Skeletal femoral measurements were recorded for Okhotsk Cultural people (5–12 century) uncovered from northern and eastern Hokkaido, Japan, in order to clarify the regional differences among the two Okhotsk groups, and to find those specific features in comparison with the other ethnic groups in Hokkaido represented by Neolithic Jomon, Epi-Jomon and modern Ainu. The results demonstrated that the femurs of the eastern Okhotsk sample, mainly from the Moyoro Shell Mound site, are significantly larger in length of the shaft, thickness of the proximal shafts, diameters of the head and neck than those of the northern Okhotsk sample from the Ohmisaki and Hamanaka sites, and also than the Jomon/Epi-Jomon and Ainu femurs. Meanwhile, the northern Okhotsk people less differed in morphometric femoral features from the Jomon/Epi-Jomon and Ainu than the eastern Okhotsk sample did. Discriminant function analyses using these femoral measurements divided the two Okhotsk samples and Jomon/Ainu at high level of accuracies (>90%), with finding the difference in both the femoral size and proportion among the shaft length and/or thickness at various portions.

View full abstract

The present study aims to assess the validity of the idea that the first molars can be congenitally missing despite the posterior molars are preserved in the permanent dentition. In addition, size and morphology of the affected molars were investigated in detail. Eleven possible cases of such a type of first molar agenesis have been observed in modern Japanese patients (five males and six females). Data were collected from plaster casts, panoramic radiographs, and a questionnaire to the patients. In general, the first molars in the dentition erupt into the oral cavity at an age around six years old. However, in the above-mentioned cases, the eruptions of the molars just behind the premolars were delayed up to around eight to ten years old. In addition, they show more reduced cusp patterns than those of ordinary first molars, being more similar to those of ordinary second molars. None of the patients had three molars on the affected side of the jaw. Moreover, the affected teeth were larger in size than ordinary second molars, probably due to compensatory interaction. Following the conventional interpretation, since any molar in the first position is regarded as first molar, the affected molars would be regarded as first molars whose eruption is delayed by two to four years due to tooth reduction. However, detailed investigation of the dental agenesis cases in the present study suggests that it is more appropriate to interpret that these affected teeth should be second molars, whose eruption was accelerated by a few years, probably due to the congenital absence of first molars.

View full abstract

It has long been acknowledged that adult Jomon people have robust and cross-sectionally flat limb bone diaphyses. In the present study, in order to discuss the formative mechanism of diaphyseal robusticity and shape, midshaft cross-sectional geometry of major long bones of the 8th fetal to 3rd postnatal month Jomon and modern Japanese were compared using micro-CT imaging. The materials examined in this study were humeri, radii, ulnae, femora, tibiae, and fibulae of 49 Jomon and 185 modern Japanese skeletal individuals. Comparisons were made in each limb bone by means of the analysis of covariance (ANCOVA) using diaphyseal length as the covariate and cross-sectional geometry as the dependent variables. It was found that the Jomon cross-sectional robusticities were consistently and significantly greater than those of the modern Japanese throughout the fetal–infant period, and that there were no significant populational differences in the growth patterns of the periosteal and endosteal dimensions, bone area, and second moments of area. It was also found that long bone cross-sectional shapes of the two populations remained almost constant during development, and that the Jomon femoral external shape tended to be anteroposteriorly flatter than that of the modern Japanese. The results of the present study indicate that the diaphyseal morphological characteristics of the adult Jomonese (greater periosteal dimensions, greater bone mass, and anteroposteriorly flatter cross section of the proximal femoral shaft) emerge early during ontogeny probably based on pattern formation effects as proposed by Lovejoy et al. (2003).

View full abstract