Petrosal orientation and mandibular ramus breadth: Evidence for an integrated petroso‐mandibular developmental unit

Abstract

The absolute and relative breadths of the mandibular ramus (MRB) display substantial variation in modern humans, and are of analytical value in paleoanthropology. According to Enlow et al. ([1969] Am. J. Orthod. 56:6-23), the ramus is the growth counterpart of the middle cranial fossa (MCF) and the pharynx. Such counterpart principles state that variation in ramus breadth is a frequent function of the horizontal alignment of the MCF, and both structures tend to covary within and between populations. These authors also suggested that lateral parts of the basicranium have a particular importance in the positioning of facial components. In the present study, this hypothesis is tested, and relationships between midline and lateral basicranial elements and ramus breadth variation are explored. Two-dimensional landmarks taken from lateral radiographs of adult crania representative of three modern human populations (Europeans, West Africans, and Japanese) were analyzed by geometric morphometry. Our results are consistent with previous counterpart analyses. Furthermore, our findings highlight the significance of the orientation of the petrous temporal to modern human mandibular ramus variation. Variation in the orientation of the petrosal bone appears to alter the spatial position of the mandible and influences MRB. Developmental integration of a petroso-mandibular unit may have important paleoanthropological implications.

Global human mandibular variation reflects differences in agricultural and hunter-gatherer subsistence strategies

“…Importantly, what this suggests is that masticatory pressure acts preferentially on the mandible rather than the maxillary region, with the maxilla altering in relation to the mandible to retain effective dental occlusion. Therefore, despite considerable integration between the mandible and the skull (25,26), the results presented here suggest that the mandible can evolve independently (e.g., 27).…”

“…This supports the idea (4,5) that it is the biomechanical properties of mastication (with huntergatherers presumably experiencing longer and more intensive bouts of chewing than agriculturalists) that is the selective force. Previous localized comparisons of hunter-gatherer and farming populations (6-9) found significant changes in the masticatory (25), zygotemporal (light gray) (22), and palatomaxilla (dark gray) (21). (B) Regions of the cranium not related to masticatory function: chondrocranium (light gray) (39) and cranial vault (dark gray) (51).…”

Hominin lower second premolar morphology: evolutionary inferences through geometric morphometric analysis

“…These relative warps reflect principal patterns of shape variation and have recently found multiple applications in paleoanthropology (Bookstein et al, 1999;Rosas and Bastir, 2002;Bookstein et al, 2003;Bastir et al, 2004Bastir et al, , 2005.…”

Limitations of traditional morphometrics in research on the attractiveness of faces

“…The flattest nasal bones are found in sub-Saharan African populations (Hanihara, 2000), but FaceGen makes East Asian nasals flatter than African nasals. Europeans tend to have shorter chins than Africans and East Asians (Bastir, Rosas, & Kuroe, 2004), but not so in FaceGen. These limitations are of little relevance to game developers or police because these groups need only to generate faces that approximate target faces.…”