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.

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Contents available as PDF only.

Contents available as PDF only.

Contents available as PDF only.

Contents available as PDF only.

Contents available as PDF only.