Flexible crinoids from the Upper Ordovician Maquoketa Formation of the northern midcontinent and the evolution of early flexible crinoids

Abstract

Three flexible crinoids occur in the Upper Ordovician Maquoketa Formation of Illinois, Iowa, and Minnesota:Protaxocrinus girvanensisRamsbottom, 1961,Clidochirus anebosnew species, andProanisocrinus oswegoensis(Miller and Gurley, 1894).Protaxocrinus girvanensisis 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.Protaxocrinuswas derived from a cupulocrinid ancestor during the Middle Ordovician.Clidochirusevolved fromProtaxocrinusor its ancestral stock prior to the Richmondian of the Late Ordovician. The RichmondianProanisocrinusand later anisocrinids are most closely related toClidochirusor its immediate predecessor. Thus, three major lineages of flexible crinoids,Protaxocrinus(taxocrinid group),Clidochirus(icthyocrinid), andProanisocrinus(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.