Taxonomic evolution of Neogene planktonic foraminifera and paleoceanographic relations

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Abstract
The taxonomic evolution of Neogene (24 Ma to present day) planktonic foraminiferal species are described using four indices: rate of speciation, rate of extinction, rate of diversification, and rate of turnover. The evolution of Neogene planktonic foraminifera is marked by three principal stages: (1) a diversification stage (24 to 16 Ma, early Miocene), (2) an equilibrium stage (16 to 5 Ma, middle and late Miocene), and (3) a declining stage (5 Ma to Recent, Pliocene and Quaternary). The early Miocene diversification was in response to an increase in polar to equatorial thermal gradients and related subdivision of surface water masses. During the middle and late Miocene, the assemblages remained close to their equilibria, with relatively low diversification rates. The decline in diversity during the Pliocene and Quaternary probably resulted from adverse effects imposed by both large‐scale paleoceanographic fluctuations that began about 6 Ma and high‐frequency climatic oscillations related to northern hemisphere glaciations and deglaciations that began at about 2.5 Ma. Bursts of evolutionary activity marked by higher rates of turnover coincided with major paleoceanographic changes. Average evolutionary rates appear to be similar for tropical, transitional, and temperate assemblages, although the actual numbers of extinctions and speciations are higher in tropical assemblages because of higher standing diversity. Contemporaneity of turnover peaks in the three climatic regimes indicates global control of paleoceanographic perturbations upon planktonic foraminiferal evolution. The observed evolutionary pattern supports the stationary model of Stenseth and Maynard Smith (1984).

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