近・現代の北海道アイヌによる熊送り儀礼の所産と酷似する特徴が認められた羅臼町オタフク岩洞窟から出土した10個体分のヒグマ遺体について14C年代測定を試みた。その結果、前処理を経てゼラチンの抽出に成功した9個体について、概ね1000-1200BPという未較正年代を得た。これにより北海道アイヌの熊送り儀礼について基本形態の成立時期を具体的な数値年代で議論できるようになった意義は大きい。また、北見市中ノ島遺跡から出土したヒグマ遺体2点についても14C年代測定を実施したところ、うち1点から357±21BPという未較正年代も得た。同遺体は擦文文化期の竪穴覆土から出土した資料であることから、同測定値は中近世には前代の竪穴の窪みが送り場として利用されたという先学の指摘を支持する証左となる。上記資料群については、合わせて測定した炭素・窒素同位体比も踏まえ、目下、海洋リザーバー効果の影響も評価の上、確度の高い歴年代も算出も試みている。無論、同位体比は北海道東部におけるヒグマ個体群の食性の変遷についても論ずる貴重なデータともなる。なお、本研究成果については、共同研究者の米田穣氏(東京大学総合研究博物館)、松林順氏(海洋開発機構)と連名で、2021年7月に開催される日本動物考古学会の年次大会で発表する予定である。
In this study, we attempted 14C dating of the remains of 10 brown bears excavated from the Otafuku-iwa Cave in Rausu Town. These remains were found to have characteristics that are very similar to those produced by the bear sending rituals conducted by the modern Hokkaido Ainu in the modern era. As a result of the dating, an uncalibrated age of approximately 1,000-1,200 BP was obtained for the 9 individuals from whom we succeeded in extracting gelatin through pretreatment processes. This result has great significance for discussions about the establishment of the essential form of the Ainu bear sending rituals in Hokkaido. In addition, as part of this study 14C dating was attempted on the remains of two brown bears unearthed from the Nakanoshima site in Kitami City, from one of which an uncalibrated age of 357 ± 21 BP was obtained. The remains in question were unearthed from the filling of a pit dwelling dating to the Satsumon period. This age supports the view of previous scholars that the depressions of earlier pit dwellings were used as sending places during the Middle Ages. Carbon and nitrogen isotope ratios were also measured for the above remains. We are now evaluating the marine reservoir effect based on these ratios in order to calculate a highly accurate calendar age. Of course, the isotope ratio also serves as valuable data for discussions concerned with changes in the diet of the brown bear population in eastern Hokkaido. The results of this research will be presented, alongside collaborators Minoru Yoneda (University Museum, The University of Tokyo) and Jun Matsubayashi (JAMSTEC), at the annual meeting of the Japanese Society of Zooarchaeology, which will be held in July 2021.
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