Molluscs removed from 12 bulk samples of the Yazoo Formation (upper Eocene), exposed in a quarry at Cynthia, Mississippi, are similar in com- position and diversity to those found in the underlying upper Eocene Moodys Branch Formation, when dif- ferences in outcrop area are considered (74% of the Yazoo species are also found in the Moodys Branch). This suggests there was no significant extinction during the late Eocene (at the P15/P16 biozone boundary) as has been reported for planktic foraminifera. Only 11.4% of the species from the Yazoo extend into the Oligocene Red Bluff Formation, suggesting a large molluscan extinction at or near the Eocene-Oligocene boundary. The presence in the lowermost Red Bluff of an assemblage with a relatively high diversity dominated by suspension-feeding bivalves suggests that the molluscan fauna had recovered from the extinction by the earliest Oli- gocene.
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