Mississippian rocks are exposed at the surface in the Mississippian Plateau (Pennyroyal) Region and occur below the surface in both of the coal fields. Mississippian rocks are absent in the Blue Grass Region and in most of the Knobs. During most of the Mississippian, Kentucky was covered by shallow tropical seas, although some very low lands may have been emergent at times in central Kentucky. Periodically, during the later part of the Mississippian, tidal deltas and low coastal plains covered large parts of Kentucky. These periods of coastal environments alternated with periods when the sea came in and inundated the region.
Thick limestones were deposited in shallow seas during the middle part of the Mississippian. Many caves were later developed in these limestones, and this area is now known as one of the world's most famous karst (cave-bearing) areas. The world's longest cave system, Mammoth Cave, is in these limestones.
Most of the Mississippian rocks found in Kentucky are marine, and many of the fossils in them are marine (sea-dwelling) invertebrates. Common Mississippian fossils found in Kentucky include corals (Cnidaria), bryozoans, brachiopods, trilobites, snails (gastropods), clams (pelecypods), squid-like animals (cephalopods), crinoids and blastoids (echinoderms), fish teeth (Pisces), and microscopic animals like ostracodes and conodonts. When there was emergent land in the form of low coastal plains, land plants and animals lived. Land plants such as seed ferns, true ferns, scale trees, and calamite trees grew in these coastal areas. Amphibians, such as the one recently found in western Kentucky, lived in estuaries and ox-bow lakes. Insects and other arthropods were probably numerous on land.
Some Mississippian rocks contain so many broken-up fossils crinoids that the Mississippian became known as the Age of Crinoids. The most common crinoid fossils are the individual button-like plates that made up the stems. A variety of crinoids are shown in the Mississippian scene).
The hickory-nut-shaped body of the Mississippian Pentremites is the most common blastoid fossil in the State. Yellow and blue stemmed blastoids are shown in the foreground of the Mississippian scene above.
Many types of sharks lived in Kentucky at that time; some had teeth for capturing swimming animals and others had teeth especially adapted for crushing and eating shellfish such as brachiopods, clams, crinoids, and squid-like animals (cephalopods).
Only one amphibian fossil has been found in Kentucky (in 1995). It was found in Mississippian sandstones on the margin of the Western Kentucky Coal Field. This amphibian was about 5 feet long and had a long, streamlined body. It probably lived most of the time in water and ate fish and other small amphibians and reptiles.