Taxonomic composition, area cover and diversity in the Upper Cretaceous limestones of southwestern Puerto Rico: A quantitative study of three coral-rudist assemblages

A quantitative paleoecological analysis was made for three coral-rudist fossil assemblages found in three successive, Upper Cretaceous limestone formations of southwestern Puerto Rico: The Cotui Limestone (Santonian), the Guaniquilla Limestone (Campanian), and the El Rayo Limestone Lens (Maastrichtian). A continuous quadrat belt placed on a horizontal transect was used for mapping and sampling purposes on each formation. Detailed drawings were made to produce a map of the fossil organisms in each area. These fossil assemblage maps were used for data analysis.; Taxonomic composition, percent cover values, and diversity were measured and compared between the three formations. Various statistical measures, such as ANOVA, Berger-Parker indexes and Bray-Curtis indexes were used to assess these parameters. Although in general larger variation was found between transects located in different environments than between the assemblages over time, the data obtained indicated that the importance of corals as reef builders was slightly increasing towards the end of the Cretaceous while that of rudists decreased.