Postcranial Remains of the Extinct Monkeys of the Greater Antilles, with Evidence for Semiterrestriality in Paralouatta1

Abstract This paper describes postcranial remains pertaining to the endemic xenotrichin callicebines of the Greater Antilles, all of which are extinct: Xenothrix mcgregori (Jamaica), Antillothrix bernensis (Hispaniola), and Paralouatta varonai and P. marianae (Cuba). These monkeys differed considerably in body size and inferred locomotor behavior. Xenothrix and Antillothrix are estimated to have weighed 2–5 kg, which is well within the middle range of body sizes found in extant South American monkeys, but Paralouatta (~9–10 kg) would have been nearly as large as the largest living platyrrhines. In line with previous studies, we interpret Xenothrix mcgregori as a rather short-limbed, slow-moving arboreal quadruped possessing some unusual features not otherwise seen in platyrrhines (e.g., adductor process or “fourth trochanter” of the femur). Its closest locomotor analog among living primates remains uncertain. Paralouatta varonai also exhibits features not seen in other platyrrhines, but in this case there are intriguing resemblances to certain Old World monkeys (e.g., retroflexed medial epicondyle and narrow trochlea on humerus, stabilization features of talocrural joint, short digital rays), especially so-called semiterrestrial cercopithecines whose locomotor repertoire includes a significant amount of movement on the ground (e.g., Cercopithecus lhoesti). At the same time, the Cuban monkey conspicuously lacks most features uniquely connected with suspensory activities, otherwise seen in all living platyrrhines of large body size. The locomotor and postural repertoire of Antillothrix is unresolved, as the only element currently available for analysis is a distal tibia. The tibia of the Hispaniolan monkey is not very informative from a functional standpoint, although it exhibits less emphasis on talocrural stabilization than does the equivalent element in Paralouatta (e.g., size of medial malleolus). The diverse postcranial specializations exhibited by xenotrichins are consistent with their long isolation (at least since Oligocene) on land masses in the Caribbean Sea.