COMBINING FOSSILS WITH MOLECULAR PHYLOGENETICS TO INVESTIGATE THE ORIGIN AND DIVERSIFICATION OF CROWN-GROUP CRINOIDEA (ECHINODERMATA)

The Crinoidea (sea lilies and feather stars) are a diverse clade of marine animals represented by more than 650 extant species and inhabit a variety of environments ranging from shallow water reefs to the deep sea. Crinoids have a remarkably rich fossil record dating back to the Early Ordovician (~480 Ma), with more than 8,000 fossil species described. As a consequence of their phenomenal taxonomic longevity, diversity, and abundance, fossil crinoids have been a major focus for macroevolutionary studies among paleontologists, especially among Paleozoic workers. In contrast, relatively few studies have examined macroevolutionary patterns in post-Paleozoic fossil or extant crinoids, and diversification dynamics of the crown group has never been studied in a phylogeny-based context. Moreover, it is not known with certainty when the crown group originated. Current hypotheses suggest the crown group either (1) originated prior to the end-Permian mass extinction, or instead (2) can be traced to an explosive post-extinction adaptive radiation of a single lineage into the disparate clades inhabiting oceans today.

Here, I present preliminary results of a study integrating fossil occurrence data with molecular phylogenetics to investigate the origin, divergence times, and diversification dynamics of crown group crinoids. I assembled a novel, concatenated sequence alignment based on previously published mitochondrial and nuclear DNA sequences for representative taxa, sampling broadly across major lineages of extant crinoids. Fossil occurrence data were obtained from the recently revised Treatise on Invertebrate Paleontology (Vol. III: Articulata) and the published literature. Phylogenetic placement for fossils was based on a combination of analyses of morphological data and recent taxonomic revisions. Bayesian phylogenetic analysis was conducted implementing the fossilized birth-death process to simultaneously estimate divergence times and diversification parameters. Results of this study will help resolve the crown group age and better characterize the complex history of macroevolutionary dynamics that shaped modern crinoid diversity.