Coccolithophore Evolutionary History
Calcareous nannofossils first appeared in the Late Triassic (~220 Ma) as abundant but low-diversity assemblages apparently restricted to low latitudes. All but one species of coccolith disappeared during an extinction event at the Triassic/Jurassic boundary (~200 Ma). Nannofossils were rapidly re-established in the earliest Jurassic (185-195 Ma) and appear to have colonized all marine environments during this time. Most major coccolith families were established during the Early Jurassic radiation. Diversity increased steadily through the Jurassic and Cretaceous, reaching a diversity-peak in the Late Cretaceous (~75 Ma). Nannofossils were severely affected by the Cretaceous/Tertiary boundary mass-extinction event (65.5 Ma) when >90% of species became extinct, including virtually all the common species. Subsequently, they recovered rapidly in the Early Paleocene, reaching a second diversity peak in the Middle Eocene (~54 Ma), comparable to that of the Late Cretaceous. The Paleocene radiation was more rapid and diverse than the Mesozoic radiations, and established significantly different coccolith families. There followed a significant decline into the Oligocene, increased diversity in the Miocene and a general decrease into the Pleistocene.
