The Mississippian limestones of the Mammoth Cave region (300-325 million years old) formed at the bottom of a shallow saltwater sea now known as the Mississippian Sea. The marine life of that ancient sea is reflected in a range of fossils interspersed through the various limestone strata and exposed on the cave walls as caves were hollowed out. Typical fossils found in the cave include crinoids, blastoids, gastropods, and the teeth of fossil sharks.