Date of this Version
Familial diversity of crinoids is relatively constant throughout the Missourian Series of southeastern Nebraska and southwestern Iowa. Beginning with the deposition of the Argentine Limestone, there appears to be an important increase in the number of crinoid specimens. The abundance of crinoids in older Missourian strata in other areas to the south suggests the presence of a pre-Argentine east-west ecological barrier that prevented the establishment of successful crinoid colonies in the Nebraska-Iowa area.
The Argentine crinoids of Nebraska and Iowa are quite similar to the lower crinoid fauna in the coeval Wann Formation of northeastern Oklahoma. Samples of Delocrinus hemisphericus (Shumard) from the Argentine of Iowa and the Wann of Oklahoma show crinoids of similar statistical parameters, suggesting they represent the same statistical population. The presence of Plummericrinus nettingi Burke in the Argentine of Iowa may help refine biostratigraphic correlations between Midcontinent Missourian strata and Appalachian Conemaugh units.
Bathronocrinus madisonensis n. sp. is described here.