Prehistoric creatures abound in Iowa roadways

MCZWachsmuthCrinoidDid you know the limestone that goes into many Iowa roadways is full of prehistoric creatures? Throughout millions of years of geologic history, when present-day Iowa was covered by oceans, sea creatures were everywhere. Fossilized fragments of sea creatures were left behind in the rocks that were deposited by these oceans.

One of most prominent groups of fossils are the crinoids. Also referred to as sea lilies, researchers say the fossils have survived about 500 million years of Earth history and crinoid skeletal fragments make up a significant portion of Iowa's limestone deposits. This limestone is used for road base, as agricultural lime, as building stone, and as a component in concrete.

Sea lilie
An artist’s rendering of sea lilies

Crinoids are actually animals related to starfish. They lived anchored to the seafloor by flexible, rooted stems. One area rich in crinoids is Southeast Iowa, particularly around the Burlington area.

When it came time to replace the U.S. 61 bridge over Flint Creek north of Burlington, Kimball Olson, our resident bridge aesthetics expert, began researching the area to come up with a concept for the bridge. When he uncovered the history of crinoids in the area, the connection to the new bridge was made.

Olson said, “When I started looking into the history of the area, it was appropriate to evoke the long geologic history in the bridge design. When I visited the site, every piece of light-colored rock I picked up was chock full of crinoids.”

limestone cliffs
The limestone cliffs near the bridge are full of the fossils being depicted on the bridge.

He then sought out expertise from Iowa DOT geologists Adriana Schnoebelen and Brian Gossman to confirm what he saw in the rocks and in the area’s history. Olson said, “We’ve been building bridges out of these animals for years. It just makes sense to give people an idea of the history.”

That tie to the history of the area is especially significant for the U.S. 61 bridge, as it will connect to the Flint River Trail, providing pedestrian and bicycle facilities on the bridge. The bridge is also less than a mile from Starr’s Cave Nature Center and the exposed limestone cliffs along Flint Creek where crinoids are prevalent.

WachsmuthThat long history of crinoid fossil collection in the Burlington area dates to the 1800s when a German immigrant merchant named Charles Wachsmuth encountered health issues. His doctor prescribed fossil collecting to improve his health. The fossils so intrigued Wachsmuth that he became world-renowned for his collections. Pieces from Wachsmuth’ s collection ended up in prestigious places like Harvard University, where he curated the collection for a period of time, and the Smithsonian Institute. 

While researching the crinoids and Wachsmuth, Olson reached out to Harvard and the Smithsonian to see if there was a possibility for collaboration. Both entities were on board with the idea and loaned the Iowa DOT “Wachsmuth” fossils. After Schnoebelen and Gossman contacted Iowa State University’s Department of Geological and Atmospheric Sciences, the Harvard fossil was sent to ISU where it was scanned in three dimensions.

Harvard crindoid final scan
3D scan of one of the fossils




Olson said, “For the Smithsonian fossil, they graciously did their own 3D scan on our behalf and sent that to us to have a model made. The two scans were then sent to a company in Belgium that provided 3D models of the fossils.”

Inspired by fossils and the idea of ocean waves in ancient Iowa, Olson began working with bridge designer Logan Wells on implementing the ideas on the U.S. 61 bridge.

“With the unique elements we wanted to incorporate into the bridge, there were some challenges for construction,” said Wells. “We wanted to use self-weathering steel plates with wave patterns cut into them as railings for the bicycle/pedestrian part of the bridge. Since we have never used this particular material in this way before, we experimented with various thicknesses of steel to make sure the barriers would be safe, but not too heavy.”

3-D models
These 3D models, made from the scans of the Harvard and Smithsonian fossils, will be used to cast images on the piers at the ends of the bridge
Side rail wave pattern
This artist’s rendering shows the illusions created by the unique railings.)



In addition to the side rails that give the feeling of being underwater by casting shadows across the trail at certain times of day, each end of the bridge will be graced with a replica of one of Wachsmuth’ s fossils. The contractor will take the models that were 3D-printed and cast them into pillars beside the trail.

Fossil on monolith View 2
This artist’s rendering shows what a pedestrian will see on the bridge.

“This project ties so many things together and makes the bridge unique to the Burlington area,” said Olson. “When the bridge is completed later this summer, it will provide motorists, bicyclists, and pedestrians with a safe way to take a fresh look at the history that surrounds them.”

Special thanks go to Harvard University’s Museum of Comparative Zoology and the Smithsonian Institution’s National Museum of Natural History for their significant contributions to this project.


Brilliant! So happy to see our bridges becoming more than an ugly chunk of concrete. I will be looking forward to crossing it and actually seeing these design elements.

Great collaboration everyone! Interesting article to read.

Very interesting. I look forward to seeing this bridge.

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