Abstract
Abstract A major parallelism in marine biotic turnover, caused by progressive intensification of cooling near the middle-late Eocene, is seen in all marine groups, both microfossils (phytoplankton, zooplankton and benthic microfauna) and macrofossils (invertebrates and marine vertebrates) (see several papers and controversial explanatory models in Prothero and Berggren, 1992). For example, the largest turnover in planktonic for aminifera affecting most of the older Eocene tropical and equatorial surface groups, a gradual extinction over 80% during 14 million years, occurred near the middle-late Eocene boundary, with 33 biotic turnover events, 18 extinctions, and 33 originations (Aubry in Prothero and Berggren, 1992). Sequential, stepwise extinction pattern during the mid-Eocene to Oligocene characterizes benthic foraminifera (Thomas in Prothero and Berggren, 1992). In gastropods and bivalves of the Gulf Coast of North America, there was a middle Eocene peak of diversity followed by a severe extinction (84 and 89%, respectively) of warm-water molluscs at the end of the middle Eocene (Hansen, 1987). In echinoids, the biggest extinction, correlated with temperature decline, was at the Terminal Eocene Event, when over 50% of the species became extinct (McKin ney et al., in Prothero and Berggren, 1992). Fish diversity, at least in some families, also declined during the middle or late Eocene (Raup and Sepkoski, 1986) but whale diversity increased dramatically by the late Eocene, possibly due to
Published Version
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