English: Fossiliferous limestone in the Ordovician of Ohio, USA.

This fossiliferous limestone surface is in the famous Cincinnatian Series of the tristate area of Ohio-Kentucky-Indiana. Rocks in the Cincinnatian 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 prominent fossil seen here is a nautiloid cephalopod. Nautiloids are squid-like creatures that construct long and slightly tapering or coiled, aragonitic, hollow shells with regularly-spaced internal walls. In the fossil record, the original aragonite shell has usually dissolved away, leaving an internal mold (an impression of the shell's interior). Nautiloids were relatively common components of Paleozoic oceans. Most species had straight, slightly tapering shells, but some had loosely coiled or tightly coiled shells. The entire group is represented in today's oceans by five living species of chambered nautilus - Nautilus pompilius, Nautilus macromphalus, Nautilus stenomphalus, Nautilus belauensis, and Allonautilus scrobiculatus.

Classification: Animalia, Mollusca, Cephalopoda, Nautiloidea

Stratigraphy: upper Waynesville Formation or Liberty Formation, Richmondian Stage, upper Cincinnatian Series, upper Upper Ordovician

Locality: talus piece along the cut wall of Caesar Creek Lake's emergency spillway (between Clarksville Road and Roaring Run), northeastern Warren County, southwestern Ohio, USA