ENCRINURID TRILOBITES FROM THE UPPER ORDOVICIAN (KATIAN) OF NORTHEASTERN IOWA

The trilobite fauna of the Late Ordovician (late Katian) Maquoketa Formation of northeastern Iowa (primarily Fayette County) contains numerous species, including generic type species, that have been widely cited in the literature of the past century. Despite dozens of references to them, most have not been revised or photographically illustrated since the original monograph of Slocom, published in 1913. Encrinurid trilobites from the formation are excellent examples. The cybeline Cybeloides iowensis (Slocom 1913) is the type species of its common and widely cited genus, to which some 15 valid and formally named species have subsequently been assigned from various parts of Laurentia. Its type material, however, has never been revised and virtually no images of the species have been published since Slocom's original work.The encrinurine Encrinuroides pernodosus (Slocom 1913), in contrast, has barely been commented upon in the literature, likely because of Slocom's tiny and difficult to interpret photograph of the holotype specimen, which has been the only image available. The Maquoketa encrinurids are revised based on new images of Slocom's type specimens housed in the Field Museum of Natural History, combined with rich new, well documented, collections made by vocational paleontologists Calvin Leverson and Arthur Gerk that were donated to the University of Iowa Paleontology Repository. The Leverson and Gerk collection includes numerous well preserved fully articulated specimens of both species. Combined with new modern photographs of the types, the Maquoketa species are transformed from poorly understood taxa known only from small photographs published over one hundred years ago to species with documentation of multiple examples of all exoskeletal elements. Clarification of the morphology of C. iowensis aids in the development of a hypothesis of relationship for the genus based on maximum parsimony. Encrinuroides pernodosus is currently assigned to a sprawling taxon of convenience (Encrinuroides currently has some 47 formally named species assigned), but thorough documentation of its morphology will help form a basis for resolution of its relationships and taxonomy.