Function

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 is known as a prehensile tail. This is a type of tail that is 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, and canids (including domestic dogs) indicate emotions through the positioning of their tails. Evolutionary pressures have led to the development of armored tails in some species, and some, such as the tails of scorpions contain venom.

Some species of lizard can detach ("cast") their tails from their bodies. This can help them to escape from predators, which are either distracted by the wriggling detached tail, or left with only the tail while the rest of the lizard flees. Tails cast in this manner generally grow back over time, though the replacement is typically darker in color than the original.

The tails of most birds end in long feathers called rectrices. These feathers are used as a rudder, helping the bird to 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 peacocks—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 tails

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. The developmental tail is thus a human vestigial structure. Infrequently, a child is born with a "soft tail", which contains no vertebrae, but only blood vessels, muscles, and nerves, although there have been a very few documented cases of tails containing cartilage or up to five vertebrae. Modern procedures allow doctors to eliminate the tail at delivery. Some of these tails may in fact be sacrococcygeal teratomas. The longest human tail on record belonged to a twelve-year-old boy living in what was then French Indochina, which measured 229 mm (9 inches). A man named Chandre Oram, who lives in West Bengal, a state in India, is famous because of his tail. It is not believed to be a true tail, however, but rather a case of spina bifida.

Humans have a tail bone (the coccyx) attached to the pelvis, in the same place which other mammals have tails. The tail bone is formed of fused vertebrae, usually four, at the bottom of the vertebral column. It doesn't protrude externally, but retains an anatomical purpose: providing an attachment for muscles like the gluteus maximus.