Halwaxiids and the Early Evolution of the Lophotrochozoans

doi:10.1126/science.1137187

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Halwaxiids and the Early Evolution of the Lophotrochozoans

Simon Conway Morris¹^* and Jean-Bernard Caron²^*

Halkieriids and wiwaxiids are cosmopolitan sclerite-bearingmetazoans from the Lower and Middle Cambrian. Although theyhave similar scleritomes, their phylogenetic position is contested.A new scleritomous fossil from the Burgess Shale has the prominentanterior shell of the halkieriids but also bears wiwaxiid-likesclerites. This new fossil defines the monophyletic halwaxiidsand indicates that they have a key place in early lophotrochozoanhistory.

¹ Department of Earth Sciences, University of Cambridge, Cambridge CB2 3EQ, UK.
² Department of Natural History, Royal Ontario Museum, Toronto, M5S 2C6, Canada.

^* To whom correspondence should be addressed. E-mail: sc113{at}esc.cam.ac.uk (S.C.M.); jcaron{at}rom.ca (J.B.C.)

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