Developments in development: What have we learned from primate locomotor ontogeny?

Abstract

The importance of locomotion to evolutionary fitness has led to extensive study of primate locomotor behavior, morphology and ecology. Most previous research has focused on adult primates, but in the last few decades, increased attention to locomotor development has provided new insights toward our broader understanding of primate adaptation and evolution. Here, we review the contributions of this body of work from three basic perspectives. First, we assess possible determinants on the timing of locomotor independence, an important life history event. Significant influences on timing of locomotor independence include adult female body mass, age at weaning, and especially relative brain size, a significant predictor of other primate life history variables. Additionally, we found significant phylogenetic differences in the timing of locomotor independence, even accounting for these influences. Second, we discuss how structural aspects of primate growth may enhance the locomotor performance and safety of young primates, despite their inherent neuromotor and musculoskeletal limitations. For example, compared to adults, growing primates have greater muscle mechanical advantage, greater bone robusticity, and larger extremities with relatively long digits. Third, focusing on primate quadrupedalism, we provide examples that illustrate how ontogenetic transitions in morphology and locomotion can serve as a model system for testing broader principles underlying primate locomotor biomechanics. This approach has led to a better understanding of the key features that contribute to primates' stride characteristics, gait patterns, limb force distribution, and limb postures. We have learned a great deal from the study of locomotor ontogeny, but there is much left to explore. We conclude by offering guidelines for future research, both in the laboratory and the field. K E Y W O R D Sallometry, gait mechanics, life history, locomotor independence, ontogeny | I N TR ODU C TI ONPrimates display an impressively broad range of locomotor behaviors, including several highly charismatic and unique behaviors not seen in other mammals, such as strepsirrhine vertical clinging and leaping, hylobatid brachiation, and hominin striding bipedalism (Fleagle, 2013;Hunt et al., 1996;Schmitt, 2010). Even primate quadrupedal locomotion, a comparatively ubiquitous locomotor mode, is characterized by several unique features relative to most other mammalian quadrupeds (Kimura, 1992;Kimura, Okada, & Ishida, 1979;Larson, 1998;Schmitt, 2010;Shapiro & Young, 2016). As such, the biomechanics, ecological context, and morphological underpinnings of primate locomotor behaviors have long been of interest in anthropology and associated fields (Dagosto & & Gebo, 1998;Le Gros Clark, 1959;Muybridge, 1887;Napier, 1967;Prost, 1965;Ripley, 1967;Wood Jones, 1916).The vast majority of previous research on primate locomotion, whether in the field or the lab, has concentrated on adult animals. To some degree, this focus on adults is understandable. The morphologic...

Ontogeny of food grasping in mouse lemurs: behavior, morphology and performance

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