Behind the fossilized teeth, bones, and claws displayed in the National Museum of Natural History’s new Fossil Hall is the story of two men and a nasty feud. During the paleontology boom of the late 1800s, scientists O.C. Marsh and Edward Cope went from good friends who named species after each other, to the bitterest of enemies who eventually ruined each other's lives and careers. Come for the dinos, stay for the grudges.