Comment on Basal Marginocephalia Snouts by Qilong
Wow, this makes it hard to argue heterodontosaurs are basal ornithischians. The snouts at least are dead ringers for the pachycephalosaur. Also makes the homology of the Tianyulong/Psittacosaurus quills much more palatable.
Various tests of the position of heterodontosaurs find them in different places, with the most recent putting them very basally. It's hard to take that just by looking at this, but then, this is based on just half of the skull. When heterodontosaurs, basal pachys and basal ceratopsians all look like the same "grade", it makes you think they are close to one another in morphospace, even if heterodontosaurs were basal to Cerapoda, basal to Neornithischia, or within Marginocephalia or its sister taxon (depending on the definition).