George A. Seiglie, 1905. "SEA LEVEL CHANGES AND CENOZOIC LARGE FORMINIFERA WITH INNER STRUCTURES", Timing and Depositional History of Eustatic Sequences: Constraints on Seismic Stratigraphy, Charles A. Ross, Drew Haman
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Sea-level changes affect organisms living on the shelves, especially the large calcareous foraminifera with photosynthetic symbiotic algae. The evolutionary patterns of Cenozoic shallow water large foraminiferal genera correlate with sea level fluctuations.
Most newly evolved genera of larger foraminifera first appeared during sea-level highstands. The number of new genera appearing in each highstand is approximately proportional to the duration of the highstand, except for the Early Oligocene. This may be a consequence of the high diversification of species of Lepidocyclina during the Oligocene, which probably occupied a diversity of ecological niches that otherwise would have been occupied by new genera. The greatest number of new genera appeared during the Middle Eocene which had the longest Cenozoic sea-level highstand. The major extinctions of large foraminifera possibly occurred during major sea-level lowstands.