Conodonts (ko'-no-dahnts) are small calcium phosphate fossils that are barely visible to the naked eye. They occur throughout Illinois, ranging from Cambrian through Pennsylvanian rocks. In other areas they continue through the Triassic. Reworked by erosion and by continental glaciers, they also are found in Ice Age sediments.
Abundantly distributed worldwide in marine sediments, conodonts are valuable because they help geologists correlate the age of rock formations from region to region and continent to continent.
The conodont-bearing animal, about which little is known, commonly contained multiple conodont elements, providing a number of fossils per individual. Evidence indicates that conodonts were swimmers and may have been precursors of higher vertebrate life.