B43
The gibbon humerus
a comparison with humans and macaques

Modern apes are characterized by their suspensory behavior, represented by a wide suite of accompanying musculoskeletal adaptations. In explaining human origins, many have hypothesized some form of suspensory ancestry. However, because extant ape anatomy exhibits extreme specializations not seen in either modern humans or our fossil ancestors, it is also probable that human ancestry never went through a modern ape-like suspensory stage of evolution. In a comparison of three humeri, we here show the striking forelimb elongation seen in the modern lesser ape, the gibbon. Although gibbons and the Japanese macaque have comparable articular and body sizes, the length of the humerus is almost twice as long in the gibbon. When the much larger body sized humans are compared, articular dimensions are about twice as large. However, in humerus length, the human and gibbon do not differ by much, attesting to the exceptional elongation of the gibbon humerus. (Gen Suwa)