 Later , Brown revised the phylogeny of Corythosaurus , and found that it was closely related , and possibly ancestral to Hypacrosaurus . The only differences he found between them were the development of the vertebrae , and the proportions of the limbs . During a study of <unk> <unk> in the 1920s , Alfred Sherwood <unk> proposed that the two orders of dinosaurs might have evolved separately , and that birds , based on the shape and proportions of their <unk> might truly be specialized ornithischians . He used both <unk> and Corythosaurus as a base model to analyze which theory is more likely true . He found that even though birds are thought of as <unk> , it is very plausible for them to have evolved their specific pelvic <unk> and anatomy if they evolved from <unk> like Corythosaurus . However , even though Corythosaurus does resemble modern birds in pelvic structure more than <unk> , birds are now thought to have descended from the latter . 
