¹School of Human Evolution and Social Change, Institute of Human Origins, Arizona State University, ²Department of Osteopathic Manipulative Medicine, Department of Physical Medicine and Rehabilitation, Michigan State University

Thursday 10:15-10:30, Ballroom B

The biomechanics of the atlantoocipital joint is poorly understood in non-human primates. Previous research suggests the atlantooccipital joint reaction force is directed anterosuperiorly in primates with orthograde and posterosuperiorly in primates with pronograde. Because joint morphology responds to the direction of the forces passing through it, postural differences should result in atlantooccipital joint morphologies that provide the necessary mechanical advantage to maintain joint stability.

The goal of this study was to explore the relationship between the orientation of the C1 superior articular facets and neck position in catarrhines. The morphology of the atlantooccipital joint was quantified using three-dimensional coordinate data collected manually with a three-dimensional digitizer while neck inclination data was taken from the literature. Though previous research used categorical classifications of posture, we used neck inclination to quantitatively represent neck posture because it more accurately characterizes habitually assumed positions. We hypothesized that the orientation of the posterior aspect of the facet would correlate strongly with neck inclination due to the theorized direction of joint reaction forces. The relationships were analyzed using phylogenetic comparative methods. Results do not support a relationship between the orientation of the superior articular facet and neck inclination. However, there is a moderate correlation between the anteroposterior curvature of the facet and neck posture. This relationship can be used to reconstruct posture in fossil species.