The exquisite preservation of soft-bodied animals in Burgess Shale-type deposits provides important clues into the early evolution of body plans that emerged during the Cambrian explosion1. Until now, such deposits have remained silent regarding the early evolution of extant molluscan lineages—in particular the cephalopods. Nautiloids, traditionally considered basal within the cephalopods, are generally depicted as evolving from a creeping Cambrian ancestor whose dorsal shell afforded protection and buoyancy2. Although nautiloid-like shells occur from the Late Cambrian onwards, the fossil record provides little constraint on this model, or indeed on the early evolution of cephalopods. Here, we reinterpret the problematic Middle Cambrian animal Nectocaris pteryx3,4 as a primitive (that is, stem-group), non-mineralized cephalopod, based on new material from the Burgess Shale. Together with Nectocaris, the problematic Lower Cambrian taxa Petalilium5 and (probably) Vetustovermis6,7 form a distinctive clade, Nectocarididae, characterized by an open axial cavity with paired gills, wide lateral fins, a single pair of long, prehensile tentacles, a pair of non-faceted eyes on short stalks, and a large, flexible anterior funnel. This clade extends the cephalopods’ fossil record2 by over 30 million years, and indicates that primitive cephalopods lacked a mineralized shell, were hyperbenthic, and were presumably carnivorous. The presence of a funnel suggests that jet propulsion evolved in cephalopods before the acquisition of a shell. The explosive diversification of mineralized cephalopods in the Ordovician may have an understated Cambrian ‘fuse’.
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We thank S. Conway Morris, D. Fuchs, A. Lindgren, A. Scheltema, C. Schander and M. Vecchione for critically reading earlier drafts; R. Gaines for comments on preservation; J.-Y. Chen, M.-Y. Zhu and J. Paterson for images of Petalilium and Vetustovermis; and Parks Canada for research and collection permits delivered to Royal Ontario Museum teams led by D. Collins. P. Fenton assisted with collections, and S. Lackie with scanning electron microscopy. This research was undertaken as part of a PhD thesis (M.R.S.) in the Department of Ecology and Evolutionary Biology, University of Toronto. Funding was provided by Natural Sciences and Engineering Research Council of Canada Discovery Grant through J.-B.C and University of Toronto fellowships to M.R.S. This is Royal Ontario Museum Burgess Shale Research Project 27.
This file contains Supplementary Information, References, Supplementary Figures 1-13 with legends and Supplementary Tables 1–2.
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