Seals, whales and the Cenozoic decline of nautiloid cephalopods

Aim Nautilus and Allonautilus, last members of the once widespread nautiloid cephalopods, are today restricted to the deep central Indo-West Pacific Ocean, for reasons that remain unclear. Cephalopod evolution is generally considered as being driven by vertebrate predation; therefore, we investigated the role of whales and seals in the decline of nautiloids through the Cenozoic. Location Global. Taxon Nautiloids, pinnipeds, cetaceans. Methods Distribution data for nautiloids, pinnipeds and cetaceans through the Cenozoic were compiled and plotted on a series of paleogeographic maps. Nautiloid shell sizes were compiled and plotted against the first appearance of pinnipeds and cetaceans in key regions. Results From the Oligocene onward, nautiloids became extinct in areas where pinnipeds appeared. The exception is the agile nautiloid Aturia, extinct globally at the end of the Miocene. A major role of odontocetes in the demise of nautiloids is not apparent, except for a few brevirostrine Oligocene taxa from the North American Atlantic and Pacific coasts, which appeared in these areas at the same time as nautilids disappeared. The Oligocene disappearance of nautiloids (except Aturia) from the American Pacific coasts coincides with the development of oxygen minimum zones (OMZs) in this region. Main conclusions We hypothesize that the Cenozoic spread of pinnipeds drove nautiloids into their present-day central Indo-West Pacific refuge. Additional factors for the local extinction of nautiloids in the Oligocene include predation by short-snouted whales and the development of OMZs, preventing nautiloids from retreating into deeper water.

Automated summary

The study investigates the decline of nautiloids during the Cenozoic period and its correlation with the appearance of pinnipeds and cetaceans. The results show that nautiloids became extinct in areas where pinnipeds appeared, except for the agile nautiloid Aturia. The decline of nautiloids in the American Pacific coasts coincided with the development of oxygen minimum zones (OMZs) in the region. It is hypothesized that the spread of pinnipeds played a major role in driving nautiloids into their present-day refuge in the central Indo-West Pacific Ocean.