Tails

The tail is the prolongation of the backbone, beyond the trunk of the body, of any animal, insect, or fish. The tail of the vertebrate is composed of flesh and bone but does not contain any viscera, or internal organs. For many aquatic animals, the tail is fundamental to their locomotive ability. These include such diverse organisms as fish, amphibians, crocodiles, otters, and whales. Squirrels and other arboreal animals use their tails to keep balance and as a rudder when they jump from branch to branch. Others, such as the spider monkey and the chameleon, use the tail as an extra limb to increase their mobility through the branches of the rainforest. The tail may also be used as a means of defense for porcupines, as a warning signal in rattlesnakes, and as a hunting weapon in alligators and scorpions. Tails are an ornamental sexual attractant in peacocks and a communication tool for dogs. Most birds do not have tails. Instead, the prolongation has been fused into the short pygostyle bone, which serves as the holder of tail feathers and assists the birds in flying.

The shape, morphology, and structure of the tail vary according to the nature and behavior of the specific animal. Burrowing insectivores, like other burrowing animals, usually have no tail. In contrast, climbing and running species have very large tails. Slow-moving animals, such as hedgehogs, have short tails, while chameleons have coiled tails.

Tails in Invertebrates

Several lizards have thick tails covered by large, spiny, hard scales. The tail is often used as a defensive measure against predators such as snakes, especially when the head and body of the lizard are wedged between rocks. Moreover, lizards are capable of shedding their tails, which wriggle in a way that may confuse their predator, thus giving them enough time to escape. Each vertebra of such a tail has a fracture line along which it splits when the tail muscles contract. A unique lizard is the Solomon Islands skink, whose prehensile tail muscles are bound to the vertebrae and to a fibrous sheath of collagen under the skin, thus creating a much stronger and more flexible tail. Stimulation of the nerve contraction in the severed position keeps the tail moving for several seconds after severing occurs. Normally, the tail splits off in one place, but in a few lizard species, such as the glass snakes (Ophisaurus), tails may be broken in more than one place. The stump usually heals very quickly, and a new tail regenerates, although it is not as long or elaborate as the original. Bioengineers in the late 1990s researched to isolate the gene responsible for the regeneration of the severed tails.

Amphibians such as tadpoles and salamanders also lose and, in many cases, regenerate their tail, which has a spinal cord. Tadpole tails have a stiff rod for support, called the notochord, while the salamander’s tail has a backbone with vertebrae. No tail is regenerated in the salamander if the spinal cord is severed, unlike the tadpoles, where the tail is reformed regardless of the fate of the severed spinal cord.

Insects use their tails in many ways, including spraying poison, stinging, communicating, laying or burying eggs, or in defense as a whip. The female long-tailed giant ichneumon wasp (Megarhyssa macrurus) uses its four-inch tail to dig into the wood on trees and rotting logs and bury its eggs. Though it is large and intimidating, it is generally harmless to humans. A scorpion's tail is a unique extension of its abdomen called a metasoma, which may be harry, thick, striped, or, rarely, a double tail. Each of their tails ends in a sharp stinger and a venom gland. Insects like swallow-tailed butterflies and luna moths do not have true tails but tail-like extensions of their back wings.

Tails in invertebrates are used in characteristic, unique ways among the different animals. Iguanas use their tails like large oars to swim in water while tucking their legs close to their bodies. When threatened, the armadillo lizard puts its tail in its mouth, rolls over, and assumes the shape of a tight ball. Day geckos use their tails as support while jumping from tree to tree to avoid their main predator, the falcon. The skink has a very short tail, whose shape is very close to that of its head. This confuses its enemies since they do not know the direction the skink will take while escaping.

Tails in Vertebrates

In most vertebrates, tails are extensions of the backbone that may serve various purposes, including flying, swimming, balancing, grasping, defense, communication, and energy storage.

The squirrel owes its name to its tail. The name is derived from the Greek words skia (“shadow”) and oura (“tail”), indicating that the tail is large enough to shade the rest of the animal's body. Unlike the bat, which is the only mammal that truly flies, the flying squirrel is the only vertebrate that glides. Using its strong and sturdy back feet to jump from the top of a tree, it flattens its tail and spreads the loose folds of the skin so that it can glide in the air. Just before landing, the gray squirrel lowers its tail first, then quickly lifts it and lands on its hind feet. When in danger, the red squirrel attempts to scare its predator by flicking its tail while using a series of noises, such as whistling, chattering, chirping, and stomping its hind feet.

Other nonmammals, such as snakes, crocodiles, and turtles, may lose their tails to predators or to accidents, although not voluntarily. In fact, some snakes, such as the African python (Calabaria) and the oriental venomous (Maticora), wave their thick, colored tails toward their enemy while retreating slowly. Diamondback rattlesnakes can rattle their tail ninety times per second. During the motion, the sonic muscles pump calcium out of the myoplasm fifty times faster than the locomotor muscles do. As a result, the filaments in the sonic muscles release each other and get ready for the next contraction much more quickly than the locomotor muscles.

Parrots (Psittaciformes) are popular birds that possess colorful and widely variable tails. In some species, the tail is short, square, or rounded. In others, it is long and pointed, but no parrots have forked tails. Birds that fly long distances tend to have longer tails, sometimes longer than the total length of their body. Climbing parrots usually possess rounded wings and blunt tails.

Long, elaborate tails are considered by evolutionists as unusual ornaments to win mates and use in elaborate courtship rituals. Wildlife scientists believe that the more attention-getting displays also indicate which bird will make a good parent. In agreement with Charles Darwin’s theory of sexual selection, female animals of some species develop a preference for armaments that now have purely ornamental functions, while others show a preference for a certain trait that males eventually have to adopt if they are to mate. Male swallows with long tails have a much higher degree of paternity and produce more biological offspring than similar birds that are short-tailed, indicating a distinct positive correlation between male tail length and paternity in this species.

Two explainations for the function of the heterocercal tail in shark locomotion have been given. The first one suggests that as a result of the lift created by beating the tail, the net force acting on the tail is directed dorsally and anteriorly. In the so-called Thomson’s model, the tail generates a net force directed through the shark’s center of gravity.

Sea animals use their tails in peculiar ways. In the depths of the species-rich Amazon River, electric fish and catfish predominate. Among the unusual incidents observed, electric fish appear to eat the tails of other fish. Eels plant their tails in burrows they dig in the sand underwater and let their bodies wave in the current while waiting for food, such as drifting tiny crustaceans, fish eggs, and plankton, to reach them. A seahorse's tail is prehensile, like a monkey's tail. Animals with prehensile tails use them to grasp onto sea grass and other objects.

Tails provide an astonishing range of purposes in mammals, some of which can be of specific help to a species. Tails in cats assist with balance. Cats will also rub up against objects, including humans, and use their tails to mark with a scent. This helps the cat delineate its boundaries. Like cats, the tails on monkeys assist with balance, but they also serve as an extra appendage to grab objects. Mammals such as coyotes and foxes use their tails to curl up and stay warm. Beavers employ their tails as an early-warning device. When danger approaches, beavers slap the water with their tails to warn other beavers. A hippopotamus will employ its tail to spread its feces, which marks its territory. Horses use their tails to brush off flies. Both wolves and dogs use their tails to communicate.

Humans do not have tails. Instead, they have three to five fused vertebrae, called a coccyx, attach to the pelvis. These assist people as they sit. Some humans may have the appearance of a tail if the coccyx protrudes too far from the body, but humans lost true tails around 25 million years ago. This occurred because of a mutation in the TBXT gene in a portion of human DNA called AluY, sometimes called "jumping genes."

Principal Terms

Arboreal: living in trees

Burrowing insectivore: an insect-eating animal that usually lives in nests formed by digging holes or tunnels in the ground

Invertebrates: animals without backbones, such as insects, frogs, and snakes

Prehensile tails: tails that are adapted for seizing and holding

Vertebrates: animals with backbones, such as mammals

Viscera: any internal body organ, such as intestines or entrails

Bibliography

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