English: Nautiloid cephalopod in limestone from the Ordovician of Kentucky, 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 most common macrofossils in Cincinnatian rocks are brachiopods and bryozoans.

The prominent fossil 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: Fairview Formation, lower Maysvillian Stage, middle Cincinnatian Series, Upper Ordovician

Locality: Jersey Ridge outcrop (= Harsha Bridge South outcrop; = Maysville West outcrop) - western side of Rt. 62/Rt. 68 roadcut through Jersey Ridge, just south of the Harsha Bridge over the Ohio River, northern Kentucky, USA (~vicinity of 38° 40’ 27.27" North latitude, 83° 47' 53.11" West longitude)