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On 12/8/06, Tim Williams <email@example.com> wrote:
True. _Abelisaurus_ and _Carnotaurus_ were both described in 1985, a year
before Gauthier coined Tetanurae. The other abelisaurids known at the time
were all poorly known and misclassified: _Indosuchus_ & _Indosaurus_
(carnosaurs), _Majungatholus_ (pachycephalosaur!), and so on. Since c.1990,
abelisaurids have almost always been recognized as ceratosaurs (or
ceratosauroids), and never as tetanurans. Ditto for noasaurids. I know
none of this is news to anyone, least of all Tom; but I think the above trip
down memory lane is an argument in favor of "stability of content".
Stability of content is not necessarily a good thing. After all, no
taxon can have stable content unless we absolutely know every member.
If abelisaurs came out closer to neotetanurans than to _Ceratosaurus_,
then the statement "abelisaurs are tetanurans" would convey something,
namely that their position changed from what we thought before.
Changing the definition of _Tetanurae_ every time new results are
found conveys a false sense of stability--the findings are changing,
but the terminology isn't.
Besides, I *understand* _Tetanurae_ to be a branch-based clade with
neotetanurans internal and _Ceratosaurus_ external. I don't understand
it to be some preset composition list. Changing the definition causes
T. Michael Keesey
The Dinosauricon: http://dino.lm.com
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