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Planktic foraminifera have been studied in detail for over a hundred years. During this time, they have been useful for biostratigraphic correlation of Cretaceous and younger deep water facies and for paleooceanographic inference. Their paleoecologic utility has been more limited, perhaps because it is based primarily on empirical comparisons of fossils with modern species occurrences. The first planktic species possibly occurred in the Triassic and by the Jurassic, simple globigeriniform species were present in tropical seas. Iterative evolution thereafter produced recurring radiations of high diversity, morphologically complex faunas interspersed with low diversity, morphologically simple faunas.

Test morphology can be interpreted as adaptations for main enance of position in the water column, defense against predators, or maintenance of a preferred orientation. Of these, water column positioning is likely to be most critical. Test morphologies may function in relation to density of the foraminiferan and its difference with water, resistance to sinking, and turbulence.

The biology and paleobiology of planktic species is poorly known, These foraminifera probably utilize different feeding, reproductive, behavioral, and life history strategies in eutrophic and oligotrophic waters. Mostof these strategies can be inferred from fossils, and therefore have considerable paleoecologic potential. Biogeographic distributions are most commonly used for paleoecology, yet it is very difficult to explain these patterns not only for foraminifera, but for other plankton as well. Six hypotheses are considered. The patterns are not determined by temperature, salinity or circulation alone, nor do they match water mass boundaries wellbecause of mixing along the edges. The idea of “core” ecosystems of more or less fixed biotic structure surrounded by wide ecotones of variable conditions and structure is supported by plankton and foraminiferal evidence. A non-exclusive hypothesis is that environmental stability or lack of it is influential in producing faunal compositions. Bipolar species may be maintained by mixing, coiling directions do not depend on temperature, and distributions on continental shelves are complex but related in general to oceanic water and depth.

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