Three flexible crinoids occur in the Upper Ordovician Maquoketa Formation of Illinois, Iowa, and Minnesota: Protaxocrinus girvanensisRamsbottom, 1961, Clidochirus anebos new species, and Proanisocrinus oswegoensis (Miller and Gurley, 1894). Protaxocrinus girvanensis is also found in the Upper Ordovician of Scotland which indicates that the ocean was narrow enough to allow at least one crinoid species to cross the barrier. The Upper Ordovician of North America and Scotland also share many common crinoid genera. Both phenetic and cladistic methods result in similar phylogenies of flexible crinoids. Protaxocrinus was derived from a cupulocrinid ancestor during the Middle Ordovician. Clidochirus evolved from Protaxocrinus or its ancestral stock prior to the Richmondian of the Late Ordovician. The Richmondian Proanisocrinus and later anisocrinids are most closely related to Clidochirus or its immediate predecessor. Thus, three major lineages of flexible crinoids, Protaxocrinus (taxocrinid group), Clidochirus (icthyocrinid), and Proanisocrinus (anisocrinids and homalocrinids), appeared during the Ordovician. Despite their rarity during the Ordovician, all three flexible lineages survived the Latest Ordovician extinction, whereas their more abundant and successful cupulocrinid ancestors were eliminated.

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