Fossil Identificaion for the Caesar Creek Spillway: Ordovician - Cininnatian
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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 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.
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 tiny 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).
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.
These use to be called Onniella meeki.
They are small, usually under an inch in length (25 mm).
These little brachiopods are usually around an inch (25 mm) in size.
These brachiopod fossils slightly under an inch in length (25 mm).
Plaesiomys subquadrata Brachiopod
These look similar to Cincinnetina brachiopods. Plaesiomys are slightly. Look carefully at the rays on the shell for identification.
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.
These use to be called Platystrophia ponderosa.
They are usually over an inch in length (25 mm).
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 belond to the Grewingkia genus.
Grewingkia Horn Coral
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.
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.
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.
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.
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.
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.