Biomechanics of great apes and human hands and feet and its relationship with positional behavior

Cheiridia are valuable indicators of positional adaptation in that they directly contact the substrate. This study examines cross-sectional geometry (CA and J) of metacarpals II-V and metatarsals I-V at 50% length across a sample (N=86) of chimpanzees, gorillas, orangutans, and humans. All cross-sectional variables are analyzed against bone length, body mass, and (body mass x bone length). RMA lines are calculated. ANOVA is performed as well as post-hoc comparisons using the Tukey’s honestly significant difference for unequal samples. The “Quick test” by Tsutakawa and Hewett (1977) and the calculation of the percent prediction error (PPE) are used to evaluate differences between species. This is the first attempt to give a biomechanical interpretation to both metacarpals and metatarsals within hominoids and to shed some light on their relationship with locomotion behaviors. Good results in characterizing the hominoids in relation to locomotion behavior are obtained when hands and feet are analyzed separately, but the best results are obtained comparing metacarpals and metatarsals of the same ray. It appears that knuckle-walker apes have a relative stronger metacarpal III and especially IV as compared to the other hominoids, and that humans have a relative stronger metatarsal V as compared to great apes. Interestingly, orangutans, which perform a quadrumanus arboreal behavior, have a relative metacarpal IV robustness between range of the knuckle-walkers and that of humans. On the whole metacarpal and metatarsal cross-sectional characteristics are strongly related to the locomotion behavior of hominoids, and may be useful in elucidating locomotion characteristics of fossil hominoids.