Ontogenetic scaling of fore- and hind limb posture in wild chacma baboons (Papio hamadryas ursinus)

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Patel, Biren A.
Horner, Angela M.
Thompson, Nathan E.
Barrett, Louise
Henzi, Peter
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Public Library of Science
Large-scale interspecific studies of mammals ranging between 0.04–280 kg have shown that larger animals walk with more extended limb joints. Within a taxon or clade, however, the relationship between body size and joint posture is less straightforward. Factors that may affect the lack of congruence between broad and narrow phylogenetic analyses of limb kinematics include limited sampling of (1) ranges of body size, and/or (2) numbers of individuals. Unfortunately, both issues are inherent in laboratory-based or zoo locomotion research. In this study, we examined the relationship between body mass and elbow and knee joint angles (our proxies of fore- and hind limb posture, respectively) in a cross-sectional ontogenetic sample of wild chacma baboons (Papio hamadryas ursinus) habituated in the De Hoop Nature Reserve, South Africa. Videos were obtained from 33 individuals of known age (12 to $108 months) and body mass (2–29.5 kg) during walking trials. Results show that older, heavier baboons walk with significantly more extended knee joints but not elbow joints. This pattern is consistent when examining only males, but not within the female sample. Heavier, older baboons also display significantly less variation in their hind limb posture compared to lighter, young animals. Thus, within this ontogenetic sample of a single primate species spanning an order of magnitude in body mass, hind limb posture exhibited a postural scaling phenomenon while the forelimbs did not. These findings may further help explain 1) why younger mammals (including baboons) tend to have relatively stronger bones than adults, and 2) why humeri appear relatively weaker than femora (in at least baboons). Finally, this study demonstrates how field-acquired kinematics can help answer fundamental biomechanical questions usually addressed only in animal gait laboratories.
Sherpa Romeo green journal: open access
Wild chacma baboons , Papio hamadryas ursinus , Hind limb posture , Forelimb posture , Joint posture , Elbow joint angles , Knee joint angles , Body mass , Biomechanics , Ontogenetic sample
Patel, B. A., Horner, A. M., Thompson, N. E., Barrett, L., & Henzi, S. P. (2013). Ontogenetic scaling of fore- and hind limb posture in wild chacma baboons (Papio hamadryas ursinus). PLoS ONE, 8(7): e71020. doi:10.1371/journal.pone.0071020