T. Michael Keesey wrote-
I guess the real question is which taxa you consider to be "essentially" ornithopodan. A node-based definition of something like clade(_Hypsilophodon_ + _Iguanodon_) for either "Ornithopoda" or "Euornithopoda" might be more aesthetically pleasing, and allow for an outside possibility of including marginocephalians.
Mickey Mortimer