著者

石田 肇 下田 靖 米田 穣 内藤 裕一 長岡 朋人

出版者

北海道大学総合博物館

雑誌

北海道大学総合博物館研究報告 (ISSN:1348169X)

巻号頁・発行日

no.6, pp.109-115, 2013-03

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The Okhotsk culture spread from southern Sakhalin Island to northeastern Hokkaido Island and the Kurile Islands from the 5th to the 12th centuries AD. The Okhotsk culture developed a considerable maritime infrastructure which was different from that of the native population in Hokkaido. The demographic structure of prehistoric hunter-gatherers contributes to our understanding of life history patterns of past human populations. Age-at-death distribution was estimated using the Buckberry-Chamberlain system of auricular surface aging and the Bayesian approach to discuss whether paleodemographic estimates can yield an appropriate mortality profile of the prehistoric hunter-gatherers in Japan. The age distributions of the Okhotsk revealed low proportions of young adults and high proportions of elderly adults. The results indicated 24.4-51.3% for the proportion of individuals above the age of 55 years. The newly-employed technique of the Bayesian estimation yielded age distributions with significant numbers of elderly individuals, which are contrary to usual paleodemographic estimates. Apical periodontitis, accompanied by considerable wear, was frequently seen in the upper first molars of the Okhotsk people. The bone cavities around the root of the upper first molars were probably caused by chronic apical periodontitis and radicular cyst. The bone cavity was clearly surrounded by sclerotic bone tissue diagnosed as condensing osteitis. Excessive amounts of secondary cementum were deposited on the root surface as a result of radicular granuloma. Pulp exposure through extreme wear very likely resulted in bacterial infection of dental pulp and periapical tissue. Degenerative changes in people of the Okhotsk culture were investigated using adult human skeletons and reconstructing their lifestyle. Findings were compared with materials obtained from skeletons from the medieval Kamakura period and skeletons of early-modern peasants on the Ryukyu Islands, Japan. Severe osteophytes on the lumbar vertebrae were more frequently seen in the Okhotsk males. Degenerative changes of the articular process were also most frequently seen in the lumbar vertebrae of the Okhotsk skeletons. This is a significant contrasted from the high frequency of degenerative changes in the cervical apophyseal joint among Ryukyu peasants. The high prevalence of elbow and knee joint changes in the Okhotsk skeletons was a strong contrast to the high frequency of hip joint changes seen in materials from Kamakura and changes in shoulder and hip joints common in materials from Ryukyu. Because the Okhotsk culture developed a considerable maritime infrastructure, the lifestyle required for sea-mammal hunting and fishing seems to have particularly affected the incidences of severe degenerative changes in the lumbar vertebrae, elbow, and knee. Isotopic signatures in bulk collagen and some amino acids inform of significant differences in the subsistence of each group. Reconstructed diets are taken into consideration to correct the marine reservoir effects on radiocarbon dates for human remains.