For many years, dinosaurs were considered ponderous, overgrown monsters doomed from the start. However, a fundamental change in thinking occurred in the late 1960s when two Yale University paleontologists noted that many aspects of their anatomy and biology were much like those of warm-blooded creatures. Paleontologist Hans Sues of the National Museum of Natural History discusses the main researchers involved, the arguments behind the new thinking, and the impact on paleobiology.