A Hirnantian holdover from the late Ordovician mass extinction: phylogeny and biogeography of a new Anthracocrinid crinoid from Estonia

Relatively few Hirnantian (Late Ordovician) crinoids are known, and none have been previously described from the palaeocontinent of Baltica. This has impaired our ability to understand patterns of extinction and biogeographic dispersal surrounding the Late Ordovician mass extinction, which triggered a major turnover in crinoid faunas. Here, we describe Tallinnicrinus toomae gen. et sp. nov., an anthracocrinid diplobathrid from the Hirnantian of northern Estonia. Tallinnicrinus is the youngest member of the Anthracocrinidae and the first representative of the family to occur in Baltica. Morphologically, Tallinnicrinus is unusual in that the radial and basal plates are in a single circlet of ten plates, similar to the anthracocrinid Rheocrinus Haugh, 1979 from the Katian of Laurentia. Phylogenetic analysis further confirms a close relationship between Tallinnicrinus and Laurentian anthracocrinids, suggesting biogeographic dispersal of the lineage from Laurentia to Baltica during the late Katian or early Hirnantian. The occurrence of this new taxon establishes that the family Anthracocrinidae survived the first pulse of the Late Ordovician mass extinction. However, the lineage remained a "dead clade walking" as it failed to diversify in the wake of the end-Katian extinction and ultimately went extinct itself by the end of the Ordovician.This dataset includes the character matrices and scripts to reproduce the phylogenetic analyses presented in the paper, including both the the parsimony analysis in PAUP* v4.0a167 (Parsimony_analysis.nex) and the Bayesian analysis in Mr. Bayes v3.2.6 (Bayesian_analysis.nex). Results from the phylogenetic analyses are included as nexus files for both the parsimony analysis (Parsimony_results.nex, which includes the 2 most-parsimonious trees recovered) and the Bayesian analysis (Bayesian_results.nex, which includes the maximum clade credibility and 50% majority rule trees). All .nex files can be opened with standard text editor programs. The Supplemental_Materials.pdf file includes descriptions of data files and figures showing the Bayesian maximum clade credibility tree and the 50% majority rule tree. Funding provided by: National Geographic SocietyCrossref Funder Registry ID: http://dx.doi.org/10.13039/100006363Award Number: NGS 60031112Funding provided by: American Museum of Natural HistoryCrossref Funder Registry ID: http://dx.doi.org/10.13039/10000583