 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 dinosaurian ilia in the 1920s , Alfred Sherwood Romer proposed that the two orders of dinosaurs might have evolved separately , and that birds , based on the shape and proportions of their ilia might truly be specialized ornithischians . He used both Tyrannosaurus and Corythosaurus as a base model to analyze which theory is more likely true . He found that even though birds are thought of as saurischians , it is very plausible for them to have evolved their specific pelvic musculature and anatomy if they evolved from ornithschians like Corythosaurus . However , even though Corythosaurus does resemble modern birds in pelvic structure more than saurischians , birds are now thought to have descended from the latter . 
 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 <a href='uninflect' title='1'><mark>were</mark></a> the development of the vertebrae , and the proportions of the limbs . During a study of dinosaurian ilia in the 1920s , Alfred Sherwood Romer proposed that the two orders of dinosaurs might <a href='been_done' title='2'><mark>have</mark></a> evolved separately , and that birds , based on the shape and proportions of their ilia might truly be specialized ornithischians . He used both Tyrannosaurus and Corythosaurus as a base model to analyze which theory is more likely true . He found that even though birds are thought of as saurischians , it is very plausible for them to <a href='been_done' title='3'><mark>have</mark></a> evolved their specific pelvic musculature and anatomy if they evolved from ornithschians like Corythosaurus . However , even though Corythosaurus <a href='uninflect' title='4'><mark>does</mark></a> resemble modern birds in pelvic structure more than saurischians , birds are now thought to <a href='been_done' title='5'><mark>have</mark></a> descended from the latter . 
Later , Brown revised da phylogeny of Corythosaurus , and found that it was closely related , and possibly ancestral to Hypacrosaurus . Tdaonly differences he found between em was thdaevelopment of the vertebrae , and thedaoportions of the limbs . durin a study of dinosaurian ilia in the da0s , Alfred Sherwood Romer proposed that the two orders of dinosaurs mite done evolved separately , and that birds , based on the sdae and proportions of their ilia might truly be specialized ornithischians . He used both Tyrannosaurus and Corythosaurus as a base model to analyze which theory is more likely tru . He found dat even though birds r thought of as saurischians , it is very plausible for themo done evolved their specific pelvic musculature and anatomy if they evolved from ornithschians like Corythosaurus . However , even though Corythosaurus do resemble modern birds in pelvic structure more than saurischians , birds are now thought to done descended from the ladar .