Several early studies suggested that heterodontosaurs were primitive ornithischians. The main hypothesis in recent years has put heterodontosaurids in as basal ornithopods. However, others have suggested that heterodontosaurs share a common ancestor with Marginocephalia (ceratopsians and pachycephalosaurs). This has support from some recent studies. A clade containing heterodontosaurs and marginocephalians has been named Heterodontosauriformes. Heterodontosaurs may even be basal to both ornithopods and marginocephalians. In 2007, a cladistic analysis suggested that heterodontosaurs are basal to all known ornithischians except "Pisanosaurus", a result that echoes some of the very earliest work on the family.