Pennsylvanian rocks are only preserved in the Eastern and Western Kentucky Coal Fields, although all of Kentucky was probably covered by Pennsylvanian sediments at one time. Erosion has completely removed Pennsylvanian rocks from all areas but the coal fields. The Pennsylvanian Period, often called the Coal Age, was a time of alternating land and sea. When the sea was out, the low coastal plains were covered with luxuriant forests of seed ferns, ferns, scale trees, calamite trees, and cordaite trees.
During times of heavy rainfall, thick accumulations of plant debris (peat) were deposited, which later became the coal that Kentucky is famous for. When sea level rose, which it periodically did, it covered the coastal peats and created large inland muddy seas. During these times, which lasted for many thousands of years, many types of marine (sea-dwelling) invertebrates and vertebrates lived in Kentucky. Common Pennsylvanian marine fossils found in Kentucky include corals (Cnidaria), brachiopods, trilobites, snails (gastropods), clams (pelecypods), squid-like animals (cephalopods), crinoids (Echinodermata), fish teeth (Pisces), and microscopic animals like ostracodes and conodonts.
The modern Lingula brachiopod looks just like the Pennsylvanian Lingula fossils (like the one above) found in Kentucky. This is why Lingula is known as a living fossil. Many other types of brachipods, like those shown below, are found in the Pennsylvanian rocks of Kentucky.
Some of the mollusk fossils found in the Eastern Kentucky Coal Field still retain their mother-of-pearl luster and even color patterns.
Shrimp-like crustaceans have also been found in Pennsylvanian rocks in the Eastern Kentucky Coal Field.
Giant water scorpions may have lived in Kentucky during the Pennsylvanian, but fossils have not been found. Spider fossils have the potential to be found in the Pennsylvanian rocks of Kentucky's two coal fields.
Tracks from horseshoe crabs have been found in Pennsylvanian rocks of the Eastern Kentucky Coal Field. These ancient horseshoe crabs were only a couple of inches long.
A millipede fossil was found recently in Pennsylvanian rocks of the Western Kentucky Coal Field. This millipede had large spines all along its body. Fossil trackways of giant millipedes called Arthropleura (animals up to 5 feet long) have been found in other areas of eastern North America and could probably be found in the Pennsylvanian rocks of Kentucky.
The first insect fossil found in Kentucky (1980) was an insect wing from the Pennsylvanian rocks of the Eastern Kentucky Coal Field. It came from an animal that had a wing span of about 4 inches, looked somewhat like a dragonfly, and could not fold up its wings. Other insect fossils will probably be found in Kentucky.
Above is a Pennsylvanian cephalopod fossil from eastern Kentucky. One cephalopod fossil that had the puncture marks of a shark that had bitten it was found in the Pennsylvanian rocks of the Eastern Kentucky Coal Field. Some Pennsylvanian sharks lived in fresh water and had forked teeth that were designed to catch other fish and swimming animals.
Scales and teeth of bony fish have been found in Pennsylvanian rocks in Kentucky. A 1-inch-long scale of a Rhizodopsis fish, that was up to 8 feet long was found in the Pennsylvanian rocks of the Eastern Kentucky Coal Field.
Only one reptile fossil has been found in Kentucky, in Pennsylvanian rocks of the Eastern Kentucky Coal Field. This fossil was a trackway of a small reptile about 15 inches long. It is currently the oldest known reptile fossil in North America. Other reptile fossils most likely exist in the coal fields of Kentucky.
The most common Pennsylvanian fossils in Kentucky are plant. Plant fossils commonly found in Kentucky include seed ferns, true ferns, calamites, cordaites, and scale-trees.
A fossil lycopod tree stump from the Pennsylvanian rocks of eastern Kentucky. The trunk is about 24 inches in diameter.
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Pennsylvanian Age (Late Carboniferous):