File:Bryozoan-encrusted fossil nautiloid (Kope Formation, Upper Ordovician; Maysville West roadcut, Mason County, Kentucky, USA) 3.jpg

English: Bryozoan-encrusted fossil nautiloid from the Ordovician of Ohio, USA.

Nautiloids were relatively common components of Paleozoic oceans. They were basically a squid-in-a-shell. Most species had straight, slightly tapering shells, but some had loosely coiled or tightly coiled shells. The shells were mostly hollow, aragonitic, and had regularly-spaced internal walls. The entire group is represented in today's oceans by five living species of chambered nautilus, all of which have a coiled shell: Nautilus pompilius, Nautilus macromphalus, Nautilus stenomphalus, Nautilus belauensis, and Allonautilus scrobiculatus.

Seen here is a partial internal mold of a nautiloid (= smooth, segmented area) - the original aragonite shell has dissolved away, leaving an impression of the inside surface of the shell. The nautiloid is encrusted by Spatiopora, a sheet bryozoan with short ridge-shaped, current-aligned monticules. The black spot near the center is a Sphenothallus "worm" holdfast.

Classification: Animalia, Mollusca, Cephalopoda, Nautiloidea

Stratigraphy: upper Taylor Mill Submember, McMicken Member, upper Kope Formation, uppermost Edenian Stage, lower Cincinnatian Series, Upper Ordovician

Locality: ~5 to 6 meters below bench 4 on the eastern side of Jersey Ridge outcrop (= Harsha Bridge South outcrop; = Maysville West outcrop) - Rt. 62/Rt. 68 roadcut through Jersey Ridge, just south of the Harsha Bridge over the Ohio River, northern Mason County, northern Kentucky, USA (~vicinity of 38° 40’ 42.48" North latitude, 83° 47' 41.01" West longitude)