Grewingkia canadensis (Billings, 1862) - fossil rugose corals in limestone from the Ordovician of Ohio, USA. (CMNH 9396, Cleveland Museum of Natural History, Cleveland, Ohio, USA)

The famous Cincinnatian Series of the tristate area of Ohio-Kentucky-Indiana has some of the richest fossiliferous rocks on Earth. Cincinnatian rocks were deposited in relatively shallow marine facies during the Late Ordovician. The Cincinnatian succession is mostly interbedded limestones and shales. Most of the limestones are event beds (= tempestites), deposited during ancient storms.

The limestone bedding plane shown above is dominated by brachiopods and rugose corals (= the large, slightly curved, tapering structures). Rugose corals are an extinct group of solitary and colonial cnidarians. They are often nicknamed "horn corals", in reference to the upside-down horn shape of the skeletons of solitary forms (Ex: <a href="https://www.flickr.com/photos/jsjgeology/15590522272">www.flickr.com/photos/jsjgeology/15590522272</a>). Solitary rugose corals made solid, tapering skeletons of calcite (CaCO3 - calcium carbonate). During life, a polyp (sea anemone animal) lived in a cup-like depression at the top of the skeleton.

Classification: Animalia, Cnidaria, Anthozoa, Rugosa, Streptelasmatidae

Stratigraphy: Richmondian Stage, upper Cincinnatian Series, upper Upper Ordovician

Locality: unrecorded/undisclosed site at or near Chasetown, northern Brown County, southwestern Ohio, USA

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