Why do animals have tails?
Animals have tails for several reasons like balance, communication, navigation, and defense.
Different animals use their tails for different reasons. A dog uses its tail to keep its nose warm when it sleeps or to express themselves by wagging it. A range animal like a horse or cow uses the tail to keep flies from biting them. A monkey uses it to balance itself in trees. A lizard uses it to fool other animals into grabbing the tail when they try to eat them; the tail breaks off and the lizard is able to run away.
Under water animals like fishes use their tails to move back and forth to swim and move in water. Kangaroos and crocodiles use the tail as defense, hitting enemies when attacked. At times, monkeys use their tail for grabbing things and climbing trees. There is no one specific function of the tail, it is used for balance by animals like cats and squirrels.
Most four-legged animals do have tails. They might use them for balance when jumping or running. Bears and hamsters are some of the animals with very small tails. Some animals are considered as tail impaired. Frogs, chimps and gorillas are examples of animals with no-tail.