RAPID DIVERSIFICATION OF PLANKTONIC-FORAMINIFERA IN THE TROPICAL PACIFIC (ODP SITE-865) DURING THE LATE PALEOCENE THERMAL MAXIMUM

The planktonic foraminiferal genera Morozovella and Acarinina rapidly (in similar to 10 k.y.) diversified during the late Paleocene thermal maximum (LPTM), giving rise to such morphotypes as M. allisonensis (ne w species), M. africana, and A. sibaiyaensis. Single-specimen isotopic analysis confirms that M. allisonensis and A. sibaiyaensis are restri cted to the LPTM carbon isotope excursion recorded at Ocean Drilling P rogram Site 865 (equatorial Pacific Ocean). The short-lived (50 to sev eral 100 k.y.) ''excursion'' taxa attest to the ephemeral effects of t he LPTM on the calcareous plankton, Single-specimen oxygen isotope dat a show that evolution of M. allisonensis and A. sibaiyaensis was accom panied by migration to deeper water depths, Ancestral M. velascoensis and A. soldadoensis were extremely rare or absent during the early sta ges of the LPTM, but immigrated back into the study area to coexist wi th their descendants in later LPTM horizons, Photosymbiosis may have f acilitated the morozovellid and acarininid diversifications during the oligotrophic conditions of the LPTM.