Colonial rugose coral in limestone in the Devonian of Ohio, USA.

The Columbus Limestone is a significant carbonate unit in the Middle Devonian of central and northern Ohio. It's actually part of a much more widespread sheet of Devonian carbonates that extends from New York State to the Midwest. The Columbus Limestone represents deposition in a subtropical, shallow-water, carbonate platform environment. The rocks are principally micritic limestones, fossiliferous wackestones, and fossiliferous packstones. Some chert nodules are present in the unit. Fossils are typical Paleozoic shallow marine invertebrates - favositid corals, rugose corals, stromatoporoids brachiopods, crinoids, blastoids, bryozoans, trilobites, bivalves, gastropods, cephalopods, rostroconchs, and tentaculites. Microfossils include conodonts and charophyte oogonia. Other fossils in the Columbus Limestone include vertebrates (fish), land plants (rare), and trace fossils. Some fossil horizons in the Columbus Limestone are partially silicified.

Seen here is a fossil colonial coral in a Columbus Limestone outcrop on Kelleys Island in Lake Erie, Ohio. Corals are essentially sea anemones (polyps) that make a skeleton, which is usually mineralized. Most corals are colonial, but some are solitary. These are rugose corals, also known as "horn corals", in reference to the tapered solid skeletons of solitary forms (best seen on weathered-out specimens).

Classification: Animalia, Cnidaria, Anthozoa, Rugosa

Stratigraphy: Columbus Limestone, Eifelian Stage, lower Middle Devonian

Locality: Glacial Grooves State Park, northwestern Kelleys Island, western Lake Erie, Ohio, USA

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