Dan Stewart of the Missouri Geological Survey was researching clay deposits in the southern Ozarks in 1942 when he came upon 8-year-old Ole Chronister at his family’s creek near Glen Allen. Dan told Ole he was looking for clays that were as old as dinosaurs.
Ole showed Dan bones that his family had found when they were digging a well. Dan recognized them as dinosaur bones and talked the Chronister family into sending them to the Smithsonian. The scientist who examined them at the Smithsonian, Dr. Charles Gilmore, believed they were from a sauropod. In a paper published in 1945, Gilmore and Stewart named the dinosaur, Parrosaurus missouriensis. It would later be determined that this identification was not correct.
The bones remained with Dr. Gilmore for about a year before he died. The Smithsonian paid the Chronister family $50 for the bones. They used the money to purchase a cow.
More discoveries in this location had to wait for the 1970s when another student at Rolla was studying the Stewart and Gilmore's research. That student, Bruce Stinchcomb, later bought the site from Ole Chronister. As excavation work continued, Stinchcomb found teeth from the dinosaur which provided evidence that it was a hadrosaur, a duck-billed dinosaur. This dinosaur, Hypsibema missouriense, was named the official Missouri dinosaur in 2004.
Discoveries are still being made. A tooth from a young tyrannosaurus, crocodile bones and remains of turtles have also been found at the site.
Hypsibema missouriensis (pronounced /ˌhɪpsɪˈbiːmə mɪˌzʊəriˈɛnsɪs/); was originally described as a sauropod by Gilmore in 1945 within the genus Neosaurus in the Journal of Paleontology. Later that year by Gilmore and Stewart renamed it as Parrosaurus because the name Neosaurus that Gilmore gave to the specimen was already used to name a different dinosaur. In 1979 the Missouri dinosaur was transferred to another family called "Hypsibema" so it became Hypsibema missouriensis (also spelled Hysibema missouriense.) The original material found consisted of thirteen vertebrae from Ripley Formation (Late Cretaceous Period) in Bollinger County, Missouri.
The species is estimated to have had around 1,000 small teeth, weighed 3–4 short tons (2.7–3.6 t) (or around as much as an elephant today), stood 10 feet (3.0 m) tall at its back, and stretched about 30–35 feet (9.1–10.7 m) from head to tail. Hypsibema missouriense lived in what is now southeast Missouri during the Campanian age of the Late Cretaceous period. It was a herbivore, its teeth were more serrated than other hadrosaurs, an indicator that the vegetation of Missouri at the time was very coarse or tough.
It became the Missouri State Dinosaur in 2004. One of the few official state dinosaurs, bones of the species are the first known discovery of dinosaur remains in Missouri. Some of the bones found at the Chronister Dinosaur Site are housed in the Smithsonian Institution in Washington D.C.