Three-dimensional craniofacial variation and occlusal wear severity among inhabitants of Hokkaido: comparisons of Okhotsk culture people and the Ainu

Abstract

Hokkaido is an intriguing region for studies of population history in Japan because of its geographical position both at the periphery in the Japanese archipelago and at the gateway to the northeastern Eurasian continent. This paper focuses on the biological relationship between two populations, Okhotsk culture people and Ainu, and investigates craniofacial variation and dental wear severity between and within the populations. Fifty-six anatomical landmarks were digitized in order to capture craniofacial shape and size components, and occlusal wear scores on the maxillary dentition were recorded as a proxy for the degree of masticatory stress. Population differences are clear in the craniofacial form: the Okhotsk skull is characterized by a high and broad face but a relatively smaller palate, high and anteriorly protruding zygoma as well as mediosuperiorly positioned temporal muscle origins, large infratemporal and mandibular fossae. However, this morphological shift is not proportional to that of the east–west regional difference within the Ainu males, each of which is detected along distinct and mutually independent principal components. Dental wear is stronger in Okhotsk than in Ainu although without any regional difference in the respective sample. Moderate association is found between the dental wear scores and the craniofacial shape components only in the Okhotsk males, suggesting that they might have suffered from a substantial amount of functional demands. These results do not reject, but suggest modifications of, a previous simple model of genetic contribution from Okhotsk culture people to the formation of the Ainu regional variation. The formation process of the Ainu remains to be studied further in both biological and cultural contexts.

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