Patas monkeys (Erythrocebus patas) living in African savanna woodlands and grassland habitats have a locomotor system that allows them to run fast, presumably to avoid predators. Long fore- and hindlimbs, long foot bones, short toes, and a digitigrade foot posture were proposed as anatomical correlates with speed. In addition to skeletal proportions, soft tissue and whole body proportions are important components of the locomotor system. To further distinguish patas anatomy from other Old World monkeys, a comparative study based on dissection of skin, muscle, and bone from complete individuals of patas and vervet monkeys (Cercopithecus aethiops) was undertaken. Analysis reveals that small adjustments in patas skeletal proportions, relative mass of limbs and tail, and specific muscle groups promote efficient sagittal limb motion. The ability to run fast is based on a locomotor system adapted for long distance walking. The patas’ larger home range and longer daily range than those of vervets give them access to highly dispersed, nutritious foods, water, and sleeping trees. Furthermore, patas monkeys have physiological adaptations that enable them to tolerate and dissipate heat. These features all contribute to the distinct adaptation that is the patas monkeys’ basis for survival in grassland and savanna woodland areas. 1. Introduction Patas monkeys (Erythrocebus [Cercopithecus] patas) live in dry, seasonal habitats in grass and woodland savannas across northern Africa between the equator and Sahara, from Ethiopia to Senegal and southwards into northern Tanzania [1]. Their adaptation to these landscapes contrasts with that of sympatric vervet monkeys (Cercopithecus aethiops) and baboons (Papio cynocephalus) [2]. The discovery that patas monkeys run at high speeds was interpreted as a unique locomotor adaptation to avoid predators [3, 4]. Skeletal features—lengthened limbs, short digits, and digital foot postures—have been cited as the anatomical bases (e.g., [3, 5–7]). Compared to New World monkeys (Ceboidea) and apes (Hominoidea) Old World monkeys (Cercopithecoidea) are remarkably uniform in body dimensions and share a “generalized quadrupedal” locomotor pattern [8]. Due to anatomical similarities, we incorporate soft tissue associated with the locomotor system to tease out potential species-specific patterns. Two studies stand out in adding new details to patas locomotor function. Based on dissections of the leg and foot and radiography and cine-film, Wood [9] linked the musculoskeleton of the hindlimb with locomotor biomechanics. Compared to baboons,
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