Size-frequency distribution and fossil occurrence of a Cretaceous bivalve Inoceramus hobetsensis from Tappu area, Hokkaido

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.publishe