Dizygocrinus: Mississippian camerate crinoid (Echinodermata) from the midcontinental United States

Abstract

The Mississippian crinoid genusDizygocrinusis revised, and the phylogeny is inferred. Eleven species are recognized, includingD. biturbinatus(Hall),D. indianaensis(Lyon and Casseday),D. caroli(Hall),D. whitei(Wachsmuth and Springer),D. originarius(Wachsmuth and Springer),D. montgomeryensis(Worthen),D. gorbyi(Miller),D. venustus(Miller),D. peculiaris(Miller and Gurley),D. mutabilis(Wachsmuth and Springer), andD. cantonensis(Wachsmuth and Springer). Nomenclatoral revisions include recognition ofD. gorbyiandD. peculiarisas valid species and designation of the following as junior synonyms:D. calvus, D. crawfordsvillensis, D. intermedius, D. mediocris, andD. somersetensis. Dizygocrinusis now recognized from both the late Osagean and Meramecian on both the eastern and western margins of the Illinois Basin.Dizygocrinusis first recognized virtually simultaneously on both the eastern and western margins of the Illinois Basin. Migration proceeded in both directions, but was most common later in the history of the genus. The principal radiation on the western basin margin was among species with generally smooth aboral cup plates, whereas on the eastern margin sculptured species account for the principal species radiation.