Institute of Human Origins, School of Human Evolution and Social Change, Arizona State University
Friday All day, Plaza Level
Researchers have studied the morphology of the foramen magnum and occipital condyles in an effort to relate these structures to posture and locomotion in fossil taxa. Previous work has shown that many basicranial features are influenced by cranial-base flexion and relative brain size, yet the effect of positional behavior on atlanto-occipital (AO) morphology has not been clarified. Demes’s (1985) model of the AO joint suggests that joint-force vectors differ between orthograde and pronograde primates, such that, in more orthograde species, the reaction forces transmitted across the AO joint are directed posterosuperiorly, whereas in pronograde taxa, reaction forces are directed anterosuperiorly.
The goal of this study was to investigate the influence of neck posture on the relative position of the occipital condyles. Aspects of Demes’s model and other biomechanical principles were utilized to develop predications for condylar position. Specifically, we tested whether anthropoids characterized by more pronograde neck postures possess more anteriorly placed occipital condyles along the margin of the foramen magnum than those with more orthograde neck postures. Basicranial features of 11 extant anthropoid species were quantified using three-dimensional coordinate data, and data on neck posture were taken from the literature. Relationships between neck posture and condylar position were analyzed using phylogenetic comparative methods. Results do not support a relationship between neck posture and condyle position, indicating that condylar position cannot be used to infer posture in fossil taxa.
Travel grant from School of Human Evolution and Social Change, Arizona State University, Tempe, AZ