No. 17 OHIOGeoFacts DEPARTMENT OF NATURAL RESOURCES • DIVISION OF GEOLOGICAL SURVEY FOSSIL COLLECTING IN OHIO Hobbyists have long known about Ohio’s great abundance and WHERE FOSSILS ARE FOUND IN OHIO diversity of fossils. Many world-famous paleontologists—geologists who study fossils—began their careers as youngsters collecting fossils Ordovician rocks in Ohio are world famous for in their native Ohio. Fossils from Ohio are important constituents the abundance, variety, and excellent preserva- of museum collections throughout the United States and Europe. tion of the fossils they contain. The limestones and shales exposed in almost every road cut or WHY OHIO HAS FOSSILS stream bed in southwestern Ohio, southeastern Indiana, and north-central Kentucky provide The area that is now Ohio was not always dry land as it is today. the opportunity to collect a bonanza of fossils. Approximately 510 million years ago (m.y.a.), Ohio was south of the Among the more abundant types of fossils col- Equator. As the North American Plate moved to its current position ORDOVICIAN lected from Ordovician rocks are brachiopods, 508–438 m.y.a. through the process of plate tectonics, tropical to subtropical seas bryozoans, gastropods, and trilobites. repeatedly transgressed over the plate. It is because of those warm Silurian rocks of western Ohio are not known seas that Ohio has the abundant fossils that people collect today. for their fossils. When the limestones and shales The seas that covered Ohio during the Ordovician, Silurian, and were fi rst deposited they were quite fossilifer- most of the Devonian Periods of the Paleozoic Era were the site of ous. Unfortunately, most of the fossils were abundant limestone deposition. Sediments that form limestone are destroyed when the limestones containing the generally only deposited under shallow, open-marine conditions, fossils were altered to dolostones. One Silurian much like the seas around Caribbean islands today. rock unit that still retains well-preserved fos- Near the end of the Devonian Period, conditions in the seas sils is the Brassfi eld Formation. The Brassfi eld covering Ohio changed, so that the sediments deposited were pri- SILURIAN is composed almost entirely of fragments of 438–408 m.y.a. marily muds and sands that would become shale and sandstone. crinoids. Even the dolomitized formations The oldest exposed major shale unit is the Ohio Shale; outcrops of contain molds and casts of fossils, in particular this shale are present from Ashtabula westward along Lake Erie to brachiopods and trilobites. Quarry operations Milan and southward to Portsmouth. These same conditions con- in western Ohio have exposed several reefs tinued into the early Mississippian Period, when the Bedford and preserved in Silurian rocks. Reefs are indicative Sunbury Shales were deposited. After deposition of the Sunbury that warm, open-marine conditions existed in Shale ceased, long intervals of extensive open-marine conditions Ohio at this time. Colonial corals are the most infrequently returned to Ohio. prominent fossil type composing reefs. Silurian During most of Mississippian time and the rest of the Paleozoic Era, rocks are well exposed in an arc from west of what is now Ohio may have been dry land in the west (Cincinnati Dayton to near Portsmouth. to Toledo), and the Appalachian Mountains were continuing to rise Devonian rocks in Ohio are as famous for to the east of Ohio; between these two areas was the Appalachian their fossil abundance and diversity as are Basin. The eastern coastline of the basin was dominated by numer- Ohio’s Ordovician rocks. There are two main ous deltas deposited by rivers carrying sediments eroded from the areas of exposure of Devonian rocks in Ohio: a ancestral Appalachian Mountains. These deltas were sites of vast north–south belt through the center of the state swamps and marshes, particularly during the Pennsylvanian Pe- then east along Lake Erie and in the northwest riod. In fact, Ohio’s Pennsylvanian rocks probably are better known corner. The shales of the Silica Formation near for their coal deposits, formed from the plant material deposited Sylvania, in northwestern Ohio, contain abun- in these wetlands, rather than for their fossils. However, because DEVONIAN dant trilobites and brachiopods. The Columbus 408–360 m.y.a. coal is composed of compressed plant material, it is a type of fossil, and Delaware Limestones, exposed from central hence the term “fossil fuel.” The marine units in the Pennsylvanian Ohio to the Lake Erie islands, are quite fossilif- rocks of Ohio are fossiliferous, containing pelecypods, gastropods, erous. Fossils in the Columbus Limestone are trilobites, echinoderms, and others. Nonmarine units of Pennsylva- notable for their large size. Perhaps the most nian and Permian age contain plant and insect fossils and remains spectacular fossils from Ohio’s Devonian rocks of fi sh, amphibians, and reptiles. come from the Ohio Shale near Cleveland. Con- Dinosaurs roamed Earth during the Mesozoic Era (245–65 m.y.a.). struction projects in and around Cleveland have Undoubtedly, dinosaurs lived in Ohio, so why haven’t dinosaur uncovered the bony armored plates and jaws skeletons been found here? The answer is that Ohio does not have of fossil fi shes known as arthrodires. any rocks dating to that time. Therefore, no dinosaur remains can be Mississippian rocks in Ohio were deposited collected in Ohio. Why doesn’t Ohio have any Mesozoic-age rocks? as deltas by rivers that fl owed westward from Two possibilities may explain this quandary: Ohio may have been the ancestral Appalachian Mountains into the above sea level and no sediments were deposited, or any sediments Appalachian Basin. A similar process is taking that were deposited during this time were eroded away. place today where the Mississippi River fl ows During the Pleistocene Epoch (2 m.y.a–10,000 y.a.), about two- into the Gulf of Mexico. Some of Ohio’s Missis- thirds of Ohio was covered periodically by ice that fl owed south sippian rocks are quite fossiliferous, containing from Canada. Remains of animals and plants that lived during abundant limonite-stained molds and casts Pleistocene time have been collected in Ohio from deposits repre- MISSISSIPPIAN of brachiopods, pelecypods, and echinoderm senting lakes and ponds, caves, and streams. Some of these remains 360–320 m.y.a. fragments. Mississippian rocks are exposed include the elephantlike mastodons and mammoths, giant beaver, from near Portsmouth northward to Lorain elk, and muskoxen. and eastward to Ashtabula. continued ➮ Pennsylvanian rocks are well exposed in eastern Ohio and were deposited primarily Identifi cation number: __________________________________ in swampy conditions associated with deltas Phylum: _______________________________________________ along the Appalachian Basin coastline. These Genus: ________________________________________________ rocks are noted for well-preserved fossil plants Species: _______________________________________________ and rare fossils of insects and amphibians. Location: ______________________________________________ Marine fossils such as pelecypods, gastropods, _______________________________________________________ and brachiopods are abundant in thin beds of Formation: _____________________________________________ PENNSYLVANIAN limestone and shale deposited when the sea Date collected: _________________________________________ 320–286 m.y.a. periodically fl ooded the coastal coal swamps. Collector: ______________________________________________ Permian rocks of Ohio are not very fossil- Identifi er: ______________________________________________ iferous. However, bones of amphibians and NOTES: reptiles and plant and insect fossils have been collected from rocks of this age. Permian rocks are exposed in southeastern Ohio near Marietta. Pleistocene glaciers left a mantle of un- A label card such as this one should accompany fossil specimens. consolidated material across northern and western Ohio. Bones of Pleistocene mammals, FURTHER READING PERMIAN particularly mastodons and mammoths, have 286–245 m.y.a. been collected from deposits of this time. Even There are many publications related to Ohio paleontology. A forests buried by the advancing glaciers have few are listed below. Out-of-print publications can be consulted at been unearthed. Deposits from this period are many Ohio libraries. A book worth special mention is Fossils of Ohio easy to see because they cover most of Ohio. (Feldmann and Hackathorn, 1996), which explains how to collect fossils, where to fi nd them, how to prepare and care for them, and WHERE TO COLLECT FOSSILS IN OHIO how to identify them. Its numerous photographic plates and line drawings will speed fossil identifi cation. The book also contains Even though Ohio is well known for its fossils, publicly ac- an extensive reference list, glossary, and indexes of generic and cessible collecting localities are actually scarce. Most sites are specifi c names of fossils. located in southwestern Ohio: Caesar Creek (Warren and Clinton Counties), Cowan Lake (Clinton County), East Fork (Clermont Brezinski, D.K., Sturgeon, M.T., and Hoare, R.D., 1989, Pennsylvanian County), Hueston Woods (Preble and Butler Counties), and trilobites of Ohio: Ohio Department of Natural Resources, Division of Stonelick (Clermont County) State Parks allow fossil collecting; Geological Survey Report of Investigations 142, 18 p. check at the ranger stations for designated collecting areas. Caesar Davis, R.A., ed., 1985, Cincinnati