John H. Ostrom’s expeditions to the Bighorn Basin of Wyoming and Montana in the 1960s resulted in discoveries and research that would change long-held concepts in paleontology. This fiftieth-anniversary edition of his now well-known description of the type specimen of Deinonychus antirrhopus revisits the work that redefined theropod dinosaurs as the intelligent, agile, and gregarious ancestors of modern birds and led in the late twentieth century to a renaissance in the study of dinosaurs and the evolution of flight.