Ontogenetic cranial and postcranial regional variation in bone strength: comparisons in two archaeological populations

Divergent developmental patterns in cranial and postcranial skeletal elements have been demonstrated in both traditional osteometric dimensions and measures of bone strength properties. These differences have been attributed to the separate driving forces of varying functional demands in each distinct regions. Additionally, it has been shown that postcranial long bone strength properties are genetically constrained relative to body size during growth. Yet, few analyses have considered whether regional patterns are similar across populations. Here we test these relationships in the Tigara and Arikara, two genetically separate archaeological populations which demonstrate differing subsistence practices. We expect that patterns of development in cranial and postcranial elements will correspond with both distinct functional demands and conserved genetic determination of body form throughout ontogeny. Strength properties and linear measurements were taken for mandibles, femora, and humeri from Arikara (Sully site; n=41) and Tigara (Point Hope, n=44) individuals. Ages ranged from infancy to younger adulthood and were determined by dental eruption, and examination of skeletal maturity. Both bending strength (Zx) and bending rigidity (Ix) were calculated for each element along the sagittal plane utilizing bi‐planar radiography, external latex molds for limb elements, and hollow beam modeling. To assess developmental relationships between crania and postcrania, variables were subjected to loess regression and percent adult attainment analyses. Results reveal divergent growth trajectories between skeletal regions within and between populations. As expected, ontogenetic attainment of strength properties followed functional demands within cranial and postcranial regions. Mandibular strength attained near‐adult strength earlier in adolescence in accordance with the onset of an adult diet. Postcranial strength continued to develop into later adolescence, related to increases in body mass particularly in femora. Interestingly, loess regressions showed that postcranial robusticity was significantly different between populations throughout growth, whereas population differences in mandibular robusticity only emerged later in adolescence. Our initial results suggest mandibular strength is developmentally plastic while postcranial robusticity is largely conserved. These differing trends are likely due to ongoing functional demands on the mandible and the relationship of postcranial elements to body size. Support or Funding Information Wenner‐Gren Foundation, Gr. 8114