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Kids: Fossils of SW Ohio


  • What is a fossil?

  • Why are fossils important?

  • How old are our fossils?

  • How did our fossils form?

  • Why can we find fossils in SW Ohio?

  • Who are the fossils?

  • Help with Rock, Fossil, or Mineral Identification

  • Where can I find fossils?

  • Great fossil resources

What is a fossil?

Fossils are not a bunch of rocks with animal parts stuck to them. They are also not just a bunch of dinosaur bones. Generally speaking, fossils are evidence of past life. This is the preserved remains, or traces of remains, of ancient animals and plants. Yes, this could involve rocks or bones, but it can also involve amber, tar, ice, and more.

Fossils provide us with information about the past. For example, our fossils here in SW Ohio are about 450,000,000 years old! Back then there were no people, so we have to look to the fossils if we hope to learn about the past. Unfortunately, fossilization is not always an easy process and we are missing many species of plants and animals that never became fossilized. Almost all fossils do not retain the organisms color (except for amber). Often only the hard body parts li shells and bones were preserved while the soft squishy body parts decomposed.

Why are fossils important?

The fossil record, the total collection of fossils in the world, is extraordinarily important to our understanding of the Earth's history. Fossils tell us which plants and animals existed in prehistoric times, and where they lived. They also tell us something about when they lived. Based on the position of fossils in the layers of the Earth's crust, paleontologists can determine which animals predate other animals and which animals lived at the same time.

Using carbon dating, paleontologists can sometimes estimate the age of fossils. This provides the age of the rock layer where the fossil was found, which helps scientists date all the other material at that level. Without fossils, we would have a much more incomplete picture of Earth's early history. (How Stuff Works)

Different fossils, depending upon how they were preserved, tell us different things about how past creatures looked. For example, fossils that are preserved in amber give us an extraordinary amount of information about the anatomy of that organism; since the organisms that are preserved in amber, mostly insects, are usually preserved intact without any disintegration of organs, muscles, and coloring. Even bones may tell a great deal about the soft anatomy. For instance, the area where the muscle attaches to the bone leaves marks that indicate size, shape, and functions of these varied organs. Also, the cavities and the the channels in skulls give us an idea of their intelligence, behavior, and their principle features. Certain parts of certain fossils can also tell us about growth, injury, disease, form, function, activities, and instincts.

Fossils also record the successive evolutionary diversification of living things, the successive colonization of habitats, and the development of increasingly complex organic communities.

Finally, study of fossils contributes greatly to the study of evolution. They are the only direct record of what has occurred in sequences of reproducing populations and in the course of the time on an evolutionary scale."

How Old Are Our Fossils?

The term "fossil" does not include any life forms that have been buried since the beginning of historic time.

The earliest evidence of life on earth is of marine animals, during the Precambrian era (4.6 billion-544 million). The oldest known Precambrian rocks, found in Africa and Australia, are believed to be more than three billion years  old. The fossils found among them are of the oldest known organisms on earth. Usually, fossils found in these old rocks are microfossils, such as elongated bacteria, Eobacterium and other water environment fossils. Bacteria represents the first stage of recognizable organized life and scientists have found well defined remains of algae and bacteria from nearly two billion years ago.

In Ohio, the oldest fossils that we can find at the surface are from the Ordovician Era (505-440 million). These Ordovician fossils are only found near the surface in SW Ohio. Elsewhere in Ohio these old rocks are covered by younger rocks.

A brief summary of the geologic history of Ohio -ODNR Geofacts

How do fossils form?

Fossils can form in a variety of different ways. Palaeontologists, people who study fossils, divide them into two major types - body fossils and trace fossils.

Body Fossils

The first type, body fossils, are the fossilized remains of an animal or plant. This includes, like bones, shells and leaves. These can be mold and cast fossils, like most of the fossilized dinosaur skeletons and big bones we see, replacement fossils, like petrified wood, or whole body fossils - mammoths caught in ice, or insects trapped in amber. Typically, soft tissue like skin, muscle and organs disintegrate after death, leaving only the hard shell or bone skeleton behind. Animals with weak skeletons, like insects and shrimps, are less likely to be preserved.

Molds and Casts - Molds and casts are other types of body fossils. A mold is an imprint left by the shell of a hard skeleton on surrounding rock, such as dinosaur bones buried beneath many layers of sediment. A mold may be internal or external. An internal mold is on the underside of shell left on the surface of rock that formed when sand or mud filled the inside of the shell. An external mold is on the outside of the shell. Whenever a shell or bone breaks out of rock, it leaves an external mold behind.

Replicas of molds are known as casts, which may be produced naturally when the space left behind after mold removal fills with sediment. Paleontologists can also produce casts from molds with latex rubber or modeling clay to learn more about fossils.

Permineralization and Petrification Fossils - When groundwater saturates a plant or animal's remains after it dies, sometimes the organism's materials dissolve, and minerals such as calcite, iron and silica replace them. The fossils form in the original shape of the organism, but the composition is different, and it is heavier. This process is known as permineralization. Petrification fossils form when the organic matter is entirely replaced by minerals and turns to stone. The original tissue is replicated in every detail. Petrified wood is an example of petrification.

Trace Fossils

The second type of fossil records the activity of an animal. Known as trace fossils, these include footprints, trackways, and coprolites (fossil poo!).

Footprints and Trackways - Footprints, trackways, trails and burrows through mud sometimes harden and become fossils known as trace fossils. These give information about how animals behaved when they were alive, such as how they moved and how and where they fed. Trackways, which are several footprints together, sometimes include impressions made by another part of the creature, such as its tail dragging behind it.

Coprolites - Coprolites (fossilized feces, also known as dung-stone) give clues to where certain animals lived and what they ate. Coprolites are rare because feces usually decay quickly. The most common coprolites are of sea organisms, particularly fish and reptiles. They consist of indigestible remains of the organism's food, such as pieces of scale, teeth, shell and bone. Coprolites are preserved by petrification or cast and mold.

How did our fossils in SW Ohio form?

Our fossils lived during the Ordovician period (505-440 million). During this time, a warm, shallow sea (deeper in eastern Ohio) similar to the Bahamas covered Ohio, which lay 20° south of the Equator. The western part of Ohio, at times,emerged as low muddy islands. Limy sediments were dominant. Volcanic activity and mountain building to the east of Ohio produced periodic layers of ash over the entire state and muddy deltaic sediments in eastern Ohio. The sea deepened in later Ordovician time, covering all of the state. At the close of Ordovician time, continental glaciation in the southern hemisphere lowered sea level and the seas retreated. (ODNR, Geofacts).

Who are the Fossils?

Fossil ID sheet to print and take with you when fossil hunting (pdf)

Download PDF • 713KB

Trilobite Fossils: Trilobites are a group of extinct arthropods (similar to crustaceans) with a hard shell. They are common in Ordovician rocks in the Cincinnati Arch. Unfortunately, almost all are fragments. Occasionally whole ones are found. The whole trilobites are usually found enrolled.  The most common two to find are Flexicalymene and Isotelus. ​ Isotelus maximus is our state fossil

Trilobites are one of the oldest animals that first lived on the Earth. They lived in the Cambrian Period and early Ordovician seas. A prolonged decline then set in before they finally became extinct in the Permian Period, about 250 million years ago. They have no direct descendants. Their closest living relatives would be the chelicerates. This group includes the horse shoe crab.

Bryozoan Fossils: ​Bryozoans are tiny organisms that live in colonies. They build exoskeletons (outer protective structures) similar to those of corals. and are often mistaken for coral. The individual bryozoan is usually less than 1 mm in size. The colonies of different species take different forms, they can be branching, twiglike, fan-like, or encrusting. Some bryozoan colonies are smooth and others have bumps covering them. Each small opening or aperture was the home for an individual bryozoan or zooecium. The small animal seals the hole with a “door” or vestibule. The Flood tore apart these colonies, leaving only piles of broken “stems” and “branches.

Bryozoans are still found in aquatic environments today, and are sometimes called moss animals.

Brachiopods - These filter feeding marine animals have a shell made of two valves, which usually differ in shape and size.  The Flood ripped the shells apart, burying piles of them in slabs of limestone. 

During the Ordovician, brachiopods were the dominant shellfish and occurred abundantly on the seafloor globally. In fact, if humans had of been around to visit the beach anytime from 550 to 250 million years ago, most of the shells you would have collected would have been brachiopods.  They are not anywhere near as abundant in our oceans as they were in the Ordovician.

Bivalve (pelecypod or clams) - Bivalve means 2 shells. Although this animal lives in a shell like the brachiopods, they were very different. The valves are the parts usually found as fossils. The elastic hinge tissue that joined the shells together usually decomposed before it cold be fossilized. This means the two shells are rarely preserved together. Pelecypods (clams) are are common in the oceans and streams of the world today.

Is it a Brachipod or Bivalve?

The easiest way to distinguish a fossil brachiopod from a fossil clam (which also occur in Cincinnatian rocks) is to determine where the line of symmetry falls between the two valves. In brachiopods, the plane of symmetry runs through each valve so that the right and left half of a single shell look identical but the two shells are different in shape and size. In a bivalve, the plane of symmetry runs between the shells so that the two shells look identical, but the right and left sides of the valves are different.

Crinoid - These were animals that attached to the seafloor on long columns. They looked a lot like flowers and so are sometimes called "Sea Lilies". Their "stem" would allow them to bend towards water currents and use their brachials as a net to trap food particles. The skeleton is made of the mineral calcite, and consists of hundreds of individual plates of different shapes and sizes. Decay of the soft tissue that held many of these plates together means that complete specimens are rare, but parts of the stem are common fossils. Crinoids are still found in oceans today

Gastropod - This is a fancy name for snail, which is in the mollusk family. "Gastro" means stomach and "pod" is movement, and if you look at a snail, it moves on its stomach.

Cephalopods - These predators are members of the phylum Mollusca and their family includes squid, octopus and nautilus. These ancient cephalopods were straight shelled squids. They could rise and fall in the ocean water like a submarine. The siphuncle was a tube in the center of the animal. When filled with air, the animal’s body floated upward. A burst of air out the back end of the siphuncle pushed the animal forward - think of the way a bottle rocket shoots off when the water is released.

Horn Coral - This is not a petrified cow horn or a dinosaur tooth, it is a type of rugosa coral. Horn corals, which are named for the hornlike shape of the individual structures built by the coral animal, were either solitary or colonial forms. Horn corals are extinct, but there are many other types of coral alive today.

Help with Rock, Fossil, or Mineral Identification

Ohio Dept of Natural Resources can help with rock, fossil, or mineral identification. If you're not sure what your rock might be, a Survey geologist may be able to help identify it. Send us some info and a picture, and we’ll do our best! Please fill out and submit a rock & fossil ID form, and include at least one photograph with your request (Ohio rocks only please).

Where can I find fossils?

If you have a creek in your backyard that is the perfect place to start. If not, always make sure you have permission to be there, and permission to collect. Many of the local parks, such as the MetroParks do not allow you to collect. So where is a public place that you can collect:

Trammel Fossil Park (Sharonville, ,Hamilton County)

Geology: Ordovician; fossils ranging from 450 to 500 million years old in interbedded shale and limestone.

For more information, call (513) 563-2985.

State Parks - Visitors should contact park management staff prior to collecting to obtain any permits and/or rules that may apply.

Hueston Woods State Park (Preble/Butler Counties)

Geology: Ordovician; fossils ranging from 450 to 500 million years old in limestone and dolomite forming the western edge of the Cincinnati Arch.

For more information, call (513) 523-6347.

Caesar Creek State Park (Clinton/Warren Counties)

Geology: Ordovician; fossils ranging from 450 to 500 million years old found in limestone forming the crest of the Cincinnati Arch. Collecting rules apply and a permit must be obtained at the U.S. Army Corps of Engineer's Visitor Center, which also features a display of fossils found at the park.

For more information about fossil hunting at Caesar Creek, call (513) 897-1050.

Cowan Lake State Park (Clinton County)

Geology: Ordovician; fossils ranging from 450 to 500 million years old found in limestone forming the eastern edge of the Cincinnati Arch.

Special permission to collect fossils must be obtained from Ohio State Parks. For more information, call (513) 897-3055.

East Fork State Park (Clermont County) – Geology: Ordovician; fossils ranging from 450 to 500 million years old in interbedded shale and limestone. Collecting rules apply. A permit must be obtained at the U.S. Army Corps of Engineers Visitor Center. For more information, call (513) 734-4323.

Geology: Silurian; fossils around 425 million years old. Located in city of Fairborn, northeast of Dayton.

For more information, call (937) 754-3090.

Stonelick State Park (Clermont County)

Geology: Ordovician; fossils ranging from 450 to 500 million years old in interbedded shale and limestone.

For more information, call (513) 734-4323.

Great fossil resources

Cincinnati Dry Dredgers - a Cinc based association of amateur geologists and fossil collectors

Karl E. Limper Geology Museum at Miami University: Learn about local geology, ask a geologist, and schedule a visit.

Ohio's Geological Walk Through Time - Located at the Natural Resources Park on the Ohio State Fairgrounds, this exhibit offers a unique learning experience for anyone interested in Ohio's natural history, including fossils, rocks & minerals, and more.

Virtual Museum of Geology:

Atlas of Ordovician Life

How Fossils Are Made sheet for students

Download PDF • 147KB

Fossil lessons and Activities

Fossil Formation

Ohio Division of Geological Survey

They are currently rebuilding their website after it was hacked (Spring/Summer 2020).

They typically have a great series called GeoFacts and by the time you are reading this, these materials may be back on their site

Fossil Crossword

Download PDF • 96KB


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