As usual for 1970's dinosaur polyphyly proposals (and BAND proposals), Thulborn never addresses which non-dinosaurian taxa are most closely related to theropods, sauropodomorphs or ornithischians. This leaves his hypothesis untestable.
This is something that mystifies me. What's the use in chipping at the consensus if you don't have an alternative to express? If we were to accept, say, that the sister-group relationship between saurischians and ornithischians is poorly supported, we'd still think they're sisters till he presents a better supported arrangement.
-- Andreas Johansson
Why can't you be a non-conformist just like everybody else?