UNCOILING THE ROLE OF CLIMATIC AND BIOTIC DRIVERS IN THE CENOZOIC DECLINE OF NAUTILIDS

Nautilids survived the end-Cretaceous mass extinction and enjoyed widespread distribution and moderate diversity in the early Cenozoic. However, today the group has been reduced to a handful of species with a restricted distribution in the western equatorial Pacific. The Cenozoic decline of nautilids coincided with profound environmental and biotic changes, including the transition to an icehouse climate and the radiation of whales and other pelagic predators, but the primary driver of nautilid extinction remains uncertain. We used optimal linear estimation to calculate the most likely extinction times for common Cenozoic nautilid genera Aturia, Aturoidea, Cimomia, Deltoidonautilus, Eutrephoceras, and Hercoglossa. We also assessed trends in the paleogeographic distribution of nautilids to document the timing of geographic restriction. Nautilid extinctions clustered in the late Eocene-early Oligocene and the middle-late Miocene, coincident with cooling events following the Eocene and Miocene climatic optima. During those warming episodes, nautilids exhibited peaks in abundance and displayed wide geographic distributions, whereas the group had fewer occurrences in the Oligocene and only a single Plio-Pleistocene fossil record. The genus Aturia had a near-global distribution in the early and middle Miocene, with evidence for in-situ populations in the eastern Pacific and western Tethys. However, by the latest Miocene Aturia was predominantly recorded from the western Pacific near the current range of Nautilus. These patterns suggest that Cenozoic climate cooling led to extinctions and progressive geographic restriction of nautilids, setting the stage for the current threatened status of the group.