Project VI: Diversification within Articulata

Although it is well-established that the Crinoidea (sea lilies and featherstars) is the sister group to all other living echinoderms, relationships within the group, particularly among living forms, remain unclear. All living species are currently placed in Articulata, generally accepted as the only crinoid group to survive the Permian-Triassic extinction event. Recent classifications have recognized five major extant taxa—Isocrinida, Hyocrinida, Bourgueticrinina, Comatulidina and Cyrtocrinida—and several smaller groups of uncertain taxonomic status.

As a first step toward better understanding crinoid phylogeny, we are using DNA sequence data for three mitochondrial and two nuclear genes to reconstruct relationships among 59 species that appear to span most of extant crinoid diversity. Several of the major groups remain intact as clades, but several groups of stalked crinoids nest among the comatulid featherstars, which lose their stalk following a postlarval stage. The arrangement lends support to an argument that these crinoids retain their stalk via paedomorphosis.

Our results also indicate that interrelationships among comatulids, which currently account for about 80% of living crinoid species, require substantial systematic revision; molecular tree topologies showed little congruence with current taxonomy. We will also seek to integrate post-Permian fossil crinoids into an overall phylogeny of Articulata.