If humans still had tails, the world might look a little different. But our ancestors lost their tails about 18 million years ago. Today, humans retain only the shortest remnants--just a few hidden bones at the base of the pelvis. Many other mammal tails are remarkably long, though, and some have a range of unusual uses.
The howler monkey of northern South America has a prehensile, or grasping, tail the same size as its body--about three feet--that it uses for navigating its native cloud- and rainforests.
The woolly monkey, a central South American tree-dweller, occasionally strolls through the forest on the ground, using its tail as a brace--nature's built-in tripod.
- In some cases, prehensile tails have a bare, sensitive pad along one side of the tip, for better sensing and gripping. Using their tails, these arboreal animals can hang or swing from tree to tree.
- Mammals use tails for everything from swimming to balancing while hopping or running to serving as the mammal-equivalent of a sleeping bag: tree squirrels wrap themselves in their bushy tails to sleep.
- An extinct animal called a creodont, found in Green River, Wyoming, had a tail that contained 51 separate bones. Scientists reason that in living mammals, a tail containing many vertebrae is more flexible and therefore more likely to be prehensile. Because of this and other evidence from the tail's anatomy, scientists think this ancient carnivore had a grasping, prehensile tail, too.