Things really began to break loose in the 1800s, with the opening of the Western Territories of North America to paleobiologists-most especially Othniel Marsh and Edward Drinker Cope. Animatronic dinosaur Engaged in a bitter feud-almost from the beginning of their paleontological careers-they competed in opened multiple quarries in the Late Jurassic Morrison Formation, quarries with wonderful names like Bone Cabin and Freeze Out Hills. From them came good skeletons of big Allosaurus, horned Ceratosaurusf and small Ornitholestes. The finding of these new dinosaur skeletons had two effects. First, dinosaurs became immensely and permanently popular with the American public, which still associates them with the frontier days. Second, the debate on the evolutionary significance of dinosaurs was intensified, with some workers suggesting that dinosaurs were ancestral to birds and warm-blooded.
By the late 1800s and through the 1920s, when the Great Depression and World War II put a damper on things, dinosaurs were being discovered in abundance in other formations in western North America, formations with more fantastic names: Lance, Hell Creek, Two Medicine, Oldman, and others. These were largely Late Cretaceous forms, among them gigantic Tyrannosaurus, its somewhat smaller relative Albertosaurus, the ostrich-mimicking Ornithomimus, and sickle-clawed Dromaeosaurus.
In a more exotic locale, Mongolia, the famous American Mu¬seum Expeditions of the twenties led by Roy Chapman Andrews found three small Late Cretaceous theropods, ones that would later become important to the question of bird origins: sickleclawed Velociraptor and Troodon, and the very bizarre headcrested Oviraptor.