Phylogeny of Arenig to Caradoc crinoids (Phylum Echinodermata) and suprageneric classification of the Crinoidea

Stepwise, parsimony-based character analysis of Arenig to Caradoc crinoids (Ordovician) indicates that Early and middle Ordovician crinoids represent a radiation largely confined to the Ordovician. Only a few middle Paleozoic families are considered to have roots among these Early and middle Ordovician genera. Also, most genera are reinterpreted as a part of larger Ordovician clades rather than being isolated in monogeneric families. Six subclasses recognized as a result of phylogenetic analysis are the Aethocrinea, Cladida, Flexibilia, Articulata, Camerata, and Disparida. Many aspects of the Treatise classification (Moore and Teichert, 1978) are followed, but significant differences exist. The zygodiplobathrid-eudiplobathrid camerate suborder distinction is not made, and disparid superfamilies are no longer recognized. The subclass Disparida is subdivided into orders rather than superfamilies. Seven Early and middle Ordovician disparid orders are recognized, and additional younger orders undoubtedly exist. Whereas disparid superfamilies in the Treatise were defined largely on aboral cup symmetry, disparid orders are defined here largely on the basis of presence and absence of radial plates and aboral cup architecture. The Calceocrinida, Homocrinida, Myelodactylida, Eustenocrinida, and Tetragonocrinida are new orders, having previously been regarded as superfamilies and subfamilies; the Maennilicrinida is a new order; and the order Hybocrinida is maintained in the subclass Disparida. Subfamilies are no longer recognized within the Homocrinidae or Cincinnaticrinidae. Other changes include new families (Agostocrinidae, Columbicrinidae, and Maennilicrinidae), one family elevated from subfamily to family (Atopocrinidae), and reassignment of families to different higher categories (Acolocrinidae to the Eustenocrinida, Agostocrinidae and Colpodecrinidae to the Cladida, Cleiocrinidae to the Rhodocrinitacea, and Porocrinidae to the Cyathocrinitacea). Reassignment of 34 genera to different families is proposed (3 of these to a different subclass). A number of family-level taxa are recognized as junior synonyms and Baerocrinus, Ontariocrinus, Baerocrinidae, and Ontariocrinidae are regarded as nomina dubia.