PRIMITIVE CLADID CRINOIDS FROM THE EARLY OSAGEAN BURLINGTON LIMESTONE AND THE PHYLOGENETICS OF MISSISSIPPIAN SPECIES OF CYATHOCRINITES

Abstract

All 19 known species of the primitive cladid crinoid genera Atelestocrinus, Cyathocrinites, Goniocrinus, Parisocrinus, Pellecrinus, and Zygotocrinus from the early Osagean Burlington Limestone of the North American midcontinent are reviewed and redescribed or, where necessary, redefined. Nine of these species are illustrated for the first time herein. Sixteen are considered valid, including C. deroseari n. sp. Of the remaining three species, one is left in open nomenclature, and two are considered nomen dubia. Pellecrinus is recognized for the first time from the Burlington Limestone, although the specimens can not be identified to the species level and are left in open nomenclature.Cyathocrinites ranges from the Middle Silurian to at least the Middle Mississippian. During the Early Mississippian Cyathocrinites experienced an evolutionary radiation with a maximum diversity of nine species in the Burlington Limestone. Phylogenetic relationships were investigated in a parsimony-based phylogenetic analysis by combining morphologic data from the Burlington species with data from the four other species of Cyathocrinites from the late Osagean and early Meramecian of the east-central United States. The Kinderhookian C. chouteauensis (Miller and Gurley, 1896) served as the outgroup. A phylogenetic analysis of 14 species of Mississippian Cyathocrinites yielded a single most parsimonious tree with a length of 28 steps (C. I. = 0.607, H. I. = 0.392, R. I. = 0.718, R. C. = 0.436). Results of this analysis suggest that at least two major clades existed within Mississippian Cyathocrinites. One clade contains C. sampsoni (Miller, 1891b), C. gilesi (Wachsmuth and Springer, 1878), C. farleyi (Meek and Worthen, 1866), and C. barydactylus (Wachsmuth and Springer, 1878). The second clade contains C. iowensis, C. kelloggi (White, 1862), C. barrisi (Hall, 1861a), C. rigidus, C. deroseari n. sp., C. asperrimus (Springer, 1911), C. lamellosus (White, 1863), and C. harrodi (Wachsmuth and Springer, 1880). Cyathocrinites multibrachiatus forms a polytomy with these two clades. Members of the first clade exhibit a unique overall morphology present only during the Mississippian, suggesting the clade arose during this time. Members of the second clade, plus C. multibrachiatus, exhibit some characters present in Cyathocrinites species as old as the Middle Silurian and, thus, may have its roots among Silurian and Devonian species.