For most of the last three decades of the nineteenth century paleontologists Edward Drinker Cope (1840-1897) and Othniel C. Marsh (1831-1899) engaged in a running battle over dinosaur discoveries in the American West. Cope, a professor at the University of Pennsylvania, was the paleontologist attached to Ferdinand V. Hayden's geological survey, with which he spent eight months of every year unearthing fossil vertebrates (animals with spinal columns). He discovered more than twelve hundred previously unknown genera or species, and The Vertebrata of the Tertiary Formations of the West (1883), his report on the Hayden survey, was soon baptized "Cope's Bible." (In geological time the Tertiary period, from five million to sixty-five million years before the present, begins with the extinction of the dinosaurs and ends before the appearance of the earliest humans; it is the first period of the Cenozoic era.) Marsh, who...