What does modern human variation in MT1 abduction angle and arch height reveal about hominid pedal morphology?

Abstract

Although modern humans exhibit many different morphologies, anthropological wisdom dictates that an effective bipedal foot is one with an adducted first metatarsal (MT) and medial longitudinal arch (MLA). The recently announced pedal morphology of Ardipithecus calls into question this assumption, prompting the question of what variation among modern human feet might reveal about the function of extinct hominid feet.Using anterior‐posterior and lateral radiographs of 50 osteological adults (aged 15–78 years, 25 women), arch height and the angle between MTs (MT12, MT23, MT34, MT45, MT15) were measured. MT12 of STW 575 and MT angles of OH 8 were measured on photographs/drawings of reconstructions.In the modern sample, MT12 ranged from 3–15° (mean = 9°, σ = 3°) and feet with more abducted 1st MT tended to have more abducted 5th MT (p = 0.051) and higher arches (p=0.018). MT12 measured 20° on STW 575 and 10° on OH 8.For MT12, STW 575 is > 3σ from the human mean, while OH 8 exhibits the human mean value. If the fossil reconstructions are accurate representations of weight‐bearing position, then the 1st MT of STW 575 was more abducted than is typically seen in modern humans, but what, if any, functional consequences accrue from this difference are less clear. As with other morphological features, effective bipedal feet can come in many forms.