hoatzin and turaco are the only extant birds with functional claws on their thumb and index finger (digit I and II) on their forelimbs, allowing them to climb trees until their adult plumage with flying feathers develops. Ostriches, emus, ducks, geese, and kiwis, for example, have a claw- or nail-like structure buried underneath the feathers at the end of their hand fingers.
Amphibians
African clawed frogs are the only amphibians with claws. Amphibian and amniote claws appear to have developed independently.
Arthropods
A chela is a scientific term for an arthropod’s “claw,” such as that of a lobster or crab (plural chelae). Chelipeds are legs that have a chela on them. Pincers are another name for chelae. The Claw of cat is an example of the claw in the phylum Arthropods.
Did You Know?
Which Animal Has the Strongest Claws?
Ans. The coconut crab has the most powerful claws compared to any animal. The pinching power of a coconut crab is proportional to its size, according to researchers at the Okinawa Churashima Foundation in Japan.