Locomotor Function and Phylogeny: Implications for Interpreting the Hominoid Fossil Record

While most researchers agree that Australopithecus afarensis moved bipedally on the ground based on numerous derived traits and preserved footprints, there are opposing views regarding the arboreal locomotor activites of this taxon. This question remains unresolved due to the potential influence of phylogenetic constraints imposed on the forelimb anatomy of early hominins, making it difficult to measure the influence of stabilizing selection on the retention of primitive forelimb traits related to arboreal locomotion. Since the limb morphology of an organism represents a compromise of these factors, it is difficult to determine the degree to which limb features indicate current locomotor adaptation or simply reflect heritage. In addition to Australopithecus afarensis, noted mosaics of features in well-known Miocene catarrhines such as Proconsul have led to difficulties in reconstructing their locomotor profiles. This study aims to assess the relative correspondence between variation in forelimb traits and locomotor behaviors of extant primates while taking evolutionary relationships into account. This approach enhances our understanding of the correspondence between locomotor behavior and skeletal anatomy across extant anthropoids, allowing the identification of the most reliable indicators of locomotion.;Phylogenetic generalized least-squares was employed to identify those forelimb traits that most closely correspond with locomotion and to construct regression models for five locomotor categories including suspension, climbing, quadrupedalism, leaping, and arboreality. These models were applied to the fossils of Australopithecus afarensis and Proconsul heseloni to infer the locomotor behavior of these extinct species.;The predictive models from this study support previous interpretations of Proconsul heseloni locomotion including above branch quadrupedalism and climbing. A small amount of terrestrial locomotion was suggested as well. With regard to Australopithecus afarensis, a small amount of arboreal climbing activities was inferred based on this species' phalangeal morphology, but caution must be taken with these results due to the confidence intervals surrounding these predictions and those of the modern human sample. While these predictive models were unable to provide clear conclusions regarding early hominin arboreal locomotion, this study suggests that phylogenetic comparative methods provide a refined assessment of locomotor function from the fossilized forelimb remains of Miocene catarrhines such as Proconsul heseloni .