In the spring of 1995, when I was only nine, my family and I took a day trip to the Falls of the Ohio State Park in Clarksville, Indiana. Located on the banks of the Ohio River, this area of 386-million year old fossil beds represents one of the largest naturally exposed Devonian fossil sites in the world. These fossil beds literally are part of the Ohio River, as during most of the summer months much of the beds are covered over by the river itself. Some fish have been found here, but the biggest stars of this Devonian wonder site are corals, trilobites, bryozoans, and brachiopods.

During the Devonian, the land that is now Indiana laid beneath a warm, tropical sea, and were located about twenty degrees south of the equator. The 220-acre area that now composes the Falls of the Ohio State Park was a coral reef-one of the largest fossil coral reefs known from anywhere in the world. During the height of its diversity, this reef was likely the home to thousands of different species of life. Today, over 600 different fossil species have been discovered there, including several type specimens.

In his 1993 article in Outdoor Indiana magazine, Troy McCormick describes the fossil layers at the Falls:

"During the 45 million year span of the Devonian Period, the oceans deposited layer upon layer of lime silt, sediments, and plant and animal remains. Of these deposits, five distinct fossil layers lie exposed at the Falls. The uppermost layer - or the youngest rock - is the Paraspirifer Acuminatus Zone, which contains fossils of brachiopods (including paraspirifers, a two-shelled animal similar to a clam); bryozoans (commonly called lace coral); trilobites; and some solitary, branching, and colonial corals.

"Experts call the second layer the Fenestrate Bryozoan-Brachiopod Zone. Named for the predominant fossils found there, this layer contains many of the same corals and brachiopods as the Paraspirifer Acuminatus Zone. Here one also can find crinoid stems in abundance. Crinoids are animals that looked like plants, sporting "roots" and "flowers." When the crinoid died, the body segments separated and fossilized, leaving small, doughnut-shaped segments. Prehistoric man used these very popular fossils, which are often called "Indian beads," to make necklaces.

"A six-inch-thick layer called the Brevispirifer Gregarius Zone follows, and contains fossils of brachiopods and gastropods (sea snails). The smallest horn corals, or cup corals, begin to appear here. One of the Falls' most unusual corals, called a stromatoporoid, first appears in this layer. Scientists haven't yet reached a verdict on exactly whether the stromotoporoid is a reef-building colonial coral or a sponge, but the creature played an important role in the makeup of the fossil bed.

"The Amphipora Ramosa Zone, commonly called the Cave Zone, attracts attention for reasons other than the matlike stromotoporoids or the branching corals. Pocket caves have developed here due to the powerful erosive powers of the Ohio River rushing across the rock. This zone occurs along the vertical cliffs of the river channel, where the cutting force of the river reaches its peak. When water and oxygen come into contact with the limestone, a weak carbonic acid forms and dissolves the limestone. This phenomenon, combined with freeze and thaw erosion and the sweeping power of the river, causes the bedrock to erode quickly and erratically, leaving shallow caves where the rock once lay.

"The oldest and most remarkable layer is the largest to be exposed. It bears the name Coral Zone because of its abundance of fossil corals - so many, in fact, that visitors find it difficult to walk on this layer without stepping on fossils exposed in the bedrock. Scientists, geologists, paleontologists, and curious explorers have flocked to the Falls Coral Zone since the 1790's. Explorers here often find upright solitary corals, branching corals, stromotoporoids, brachiopods, a colonial coral called pipe organ coral, another called honeycomb coral, and hexagonaria (known as "Petosky Stone" in Michigan). The largest of the horn corals (Siphonophrentis elongata) sits in this layer and approaches four feet in length. Some of the "coral heads" of the colonial corals measure six to eight feet in diameter!"

Despite this abundance of fossils, since the area is a state park, fossil collecting of any kind is prohibited. Instead, the visitors' center and park website list fossil sites where specimens can be legally collected for free.

During my visit, I didn't take many photos, as I was only nine, didn't have a camera, and didn't like fossils all that much then. Regardless, this is what I have.


Falls of the Ohio Fossil Beds


Mammoth and Shark Display


© 1997 brusatte@theramp.net

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