A new Early Ordovician crinoid, Migmacrinus nov. gen., has the most plesiomorphic arms and oral region of any known member of the class. These earliest crinoids provide information leading to syntheses of paleontological and neontological data with statistical phylogenetic approaches that enhance understanding of the origins of the Crinoidea. Maximum parsimony and undated Bayesian analyses indicate that migmacrinids represent a monophyletic, previously unrecognized stem crinoid lineage, although the Bayesian tip-dating analysis is equivocal for the exclusive relationship of migmacrinids + crinoids. Nevertheless, there is evidence that an emended diagnosis for Crinoidea should encompass plesiomorphic traits of the new taxon, Migmacrinidae nov. fam. Tip-dated inference provides strong statistical support that one of the two newly named species of Migmacrinus nov. gen. is the direct ancestor of the other. This is among the first examples of two new species shown by phylogenetic methods to be an ancestor–descendant pair. This analysis also suggests that the Crinoidea originated as early as the late Cambrian. The view that blastozoans (eocrinoids, rhombiferans, diploporitans, among others) were non-monophyletic because crinoids emerged from within them, is not supported. Blastozoans had a separate origin from crinoids among pentaradiate echinoderms near the onset of the echinoderm record, during or before the early Cambrian, and long before the appearance of crinoids. Despite their rarity, migmacrinids were widely distributed. Migmacrinus koilos nov. gen., nov. sp. occurs in the Laurentian Wah Wah Formation, western Utah, USA, while M. kunduraorum nov. gen., nov. sp. is from the Gondwanan Saint-Chinian Formation, southern France. ? Migmacrinus sp . , an isolated arm, is from the Laurentian Garden City Formation, southeastern Idaho, USA.