Palaeobiology of a Biradiolites mooretownensis rudist lithosome: Seasonality, reproductive cyclicity and population dynamics

During the Cretaceous, rudist bivalves were among the most important benthic carbonate producers on tropical to sub-tropical carbonate platforms. Yet questions concerning the biology of rudist bouquets remain unanswered to a great extent. In this study a monospecific bouquet of the small radiolitid rudist Biradiolites mooretownensis has been evaluated from a palaeobiological angle. Three-dimensional, high-resolution, quantitative analysis provides a detailed evaluation of growth and reproduction in an in situ rudist association. A total of 1237 consecutive tomograms with a vertical spacing of 0.1mm were produced of which 1150 have been digitally measured for total area, number of specimens, packing density, spat density, recruitment, survival time, mortality and accommodation space. The results show constant coverage of about 60%, a stable packing density of 3.2 specimens per cm ² and constant reproduction throughout the bouquet. Time series analysis (spectral analysis) using PAST statistical software shows cyclic spat density every 14.9mm of vertical growth. Combined with the results of the δ ¹⁸O isotope analysis (showing cyclicities of 14mm) one reproduction cycle appears to be annual. 46.4% of all counted specimens died before 3mm of vertical growth. More than 93% of the initial spat does not exceed 15mm shell height or 1year respectively. Two mortality peaks in the juvenile's life at 4 and 10-15mm shell height either represent important obstacles in the ontogenetic development of the species or reflect external influences. □ Biradiolites, grinding tomography, palaeobiology, population dynamics, reproduction, rudists, sclerochronology, seasonality.