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44548-B8
A Composite Standard Biostratigraphic Database for Assessing Rates of Foraminiferal Origination and Extinction During the Late Paleozoic Ice Age

John R. Groves, University of Northern Iowa

During the first year of the project undergraduate student assistants and I compiled a database consisting of the oldest and youngest known stratigraphic occurrences of 1,698 species of microfossils. The second (current) year of the project, again with undergraduate assistants, was devoted to the analysis of diversity trends, origination and extinction frequencies, and provincialism relative to extrinsic events that might have influenced foraminiferal evolution. Foraminiferal species diversity increased throughout Mississippian and Pennsylvanian time leading up to its peak at the Pennsylvanian-Permian boundary. Foraminifers then experienced a steep decline in diversity during the Early Permian. Frequencies of origination and extinction broadly tracked changes in global diversity. From Late Mississippian time onward, patterns in total foraminiferal diversity were dominated by fusulinoideans. There is no clear relationship between rates of foraminiferal evolution and the alternating glacial and nonglacial intervals that characterized the Late Paleozoic ice age. Rather, high rates of origination and extinction might reflect instability of neritic environments as a consequence of high-frequency, high-amplitude base level fluctuations. More importantly, the advent of algal symbiosis in fusulinoideans was a physiologic innovation that promoted diversification as these symbiont-bearing taxa experimented with morphologic adaptations for partitioning the low-nutrient environments to which they were specialized. Growth to large size and delayed maturation in fusulinoideans might have been enabled by the Late Paleozoic hyperoxic atmosphere and the widespread development of oligotrophic, carbonate platform and shelf environments. The Late Paleozoic history of foraminiferal diversification was influenced also by closure of the Rheic Ocean beginning in Late Mississippian time. Foraminiferal associations on opposite sides of Pangaea exhibited relatively high similarity prior to the closure, but then similarity decreased steadily after destruction of the subequatorial marine corridor. Arctic-Eurasian and North American associations were nearly isolated from one another throughout the main burst of fusulinoidean diversification, so that parallel lineages developed independently in the two regions, resulting in considerable taxonomic duplication.

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