Further progress on the Laetoli trails

Abstract

In addition to showing that bipedalism notably preceded the appearance of stone tools and ballooning brains in the paleontological record, the 3.5 million-year-old footprint trails at Laetoli Site G, Tanzania, provide an unprecedented opportunity to discern the pedal morphology and gaits of Pliocene Hominidae. Although plantar prints had been collected for unshod people, studies of gait had been performed only on subjects who habitually wore shoes. Initial inferences about the Laetoli printmakers seemed to be limited by this comparative data. Therefore, we expanded the base for interpreting fossil hominid footprints with a study of > 70 never shod Machiguenga in Cuzco Department, Peru. In all discernible plantar features, including foot indices, an interdigital space between the hallux and second toe, anterior “fanning” of the foot, a medial longitudinal arch, and overall morphology, the Laetoli G impressions are matched by Machiguenga footprints. No features of gait, viz. foot angles, stride widths, or step lengths, demonstrate that the Laetoli creatures were naturally less efficient bipeds than we are. On average, Machiguenga stride widths are narrower than those of Laetoli G-3 and shod Yankees but only slightly narrower than those of Laetoli G-1: this may be ascribed to custom, to differences in the substrates upon which they walked, or to both factors. The Laetoli hominids progressed slowly by modern human standards, but their inferred paces are within the range of walking Homo sapiens.