Late Osagean and Meramecian Actinocrinites (Echinodermata: Crinoidea) from the Mississippian stratotype region

Abstract

ActinocrinitesMiller from the Mississippian stratotype region of Illinois, Iowa, and Missouri are redescribed and redefined based upon study of the type material and morphometric analyses.Actinocrinites pernodosus, A. lowei, A. jugosus, A. gibsoni, andA. probolosn. sp. are recognized as valid species that occur in these strata. A combination of both metric and qualitative characters must be used to differentiate these species.Actinocrinitesis known from the Montrose Chert Member of the Keokuk Limestone, the Keokuk Limestone, and the lower part of the Warsaw Formation, all late Osagean, in the stratotype region. In addition,Actinocrinites pernodosusandA. loweiare reported from the early Meramecian upper part of the Warsaw Formation, which is the first Meramecian occurrence ofActinocrinitesin the stratotype region.Actinocrinites probolosn. sp. was ancestral toA. lowei, and the latter was probably ancestral toA. pernodosus.Nomenclatural and systematic acts include the following: 1)Actinocrinites lowei(Hall, 1858) is the senior synonym ofActinocrinus brontesHall, 1860,Actinocrinites lobatus(Hall, 1860), andA. unicarinatus(Hall, 1860); 2)Actinocrinites jugosus(Hall, 1860) is the senior synonym ofA. augustatusMiller and Gurley, 1894; and 3) the concept applied incorrectly toA. lobatusby Wachsmuth and Springer (1897) represents a distinct species,Actinocrinites probolosn. sp.