Evolutionary trends of tropical calcareous nannofossils in the Late Neogene

Examination of Middle-Late Miocene sediments recovered during ODP Leg 154 in western equatorial Atlantic has led to identification of evolutionary transitions in some groups of late Neogene calcareous nannofossils. Through analyses of high resolution samples (10-cm sample interval equivalent to average interval of 6 kyr) we were able to document the origin of the genera Catinaster, Amaurolithus, and Ceratolithus, and the nannofossil species Discoaster berggrenii and D. quinqueramus. The presence of intermediate morphotypes between end-members representing distinct species sheds new light on phylogenetic relationships and/or confirms relationships suggested in previous studies. The mode and timing of the evolutionary transitions described are discussed. Successive branching from Triquetrorhabdulus rugosus is demonstrated for Amaurolithus primus, 'Amaurolithus amplificus', and Ceratolithus acutus. A new genus is therefore established, Nicklithus, type species Nicklithus amplificus n. comb. A new species is described, Ceratolithus larrymayeri n. sp. The genera Triquetrorhabdulus, Amaurolithus, Nicklithus and Ceratolithus all belong to the family Ceratolithaceae.