Streptaster vorticellatus fossil edrioasteroid (Bellevue Formation, Upper Ordovician; Jersey Ridge roadcut, northern Kentucky, USA) by James St. John Via Flickr: Streptaster vorticellatus (Hall, 1866) - fossil edrioasteroid from the Ordovician of Kentucky, USA. (13 mm across) Edrioasteroids are an extinct group of sessile, benthic, filter-feeding echinoderms - they’re related to starfish, brittle stars, sea urchins, sand dollars, and sea cucumbers. They are attractive and much-sought-after fossils among collectors and professional paleontologists. Edrioasteroids have circular to subcircular, blister-like skeletons (originally inflated during life) with five, frequently curved, ambulacral structures that held tube feet used in feeding. The skeleton consists of small calcitic plates that frequently overlap, especially along the border areas. They were obligate encrusters and attached themselves to inorganic or biologic hard substrates (frequently hardgrounds or brachiopods). Edrioasteroids are known from the Cambrian to the Pennsylvanian. Shown above is a perfect Streptaster vorticellatus edrioasteroid from the Cincinnatian outcrop belt of northern Kentucky, USA. It is encrusting a fossiliferous limestone hardground. Hardgrounds are synsedimentarily cemented portions of the seafloor, usually involving carbonate sediments. Sessile, benthic organisms have to cement themselves onto, or bore into, hardground surfaces. This Streptaster-bearing hardground horizon was discovered in spring 1998. The encrusting biota includes trepostome and cyclostome bryozoans, crinoid holdfasts, cornulitid worm tubes, and the edrioasteroids Streptaster vorticellatus, Carneyella pilea, Carneyella ulrichi, and Curvitriordo stecki. Trypanites borings are also present on the hardground. The edrioasteroid fauna has generated much excitement, resulting in quarrying of the horizon and intense collecting by professionals and collectors. Classification of Streptaster: Animalia, Echinodermata, Echinozoa, Edrioasteroidea, Hemicystitidae Stratigraphy: ~mid-Bellevue Formation (part of the "Grant Lake Formation"), middle Maysvillian Stage, middle Cincinnatian Series, middle Upper Ordovician Locality: Jersey Ridge outcrop (Harsha Bridge South outcrop; Maysville West outcrop) - southern end of western side of Rt. 62/Rt. 68 roadcut through Jersey Ridge, just south of the Harsha Bridge over the Ohio River, northern Kentucky, USA (38° 40’ 27.27" North, 83° 47' 53.11" West). -------------------- Literature on this hardground horizon: Sumrall, C.D., C.E. Brett, P.T. Work & D.L. Meyer. 1999. Taphonomy and paleoecology of an edrioasteroid encrusted hardground in the lower Bellevue Formation at Maysville, Kentucky. pp. 123-131 in Sequence, cycle & event stratigraphy of Upper Ordovician & Silurian strata of the Cincinnati Arch region. 1999 Field Conference of the Great Lakes Section, SEPM-SSG (Society for Sedimentary Geology) Field Trip Guidebook. [reprinted 2001 in Kentucky Geological Survey, Series XII, Guidebook 1: 123-131.] Berg, M.V. 2000. Paleoecology and paleoenvironment of an Upper Ordovician hardground (Grant Lake Formation, Cincinnatian Series, northern Kentucky). pp. 240-243 in Thirteenth Keck Research Symposium in Geology, Proceedings, Whitman College, Walla Walla, Washington, April 2000. Sumrall, C.D. 2010. The systematics of a new Upper Ordovician edrioasteroid pavement from northern Kentucky. Journal of Paleontology 84: 783-794.
