A tail serves a specific purpose for any species of animal that has one but this purpose can differ from species to species. Birds, primates, cats, dogs, certain marine creatures, rodents, and reptiles all are examples of species of the animal kingdom that have tails, but the task this tail performs is different between every one of them.
When it comes to any type of birds of flight the tail serves the purpose of helping in direction when flying and also helps the bird obtain flight. In flightless birds that swim it serves the purpose of direction in the water. In flightless birds that stay on dry land the tail serves the purpose of attracting mates and usually nothing else. This would account for the more elaborate and somewhat pointless tail feathers of a peacock.
Most primates have a prehensile tail which allows the animal to grab things in their environment with their tails. This is what gives primates the particular ability to swing from trees and pick up fruit with their tails. Other animals have what is called a partially prehensile tail which means they can use it to swing from trees but not to pick up things. Examples of animals that have a partially prehensile tail are an anteater, snakes, and tree porcupines.
The purpose of a tail with marine creatures is locomotion. The tail of any creature that lives either part or all of their life in the water helps them move in any direction and keeps them from sinking to the bottom.
Farm animals such as cows, horses and goats have their tails for one reason and one reason only, to keep insects from biting them which could cause diseases within the animals. They swat themselves with their tails to upset the insects which, in turn, keeps the insects from causing discomfort with the animals.
In certain species the tail can be used as a defensive mechanism. When a predator grabs a lizard, the tail can safely detach and the lizard can re-grow it later. Rattlesnakes use their rattle to warn off predators. White-tailed deer use their tail to warn each other about potential danger.
When it comes to dogs and cats, both of them use their tails to communicate emotions, dogs more than cats, but cats also use theirs for counterbalance. Such as when a cat is in a fence and walking across it, the tail keeps it from falling off.
Tails play an important role in the lives of animals, that actually have one, and do have many more purposes than just counterbalance such as swimming, swinging from trees, and as defense mechanisms. If the animals that do have tails were to lose them they may not be able to function in their environment properly – that is why they are so crucial to these animals.
References:
http://www.wisegeek.com/what-is-the-purpose-of-a-tail-in-animals.htm
