This new analysis of dinosaurs and their near relatives, published today in the journal Nature, concludes that the ornithischians need to be grouped with the theropods, to the exclusion of the sauropodomorphs. It has long been known that birds (with their obviously ‘bird-like’ hips) evolved from theropod dinosaurs (with their lizard-like hips). However, the re-grouping of dinosaurs proposed in this study shows that both ornithischians AND theropods had the potential to evolve a bird-like hip arrangement- they just did so at different times in their history.
http://www.nature.com/nature/journal/v543/n7646/full/nature21700.html
http://www.nature.com/news/dinosaur-family-tree-poised-for-colossal-shake-up-1.21681
http://www.cam.ac.uk/research/news/new-study-shakes-the-roots-of-the-dinosaur-family-tree
http://www.sciencemag.org/news/2017/03/t-rex-gets-new-home-shakeup-dino-family-tree