The semi-/prehensile tail has independently evolved at least 14 times across 50 genera from 14 families of arboreal mammals, including Cebidae and Atelidae within Platyrrhini (New World monkeys) [1, 2]. Despite the importance of the semi-/prehensile tail for balance and support during locomotion and suspensory postures [3-8], literature lacks description about its motor coordination and control. Here, we report that wild bearded capuchin monkeys, Sapajus libidinosus (previously known as Cebus libidinosus) use their semi-prehensile tail as a variable cantilever; the vestibular and/or kinaesthetic cues associated with downward motion apparently trigger anchoring by the tail at the moment its support is needed to prevent the body from dropping. …show more content…
An analysis of the slow-motion video recordings revealed that a monkey would orient its tail around a supporting branch of a tree prior to leaning forward such that the tail could be anchored over the branch at any given moment. It would then lean forward with its forearms extended, and would anchor a variable length of its tail only after it had oriented its body obliquely, instead of anchoring the tail prior to or immediately after it had leaned forward. Comparative studies are required to elaborate if other genera with the semi-/prehensile tail use it similarly, suggesting a conserved movement pattern, or if primates differ from others in this domain, as they do with regard to several aspects of manual functions and