Fifth metatarsal morphology does not predict presence or absence of fibularis tertius muscle in hominids

The leg muscle fibularis tertius (formerly peroneus tertius) is occasionall y absent in humans, but it is rarely found in other primates. Phylogenetica lly and functionally it appears to be linked to efficient terrestrial biped alism. An osseous indicator of the muscle would therefore be useful for int erpreting the locomotor behavior of fossil hominids. To determine whether t he presence of fibularis tertius can be detected osteologically, we isolate d 58 human fifth metatarsals, noting which came from cadavers lacking the m uscle. The bones were then ranked according to two characters that have bee n said to suggest presence of fibularis tertius in australopithecines: (1) sharpness of the dorsal shaft edge and (2) size and prominence of the dorsa l tubercle. Presence of the muscle showed little association with the ranke d characters, and the two criteria were uncorrelated. For example, one indi vidual lacking a fibularis tertius exhibited nearly maximal expression of b oth features, whereas another possessing the muscle showed the weakest deve lopment of both. Only one of the 58 bones had a line comparable to that see n on SK 33380, a robust australopithecine fifth metatarsal from Member 3 of Swartkrans, South Africa. We conclude that fifth metatarsal morphology off ers little reliable information about the presence of fibularis tertius or the timing of its appearance in the human career. (C) 2000 Academic Press.