1Anthropology, Florida Atlantic University, 2Anthropology, University at Albany
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The Paranthropus head is characterized by a number of features traditionally thought to be related to heavy chewing, including large, thick-enameled cheek teeth, a tall mandibular ramus and face, thick palate, and large, flaring zygomatic arches. McCollum [Science 284 (1999): 301-305] proposed that palatal thickening is a response to developmental integration between a tall mandibular ramus, oral and nasal functional matrices, and the vomer, which inserts onto the premaxilla in Paranthropus and thus causes the palate to thicken instead of rotate during vertical expansion. In this study, we tested whether palate thickness increases as a byproduct of differential increases in size of the oral and nasal functional matrices related to growth in the mandibular ramus. To test this hypothesis, we collected 3D volume and landmark data from computed tomography (CT) scans of orangutan, gorilla, chimpanzee, and modern human skulls, and crania for fossil hominin species including Australopithecus africanus, Paranthropus robustus, and P. boisei. Following McCollum’s model, we hypothesized that palate thickness and nasal cavity size would scale with positive and negative allometry, respectively, relative to posterior facial height, and that nasal cavity size would scale predictably with cranial proxies for body size. Against expectation, palate thickness does not correlate with posterior facial height, and nasal cavity size scales with isometry or slight negative allometry. Moreover, nasal cavity size is only moderately correlated with cranial size proxies. These results suggest that developmental constraints related to growth counterpart relationships in the skull are unlikely to affect palate thickness in the genus Paranthropus.