The tail is the section at the rear end of certain kinds of animals’ bodies; in general, the term refers to a distinct, flexible appendage to the torso. It is the part of the body that corresponds roughly to the sacrum and coccyx in mammals, reptiles, and birds. While tails are primarily a feature of vertebrates, some invertebrates including scorpions and springtails, as well as snails and slugs, have tail-like appendages that are sometimes referred to as tails. Tailed objects are sometimes referred to as "caudate" and the part of the body associated with or proximal to the tail are given the adjective "caudal".
Based on this definition, the tail of a snake would typically consist of a small portion of the rear end of its body, where none of its vital organs are being housed, and begin at its last rib, contrary to the commonly held assumption that the tail begins precisely at the middle of the snake's body due to its linear shape.
Animal tails are used in a variety of ways. They provide a source of locomotion for fish and some other forms of marine life. Many land animals use their tails to brush away flies and other biting insects. Some species, including cats and kangaroos, use their tails for balance; and some, such as New World monkeys and opossums, have what are known as prehensile tails, which are adapted to allow them to grasp tree branches.
Tails are also used for social signaling. Some deer species flash the white underside of their tails to warn other nearby deer of possible danger, beavers slap the water with their tails to indicate danger, and canids (including domestic dogs) indicate emotions through the positioning and movement of their tails. Some species' tails are armored, and some, such as those of scorpions, contain venom.
Some species of lizard can detach ("cast") their tails from their bodies. This can help them to escape predators, which are either distracted by the wriggling, detached tail or left with only the tail while the lizard flees. Tails cast in this manner generally grow back over time, though the replacement is typically darker in colour than the original. Various species of rat demonstrate a similar function with their tails, known as degloving, in which the outer layer is shed in order for the animal to escape from a predator.
Most birds' tails end in long feathers called rectrices. These feathers are used as a rudder, helping the bird steer and maneuver in flight; they also help the bird to balance while it is perched. In some species—such as birds of paradise, lyrebirds, and most notably peafowl—modified tail feathers play an important role in courtship displays. The extra-stiff tail feathers of other species, including woodpeckers and woodcreepers, allow them to brace themselves firmly against tree trunks.
Human embryos have a tail that measures about one-sixth of the size of the embryo itself. As the embryo develops into a fetus, the tail is absorbed by the growing body. Infrequently, a child is born with a "soft tail", which contains no vertebrae, but only blood vessels, muscles, and nerves, but this is regarded as an abnormality rather than a vestigial true tail, even when such an appendage is located where the tail would be expected. Fewer than 40 cases have been reported of infants with "true tails" containing the caudal vertebrae, a result of atavism.
Humans have a "tail bone" (the coccyx) attached to the pelvis; it comprises fused vertebrae, usually four, at the bottom of the vertebral column. It does not normally protrude externally - humans are an acaudal (or acaudate) species.
Pig (Sus domestica)
Glyptodon (Glyptodon asper)
Longhorn cowfish (Lactoria cornuta)
Grévy's zebra (Equus grevyi)
American alligator (Alligator mississipiensis)
Hippopotamus (Hippopotamus amphibius)
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[...] every human fetus has, at between four and five weeks of age, 10-12 developing tail vertebrae that extend beyond the anus and legs, accounting for more than 10 percent of the length of the embryo.
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- "acaudal". Oxford English Dictionary (3rd ed.). Oxford University Press. September 2005. (Subscription or UK public library membership required.)
- "acaudate". Oxford English Dictionary (3rd ed.). Oxford University Press. September 2005. (Subscription or UK public library membership required.)
- Media related to Tails at Wikimedia Commons