Evolution of Silurian Pentamerid Communities in Wisconsin

Abstract

Silurian pentamerid communities in Wisconsin include the Middle Llandovery Virgiana Community, the Upper Llandovery to Lower Wenlock Pentamerus and Pentameroides Communities, and the Wenlock Apopentamerus and Kirkidium Communities. Llandovery to Lower Wenlock pentamerid communities are widely distributed across Wisconsin, while later Wenlock communities occur only in local areas with reefs. In addition to their dominant species of pentamerid brachiopods, these communities also include nineteen guilds of stromatoporoids, corals, bryozoans, other brachiopods, molluscs, trilobites and pelmatozoans. Large-scale evolutionary changes from Middle Llandovery to Wenlock time are documented from data on relative abundances of taxa, guild composition, and species diversity. Trends include increase in species diversity, increase in number of guilds, and increase in complexity of epifaunal tiering. These trends are part of the general ecologic diversification of Silurian marine benthos that followed the Late Ordovician extinction event.