Mike Keesey wrote:
>I realize Scott and David already know this, but I'll emphasize the point,
>anyway: _Tetanurae_ is a
>branch-based clade, so its basalmost members are probably virtually
>indistinguishable from the basalmost membes of the sister clade,
>_Ceratosauria_. Also, of course, _Tetanurae_ and
>_Ceratosauria_ are equally old. (This is true by definition; it doesn't
>matter whether coelophysoids are ceratosaurs or not.)
Right. Ceratosauria is defined to *include* _Ceratosaurus_, and Tetanurae
is defined to *exclude* _Ceratosaurus_. Thus, they have to be sister taxa.
We could conceivably recover a phylogeny in which traditional Ceratosauria
is paraphyletic, with coelophysids, dilophosaurids, ceratosaurids, and
abelisauroids as successive outgroups. In this case, abelisauroids would be
basal tetanurans!