"Celebrating the Richness of Paleontology through Fossil Hunting"

fossilera logo
Guide to Fossil Hunting at Caesar Creek State Park, Ohio


Caesar Creek Spillway Fossil Identification - Ordovician Fossils

Fossil Identification Caesar Creek

Caesar Creek Spillway: Fossil Identification Page

Ordovician Reef Fossils

Click on the type of fossil or scroll down to browse:



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.

There are over a dozen trilobites found in this strata. By far the most common two are Flexicalymene and Isotelus.

Flexicalymene Trilobites

Flexicalymene trilobites in the Caesar creek area are reduced in size and most often found enrolled. They are usually the size of a fingernail or smaller. When searching for them, they superficially look like tiny brachiopods, so take your time, look closely, and you may find one!

This is a typical flexicalymene retrorsa minuens trilobite fossil that can be found at Caesar Creek. Yes, they are tiny.

Isotelus Trilobites

Isotelus trilobites get quite large; they can reach lengths of over a foot!
At Caesar Creek they are found as abundant fragments scattered about the llimestone floor.

The only chances of finding a whole one here is to find a small enrolled one, similar in size to the enrolled flexicalymene trilobites.

This is a large isotelus maximus that is on display at the visitor center.

This picture shows how they are found; as fragments. All of those orangish looking pieces are fragments of isotelus trilobites. The fragment on the right side is part of an isotelus cephalon (head).

Brachiopod Fossils

Brachiopods look like little clams, however, they are actually very different.
Brachiopods are one of the most abundant fossils in the Paleozoic, and this shows at Caesar Creek, where they are so numerous, one must walk on them.
Some Brachiopods are still alive today, but Pelecypods (clams and such) far outnumber them.
There are many different types of Brachiopods at Caesar Creek. Many look nearly identical. Below are a few of the more common ones that can be found.

Cincinnetina Brachiopod

These use to be called Onniella meeki.
They are small, usually under an inch in length (25 mm).

Lepidocyclus Brachiopod

These little brachiopods are usually around an inch (25 mm) in size.

Plaesiomys subquadrata Brachiopod

These look similar to Cincinnetina brachiopods. Plaesiomys are slightly. Look carefully at the rays on the shell for identification.

Rafinesquina Brachiopod

Rafinesquina are usually between 1 - 2 inches in size (25-50 mm). This is a cluster of them. The cluster is probably due to currents during a storm deposit.

Vinlandostrophia Brachiopod

There are a few species of Vinlandostrophia Brachiopods. They all look very similar to one another. A large species of this brachiopod is called Vinlandostrophia ponderosa.

This is probably a V. cypha brachiopod.

Coral Fossils

There are a few different types of coral. Two common ones at Caesar creek are:

Tabulate corals are colonial. Individuals are usually less than a millimeter across. Thousands of them make a tabulate coral head, kind of what you see in a coral reef today. Tabulate corals are caesar creek are often too large to collect (larger than your palm).

Rugosa corals, or horn corals are usually solitary. Most of them have a cone shape, and look like a little horn. These types of corals are often confused as dinosaur teeth by inexperienced people. The Rugosa coral would sit upright, like an ice cream cone. The top would contain the coral polyp, where the little tentacles would catch its food.

Grewingkia Horn Coral

The larger horn corals found at Caesar Creek belong to the Grewingkia genus.

Here is another Grewingkia horn coral. The bottom half has Bryozoa groing on it.

Streptelasma Horn Coral

Streptelasma horn corals are also found at Caesar Creek. They are much smaller than Grewingkia.

Bryozoan Fossils

Bryozoans, or moss animals, are colonial invertebrates. They are probably the most common fossil at Caesar Creek. They look similar to corals, but are not the same. A bryoza colony contains hundreds of individual polyps called zooids. Each zooid is less than a millimeter across. Some colonys have specialized zooids that perform specific functions. One type of bryozoa has zooids that enable it to slowly move!

Two kinds of Bryozoa are commonly found at Caesar Creek: Branching and Encrusting.

Branching bryozoa is commonly mistaken for coral, as the colony branches kind of like a tree. Branching Bryozoa are shown below.

Encrusting bryozoa grow their colony over other animals. When collecting brachiopods and horn corals, be sure to look at them closely, a number of them have encrusting bryozoa growing on them. The Grewingkia horn coral shown in the horn coral section above has encrusting bryozoa on it.

Branching Bryozoa

This is a type of branching bryozoa. At Caesar Creek, almost every rock has bryozoa on it somewhere!

These are pieces of branching bryozoa. These little fossil pieces litter the floor of the spillway.

Cephalopod Fossils

If you don't know what a Cephalopod is, think of a squid. However, unlike squids of today, the cephalopods in the Ordovician had their shells on the outside of their body instead of the inside. These cephalopods were called straight shelled cephalopods. The animal would live inside the largest chamber in the front. Its head and tentacles would stick out. This is similar to how a nautilus is today, except that a nautilus has a coiled shell.

This is how cephalopods are usually found, partly weathered and eroded away.

Gastropod Fossils

Gastropods are snails. Think escargot! Usually the inside of the shell of gastropods are preserved when fossilized, this makes a nice internal mold fossil. These internal molds look coiled, like in the image above.

Crinoid Fossils

Crinoids, or sea lillys, look like a little flower. They have a root (holdfast) that attaches to an object on the sea floor, they have a stem (columnal), then an array of arms (crown) that filter feed.
At Caesar Creek, usually stem fragments are found. Occasionally part of a crown can be found. The image above shows stem fragments. The fragments are all less than an inch across.

These are small stem fragments fro crinoids. They are abundant in the spillway.

Recommended Ohio Book:

Fossils of Ohio (Bulletin 70)
By Rodney M. Feldmann (ed)
Copyright 1996
State of Ohio Div. of Geological Survey

This book is a MUST for anyone collecting in Ohio or nearby Devonian formations. It has detailed descriptions and images of 100's of fossils one can find throughout Ohio, including the Cincinnati Arch. It can be ordered through the Ohio DNR website, just search for "Fossils of Ohio (Bulletin 70)"

Recommended Trilobite and Fossil Hunting Books:

The Trilobite Collector's Guide
Andy Secher, 2024

This book by Andy Secher, a leading trilobite collector, offers a captivating journey into the world of these ancient arthropods. With over 400 stunning photos, entertaining top-ten lists, invaluable collecting tips, and ways to spot a fake trilobite, it's a must-have for fossil enthusiasts!

Trilobites: Common Trilobites of North America (A NatureGuide Book)
Jasper Burns, 2000

An excellent guide for identifying North American trilobites, featuring meticulous line drawings and concise information on classification, geologic range, and distribution. Ideal for enthusiasts seeking detailed insights and accurate identification of these ancient arthropods.

101 American Fossil Sites You've Gotta See
Albert B Dickas, 2018

This is a great updated fossil sites book with at least one fossil site in each state. Each site is broken into 2 pages. One has detailed information, such as directions, GPS coordinates, formation information, etc... The other is dedicated to images of the site and the fossils found there. It also gives information on fossil 'viewing' sites such as dinosaur trackways, museums, and active excavations.
Plus, my fossil photos are peppered throughout this book!

About the Author

Contact Us

To ask Questions about Paleontology, Fossil Identification, Image Use, or anything else, email us. is very active on Facebook, you can also message us there!

We don't buy or sell fossils, so please don't email us asking about the value of a fossil or fossil purchases.

Visit us on Social Media:

Enjoy this website?
Consider a Paypal / Credit Card donation of any size to help with site maintenance and web hosting fees:

Privacy Policy and Legal Disclaimer

Back to the TOP of page

© 2000 - 2024 : All rights reserved


fossilguy logo is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to