COMPARATIVE AND FUNCTIONAL MYOLOGY OF THE PREHENSILE TAIL IN NEW-WORLD MONKEYS

The caudal myology of prehensile-tailed monkeys (Cebus apella, Alouatt a palliata, Alouatta seniculus, Lagothrix lagotricha, and Ateles panis cus) and nonprehensile-tailed primates (Eulemur fulvus, Aotus trivirga tus, Callithrix jacchus, Pithecia pithecia, Saimiri sciureus, Macaca f ascicularis, and Cercopithecus aethiops) was examined and compared in order to identify muscular differences that correlate with osteologica l features diagnostic of tail prehensility. In addition, electrophysio logical stimulation was carried out on different segments of the inter transversarii caudae muscle of an adult spider monkey (Ateles geoffroy i) to assess their action on the prehensile tail. Several important mu scular differences characterize the prehensile tail of New World monke ys compared to the nonprehensile tail of other primates. In atelines a nd Cebus, the mass of extensor caudae lateralis and flexor caudae long us muscles is more uniform along the tail, and their long tendons cros s a small number of vertebrae before insertion. Also, prehensile-taile d monkeys, especially atelines, are characterized by well-developed fl exor and intertransversarii caudae muscles compared to nonprehensile-t ailed primates. Finally, Ateles possesses a bulkier abductor caudae me dialis and a more cranial origin for the first segment of intertransve rsarii caudae than do other prehensile-tailed platyrrhines. These myol ogical differences between nonprehensile-tailed and prehensile-tailed primates, and among prehensile-tailed monkeys, agree with published os teological and behavioral data. Caudal myological similarities and dif ferences found in Cebus and atelines, combined with tail-use data from the literature, support the hypothesis that prehensile tails evolved in parallel in Cebus and atelines. (C) 1995 Wiley-Liss, Inc.