New insights into the earliest occurrence, possible evolutionary lineage, palaeogeography and palaeoclimatic implications of Nicklithus amplificus: Evidence from the Adriatic Sea, Indian Ocean and Paratethys

Abstract

Relatively large specimens (6–12 μm long) of the nannolith Nicklithus amplificus are characteristic of the late Miocene, having evolved in NN11 from the typical Miocene species Orthorhabdus rugosus. The present study was performed in order to identify the earliest occurrence, and to examine the evolutionary lineage, palaeogeography and palaeoclimatic implications, of N. amplificus in the Indian Ocean, incorporating information on its youngest record from the Paratethys. In addition to this, other members of the Ceratolithaceae from the Mediterranean region were used to add to our understanding of the phylogenetic lineage. The first relatively small (<6 μm long) N. amplificus occurs earlier, in the late Eocene (NP19–20), in the Mediterranean, in assemblages containing Amaurolithus tricorniculatus and Ceratolithus cf. atlanticus, and in the early middle Miocene (NN4) in the Indian Ocean. Its migration to the Paratethys took place at 11.2 Ma (in NN8), where it occurs in assemblages containing A. tricorniculatus and Amaurolithus primus. Combined, this evidence suggests a different origin and ancestry for N. amplificus. Based on morphological similarities with the Cretaceous genus Ceratolithina, a new phylogeny is proposed. Our latest record of the smaller specimens in marginal seas correlates with a global hothouse to warmhouse scenario, while the occurrence of the larger specimens corresponds to the coolhouse conditions of the late Tortonian to Recent. The revised palaeogeographic distribution of N. amplificus during the Miocene, with its slight diachroneity in the late Miocene, corresponds to the closure of global oceanic corridors and a warm climate, more characteristic of lower latitudes.