The Official City of Cincinnati Fossil
By: Brenda Hunda, Curator of Invertebrate Paleontology
In 2002, the citizens of Cincinnati chose Isorophus cincinnatiensis as their Official City Fossil, accompanied by an official proclamation from then-Mayor Charlie Luken. The Cincinnati Dry Dredgers – a group of amateur paleontologists and geologists that have collected fossils and studied paleontology in the region for over 80 years – chose five candidates for the official Cincinnati fossil. These included the trilobite Flexicalymene meeki, the brachiopod Hebertella occidentalis, the crinoid Cincinnaticrinus pentagonous, the edrioasteroid Isorophus cincinnatiensis and the horn coral Grewingkia canadensis. Citizens and school children cast 4,306 votes in Cincinnati Museum Center’s Nature’s Trading post and Isorophus cincinnatiensis won with 35.2 % of the votes. Flexicalymene meeki came in second with 30.4%.
Next to crinoids, edrioasteroids are the most common echinoderm in our local rocks, known as the Cincinnatian Series. They possess three (among many) immediately obvious echinoderm features: (1) they have five-fold symmetry, (2) their bodies are made up of plates and (3) they have a water vascular system. They lived in the ocean that covered this region some 450 million years ago during the Late Ordovician.
Edrioasteroids are a distant relative of sea stars (“starfish”), and indeed we can think of them as an “upside-down starfish on a dinner plate.” These quarter-sized sea creatures were encrusters, much like barnacles on rocks or on the hulls of ships. They attached themselves to hard surfaces, such as brachiopod valves (Fig. 1), clam shells and hardgrounds (semi-solidified patches of ancient sea bed). Because they were attached on their ventral surface, all of the anatomy we typically think of on the undersurface of a sea star now has to be on their upper surface. Their resemblance to sea stars comes from the five ambulacral tracts (Fig. 2), or food grooves, that converge on the central mouth on its upper surface. The body is covered with shingling, armor-like plates and the animal attached to shells with a ring around its perimeter. Edrioasteroids first appeared in the fossil record in the Cambrian Period (541 - 485 million years ago), but went extinct in the Permian (298 - 251 million years ago).
Isorophus cincinnatiensis is a fitting choice for city fossil for many reasons. It is named after the city of Cincinnati, edrioasteroids are more common and diverse in Cincinnati than anywhere else on Earth and most of the landmark papers on edrioasteroids in the scientific literature were investigations of specimens from Cincinnati. Although considered a rare fossil, they occasionally can be found by the hundreds or thousands in Cincinnatian strata with just the right preservational conditions. Thin limestones covered with brachiopods are the ideal substrate for edrioasteroids, so don’t forget to look closely at brachiopod valves when fossil hunting.
Few cities have official fossils, and apparently just two do in the United States: Cincinnati and Fruita, Colorado, which is represented by the dinosaur Ceratosaurus. The fact that Cincinnati has its own official fossil speaks to the importance of our paleontological heritage.
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