Endocerids: suspension feeding nautiloids?

ABSTRACT

For a long time all extinct cephalopods of the subclass Nautiloidea were considered as ecological analogues of the Recent Nautilus. Recently this view has been rejected: it is now known that among the nautiloids there were not only demersal predators but also epipelagic animals whose life-style and reproduction differed from those of the Nautilus. However, the habits of some nautiloid orders is still poorly understood. One of the most enigmatic cephalopods is the Early Paleozoic nautiloid order Endocerida. Endocerids differ from other nautiloids: they reached gigantic sizes (up to 9 meters), had a wide siphuncle tube and were widespread and numerous during the Ordovician. Since they were an important component of many Ordovician ecosystems, without the understanding of their habits and feeding strategies a correct reconstruction of these ecosystems is impossible. Until now, endocerids have been considered as dominant apex predators, however, this assumption is based on an analogy with the Nautilus mode of life, while the features of the structure of endocerid shells do not confirm this idea and furthermore contradict it. In this article, a new hypothesis is proposed and debated: according to it, the endocerids were planktotrophic cephalopods and the largest of them were giant suspension feeders.

KEYWORDS:

• Ordovician
• Nautiloidea
• Endocerida
• suspension-feeding
• plankton

Acknowledgments

I am very grateful to Chingiz Nigmatullin (AtlantNIRO, Kaliningrad, Russia) for provided literature and fruitful discussion on the topic of this article. Very accurate and beautiful reconstruction of endocerids based on my sketch was drawn by paleoillustrator Andrey Atuchin (Kemerovo, Russia). I am also very grateful to Kenneth De Baets (Friedrich-Alexander-University of Erlangen-Nürnberg, Erlangen, Germany), David Evans (Natural England, Peterborough, United Kingdom) and Björn Kröger (University of Helsinki, Helsinki, Finland) for their very useful comments, advice and criticism, which helped to greatly improve the manuscript. Special thanks to Steve Ford (Vancouver, Canada) who went over and edited the manuscript with me to improve English.

Disclosure statement

No potential conflict of interest was reported by the author.

Additional information

Funding

The research was supported by the program of the Presidium of Russian Academy of Sciences No. 17 (project No. 0135-2018-0050).