Tail

A tail is an elongated posterior body part found in many animals, extending beyond the main trunk. In vertebrates it is typically composed of caudal vertebrae, muscles, tendons, and skin; in invertebrates the tail may be a simple terminal appendage such as a pair of cerci or a fused structure like a pygidium. Tails vary widely in length, structure, and function across species.

In fishes, the tail forms the caudal fin, which provides propulsion and steering. In mammals, tails range from short and nearly invisible to long and highly mobile, helping with balance, signaling, and sometimes grasping or fat storage in certain species. Birds have tails of fused vertebrae and tail feathers that assist in steering during flight and in social displays. Reptiles use their tails for balance, locomotion, and, in some species, defense or fat storage. Many invertebrates also possess tail-like structures, such as insect cerci or crustacean tail plates.

Functions of tails are diverse and often related to ecology and behavior. They aid in locomotion and maneuverability, help maintain balance in uneven terrain, and serve communicative roles through posturing or color displays. Some species have prehensile tails that can grasp branches, while others can shed or autotomize their tails to escape predators and subsequently regenerate them, as seen in many lizards.

Evolution and development: in humans, the tail is vestigial, ending in the coccyx, and embryos briefly develop a tail that later regresses. Many species exhibit tail variation through evolution, including tailless lineages and regrowing tails after injury. The term “tail” is also used metaphorically for the trailing end of objects, such as the tail of a comet or the tail of an aircraft.