title: Cephalopod origin and evolution: A congruent picture emerging from fossils, development and molecules: Extant cephalopods are younger than previously realised and were under major selection to become agile, shell-less predators.
abstract: Cephalopods are extraordinary molluscs equipped with vertebrate-like intelligence and a unique buoyancy system for locomotion. A growing body of evidence from the fossil record, embryology and Bayesian molecular divergence estimations provides a comprehensive picture of their origins and evolution. Cephalopods evolved during the Cambrian (∼530 Ma) from a monoplacophoran-like mollusc in which the conical, external shell was modified into a chambered buoyancy apparatus. During the mid-Palaeozoic (∼416 Ma) cephalopods diverged into nautiloids and the presently dominant coleoids. Coleoids (i.e. squids, cuttlefish and octopods) internalised their shells and, in the late Palaeozoic (∼276 Ma), diverged into Vampyropoda and the Decabrachia. This shell internalisation appears to be a unique evolutionary event. In contrast, the loss of a mineralised shell has occurred several times in distinct coleoid lineages. The general tendency of shell reduction reflects a trend towards active modes of life and much more complex behaviour.
authors.affiliation: Museum für Naturkunde Berlin, Berlin, Germany.
authors.forename: Björn
authors.initials: B
authors.lastname: Kröger
authors.forename: Jakob
authors.initials: J
authors.lastname: Vinther
authors.forename: Dirk
authors.initials: D
authors.lastname: Fuchs
mesh_terms: D000818:Animals; D005075:Biological Evolution; D049830:Cephalopoda / Q000033:anatomy & histology* / Q000145:classification / Q000196:embryology / Q000235:genetics*; D005580:Fossils; D006433:Hemocyanins / Q000235:genetics; D009024:Morphogenesis; D010802:Phylogeny; D011235:Predatory Behavior; D012641:Selection, Genetic
chemical_list: D006433:Hemocyanins