PALEOCEANOGRAPHY, VOL. 2, NO. 5, PAGES 445-456, OCTOBER 1987 EVOLUTIONARY CHANGES IN SOME LATE NEOGENE PLANKTONIC FORAMINIFERAL LINEAGES AND THEIR RELATIONSHIPS TO PALEOCEANOGRAPHIC CHANGES Bj6rn A. Malmgren Department of Paleontology, University of Uppsala,Uppsala, Sweden W.A. Berggren Departmentof GeologyandGeophysics WoodsHole Oceanographic Institution Woods Hole, Massachusetts Abstract. The timing of evolutionary changes in some late Neogenelineages of planktonicforaminifersand major paleoceanographic events are evaluated to assess possible correspondences between paleoclimatic change (in a broad sense) and evolutionary innovations. Previously published data on evolutionary changes in the Globorotaliainflata lin- eage,the Globorotalia tumidalineage,and the Globoro- talia truncatulinoides lineage,and new data on the Sphae- roidinella dehiscens lineage,are used in the study.Most evolutionary rate changes in theselineages are shown to oc- cur near timesof major paleoceanographic events.For example, rapid increase in conicality andweakening of the keel in the G. inflata lineagein the latestMiocene co- incided with the 6.2-Ma event (globalcooling, sealevel regression, and shift in carbonisotope ratiosin forami- niferaltests).Disappearance of keeledmorphotypes (Glo- borotalia conomiozea) in the same lineage,and appearance of nonkeeled forms with rounded periphery (Globorotalia puncticulata) coincided with the return of warmer,more stable climaticconditions, and transgressions at the Mio- cene/Pliocene boundary (5.3 Ma). Phyletic transformation from Globorotalia plesiotumida into G. tumida also took placeacross this boundary, and supplementary apertures first developed in the S. dehiscens lineage.Supplementary apertures in the S. dehiscens lineage were rare through the early Pliocene but became rapidlydominant in the popu- lationsin the interval between3.4 and 3.3 Ma, where major Copyright1987 by the AmericanGeophysical Union Papernumber7PO663. 0883-8305/87/007P-0663510.00 paleoceanographic changes occurred (the 3.4- to 3.2-Ma eventmarked by cooling of surface watersand increased production of bottomwaters at highlatitudes, resulting in strengthening of oceanvertical and horizontalgradients). Formswithout a supplementary aperture became extinct only 0.3-0.4 m.y. later (3.0 Ma), and at aboutthe same time, G. inflataappeared in the fossil record. Although evolutionary change exhibits striking temporal correlation with climaticchange,someevolutionary time series do not show anyobvious relationship to paleoclimate: chamber numberin the final whorl in the G. inflatalineage and coni- cality in G. truncatulinoides. INTRODUCTION Darwinian principles predictthat evolutionary change is directed by naturalselection operating to optimallyadapta population of organisms to their habitat.Modern plank- tonicforaminiferalspecies are knownto be restricted to distinct depths or depth intervals in thewatercolumn [B6, 1977],andsuch vertical segregation has existed since the Cretaceous [Douglas andSavin,1978; Boersma and Shackleton, 1981].Most hypotheses advocated to explain planktonic foraminiferal evolution invoke adaptive thres- holds induced by changing depthstratification in the ocean surface waters asthe major controlling mechanism [Cifelli, 1969; Lipps, 1970, 1985;Douglas and Savin,1978; Hart, 1980; CaronandHomewood,1982/83]. Close relationships between planktonic foraminiferal diversity andpaleocli- matethrough their evolutionary history [Cifelli, 1969; Berggren, 1969b; Frerichs, 1971;Stehliet al., 1972; Thu- nell, 1981] may be related to changing density stratification induced by temperature (and salinity) changes ratherthan to temperature itself[Douglas andSavin, 1978].