56-10 On the Origin of Flexibilia: Modeling the Rise and Ecomorphological Radiation of a Major Crinoid Clade in a Bayesian Phylogenetic Framework

Session: Phylogenetic and Computational Approaches in Paleobiology and Paleoecology, Part II

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The Late Ordovician mass extinction (LOME), the first of the five largest episodes of abrupt, catastrophic diversity decline observed in the Phanerozoic marine fossil record, represents an interval of significant and long-lasting restructuring of marine biotas in response to geologically rapid environmental change. The LOME caused major shifts in the taxonomic richness and ecologic abundance of crinoid higher taxa, and the differential extinction of various crinoids leads to intriguing questions about what ecomorphological traits are likely to drive these extinction filters, and, similarly, what traits are impacting rebound dynamics during wholesale restructuring of post-LOME communities. While previous work has focused on elucidating the effects of the LOME on various aspects of paleocommunities, there remains much yet to be done within a temporally constrained phylogenetic framework to gain deeper insight into mechanisms driving mass extinction selectivity and subsequent faunal rebound. Specifically, the use of tip-dated fossil phylogenies along with paleontologically-motivated phylogenetic comparative methods (PCMs) permits novel modeling approaches for investigating the tempo and mode of diversification in multiple, quasi-independent macroevolutionary currencies: taxonomic diversity, morphologic disparity, and functional ecology.      

Here, we present preliminary results of a study aimed at clarifying the origin and radiation of Superorder Flexibilia from its hypothesized closest relatives, members of the species-rich cladid genus Cupulocrinus. We construct a species-level phylogenetic tree of 20+ Ordovician–Silurian cupulocrinid and early flexible taxa using Bayesian tip-dating phylogenetic methods incorporating the fossilized birth–death process. We then use that phylogenetic framework to fit multiple process-based macroevolutionary models of trait diversification across three morphologic characters directly related to crinoid feeding and development: body size, filtration fan area, and calyx complexity. Five alternative hypotheses of trait diversification are tested, including time-homogenous Brownian Motion and Ornstein-Uhlenbeck models as well as time-heterogenous combinations of the two involving shifts in tempo and/or mode across the LOME. Exploration of PCM model support and parameters, and attention to trait selectivity (or lack thereof) at various hierarchical scales across the tree, is an exciting opportunity to investigate the nuance in how the tempo and mode of morphologic and taxonomic diversification progressed in flexible crinoids across a major mass extinction event.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

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