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

Crinoids have Ordovician origins and are unique among living echinoderms in their attachment to the substrate. Most diversity is within Comatulida (feather stars), which are generally mobile as adults and most common in shallow waters. The otherwise mostly sessile, stalked and mainly deep-water diversity—sea lilies—encompasses Isocrinida, Hyocrinida and Cyrtocrinida. Relationships among Palaeozoic crinoids are well established, but relationships within much of the crown group (Articulata) remain uncertain, including the root position for the clade. We present the first phylogenomic analyses of crinoids reliant on novel transcriptomic and targeted-exon capture, spanning 119 terminals. We resolve Isocrinida as the sister group to the remainder of Articulata, which subdivides 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. Further taxonomic revisions within Comatulida are needed, with major problems remaining, particularly within Antedonidae. Divergence time estimates place the origin of Articulata within the Permian, contradicting the prevailing views that consider the clade a post-Palaeozoic radiation. Revision of the Permian fossil record is needed to understand the emergence of living crinoids.