Among the "objects worthy of notice" listed by Thomas Jefferson in his instructions to Meriwether Lewis were "the remains or accounts of any [animals] which may be deemed rare or extinct," such as the mammoth and the "megalony"X--Jefferson's hypothetical "enormous animal incognitum."1
Meriwether Lewis, his innate curiosity combined with an exceptional capacity for concentration and analysis, learned as much as Jefferson and Caspar Wistar could teach him about the new science which nearly fifty years later would be called paleontology. En route down the Ohio River in the autumn of 1803, he made a short side trip to Big Bone Lick, near Covington, Kentucky, which had recently been excavated by a Cincinnati physician, Dr. William Goforth. Lewis wrote Jefferson the details of his visit, promising to send him a tusk of a mammoth, two "grinders," and several other specimens. Unfortunately, the shipment went astray. In 1807 Jefferson hired William Clark to supervise a new excavation there.
During the expedition, however, the men found only a few fossils. On May 30, 1804, they reportedly picked up a "petrification" of some sort in the vicinity of Tavern Cave, in Missouri, but it has long since been lost or misplaced. And on July 25, 1806, Clark found what was probably a dinosaur bone in the bank of the Yellowstone River in the Cretaceous Hell Creek sandstone formation near Billings, Montana, but it too has disappeared. Clark guessed it was the rib of a prehistoric fish; the name dinosaur was not to enter scientific vocabulary until 1842.
1. Letters of the Lewis and Clark Expedition with Related Documents, 1783-1854; 2nd ed. (2 vols., Urbana: University of Illinois Press, 1978),16, 126-32.