Ohio is a great state for viewing and collecting fossils. All of the state's bedrock (consolidated rock underlying soil and till) exposed at the Earth's surface is sedimentary rock, and most of it contains fossils. Some rocks, such as many Ordovician-age limestones of southwest Ohio, are primarily composed of fossils. Ohio has numerous world-famous fossil deposits, such as the Upper Ordovician shales and limestones around Cincinnati, the Lower to Middle Devonian Columbus Limestone in central Ohio, the Middle Devonian Silica Formation shales and limestones of northwest Ohio, the Upper Devonian Cleveland Member of the Ohio Shale, and the Upper Carboniferous (Pennsylvanian) cannel coal (oil shale) from the former Linton coal mine. Overlying Ohio's bedrock deposits, scattered Pleistocene (Ice Age) deposits have produced fossils of mastodons, mammoths, short-faced bears, giant ground sloths, and giant beavers, among others.

Ohio's Fossil-Bearing Deposits

The early to middle Paleozoic Era in Ohio

Ranging from approximately 450 to 359 million years old, the lower to middle Paleozoic carbonate rocks exposed at the surface in western and central Ohio were deposited at a time when the land that is now Ohio was covered by warm, clear, shallow seas. The limestones and dolostones that formed from sediments in these seas contain the remains of marine invertebrates such as corals, echinoderms, brachiopods, cephalopods, and trilobites, as well as more abundant vertebrates such as bony fish, placoderms, and early sharks during the middle Paleozoic (Devonian Period). The large trilobite Isotelus (pictured here) from the Upper Ordovician rocks near Cincinnati is Ohio's official State Invertebrate Fossil. During the Late Devonian Period, the inland sea deepened and the seafloor conisted of stagnant black muds that would eventually form the Ohio Shale, exposed in the central and northeast Ohio. There was little life on the sea bottom at this time, but the large placoderm Dunkleosteus terrelli (as seen on the cover of Bulletin 70: Fossils of Ohio) and other fish inhabited the fertile surface waters. D. terrelli was named the official Fossil Fish of Ohio in December 2020.

The late Paleozoic Era to the Present Day in Ohio

The upper Paleozoic rocks in eastern Ohio, also deposited long before the first dinosaurs (approximately 359–290 million years ago), are a mix of marine and terrestrial (land) deposits that formed when Ohio alternated between shallow marine and lowland coastal environments. The Upper Carboniferous (Pennsylvanian) shales, siltstones, sandstones, and coal shales of eastern Ohio contain fossils of invertebrates, such as giant cockroaches and millipedes, coal swamp trees such as Lepidodendron, and vertebrates in the form of fish, amphibians, and reptiles. Platyrhinops lyelli (pictured here), a frog-like amphibian from the Upper Carboniferous (Pennsylvanian) cannel coal of a former coal mine near the former town of Linton in eastern Ohio, Jefferson County. The youngest bedrock strata in Ohio, deposited during the early Permian Period about 299–290 million years ago, contain remains of the large sail-backed, mammal-like reptiles Edaphosaurus and Dimetrodon.

Rocks younger than early Permian age were either not deposited in Ohio or were completely eroded during the last 290 million years. Dinosaurs likely lived within the state during the Mesozoic Era; however, no rocks from that era survived here and therefore Ohio lacks dinosaur fossils. Some very recent Cenozoic Era deposits, from the latter part of the Pleistocene Epoch (Ice Age) were deposited above the Paleozoic bedrock. The surviving deposits frequently are in low spots, such as glacial lakes and peat bogs. Some of the fossil plant and animals from Ohio's Ice Age resemble species living today in cooler, more northerly climates, but other fossils represent species now extinct, such as the mastodon and giant beaver (illustrated here).

Places to view and collect Ohio Fossils

There are many places around Ohio to view fossils: in natural settings, such as at state parks; in building stones, such as in the walls, columns, and steps of the Ohio Statehouse (such as Goldringia cyclops, shown here); and in museums. Among the best places to learn about Ohio's fossils are natural history museums (listed under External Resources, at right).

For information on viewing and collecting fossils, see our Fossil Collecting in Ohio webpage. Information about some of Ohio's common fossils can be found in the Fossils Species Index.