PHYLOGENOMIC ANALYSIS OF BRACHIOPODA AND PHORONIDA: IMPLICATIONS FOR MORPHOLOGICAL EVOLUTION, BIOMINERALIZATION, AND THE CAMBRIAN RADIATION

Within Lophotrochozoa, brachiopods and allied clades are among the first biomineralized Cambrian metazoans to appear and represent a major component of the oldest known fossil record of animals. While the brachiopod fossil record is ultimately the key to determining character homology and polarity during the evolution of the brachiopod body plan, correctly reading this record has been clouded by disagreement about relationships among the crown clades. Specifically, the monophyly of brachiopods with respect to phoronids, and the relationships of the calcitic-shelled to phosphatic-shelled brachiopods, are both open questions. Much of this phylogenetic uncertainty stems from difficulties in rooting the tree of brachiopods, phoronids and their sister groups within the Lophotrochozoa. Phylogenomics—the analysis of hundreds to thousands of orthologous genes in concatenated supermatrices—has been instrumental in resolving difficult phylogenetic relationships in diverse metazoan clades. This is accomplished through reduction of random error in combination with careful evolutionary model selection. We have conducted the first such extensive phylogenomic investigation of Brachiopoda/Phoronida with analyses that combine novel sequence data with all publicly available brachiopod and phoronid transcriptomes and a broad range of protostome outgroups. Analyses were run under best fitting evolutionary models (LG amino acid substitution matrix and a gamma model of rate heterogeneity) utilizing a published 106-gene lophotrochozoan ortholog set. Preliminary results strongly (99% bootstrap) support a monophyletic Brachiopoda with Phoronida as sister group within Lophotrochozoa. Weak support is found for Inarticulata. Investigation of fossil and molecular data in this integrated framework provides novel insight into brachiopod biomineralization and evolutionary patterns during the Cambrian radiation.