Analysis of middle Eocene to early, Oligocene calcareous and siliceous microfossils shows gradual biotic changes with no massive extinction event across the Eocene/Oligocene boundary. Biotic changes in the late Paleogene appear to reflect changing paleoclimatic and paleoceanographic conditions and do not support suggestions of a catastrophic biotic event caused by a bolide impact at the Eocenel Oligocene boundary.