In the 1960s, paleontologist John Ostrom began work on the theropod "Deinonychus". His findings, which were expanded upon by his student Robert T. Bakker, contributed to the Dinosaur Renaissance, a revolution in the study of dinosaurs. Of particular importance were a reevaluation of the origin of birds that showed them to be closely related to coelurosaurian dinosaurs, reappraisal of dinosaur physiology that suggested they were not the sluggish cold-blooded animals that they had long been assumed to be, and a recognition that dinosaurs formed a natural group.