北海道小平町達布地域における白亜紀二枚貝Inoceramus hobetsensisのサイズ分布と産状

概要

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Size-frequency distribution and mode of occurrence of a Late Cretaceous inoceramid bivalve Inoceramus hobetsensis NAGAO & MATSUMOTO, 1939 were examined. A large number of samples, all of which were recovered from the Upper Cretaceous of the Tappu area, northwestem Hokkaido, show chronological change in the size-frequency distribution pattern. The proportion of the frequency of relatively small individuals (20-40 cm in size) tends to increase toward the upper sequence of the range of this species. The relative frequency of huge individuals (60-80 cm in size) also increases in the upper part, although the mode of fossil occurrence indicates that the size-frequency distribution might be biased by post-mortem taphonomic processes. The result of this study suggests change through time in the characteristics of the growth curve and/or mortality of this species.