Functional articulation of some hominoid foot bones: implications for the Olduvai (hominid 8) foot

Abstract

Previous observations on twelve fossil foot bones (Olduvai 8: Day and Napier, '64) together with multivariate morphometric studies of one of them, the talus (Day and Wood, '68) suggested human-like bipedality for this foot. Subsequent studies showed the conclusions on the talus to be wrong: The fossil talus, as defined by eight measures, does not resemble that of man but is reminiscent of those of creatures known (extant--orangutans) or believed (extinct--some fossil apes and monkeys) to be arboreal in habitus (Oxnard '72; Lisowski, et al., '74, '76). A reassessment of the entire Olduvai 8 foot is therefore necessary to answer the problem posed by a foot that has a non-human talus with, apparently, a human arched pattern of the remaining tarsal and metatarsal bones. The dry bones of a series of feet of extant hominoids have been rearticulated and are found to be close to the actual relationships presented by dissected specimens in which ligaments, articular cartilages and soft tissues are present. Similar rearticulation applied to casts of the individual Olduvai foot bones produces a structure that is not arched in the same manner as the human foot; it displays features that ally it more closely with the feet of various apes. Sections of casts of the already rearticulated Olduvai foot (from both the Wenner Gren Foundation and the Kenya National Museums) show that the human-like appearance of the original rearticulation is due to a series of incorrect osteological alignments. Although casts do not permit study of surface features, the dimensions of the casts are sufficiently accurate to permit rearticulation in this manner. It is thus clear, a) that the Olduvai foot is not adated for bipedality in the manner of man, and b) that it displays features in which it resembles the feet of arboreal creatures. Such anatomical characters as relate to bipedality in the fossil suggest usage as in an arboreal species that also walks bipedally with flattened arches (like a chimpanzee or gorilla) rather than with the high arches of man.