Ed Yong in The Atlantic:
For most of my life, I’ve believed that the dinosaurs fell into two major groups: the lizard-hipped saurischians, which included the meat-eating theropods like Tyrannosaurus and long-necked sauropodomorphs like Brontosaurus; and the bird-hipped ornithischians, which included horned species like Triceratops and armored ones like Stegosaurus. That’s how dinosaurs have been divided since 1887. It’s what I learned as a kid. It’s what all the textbooks and museums have always said. And according to Baron, a Ph.D. student at the University of Cambridge, it’s wrong.
By thoroughly comparing 74 early dinosaurs and their relatives, Baron has radically redrawn the two major branches of the dinosaur family tree. Defying 130 years of accepted dogma, he splits the saurischians apart, leaving the sauropods in one branch, and placing the theropods with the ornthischians on the other. Put it this way: This is like someone telling you that neither cats nor dogs are what you thought they were, and some of the animals you call “cats” are actually dogs.
More here. [Thanks to Ali Minai.]