Iowa Public Television


Devonian Fossil Gorge, Iowa City, Iowa

Did you know that Iowa was once part of a large continent south of the equator, covered by warm, shallow seas? The sea beds are still here and Dan Kaercher explores the ancient fossil gorge in Johnson County.

Did you know that Iowa was once part of a large continent south of the equator covered by warm shallow seas?  We're not that far south but the sea beds are still here.  This may look like an ordinary rock bed but it is actually a 375 million year old sea floor.  The fossils found here predate dinosaurs by 200 million years.  With me is Terry Escher who is a Park Ranger for the U.S. Army Corp of Engineers and she gives lots of tours of this Devonian fossil bed.  Terry, the shear age of this site and its history is just incredible.  Give me a little perspective will you?

 Terry Escher:  Well, just like you said before, it is before dinosaurs.  Way before dinosaurs.  I tell the kids they will not find any - there will be no dinosaur bones down here.  It was the Devonian Age, the "Age if Fishes". 

 Dan Kaercher:  To really help me get a better sense of the "Age of Fishes", I took a 20 minute jaunt to Iowa City and the University of Iowa's Museum of Natural History where there is a permanent display of a Devonian sea bed. 

 Ashlee Gloede:  Well, this is 360 million years ago and our model here is just a baby.  So, this is a Dunkleosteus and they could get the size of a school bus.  So we call him Dunkey for short because Dunkleosteus is a pretty hard name for kids to say. 

 Dan Kaercher:  Ashlee says lots of school classes visit this exhibit before going to the fossil gorge so they can better visualize the sea life.

 Ashlee Gloede:  It gives you a better visual.  You can see here we have crinoids.  At the gorge you will find just part of their stem.  So, it will look like little tiny cheerios everywhere.  And down here at the bottom we have some trilobites and at the gorge you will just see imprints of maybe their tail or parts of their body. 

 Dan Kaercher:  While it is great to see the big picture of life as it was in the gorge, I really enjoy seeing the actual fossils. 

 Terry Escher:  And just sometimes just like somebody is looking for a contact lens, I say you have to stop and look. 

 Dan Kaercher:  Oh yeah.

 Terry Escher:  And then you can see a little crinoids’ stem pieces, stem plates.  There are some over there.  But you kind of have to stop and look for a few minutes, a few seconds anyway.  There is a really good example of the colonial coral hexagonaria. 

 Dan Kaercher:  Unbelievable.  I had a guide with me but there is informational signage and a brochure to make it easy to do a self-guided tour. Here is the number five. 

 Terry Escher:  A really large stem from a crinoid.  Some people call them sea lilies but again they are an animal related to starfish.  But most of them won't be that big.  This is kind of a cool one here.  Unusual.  Brachiopod here.  It is one of the larger ones here.  Better specimens.  Brachiopods - they were stationary.  They were attached to the ocean floor. 

 Dan Kaercher:  This ocean floor part of Iowa's geologic history wasn't revealed until after the 1993 floods.  The Coralville Dam couldn't hold back all the rain water and the excess flowed over the emergency spillway for 28 days.  The water scoured up to 15 feet of soil.  Then in 2008 flood waters again swept through here widening the gorge and revealing even more fossils. 

 Terry Escher:  Each event, you know it was a very bad thing.  There were a lot of bad things happening all around the state.  But when the water went down we actually got something good out of it.  We had a little silver lining in the cloud.  And down here it is so unique because it is all laid out at your feel.  Most of the time when geologist/paleontologists are studying rocks it kind of - and layers.  But down here it is just all at your feet. 

 Dan Kaercher:  Terry says one of the larger finds after the '93 flood was part of the Dunkleosteus fish we mentioned earlier.  That discovery, part of the neck plate, is on display at the Coralville Lake Visitor's Center. 


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