鳥浜貝塚出土有溝砥石の年代と形態測定学的分析

摘要

The emergence of grinding stones with grooves is one of the hallmarks indicating the beginning of bow-and-arrow hunting. In the Japanese islands, grinding stones with grooves appeared from the Incipient Jomon period, which coincides with the timing when arrowheads drastically increased. Although the grinding stone with grooves has been considered to be used as an arrowshaft smoother, its real function is little known so far. The present study conducted a morphometric analysis of a grinding stone with grooves from the Torihama shell mound in Fukui Prefecture, central Japan, in order to better understand the function. To confirm the chronological position of the grinding stone with grooves, we undertook radiocarbon dating of two walnuts (Juglans ailantifolia) recovered from the layer from which the grinding stone with grooves was unearthed. The radiocarbon determinations show10，160±35 BP and 10,070±30 BP that are calibrated to 12,030-11,650cal BP and 11,770-11,400cal BP respectively using IntCall3 calibration curve and OxCal platform. The age range suggests that the grinding stone with grooves from the Torihama shell mound dates from the Pleistocene-Holocene transition. The morphometric analysis of the 3D-data on a groove that most clearly formed on this grinding stone indicates that the groove runs straight and its surface shape shows a small deviation in morphometric values. The high straightness and significantly high morphometric standardization of the groove suggest that the groove was formed due to smoothing of a rod-like material, such as an arrowshaft.%本稿では，鳥浜貝塚から出土した有溝砥石の年代と機能を知るため，同一層準から出土した種 実遺体の~(14)C年代測定と有溝砥石の形態測定学的分析を行った.ォニグルミ内果皮の年代測定の 結果，12.030～11,400cal BPの年代が得られ，鳥浜貝塚の有溝砥石が更新世から完新世へ移行 する時期に残されたことがわかった.また，有溝砥石の三次元スキャンデータを解析したとこ ろ.溝の形状が極めて均一であることがわかった.このような均一な溝は，棒状のものを研磨す る時にしか形成されない.したがつて，鳥浜貝塚出土有溝砥石も，矢柄のような棒状のものを研 磨するために使用された可能性が高いことが予想された.