Spatio‐temporal transitions in Paleozoic Bivalvia: An analysis of North American fossil assemblages

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Abstract
To understand the radiation of any higher taxon, it is important to establish the degree to which global diversification may have been associated with, and possibly dependent on, local paleoenvironmental transitions. In this paper, paleoenvironmental changes accompanying the Paleozoic radiation of the Class Bivalvia are evaluated using a literature‐derived, genus‐level data base of 505 Paleozoic benthic marine fossil assemblages, mainly from North America. A series of contoured time‐environment diagrams, constructed to evaluate spatio‐temporal patterns in the Class as a whole and in constituent life habit groupings, reveals that the Paleozoic spatio‐temporal history of bivalves was dynamic. During their initial Ordovician radiation, bivalves quickly became established in both nearshore and offshore settings, although their highest diversities were generally nearshore. As the Paleozoic progressed, their importance in deepwater and carbonate‐rich environments, where they had previously not been of major significance, increased noticeably; elements of these patterns can be recognized in all four major Paleozoic life habit groups. Processes responsible for these spatio‐temporal transitions probably include a complex set of interacting mechanisms not all of which are related to innate biological characteristics of the group.