Macroevolutionary transition in crinoids following the Late Ordovician extinction event (Ordovician to Early Silurian)

Abstract

The end-Katian (Late Ordovician) crinoid mass extinction triggered the change from the Early to the Middle Paleozoic crinoid evolutionary faunas (CEFs). This was a change from diplobathrid camerate-disparid-hybocrinid dominated faunas to faunas dominated by monobathrid camerate, cladid, and flexible crinoids. All clades suffered extinctions at the end-Katian event, but diplobathrid camerates, disparids, and hybocrinids suffered higher rates of extinction. The primary amount of diversification occurred in clades that would become dominant during the Silurian. However, the formation of the characteristic Middle Paleozoic CEF was protracted beyond the Late Ordovician extinction event. Monobathrid camerates and flexibles diversified through the Llandovery, but both dendrocrinid and cyathocrinid cladids did not diversify until later. Monobathrid camerate genera and families diversified, the flexible diversification was largely at the genus level, cyathocrine diversification was largely among families, and dendrocrinids did not diversify significantly until after the Llandovery. Overall disparity decreased during the end-Katian extinction by reducing the disparity within each clade. Disparity remained fairly constant during the Hirnantian but increased significantly during the Llandovery by both increasing disparity within clades and expanding the morphospace of the disparids due to the radiation of families with new morphologies. North America was the biogeographic center of origination for the families that survived to become dominant Silurian clades.