The level of lowest appearance of the genus Globigerinoides is used widely as a guide to the Oligocene-Miocene boundary, though reported to fall within the upper Oligocene or the lower Miocene at certain localities. An unusually discrepant case is recorded where Globigerinoides quadrilobatus primordius is present in the base of the Globigerina ciperoensis Zone and its diversification into more advanced subspecies is evident below the advent of Globorotalia kugleri sensu lato. Also anomalous are the presence of Globigerinita incrusta in the upper Oligocene and the unusual scarcity of Catapsydrax spp. in the Oligocene-Miocene interval. The change from Globigerina to Globigerinoides may be a functional response to environmental change rather than a genetic response to evolut onary tendencies. All the apparent anomalies may be related to initial warming after the cool paleoclimatic phase that typified the Oligocene.