Proceedings of the Royal Society B: Biological Sciences
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A molecular palaeobiological hypothesis for the origin of aplacophoran molluscs and their derivation from chiton-like ancestors

Jakob Vinther

Jakob Vinther

Department of Geology and Geophysics, Yale University, PO Box 208109, New Haven, CT 06520-8109, USA

[email protected]

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Erik A. Sperling

Erik A. Sperling

Department of Geology and Geophysics, Yale University, PO Box 208109, New Haven, CT 06520-8109, USA

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Derek E. G. Briggs

Derek E. G. Briggs

Department of Geology and Geophysics, Yale University, PO Box 208109, New Haven, CT 06520-8109, USA

Yale Peabody Museum of Natural History, Yale University, PO Box 208109, New Haven, CT 06520-8109, USA

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and
Kevin J. Peterson

Kevin J. Peterson

Department of Biological Sciences, Dartmouth College, Hanover, NH 03755, USA

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Published:https://doi.org/10.1098/rspb.2011.1773

    Aplacophorans have long been argued to be basal molluscs. We present a molecular phylogeny, including the aplacophorans Neomeniomorpha (Solenogastres) and Chaetodermomorpha (Caudofoveata), which recovered instead the clade Aculifera (Aplacophora + Polyplacophora). Our relaxed Bayesian molecular clock estimates an Early Ordovician appearance of the aculiferan crown group consistent with the presence of chiton-like molluscs with seven or eight dorsal shell plates by the Late Cambrian (approx. 501–490 Ma). Molecular, embryological and palaeontological data indicate that aplacophorans, as well as chitons, evolved from a paraphyletic assemblage of chiton-like ancestors. The recovery of cephalopods as a sister group to aculiferans suggests that the plesiomorphic condition in molluscs might be a morphology similar to that found in monoplacophorans.

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