Dinosaurs in Iowa

Did dinosaurs once live in Iowa? The simple answer is: “Yes, without a doubt!” Iowa has rocks like those where fossils have been found in nearby states. Surely dinosaurs didn’t stop at the state lines. However, the actual proof is limited to just a few fossils.

The Age of Dinosaurs

Dinosaurs ruled the land for about 170 million years, during the Late Triassic, Jurassic and Cretaceous periods. Close to 65 million years ago, a mass extinction ended the “Age of Dinosaurs.” The best evidence of dinosaurs in Iowa is found in rocks from the Cretaceous period.

Cretaceous Creatures

About 95 to 100 million years ago, the climate was much warmer. Iowa rivers drained to the west where there was a sea. Mud, clay and sand (sediments) carried in these ancient rivers sank to the bottom. Sometimes, the bones of an animal became buried within the sediments. There, the bones were protected. The sediments, and the bones inside, eventually hardened into rocks. Rocks from this time period are known as the Dakota Formation.

In 1928 the first dinosaur fossil of the Dakota Formation was found on the Missouri River bluffs near Decatur, Nebraska. This is only about one mile from the Iowa border.

The fossil was a piece of a femur (leg bone). It has not been completely identified. However, its features show that it was a large ornithopod. Ornithopods were two-footed, plant-eating dinosaurs. The femur likely came from an early hadrosaur. Hadrosaurs are the “duck-billed” dinosaurs. They were the most numerous and diverse group of dinosaurs at that time in North America.

Since then, other dinosaur fossils have been found in northern Kansas, eastern Nebraska, and Minnesota. They include more hadrosaur bones, three-toed ornithopod footprints, and partial skeletons of ten-foot-long, heavily armored ankylosaurian dinosaurs known as Silvisaurus.

In 1982 a piece of fossil bone was found in Guthrie County. The small fragment was discovered in Dakota Formation river gravels. To see if it came from a dinosaur, the piece had to be studied under a microscope. Then scientists could see that it had bone structure much like typical dinosaur bones. Finally, Iowa had a Dakota Formation dinosaur fossil of its very own.

Mosasaurs and Pterosaurs

During the later Cretaceous Period, the shallow sea covered western Iowa. Plesiosaurs (marine reptiles) swam through the waters in search of fish and other prey. Their fossilized bones have been found in the layers of shale and chalk that were once the bottom of this sea. Mosasaurs (giant sea lizards) and pterosaurs (large flying reptiles) were also common. Their fossils have been found in similar rock layers of the same age in nearby areas.

Occasionally a dead dinosaur would float out to sea and settle to the bottom. Hadrosaur and ankylosaur bones and teeth have been discovered in similar rocks in Minnesota, South Dakota and Kansas. This makes scientists believe these dinosaurs may have also lived in what is now western Iowa.

Dead Dinosaurs on the Move

Long after the dinosaurs were extinct, huge glaciers moved up and down Iowa. During the “Ice Age” (the last 2.5 million years), advancing glaciers gathered rocks from the northern Great Plains. As the glaciers melted, they dropped lots of these rocks in Iowa as gravel. Two dinosaur bones have been found in Iowa's glacial gravels. These are the best dinosaur fossils found in the state so far.

Charlie Gillette of Dickinson County found a dark-colored, three-inch fossil bone. He picked it out from a load of landscaping rocks that came from a nearby gravel pit. His uncle, Jack Neuzil was a retired educator and dinosaur fan. He thought the bone could be from a dinosaur. An expert later identified it as a tail vertebra, possibly from a hadrosaur.

Then a second dinosaur vertebra from Iowa came to light. Doris Michaelson of Bellevue read a newspaper article about dinosaurs in Iowa. She took a bone in to the Iowa Geological Survey. The bone had been found by her father, John Holdefer. Sometime in the mid-1930s, he picked up the fossil bone from a conveyer in a gravel pit near Akron in Plymouth County. The bone had been kept on a shelf. Sometimes, the family used it as a doorstop. That doorstop turned out to be a four-inch dinosaur vertebra, likely from a hadrosaur.

Luck of the dinosaurs

To discover dinosaur bones, you need to understand a region’s geology (where to look), have lots of patience (keep looking), and be a bit lucky. It’s only a matter of time before someone finds the next dinosaur fossil from Iowa. So keep looking!

By Brian J. Witzke. Used with permission from the Iowa Department of Natural Resources Geological Survey. Adapted from their Web site and original article in Iowa Geology 2001, No. 26, Iowa Department of Natural Resources.

 

 


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