A NEW SPECIES OF PARADIABOLOCRINUS FROM THE UPPER ORDOVICIAN OF CENTRAL KENTUCKY (CURDSVILLE MEMBER, LEXINGTON LIMESTONE)

Late Ordovician crinoids undergo an explosion in morphologic and taxonomic diversity that plays a significant role in shaping the evolutionary history of crinoids. Therefore, it is important to recognize the components of these Early Paleozoic ecosystems. Herein we describe a new species of Paradiabolocrinus from the Upper Ordovician Curdsville Member of the Lexington Limestone of central Kentucky. The Curdsville Member is composed of horizontally bedded, massive, and highly fossiliferous packstones with a diverse assemblage of sponges, brachiopods, bryozoans, trilobites, and echinoderms (including crinoids, paracrinoids, cyclocystoids, edrioasteroids, and stylophorans). The limestone bedding surface is uneven, extensively burrowed, with evidence of firm to hard ground development. Large ripples are present on the bedding plane indicating high energy deposition. In between the large-scale ripples are muddy shale lenses that are deposited in the topographic lows that often preserve intact echinoderm remains. Though the Curdsville echinoderm assemblage has been extensively studied, a new species was recently found in Garrard County. The new crinoids are similar to the common Diabolocrinus, but differ in the presence of intersecundibrachs and abundant, small interbrachial plates, which are the defining traits of Paradiabolocrinus. This rare genus is known from the Bromide (Oklahoma) and Benbolt Formations (Tennessee and Virginia), but differs from the previously described species by the lack of prominent median ray ridges and sinuous ridges on the calyx plates. This find provides a clearer view of Late Ordovician community composition and paleoecology. The new crinoids also represent the most complete species within the genus with an intact proximal stem, calyx, arms, and pinnules enabling a more complete description of the generic morphology and further establishing the close phylogentic relationship between Diabolocrinus and Paradiabolocrinus.