MONOBATHRID MYSTERIES: UNRAVELING CRINOID MORPHOLOGY AND PHYLOGENY ACROSS THE ORDOVICIAN MASS EXTINCTION AND SILURIAN RADIATION

The Late Ordovician ended with the first of the “Big Five” mass extinctions in Earth’s history. This extinction is widely accepted to be non-selective, however, across the extinction horizon the fossil record shows notable faunal turnovers, largely attributed to the following Silurian radiation. Within Crinoidea, previous studies have shown this timeframe coincides with the transition from the Early to Mid-Paleozoic Crinoid Evolutionary Fauna. Within camerates, this clade dominance shifts from the pre-extinction dominance of the diplobathrids to post-extinction dominance of monobathrids. In order to test the driver(s) of this faunal shift, a phylogenetic framework is needed to more effectively tease out patterns of differential extinction versus post-extinction diversification. Previous phylogenetic studies of Ordovician camerates have identified the relationship of monobathrids as the sister group to diplobathrids. However, phylogenetic research regarding monobathrids overall is limited, and little work has been done to address the relationships of the two major monobathrid clades (Glyptocrinidae and Compsocrinidae), as well as relationships at lower taxonomic levels.

This study seeks out, for the first time, the phylogenetic relationships of monobathrid camerates from the Early Ordovician to Middle Silurian (Wenlockian). Our study investigates the monobathrid clade to the genus level with three diplobathrids set as the outgroup. This high-resolution study explores approximately 70 taxa and over 120 character states coded from museum specimens and published literature. A combination of parsimony and Bayesian methods are employed to evaluate congruence between results of alternative phylogenetic methods and tease out complicated relationships within Monobathrida. Preliminary results presented here focus on the Compsocrinidae, the most diverse group of monobathrids. These results provide insight into the monophyly of monobathrid subclades, the relationships of monobathrid genera, and patterns of morphological evolution among pre- and post-extinction monobathrids. The inferred phylogenies will also provide a framework for future studies of extinction selectivity and diversification dynamics, as well as the link between trait evolution and faunal turnover.