Radiation of Cenozoic Planktonic Foraminifera

The general aspects of planktonic foraminiferal radiation during the Cenozoic are shown by the distributional patterns of several morphotypic groups. There were two major radia-tions, one occurring during the Paleogene, the other during the Neogene. The radiations followed severe reductions in diversity which occurred at the close of the Cretaceous and again during the mid-Tertiary. Distributional patterns are iterative, and the Neogene radiation is essentially a repetition of what occurred during the Paleogene. According to the present interpretation, the ilerative patterns reflect major changes in the dynamic structure of surface waters. By analogy with the distribution of the modern fauna, it is suggested that thermal barriers were degraded during times of reduction and the oceans were uniformly cool. During the radiations thermal gradients were restored and the struc-ture of the surface waters was essentially as it is today. The Foraminifera have left a geologic record that is probably more continuous and perhaps the subject of more study than that