Tidal growth patterns and growth curves of the Miocene potamidid gastropod Vicarya yokoyamai

Abstract

Continuous growth sequences are recorded in vertical (=median longitudinal) sections of the columella of the fossil potamidid gastropod Vicarya yokoyamai Takeyama, from subtropical Miocene faunas of Japan. Shells from the Mizunami, Uchiura, Bihoku, and Masuda groups show semidiurnal tidal growth patterns. This suggests that V. yokoyamai lived in the intertidal zone. Growth curves were reconstructed on the basis of numbers of tidal growth lines. These growth curves were found to be very similar with one another, and indicated that shell-height increased from 1.5cm to 8cm in two years.