INFLUENCE OF SUBSTRATE ON BRACHIOPOD DIVERSITY DURING THE EARLY TO MIDDLE PERMIAN

Early-to-Middle Permian rocks record a dynamic interplay between biocalcifier-dominant and biosiliceous-dominant marine ecosystems. It is unclear if, and how, these differently biomineralized substrates influenced faunal diversity of contemporaneous faunas over millions of years. To test for a connection, we first apply logistic regression models to predict brachiopod genus survival as a function of substrate in the Early and Middle Permian, using data from the Paleobiology Database, with brachiopod occurrences characterized as simply carbonate or siliciclastic. Second, we included finer resolution of substrate, also based on the database. Finally, we use published literature and new field observations to apply a refined set of substrate categories, including chert, to the key Permian stratigraphic units of the American West. In the preliminary analysis, we find that siliciclastic substrates have a greater impact on background extinction during the early Permian, and carbonate substrates are more important during the middle Permian. The pattern holds when using a finer classification from the database. Chert, finally, is also important, but demonstrates a different degree of extinction selectivity depending on timing, geography, and taxonomic order of brachiopod. Taken together, we interpret these data to support a model of ecosystem-driven phase shifts in benthic biomineralization, where the particular animals present may be more important than the global-scale climate or geochemical cycling.