S5.6 Jan. 5 Rocks and Clocks: Integrating Fossils and Molecules to Date Transitions in Early Animal Evolution COLLINS, Allen/G*; CARTWRIGHT, Paulyn; NOAA; University of Kansas email@example.com
Among the key transitions in early animal evolution are those that occurred near the origins of multicellularity: the sponge body plan, epithelial tissues, guts, colloblasts, cnidae, bilaterality and mesoderm. Determining the relative order of these events is reasonably straight-forward as relationships of early diverging animal lineages become better understood. Despite progress on early metazoan phylogenetics, the absolute dates of various transitions in early animal evolution remain obscure. Some estimates from molecular sequence data substantially pre-date animal origins of Metazoa in the fossil record. More recent molecule-based estimates have narrowed the disparity, but the assumptions upon which these estimates are derived are controversial. We use recently uncovered evidence for deeply-nested cnidarian clades that existed during the Cambrian to carry out a new set of molecular estimates for the origins of key animal groups. Our estimates also substantially pre-date all known paleontological evidence for the presence of animals. We evaluate the current available molecular dating methods using these data and explore the possible implications of these early dates for the origin and diversification of early animal life.