1Pathology and Anatomical Sciences, University of Missouri School of Medicine, 2Basic Medical Sciences, University of Arizona College of Medicine - Phoenix
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The vertically thickened hard palate of Paranthropus, like many other derived craniodental features in this species, has been explained by Rak (1983) as an adaptation related to the consumption of a hard/tough and an associated increase in masticatory forces relative to its sister taxa Australopithecus. Experimental studies of diet-related morphological plasticity in the mammalian hard palate have demonstrated that cross-sectional properties of the structure, such as cortical thickness and trabecular density, covary with dietary material properties. Assuming similar osteogenic responses to variation in dietary mechanical properties and loading levels, we hypothesize that if the hard palate in Paranthropus was subject to greater masticatory stresses relative to the same structure as Australopithecus, the former genus should exhibit a thicker palate, thicker cortical bone across the oral lamina, and greater trabecular density. To test this hypothesis, sequential coronal cross-sections of the hard palate were obtained from computed tomography (CT) scans of fossil specimens of both genera (n=17). Results show that Paranthropus has a significantly (p<0.05) taller anterior palate with thicker cortical bone along the anterior oral lamina when compared to Australopithecus. Although the quantity of fossil evidence is limited by preservation, this study tentatively supports the hypothesis that the morphology of the hard palate in Paranthropus was influenced by high levels of cyclical and/or peak masticatory strains during postcanine biting and chewing. Thus, variation in the hard palate of australopithecines is consistent with the observed craniodental variation, suggesting a divergence in dietary material properties and masticatory behavior between the two genera.