Department of Pathology & Anatomical Sciences, University of Missouri
Saturday All day, Plaza Level
Curvature of the zygomaticoalveolar (ZMA) crest is widely discussed in phylogenetic and biomechanical assessments of craniofacial morphology in Middle and Late Pleistocene Homo. However, the complex curvilinear morphology of the ZMA crest has proven difficult to accurately quantify with traditional methods, significantly impeding previous attempts at evaluation. In this study, nine semilandmarks derived from a ridge curve between zygomaxillaire and the alveolar border were employed to accurately measure ZMA crest curvature in a large sample of fossil Homo (n = 71) and recent humans (n = 303). A principal components analysis following Procrustes superposition of all semilandmark configurations reveals that PC1 accounts for 57.6% of the total variance and contrasts the degree of curvature along the entire length of the crest (i.e., straight vs. parabolic), while PC2 (18%) contrasts curvature along the lateral ZMA crest related to the medial or lateral positioning of a malar tubercle. Interestingly, PC1 was found to be significantly correlated with facial size both inter- and intraspecifically in Homo, indicating that larger faced individuals predictably exhibit straighter ZMA crests, while smaller faced specimens exhibit more arched ZMA crests. Moreover, while contrasted at each end of the size spectrum, ZMA crest curvature actually arrays along a continuous gradient of facial size, and is thus not truly dichotomized into the "arched" versus "straight" polarities often described in the paleoanthropological literature. These results have implications for both the Accretion model of Neandertal evolution, and arguments related to the more “modern” facial morphologies of H. antecessor and Chinese H. erectus.
This research was supported by grants from the Wenner-Gren Foundation, Leakey Foundation, and the University of Iowa.