And really: those who have argued for a "thecodont" origin since the 1970s
(Tarsitano, Martin, etc.) argued for relationships with animals that
thecodont workers (Charig, Parrish, Chatterjee) would not consider
thecodonts at all!!
Considering avicephalans "thecodonts" was made possible by the absence of
tree-thinking. In precladistic times, all but maybe the real specialists on
any group didn't imagine a group as a twig, they imagined it as a blob on a
romerogram. Such blobs lack internal structure; the fact that no avicephalan
fits into the "thecodont" tree didn't matter because people simply didn't
think of it. At best, blobs on a romerogram consist of more blobs with
stippled lines between them; adding one more little blob for
*Megalancosaurus*, supported on a stippled line that originates from a
free-floating question mark, is no big affair (if only you believe that
*Megalancosaurus* has The Defining Feature, the antorbital fenestra).
I grew up with outdated books. I remember the precladistic ways of thinking
very well. :-)