Spatio‐temporal transitions in Paleozoic Bivalvia: A field comparison of upper Ordovician and upper Paleozoic bivalve‐dominated fossil assemblages

Publisher Website
Google Scholar
Abstract
Because of the uncertain relationship between relative abundance and taxonomic richness, abundance data are potentially critical components in any analysis of faunal dominance within fossil assemblages. However, such data are often not available in the literature. In this paper, relative abundance data collected during field work at 25 Upper Ordovician and 22 Upper Pennsylvanian to mid‐Permian localities are used to evaluate Paleozoic transitions in the environmental distributions of bivalve molluscs. On the basis of multivariate analyses of these data, it is shown that even early in their history, during the Ordovician, bivalves were generally not restricted in abundance to just marginal environments. They apparently thrived in terrigenous—dominated regions, both nearshore and offshore, but were less abundant in carbonate settings. However, by the late Paleozoic, bivalve abundances had increased in some carbonate environments, in part because of the growing abundances of free‐burrowing suspension‐feeders, which had been substantially less abundant even in terrigenous environments earlier in the Paleozoic. The results of this study corroborate those of a companion analysis, using literature‐derived data, of paleoenvironmental diversity transitions exhibited by Paleozoic Bivalvia.