Phylogenomic of extant Crinoidea (Echinodermata) reveals extensive morphological homoplasies and a Permian origin

Crinoids are echinoderms with ancient origins in the Ordovician, unique among living forms in possessing structures of attachment to the substrate. Their diversity is concentrated within Comatulida (the feather stars), which includes mobile and generally shallow-water species. The otherwise mostly sessile, stalked, and deep-water diversity—the sea lilies—encompasses Isocrinida, Hyocrinida, and Cyrtocrinida. While the relationships among Paleozoic crinoids are well established, the phylogeny of the crown group (Articulata) remains uncertain. We present the first phylogenomic analyses of crinoids reliant on novel transcriptomic and targeted-exon capture datasets spanning 119 terminals. We resolve Isocrinida as the sister group to the remainder of Articulata, which is further subdivided into Comatulida and a clade of Hyocrinida + Cyrtocrinida. We corroborate the placement of the stalked Bourgueticrinina within the otherwise stalkless comatulids, but also find the unusual feather star Atopocrinus closest to the stalked hyocrinids, showing the extreme lability of these body plans. Taxonomic revisions within Comatulida are much needed, with major problems particularly within Antedonidae. Divergence time estimates place the origin of Articulata within the Permian, contradicting the prevailing views that consider the clade a post-Paleozoic radiation. A revision of the Permian fossil record is needed to understand the emergence of living crinoids.