101-10 The Order of Survival: Clade Conflicts in Silurian Crinoids

Session: Paleontology, Biogeography/Biostratigraphy & Phylogenetic/Morphological Patterns

Presenting Author:

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Abstract:

The first of the “Big Five” mass extinctions occurred during the Late Ordovician (LOME; 445.2-443.8mya). At this time in the rock record, massive faunal turnovers are observed across the extinction horizon within many groups of marine invertebrates. The primary influence on this turnover has been largely attributed to a differential recovery response of groups during the Silurian radiation, as opposed to the impact of the Ordovician extinction itself, which removed approximately 85% of marine species from Earth’s oceans. Studies within Crinoidea have correlated this timeframe with a shift from Early to Mid-Paleozoic Crinoid Evolutionary Faunas. Crinoid groups such as the camerates experience a shift in clade dominance during this time. Diplobathrids (with an infrabasal circlet) dominated the Ordovician and yielded to the post-extinction dominance of the monobathrids (without infrabasal circlet), which diversified to reach more than 300 known genera before their extinction in the Permian.

Phylogenetic analysis of genera across the extinction boundary and into the Silurian radiation clarifies patterns of differential extinction and post-extinction diversification. Research regarding the phylogenetic relationships of monobathrids is largely absent and little work has been done to address the relationships of the two major monobathrid clades (Glyptocrinidae and Compsocrinidae). This study seeks out, for the first time, the phylogenetic relationships of monobathrid camerates from the beginning of the Ordovician to the end of the Silurian. Investigating the monobathrid clade at the genus level, this high-resolution study explores 75 taxa and 112 characters coded from museum specimens and published literature, using the oldest known camerate (Eknomocrinus wahwahensis) as the outgroup. Through a combination of parsimony analysis and Bayesian methods, congruence between results of alternative phylogenetic methods clarifies the complicated relationships within Monobathrida. The inferred phylogenies provide a framework for understanding character evolution, extinction selectivity and radiation, as well as the link between trait evolution and faunal turnover. These results provide insight into the monophyly of camerates, the relationships of monobathrid genera, and the traits that allowed the monobathrids to become the dominant group of camerates following the extinction.

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

doi: 10.1130/abs/2025AM-6218

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