Dragon Teeth

"William Johnson is a student at Yale college. Reckless and risk-taking, he makes a bet with his rival, a student named Marlin, that he will go west the following summer. Johnson then attempts to join Prof. Othniel Charles Marsh on his yearly expedition fossil hunting in the Badlands. Marsh is reluctant until Johnson lies, saying that he is a photographer. Johnson learns to take photographs and leaves with Marsh at the appointed time. However, upon learning of Johnson's Philadelphia background, Marsh begins to suspect that he is a spy for Edward Drinker Cope, a rival paleontologist. Marsh abandons Johnson in Cheyenne." (cited from the first paragraph of the Wikipedia synopsis)