A
dewclaw is a
vestigial digitVestigiality describes homologous characters of organisms which have seemingly lost all or most of their original function in a species through evolution. These may take various forms such as anatomical structures, behaviors and biochemical pathways. Some of these disappear early in embryonic...
of the
footThe foot is an anatomical structure found in many vertebrates. It is the terminal portion of a limb which bears weight and allows locomotion...
of many
mammalMammals are a class of vertebrate animals whose females are characterized by the possession of mammary glands while both males and females are characterized by sweat glands, hair, three middle ear bones used in hearing, and a neocortex region in the brain.Mammals are divided into three main...
s,
birdBirds are winged, bipedal, endothermic , vertebrate animals that lay eggs. There are around 10,000 living species, making them the most numerous tetrapod vertebrates. They inhabit ecosystems across the globe, from the Arctic to the Antarctic. Birds range in size from the Bee Hummingbird to the ...
s, and
reptileReptiles, or members of the class Reptilia, are air-breathing, generally "cold-blooded" amniotes that generally have skin covered in scales or scutes. They are tetrapods and lay amniote eggs, whose embryos are surrounded by the amnion membrane...
s (including some extinct orders, like certain theropods). It grows higher on the leg so that in
digitigradeA digitigrade is an animal that stands or walks on its digits, or toes. Digitigrades include walking birds , cats, dogs, and most other mammals, but not humans, bears, and a few others...
species, when the animal is standing, it does not make contact with the ground.
DogThe dog is a domesticated form of the Gray Wolf, a member of the Canidae family of the order Carnivora. The term is used for both feral and pet varieties. The domestic dog has been one of the most widely kept working and companion animals in human history...
s almost always have dewclaws on the inside of the front legs and occasionally also on the hind legs. Unlike front dewclaws, rear dewclaws tend to have little bone or muscle structure in most breeds.
A
dewclaw is a
vestigial digitVestigiality describes homologous characters of organisms which have seemingly lost all or most of their original function in a species through evolution. These may take various forms such as anatomical structures, behaviors and biochemical pathways. Some of these disappear early in embryonic...
of the
footThe foot is an anatomical structure found in many vertebrates. It is the terminal portion of a limb which bears weight and allows locomotion...
of many
mammalMammals are a class of vertebrate animals whose females are characterized by the possession of mammary glands while both males and females are characterized by sweat glands, hair, three middle ear bones used in hearing, and a neocortex region in the brain.Mammals are divided into three main...
s,
birdBirds are winged, bipedal, endothermic , vertebrate animals that lay eggs. There are around 10,000 living species, making them the most numerous tetrapod vertebrates. They inhabit ecosystems across the globe, from the Arctic to the Antarctic. Birds range in size from the Bee Hummingbird to the ...
s, and
reptileReptiles, or members of the class Reptilia, are air-breathing, generally "cold-blooded" amniotes that generally have skin covered in scales or scutes. They are tetrapods and lay amniote eggs, whose embryos are surrounded by the amnion membrane...
s (including some extinct orders, like certain theropods). It grows higher on the leg so that in
digitigradeA digitigrade is an animal that stands or walks on its digits, or toes. Digitigrades include walking birds , cats, dogs, and most other mammals, but not humans, bears, and a few others...
species, when the animal is standing, it does not make contact with the ground.
Dogs
DogThe dog is a domesticated form of the Gray Wolf, a member of the Canidae family of the order Carnivora. The term is used for both feral and pet varieties. The domestic dog has been one of the most widely kept working and companion animals in human history...
s almost always have dewclaws on the inside of the front legs and occasionally also on the hind legs. Unlike front dewclaws, rear dewclaws tend to have little bone or muscle structure in most breeds. Sometimes some dogs will even have more than one dewclaw on the same foot; often at least one of these dewclaws will be poorly connected to the leg and in this case it is often surgically removed. When a dog has extra dewclaws in addition to the usual one on each front leg, the dog is said to be
double dewclawed. There is some debate about whether a dewclaw helps dogs to gain traction when they run because, in some dogs, the dewclaw makes contact when they are running and the nail on the dewclaw often wears down in the same way that the nails on their other toes do, from contact with the ground. However, in many dogs the dewclaws never make contact with the ground; in this case, the dewclaw's nail never wears away, and it is then often trimmed to keep it to a safe length.
The dewclaws are not dead appendages. They can be used to lightly grip bones and other items that dogs hold with the paws. However, in some dogs these claws may not appear to be connected to the leg at all except by a flap of skin; in such dogs the claws do not have a use for gripping as the claw can easily fold or turn.
There is also some debate as to whether dewclaws should be surgically removed. The argument for removal states that dewclaws are a weak digit, barely attached to the leg, so that they can rip partway off or easily catch on something and break, which can be extremely painful and prone to infection. Others say the pain of removing a dewclaw is far greater than any other risk. For this reason, removal of dewclaws is illegal in many countries. There is, perhaps, an exception for hunting dogs, which can easily tear the dewclaw when running in overgrown vegetation. If a dewclaw is to be removed, this should be done when the dog is a puppy, sometimes as young as 3 days old, though it can also be performed on older dogs if necessary (though the surgery may be more difficult then). The surgery is fairly straight-forward and may even be done with only local anesthetics if the digit is not well connected to the leg. Unfortunately many dogs can't resist licking at their sore paws following the surgery, so owners need to remain vigilant.
In addition, for those dogs whose dewclaws make contact with the ground when they run, it is possible that removing them could be a disadvantage for a dog's speed in running and changing of direction, particularly in performance dog sports such as
dog agilityDog agility is a dog sport in which a handler directs a dog through an obstacle course in a race for both time and accuracy. Dogs run off-leash with no food or toys as incentives. The handler can touch neither dog nor obstacles...
.
There also exists in
folkloreFolklore is the body of expressive culture, including stories, music, dance, legends, oral history, proverbs, jokes, popular beliefs, customs, and so forth within a particular population comprising the traditions of that culture, subculture, or group. It is also the set of practices through which...
a story that claims that dogs that have not had their dewclaws removed are immune to snakebite. In America, some pups are commonly sold by breeders "dewclawed", that is with the dewclaws removed (as by a
vetVet may refer to:* Veterinarian, a professional trained to diagnose and treat illness in animals.* Veteran, a person with long experience in a particular area, most often in military service during wartime.** Veteran tree, a culturally significant tree...
) for perceived health and safety reasons. A few breed standards also call for it.
Rear dewclaws
Canids have four claws on the rear feet, although some domestic dog breeds or individuals have an additional claw. A more technical term for this fifth claw on the rear legs is
hind-limb-specific preaxial polydactylyPolydactyly or polydactylism , also known as hyperdactyly, is a congenital physical anomaly in humans having supernumerary fingers or toes...
. Several genetic mechanisms can cause rear dewclaws; they involve the
LMBR1Limb region 1 protein homolog is a protein that in humans is encoded by the LMBR1 gene.-Further reading:...
gene and related parts of the genome.
Hoofed animals
Hoofed animals walk on the tips of special toes, the
hoofA hoof is the tip of a toe of an ungulate mammal, strengthened by a thick horny covering. The hoof consists of a hard or rubbery sole, and a hard wall formed by a thick nail rolled around the tip of the toe. The weight of the animal is normally borne by both the sole and the edge of the hoof wall....
s. Cloven-hoofed animals walk on a central pair of hoofs, but many also have an outer pair of dewclaws on each foot. These are a little further up the leg than the main hoofs, and similar in structure to them. In some species (such as
cattleCattle are the most common type of large domesticated ungulates. They are a prominent modern member of the subfamily Bovinae, are the most widespread species of the genus Bos, and are most commonly classified collectively as Bos primigenius...
) the dewclaws are much smaller than the hoofs and never touch the ground. In others (such as
pigPigs are a genus of even-toed ungulates within the family Suidae. The name hog most commonly refers to the domestic pig in everyday parlance, but technically encompasses several distinct species, including the wild boar...
s and many
deerDeer are the ruminant mammals forming the family Cervidae. They include for example Moose, Red Deer, Reindeer, Roe and Chital. Animals from related families within the order Artiodactyla are often also considered to be deer – these include muntjac and water deer...
), they are only a little smaller than the hoofs, and may reach the ground in soft conditions or when jumping. Some hoofed animals (such as
giraffeThe giraffe is an African even-toed ungulate mammal, the tallest of all land-living animal species, and the largest ruminant. It is covered in large, irregular patches of yellow to black fur separated by white, off-white, or dark yellowish brown background. The average mass for an adult male...
s and modern
horseThe horse is a hoofed mammal, a subspecies of one of seven extant species of the family Equidae. The horse has evolved over the past 45 to 55 million years from a small multi-toed creature into the large, single-toed animal of today...
s) have no dew claws.
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