In the early 1940s, farmers digging a well in Bollinger County, about 100 miles south of St. Louis, made an unexpected discovery: tail bones from a long, lost dinosaur. Now, paleontologists say they know what the rest of it looks like.

A team from Chicago’s Field Museum recently finished excavating what experts say is the fullest skeleton yet of a Parrosaurus missouriensis, a 30-foot-long, 3-ton plant-eater that roamed the area tens of millions of years ago when the state was on the eastern shore of a sea cleaving North America in two.

The operation marks a turning point in an 80-year effort to understand a rare patch of Cretaceous Period rock east of the Great Plains, where much from the time of the dinosaurs has been weathered away. It sets the record straight on a creature celebrated as Missouri’s state dinosaur, gives scientists tools to discover more about the environment then — and has paleontologists hopeful they’re just scratching the surface.

“We’re getting a look at the ecosystem 77 million to 90 million years ago,” said Peter Makovicky, a paleontologist at the University of Minnesota who oversaw the excavation. “And there’s no reason to think there isn’t much more to be collected in the coming years.”

It’s been a long time coming. The bones were discovered around 1942 on the Chronister family’s farm near the small town of Marble Hill. A state geologist talked the Chronisters into sending the bones to the National Museum in Washington, part of the Smithsonian Institution. Paleontologists there declared them part of a long-necked sauropod, like the Brontosaurus that adorns the Sinclair Oil logo. The museum paid the Chronisters $50 for the bones.

Lulu Chronister spent the money on a cow. And that was that. There was little discussion of the site in the public record for the next 40 years.

Then, in 1982, the Chronisters sold the farm to a geologist, and digging restarted in earnest. In 1989, they unearthed a tooth from a relative of Tyrannosaurus rex and, in the 1990s, prehistoric turtles.

About a decade later, self-taught fossil hunter Guy Darrough, now curator of the Ste. Genevieve Museum Learning Center, uncovered a second Parrosaurus — a juvenile.

It wasn’t all there: An initial excavation found only parts of the skull and the upper portions of the limbs. But there was enough to challenge the 1945 classification of the creature: It appeared less like a long-necked sauropod and more like a duck-billed hadrosaur. Darrough said the sharper, serrated teeth alone gave it away. Sauropods have thin, peg-like teeth.

“It was nothing like a sauropod jaw,” Darrough said.

In 2017, at Darrough’s urging, the Field Museum began its own excavation. And for the past four years, they’ve been digging up parts of a third Parrosaurus. This skeleton was better. It had a fuller skull, set of limbs and trunk bones than the juvenile. And it revealed something new about the species, Makovicky said:

It lacked the crests of later hadrosaurs, had bigger teeth — and the kicker: an unexpected 3-inch thumb spike on its front feet, possibly for defense or for males to use in sparring to impress females.

The bones will eventually go to Chicago for further research. Makovicky said tests could be run on the dinosaur’s teeth to get a better sense of the temperatures it lived in and whether the area was wet or dry. He’s also hoping to get some rock samples from the site to better pin down its age.

“We can start asking some broader questions about the environment,” he said.

Darrough said he’s hopeful the Field Museum will also re-create the Parrosaurus skeleton for public exhibit and expects to get his own copy. In the meantime, he started work getting the juvenile skeleton ready for viewing at the museum in Ste. Genevieve. He already has a name for the exhibit — “Tale of a Tail” — and plans to make 3D prints of the leg with the spiked thumb.

“Kids will be able to shake hands with the Missouri dinosaur,” he said.

Darrough and Makovicky said they’ll also keep digging. They recently found the tail of another Parrosaurus missouriensis — which makes four — as well as some crocodilians and more than a dozen ancient turtles, and they’re optimistic they’ll find more dinosaurs. The Tyrannosaur tooth has them hoping for a meat-eater.

“Even just a jaw,” Darrough said, “would be phenomenal.”

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