One fine day last year, I finished up a module in Hong Kong University's Dinosaur Ecosystems course about Saurichians and Ornithischians and then went to the news. There, to my surprise and slight discontent, was an article announcing everything I just learned was wrong.
The Clade Ornithoscelida had been erected which violently yanked theropods from Saurischia and placed them alongside ornithischians. This left poor old Sauropods alone with herrarosaurs. At first it made no sense, but then a picture formed in my head of evidence supporting it. The proto feathers of Psittacosaurus make more sense if they are grouped with Theropods, and both tend toward bipedalism. And with such a dramatic result, I assumed the reasoning was mighty well vetted.
Fast Forward to few days ago as I take a dinosaur 101 course with University of Alberta. It begins the explanation for the placement of dinosaurs and their relations. Then it explains ornithischians and.... Wait a minute! You can’t put theropods next to sauropods like that, we just learned that was wrong! Wait, did we? Has the scientific community discredited this revision, is it arguing it, or is it simply sluggish to implement it?
@Troodon maybe you could shed some light.