Animal tails perform a vast array of physical functions, from working as a cheetah’s counterbalance when cornering at high speeds to delivering a powerful blow in the case of the crocodile, or even communicating emotion, when a pet hound wags its tail. An animal with a prehensile tail, however, has a special ability to grip on to things with its specialised appendage – using it as a kind of extra limb.
Among other animals, fully prehensile-tailed creatures include species from the New World order of primates, which are native to rainforest regions in South America. Here, where the branches of the tree canopy can be widely spaced, animals had to develop a suitable mechanism to assist them in traversing these large gaps in the rainforest over many thousands of years. Spider monkeys, for instance, use their agile tails for additional balance and locomotion when swinging through the treetops.
Such a tail is required to suspend the entire weight of a creature and so the skeleton and muscular structure of prehensile tails must be resistant to both torsion and bending, and capable of generating higher forces than regular tails. An opossum, for example, dangles upside down by its tail while using its hands to pick food. The tip of the tail can curl round branches and trunks and some prehensile-tailed mammals even have patches of bare skin or scales – instead of fur – for a non-slip grip on surfaces such as branches.