Diaphyseal and joint properties of metacarpals and metatarsals of Hominoidea and their relationships with locomotor behavior. American Journal of Physical Anthropology

In a previous study conducted on humerus, radius, ulna, femur, and tibia,Ruff (2002) found that great apes have larger joints surface areas relative to diaphyseal crosssectional size than monkeys, and that associations between these structural proportions and locomotion can be demonstrated across hominoids. Here I want to determine if structural proportions of metacarpals and metatarsals are useful to distinguish locomotor modes within hominoids. To that purpose I compare distal joint surface areas and mid-diaphyseal crosssectional properties (section modulus) of metacarpals and metatarsals in a sample of 85 hominoids (chimpanzee, gorilla, orangutan, and human). Both joint to shaft and metacarpal to metatarsal of the same ray proportions were calculated and compared between species. Results show that orangutans have the greatest distal articular surfaces relative to mid-diaphyseal section modulus for both metacarpals and metatarsals, followed by African great apes. Humans show the lowest values. Differences among species are statistically significant. This is probably a consequence of the greater amount of mobility in the proximal phalanx/distal metacarpal or metatarsal articulations in great apes as compared to humans. Interlimb comparisons show the relatively greatest metacarpal distal joint in African great apes. This may be a consequence of the greater dorsiflexion of the fingers in African great apes during knucklewalking locomotion. These results are in agreement with results obtained using limb long bones and can be applicable to fossil material which is often fragmentary and requires that inferences on locomotion of extinct species be obtained from a single bone or a few bones.