In 2006, geologists isolated complex organic molecules from 350-million-year-old fossils of crinoids—the oldest such molecules yet found. Christina O'Malley, a doctoral student in earth sciences at The Ohio State University, found orange and yellow organic molecules inside the fossilized remains of several species of crinoids dating back to the Mississippian period.[6]

1. Crinoid columnals are generally small circular fossils, a centimeter or less in width. They may have a hole toward the axis (bead shape) but are common without holes as well. Crinoid columnals are common in limestones and shales throughout Kentucky, especially central Kentucky and around Cumberland Lake. 2. Cross sectional views or views looking down on the tops or cups of horn corals can have a circular appearance. Most corals will have grooves or lines radiating out from the axis. They are generally less than 3 or 4 centimeters in width. 3. Cross sectional views through some types of bryozoans are circular. Such sections are generally less than a centimeter in width and are common in Ordovician limestones of central Kentucky. 4. Atrypa, Orbiculoidia, and some productid brachiopods have circular shapes at certain orientations and do not have grooved ornamentation like many other shelled fossils. Look to see if you can see a tiny protrusion on one side of the shell that might be a hinge to the shell valves.