A Functional Model for Masticatory-Related Mandibular, Dental, and Craniofacial Microevolutionary Change Derived From a Selected Southeastern Indian Skeletal Temporal Series

In the present study, 66 metric as well as numerous morphological observations are utilized from 299 individuals representing a skeletal temporal series (Archaic, Woodland, Mississippian) from West, Middle, and East Tennessee. These groups reflect a documented subsistence shift from a relatively hard-textured, hunting and gathering Archaic to a soft-textured, Mississippian agricultural diet. Mandibular, craniofacial, and mandibular anterior dental dimensions are compared within and between these groups in order to evaluate a model of masticatory-related diachronic change in the mandibular complex.

This model proposes strong correlations between mandibular, craniofacial, and mandibular anterior dental measurements within each group. Cumulative age-related functional stress is expected to be higher in the Archaic. Across the temporal groups, gracilization in linear dimensions of the mandible, lower face, and mandibular anterior teeth is predicted, as well as change in the size and orientation of masticatory muscles. Indications of functional (masticatory-related) skeletal stress in the mandible and lower face are expected to decrease through time. It is hypothesized that these changes are the result of the documented dietary shift noted above.

Results indicate a fair amount of congruency with the model expectations. Intercorrelations between the 66 measurements are weaker than predicted; however, fairly strong relationships are noted between height of the mandible and face within both the Archaic and Mississippian. Mandibular measurement age variation is greater in the Archaic compared to the Mississippian. This difference is interpreted within the context of greater masticatory functional demands and thus cumulative stress for Archaic mandibles. Neither Archaic nor Mississippian facial dimensions vary significantly with age. Age-related dental variability is similar between the two groups.

In the between-group (temporal) comparison, reductions in several linear dimensions of the mandible, lower face, and mandibular anterior dentition are documented through time. And, masticatory muscles become less robust and more posteriorly oriented. Many manifestations of skeletal masticatory-related stress (e.g., midfacial prognathism) reduce as well. Several dimensions (e.g., total mandibular length), however, increase across the temporal span. All of these results are used in a revision of the model of masticatory-related microevolutionary mandibular and craniofacial change.