Geographic Diversity of Late Ordovician Corals and Bryozoans in North America

Diversity data for late Ordovician corals and bryozoans in North America were collated from all available published faunal reports. The sampling bias inevitable in literature-derived data was filtered out by elimination of low-valued points, calculation of the Shannon-Weaver diversity index at the generic level, and polynomial trend surface analysis. Generic diversity values were tested against paleolatitude and lithofacies by means of the Chi-squared statistic. Coral diversity is significantly higher in carbonate than in detrital lithofacies. Bryozoan diversity is independent of lithofacies, but is significantly higher offshore than nearshore, probably reflecting paleobathymetry.