BEGIN:VCALENDAR VERSION:2.0 PRODID:-//Talks.cam//talks.cam.ac.uk// X-WR-CALNAME:Talks.cam BEGIN:VEVENT SUMMARY:The origin of a phylum: soft-bodied fossils and early mollusc evol ution - Martin Smith\, University of Cambridge DTSTART:20121120T163000Z DTEND:20121120T173000Z UID:TALK38988@talks.cam.ac.uk CONTACT:John Maclennan DESCRIPTION:How did the molluscs originate? Molecular and morphological st udies give different answers to this question. The traditional morphologic al story envisages worm-like primordial molluscs that eventually gained a shell\, ultimately diversifying to produce the complex anatomies of cuttle fish\, snails and clams. But molecular studies are converging on a differe nt topology\, where shell-less molluscs represent a highly derived rather than primitive state. This concept finds support from recent fossil finds\ , and a new 965-character morphological supermatrix suggests that the trad itional model represents an artefact of the techniques used to analyse mor phological data. When a more appropriate model of evolution is employed\, morphological data reproduce the “molecular” topology. This tree indic ates that modern molluscs are all highly derived\, so extant taxa can tell us little about molluscan evolution – the fossil record offers an inval uable window on the origin of molluscs.\nShelly fossils are often ambiguou s\, so we must turn to exceptional “soft-bodied” fossils if we are to identify early molluscs. The contentious Wiwaxia\, known from the Cambrian Burgess Shale (~500 Ma)\, has been interpreted as an annelid worm. It lac ks a shell\, and is covered in carbonaceous spines and scales. New observa tions reveal similarity between its mouthparts and sclerites and those of molluscs\, and reveal a molluscan creeping foot. Quantitative analysis sho ws that its detailed anatomy strongly supports a molluscan affiliation\, a nd places the taxon near the base of the molluscan tree.\nMolluscs seeming ly evolved from a Wiwaxia-like ancestor – but how fast did the modern gr oups arise? Most molluscan classes leave their first shelly fossils late i n the Cambrian period\, suggesting a gradual diversification. But another soft-bodied taxon from the early Cambrian\, Nectocaris\, strikingly resemb les the derived coleoid cephalopods. Could molluscs really have diverged s o early? Nectocaris’s interpretation has been controversial\, but detail ed anatomical observations uphold its similarities to the cephalopods. Whe ther this resemblance represents common ancestry or profound convergence\, the molluscs rapidly attained body plans as complex and disparate as thos e seen today.\n\nReferences\n\n1 Smith\, M. R. 2012 The mouthparts of Odon togriphus and Wiwaxia: implications for the ancestral molluscan radula. Pr oceedings of the Royal Society B: Biological Sciences 279\, 4287–4295. ( doi:10.1098/rspb.2012.1577)\n\n2 Smith\, M. R. & Caron\, J.-B. 2010 Primit ive soft-bodied cephalopods from the Cambrian. Nature 465\, 469–472. (do i:10.1038/nature09068)\n\n3 Smith\, M. R. & Caron\, J.-B. 2011 Nectocaris and early cephalopod evolution: Reply to Mazurek & Zatoń. Lethaia 44\, 36 9–372. (doi:10.1111/j.1502-3931.2011.00295.x)\n\n4 Smith\, M. R. 2013 Af finity\, ecology and diversity of the early “cephalopod” Nectocaris. P aleobiology in press.\n\n5 Todt\, C. & Wanninger\, A. 2010 Of tests\, troc hs\, shells\, and spicules: Development of the basal mollusk Wirenia argen tea (Solenogastres) and its bearing on the evolution of trochozoan larval key features. Frontiers in zoology 7\, 6. (doi:10.1186/1742-9994-7-6)\n\n6 Telford\, M. J. & Budd\, G. E. 2011 Invertebrate evolution: bringing orde r to the molluscan chaos. Current Biology 21\, R964–R966. (doi:10.1016/j .cub.2011.10.029)\n\n7 Sutton\, M. D.\, Briggs\, D. E. G.\, Siveter\, D. J .\, Siveter\, D. J. & Sigwart\, J. D. 2012 A Silurian armoured aplacophora n and implications for molluscan phylogeny. Nature 490\, 94–97. (doi:10. 1038/nature11328) LOCATION:Harker 1 seminar room\, Department of Earth Sciences END:VEVENT END:VCALENDAR