File:Bryozoan-encrusted fossil nautiloid internal mold (Richmondian Stage, Upper Ordovician; Caesar Creek Lake spillway, Ohio, USA) 1.jpg

English: Bryozoan-encrusted fossil nautiloid from the Ordovician of Ohio, USA. (4.0 centimeters across)

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.

Shown above is a partial internal mold of a nautiloid - the original aragonite shell has dissolved away, leaving an impression of the inside surface of the shell. The nautiloid is encrusted by some sheet bryozoans (see the entire right side and much of the left side). The pits may be borings or pseudoborings.

Classification: Animalia, Mollusca, Cephalopoda, Nautiloidea

Stratigraphy: float from the upper Waynesville Formation or the Liberty Formation or the lower Whitewater Formation, Richmondian Stage, upper Cincinnatian Series, upper Upper Ordovician

Locality: loose piece from Caesar Creek Lake's emergency spillway, northeastern Warren County, southwestern Ohio, USA