Meeting Abstract

61.4  Tuesday, Jan. 6  Parallel evolution of key innovations in a phylum of modular animals DICK, M.H.; GORDON, D.P.; LIDGARD, S.*; MAWATARI, S.F.; Hokkaido Univ., Sapporo, Japan; National Institute of Water and Atmospheric Research, Wellington, New Zealand; Field Museum, Chicago; Hokkaido Univ., Sapporo, Japan slidgard@fieldmuseum.org

Analysis of convergent structures is emerging as a powerful tool to address how complex evolutionary novelties arise. Yet clear examples of convergence in key innovations, those correlated with extensive species radiations, are rare. In cheilostome bryozoans, a major group of colonial animals, the costal shield and ascus were key innovations correlated with an explosive radiation beginning in the Cretaceous about 80 my ago; these innovations are integral to a major evolutionary trend for increased frontal protection of zooids. Here we establish the independent origin of costal shield and ascus in a bryozoan lineage less than 12 my ago. A COI molecular phylogeny and the fossil record indicate that the evolutionary trajectories in the Cretaceous radiation and the Neogene lineage are remarkably parallel, apparently shaped both by predation as a continuous, diffuse selective force and by a functional constraint. Facilitated by the overt modularity of bryozoan phenotypes, our analysis demonstrates how complex structures can rapidly originate through stepwise morphological transitions involving the novel integration of modular elements.