Guy Darrough told KTVI News that he alerted both organisations to the dinosaurs after unearthing a juvenile not far from St Louis.
The fossil researcher said he could not “imagine anything that’s more impressive than what we’ve discovered here,” and that it was a “world-famous discovery.”
Adult and juvenile fossils of the Parrosaurus missouriensis, a genus of a dinosaur known as duck-bills, were afterwards found at the undisclosed location by Field Museum and Sainte Genevieve researchers.
Duck-bills were herbivores that could reach 25 to 30 feet in length, and had a duck beak-shaped mouth and snout, for which the species was named.
The species is also considered the official dinosaur of Missouri.
Mr Darrough added: “I eventually talked to Pete Makovicky, curator of dinosaurs at the Field Museum. He came down and looked and said, ‘Yeah, you guys got dinosaurs.’”
Mr Makovicky described the location of the discovery as “a really remarkable site” and “one of the best dinosaur localities east of the Great Plains” when speaking with KTVI.
KTVI News reported that the original property owners reportedly found bones in the 1940s, but no research was carried out after that.
It is the first time a Parrosaurus missouriensis has been found in the US, and the finding was described as a new species of the duck-bill.
The fossilised remains of the juvenile found by Mr Darrough are set to go on display when the Genevieve Museum Learning Center officially opens, it confirmed on Facebook.