A RE-EVALUATION OF THE SYSTEMATICS OF ERISOCRINUS, A PENNSYLVANIAN CLADID CRINOID
The systematics study of the genus Erisocrinus, a largely Pennsylvanian-age group, took into account the 37 species proposed since its naming in 1865. Species previously synonymized or reassigned by other authors were examined. Those species still named within the genus Erisocrinus were evaluated on the basis of a new diagnosis of Erisocrinus, created through both a thorough examination of all the specimens used in the study and previous diagnoses.
Eight species were removed from the genus because of their obvious deviations from the genus diagnosis. Six of the eight species were reassigned to other genera within the family Erisocrinidae (Genus Sinocrinus Tien 1926 and Genus Exaetocrinus Strimple and Watkins 1969). As a result of this study, a large majority of Permian-age species and all species named outside of the mid-continental United States are no longer considered to belong within the genus.
The remaining twelve species were analyzed based on measurements of radial height and width, basal height and width, and stem diameter. Both normalized and non-normalized data were analyzed using Principal Components Analysis to determine which of the five variables contributed to intraspecific variation. The species data were also analyzed using neighboring cluster analysis and k-means cluster analysis to determine the relationships among the species. These analyses show that a number of the twelve species are statistically indistinguishable from one another and should be synonymized.
This study redefines the temporal span of the genus as being present primarily during the Pennsylvanian, with only two species surviving into the Early Permian. As redefined in this study, Erisocrinus is restricted entirely to the mid-continental United States.