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Abstract: A revision of the coccolithophores in the extinct Order Discoasterales is made possible by the realization that the coccoliths in this order were delicate skeletal entities similar in every way to the coccoliths secreted in today’s oceans, and not the massively crystallized objects that are found as fossils in deep-sea calcareous oozes. Phylogenetic reconstruction based on morphostructural analysis of the original coccoliths properly oriented with regard to the live cell leads to the establishment of the earliest Paleocene genus Biantholithus at the root of the Cenozoic proliferation of the order into 16 mostly highly diverse genera. Identification of the stem genus, with its spherical coccosphere, low coccolith count, and no flagella opening, permits a reconstruction of the coccospheres in different lineages leading to the crown taxa of the late Neogene. Due to the unusual texture or shape of their coccoliths, the Discoasterales coccospheres were remarkably cavernous, with minimal calcified matrix, particularly in these crown taxa. Several lines of evidence indicate that this was part of an adaptive strategy towards oligotrophy. The >64-million-year longevity of the Cenozoic Discoasterales, to which about a quarter of all Cenozoic fossil species belongs, reflects the adaptive potential of the basic wedge-shaped element of its coccoliths in an ever-changing ocean.

Abstract Middle Miocene-upper lower Aptian calcareous nannofossils were recovered from Sites 1183–1187 drilled by Ocean Drilling Project Leg 192 on the Ontong Java Plateau. Nannofossil biostratigraphy indicates the presence of six unconformities among the five Leg 192 sites. These are: (1) between the lowermost Albian and upper middle Albian; (2) between the upper Albian and middle Coniacian; (3) within the lower Maastrichtian; (4) between the lower upper Maastrichtian and basal Danian; (5) within the upper Palaeocene; and (6) between the Oligocene and Miocene. Previous drilling before Leg 192 on the Ontong Java Plateau and in the SW Pacific (Legs 30 and 130) indicated two episodes for major emplacement of basement during the earliest Aptian and Turonian. The Leg 192 drilling was not able to confirm either of these episodes, but instead indicated that the emplacement of basement on the Ontong Java Plateau was relatively continuous from the latest early Aptian to latest Aptian. Results from Sites 1184 and 1185 indicate the possibility of another magmatic episode during the middle Eocene (Zone NP16).