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Integrative and Comparative Biology Advance Access originally published online on July 20, 2007
Integrative and Comparative Biology 2007 47(5):744-751; doi:10.1093/icb/icm071
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© The Author 2007. Published by Oxford University Press on behalf of the Society for Integrative and Comparative Biology. All rights reserved. For permissions please email: journals.permissions@oxfordjournals.org.

Fossils and phylogenies: integrating multiple lines of evidence to investigate the origin of early major metazoan lineages

Paulyn Cartwright1,* and Allen Collins{dagger}
*Department of Ecology and Evolutionary Biology, University of Kansas, 1200 Sunnyside Avenue, Lawrence, Kansas 66045, USA; {dagger}National Systematics Laboratory of NOAA Fisheries Service, National Museum of Natural History, MRC-153, Smithsonian Institution, PO Box 37012, Washington, DC 20013-7012, USA

Correspondence: 1E-mail: pcart{at}ku.edu

Understanding the nature and timing of metazoan origins is one of the most important, yet elusive, questions in evolutionary biology. Fossil data provide the most tangible evidence for the origin of early animal lineages, although additional evidence from molecular phylogenetics, molecular clock studies, and development has contributed to our current understanding. We review several lines of evidence to explore the nature and timing of early metazoan evolution and discuss how these data, when considered together, provide a more cohesive picture of the origin of animal diversity. We discuss how trace fossils and biomarkers provide compelling evidence for the origins of Bilateria and siliceous sponges. Using a molecular phylogenetic framework for metazoans, we discuss how fossils can be used to date the origin of clades. We use these fossil dates to perform a relaxed molecular clock analysis for estimating dates of nodes when no fossils are available. We also discuss current data from developmental biology that suggest that early metazoans possessed a sophisticated molecular toolkit for building complex body plans. We conclude that the best evidence for the origin of major metazoan lineages lies in the careful interpretation of the fossil record and that these data, when considered with phylogenetic and developmental evidence, support the notion that the Cambrian radiation is a real phenomenon that marks a critically important time in the history of life.

From the symposium "Key Transitions in Animal Evolution" presented at the annual meeting of the Society for Integrative and Comparative Biology, January 3–7, 2007, at Phoenix, Arizona.


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