Harry Govier Seeley gave us something that neither Huxley, Cope nor the infamous Marsh could (but this was not from a want of trying). In 1887 H.G. Seeley gave us the lasting major division within Richard Owen's tribe of beasties, giving us the saurischian and ornithischian dinosaurs. You have already met the tooth and claw of the saurischia ('lizard-hipped') that ultimately gave rise to all birds today. Now this is the rub, the ornithischian ('bird-hipped') dinosaurs have nothing to do with birds, other than being the sister group to the saurischia that did...confused? When folks say, 'Whats in a name', maybe here hindsight would have made Seeley chuckle. His division is robust, but the names often confusing, given each groups evolutionary products...sadly zero for the ornithischian dinosaurs post-Cretaceous. One thing about this group, if you visit the AMNH in New York, you'll get to see some of the most important ornithischian fossils from north America. Here is a brief tour of the said gallery.