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Fossil Identification Devonian of Ohio

Silica Shale: Fossil Identification Page

Ordovician Reef Fossils


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Trilobites


Trilobites are a group of extinct arthropods (similar to crustaceans) with a hard shell. They are common in Devonian rocks of Ohio. Unfortunately, almost all are fragments. Occasionally whole ones are found. The whole trilobites are usually found enrolled.

The most common type of trilobite found is Eldredgops milleri (Formerly known as Phacops rana).


Eldredgops milleri (Formerly known as Phacops rana)

Like all fossils found in the Silica Formation, trilobites are exquisitely preserved. Eldredgops trilobites grew to large sizes in the Silica shale. Some of the best Eldredgops trilobites in the United States come from the Silica Shale.


This rock shows how these trilobite fossil are more typically found; bits and pieces.

Formation: Silica
Age: Middle Devonian ~370 - 400 m.y
Location: Silvania, OH
Size: The black trilo cephalon (head) is ~1" across (25mm)



Many other Trilobites in the Silica Formation are enrolled, like this one.

Formation: Silica
Age: Middle Devonian ~370 - 400 m.y
Location: Paulding, OH
Size: ~ 1.3" across (34mm)



This is another enrolled Eldredgops (Phacops) Trilobite fossil. This one is a little smashed, as the pygidium (tail) is pushed inside the Thorax.
It has a couple small flakes of pyrite stuck to it.

Formation: Silica
Age: Middle Devonian ~370 - 400 m.y
Location: Paulding, OH
Size: ~ 1.4" across (35mm)



This a large Eldredgops (Phacops) trilobite. Unfortunately the pygidium (tail) is missing.

Formation: Silica
Age: Middle Devonian ~370 - 400 m.y
Location: Paulding, OH
Size: ~ 2.2" across (55mm) - longer if it had the pygidium



Brachiopod Fossils



Brachiopods are similar to mollusks, like clams, however, they are not closely related. Unlike most present day mollusks, the two shells of a brachiopod were different sizes.

Brachiopods were the dominant form of life in the seas in most of the Paleozoic, including the Devonian. Therefore, they are a very common fossil of the Devonian coral reefs in Western New York. Dozens upon dozens of species and genera can be found in the fossilized Devonian coral reefs.

Many genera and species Brachippods occur in the Silica Shale, the Devonian of Ohio. Below are a few example fossils.



Mucrospirifer mucronatus (Conrad)

M. Mucronatus is a small to medium sized brachiopod fossil. It is very beautiful in that the hinge line is straight and very long, ending in a spine-like point. The term Mucronate means to end abruptly in a point.
Unfortunately, the mucronate ends are often broken off.

They are very wide, usually 3 or 4 times wider than the height. They have radial striations, and often numerous growth lines are visible.


These are fairly abundant in the Silica Formation.



This is a plate of Mucrospirifers. Plates of these brachiopods are very common, however they take an air abrasive unit to properly prep. Each brachiopod is approximately 2" on this plate.



Mediopirifer Audaculus (Spirifer Audaculus)

These fossil brachiopods are more robust looking than M. mucronatus. Also the hinge line is not as straight as in M. mucronatus, and they are less elliptical, in that their width and height are not in as extreme proportions as M. mucronatus. They have more of a semi-circle shape.



These are two fossil brachiopods still cemented together with matrix.



Stropheodonta Demissa (Conrad)

This is a medium sized brachiopod fossil. It has an easily identifiable shape, looking like a half-circle. The pedical valve is very convex, while the brachial valve is concave. It also has strong radial striations running the length of both shells.

There is a very similar looking brachiopod called Megastrophia concava. However, it is much larger in size.



These fossil brachiopods are fairly common in the Silica Shale of Ohio.





Megastrophia concava

These giant brachiopods are one of the larger types of Brachiopod fossils found in the Silica shale. They look like Stropheodonta brachiopods, but are MUCH larger.





Coral Fossils


The Silica Formation contains a rich variety of corals. The corals easily weather from the shale and are therefore easy to collected. The genera in the images below include: Bethanyphyllum (Stumm), Heliophyllum (Hall), Heterophrentis (Hall), and possilbly others.



Horn Corals

Horn corals are solitary corals that are cone shaped. They are abundanct in the Silica Shale.










Recommended Books for Fossils of Ohio:




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 link above.




A Sea without Fish: Life in the Ordovician Sea of the Cincinnati Region (Life of the Past)
Life of the Past series: Richard Arnold Davis, David L. Meyer
Copyright 2009, Indiana University Press

This book gives a comprehensive view of life in the Ordovician seas. This wonderful introduction to the geology and paleontology of life in Ohio 450 million years ago is full of illustrations. If you have ever wondered what exactly the Ordovician of Ohio and the surrounding states looked like, this is your window!





Ohio Rocks!
By Albert B. Dickas
The author, a personal acquaintance of mine, is a Geologist that grew up in Ohio. His book is filled with beautiful pictures and wonderful information about Ohio's most interesting geologic sites. He does a great job writing these type of books. I recommend this book for anyone who lives in or is curious about Ohio's interesting geologic past.



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