In the late 19th century, brash young scientist Edward Copeland pursues a vendetta against Osgood Marshall, chair of Yale's paleontology department. The two men's feud begins when Osgood steals an important find from the less-experienced Edward. Osgood goes on to humiliate Edward front of the scientific community by sabotaging Copeland's unveiling of a mounted dinosaur skeleton. Edward vows revenge, and runs off with Osgood's daughter to the West. Edward hopes to find the evidence he needs to discredit Osgood by raiding his dig sites in New Mexico. With the help of a drunken, pre-teen guide, he manages to do just that. But Osgood Marshall has more than a few tricks up his sleeve as well, and Edward will have to confront the professor, cowboys, Indians, two dead horses, and a crate of dynamite in order to get what he wants. Inspired by actual events, When Dinosaurs Roamed the Earth is a testament to the greatness of science as well as the petty hearts of men.