Ontogenetic Shape Change in the Human Cranial Base and its Relationship to Positional Behavior

Abstract

The cranial base is frequently used to make inferences about upright posture in the hominin fossil record, particularly as it relates to the earliest evidence of bipedalism. There is contention, however, regarding which aspects of cranial base morphology best reflect upright posture. The goal of this study is to evaluate how changes in cranial base morphology may relate to changes in positional behavior throughout human ontogeny. A close relationship between positional behavior and cranial base morphology would support the use of similar morphological features to reconstruct posture in fossil hominins. The study sample included an ontogenetic series of crania (n=33) ranging in age from neonate to adult. Crania were grouped based on ages at which humans undergo changes in positional behavior. Three dimensional landmark data were acquired either from computed tomography scans or digitized from an archaeological collection. Data were analyzed using Morphologika2 and MorphoJ software. Specifically, Principal Components Analysis was used to determine differences in cranial base shape among age groups. Results demonstrate age‐related changes in nuchal plane length, anterior cranial base length, and occipital condyle position congruent with the acquisition of upright posture in human infants. This analysis supports the use of features such as cranial base length and occipital condyle position as a tool to reconstruct posture in fossil hominins and identifies future avenues of study.Support or Funding InformationFunding for analysis provided by Barrett, the Honors College at Arizona State University