Peter M. Galton is a British paleontologist working in the United States; he is known for naming several dinosaurs, including the Dracopelta and Bugenasaura, and for naming the order Herrerasauria. With Robert Bakker, he championed the cladistic theory to show that birds are modern-day dinosaurs. Galton showed that the Hypsilophodon did not live in trees; that hadrosaurs did not drag their tails (the tail was used as a counter-balance for the head); and that some dinosaurs, such as the pachycephalosaurs, would butt their heads together like modern-day rams.