Fossil-bearing sites containing predominantly mastodon, Mammut americanum, remains were discovered west of the Mississippi River on the Osage River in Upper Louisiana only a few decades after the discovery by Longueuil of similar remains at Big Bone Lick in Kentucky. The first excavations were conducted in the 1790s by Pierre Chouteau, a fur trader and member of the founding family of St Louis. Chouteau’s work was documented by several early travelers, including Georges-Henri-Victor Collot and later by Meriwether Lewis and William Clark, among others. It was from Chouteau’s excavation that the first mastodon molar from west of the Mississippi River reached Baron Georges Cuvier in Paris, having been sent from Philadelphia by Benjamin Smith Barton. Early nineteenth-century travelers continued to mention the Osage River locality and, by 1816, William Clark displayed fossil specimens in his St Louis Museum. By 1840 the indefatigable fossil collector and museum entrepreneur, Albert C. Koch, began extensive digging in the Osage River basin along with sites in the Bourbeuse River valley and at Kimmswick along the Mississippi River in Missouri. Koch’s extensive collection of mastodon bones enabled him to assemble a mounted specimen that he named the Missourium, an exaggerated and poorly reconstructed skeleton that was later identified and properly reassembled by Richard Owen at the British Museum. The specimen was later purchased by the trustees of that museum. The publicity surrounding Koch’s work stimulated a veritable ‘bone rush’ to the Osage River in the years preceding the Civil War, with some of the fossils making their way into the collections of the American Philosophical Society and the Academy of Natural Sciences in Philadelphia. Following the Civil War, interest shifted to the Mississippi valley and the Kimmswick site just south of St Louis, where ongoing excavations became an attraction during the 1904 Louisiana Purchase Exposition in St Louis. C. W. Beehler, a St Louis resident, was responsible for the work, a venture that attracted scientists from the Smithsonian as well as other institutions. While none of the principals in the early exploration of fossil sites in Missouri had scientific training, the fact that their collections were passed on to scientific practitioners in Philadelphia, Washington, Paris, and London contributed to the expanding body of information that aided in the development of the field of vertebrate paleontology.