A geometric morphometric assessment of the foot of Oreopithecus

Oreopithecus is an enigmatic primate from the Miocene of Italy. It has been the subject of more than a century of controversial research and debate. Most recently, the claim that Oreopithecus exhibited a substantial degree of bipedal behaviour has permeated the literature. Specifically, the pedal anatomy of Oreopithecus has been suggested to be unique among the hominoids and this has been advanced as evidence for bipedal adaptations in this taxon. The possibility that Oreopithecus was a bipedal ape is examined using geometric morphometric techniques to assess the shape of Oreopithecus pedal remains in comparison to other well-known species, and functional interpretations are drawn from these results. This study has examined the medial column of the pedal skeleton of five extant primate taxa, as well as that of Oreopithecus, Homo habilis, and Nacholapithecus. The possible function of the foot is considered in the context of published information regarding the rest of the postcranial skeleton of Oreopithecus and the known positional behaviour of the extant species used in the study. It is found that Oreopithecus closely resembles the African ape condition in the shape of its pedal skeleton, though there are subtle differences; however, none of the differences found in the pedal skeleton of Oreopithecus offer support to the contention that the foot was especially well-adapted to bipedal behaviour. The morphology of the medial cuneiform suggests that the degree of abduction of the hallux was comparable to that observed in Pan. Similarly, the morphology of the navicular, and the lateral and intermediate cuneiforms, indicate that the orientations of the articulations of the midfoot had a configuration that was more or less the same as that observed for extant African apes, particularly Pan. It is therefore concluded that Oreopithecus was probably not habitually bipedal. But the results presented here do not in and of themselves preclude bipedalism from its locomotory repertoire, as bipedal behaviour is exhibited among the extant apes to which it is similar. However, the finding that the foot of Oreopithecus was significantly smaller than it is in any extant ape casts doubt on the likelihood of any significant level of bipedalism and may indicate that Oreopithecus was adapted to a forelimb dominated locomotory strategy