Endocerids: suspension feeding nautiloids?

Abstract

ABSTRACTFor 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.