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On 12/9/06, Tim Williams <email@example.com> wrote:
In this situation, there is a difference between "stable" and "immutable".
I think a given clade can still be "stable" while new taxa are added and old
taxa are removed.
I don't see the distinction. Can you give an example?
I really think the only thing that can be stabilized is definition.
Stabilizing content means asserting something about phylogeny.
What's important in preserving "taxonomic stability" is
to prevent the taxonomic content from diverging too far from historical
Well, as pointed out earlier, some abelisaurs were included in
_Tetanurae_ originally. I would also like to point out that
_Tetanurae_ is not a co-opted traditional taxon--it is a
phylogenetically-defined clade and has been from its inception. Thus,
there's no "traditional concept" to conform to--it is everything
closer to birds than to _Ceratosaurus_, period.
For example, Yates (2007) re-defined the branch-based clade Sauropoda such
that _Plateosaurus_ was replaced by _Melanorosaurus_ as the external
This is a different matter, since _Sauropoda_ was coined outside of
phylogenetic nomenclature, and is being brought "into the fold".
Arguably, the original phylogenetic definition was simply not very
good at capturing the historical usage. For _Tetanurae_, on the other
hand, the original phylogenetic definition *is* the historical usage.
If abelisaurs are tetanurans, I want to know about it--I don't want it
to be covered up by a new definition of _Tetanurae_.
T. Michael Keesey
The Dinosauricon: http://dino.lm.com
Parry & Carney: http://parryandcarney.com
ISPN Forum: http://www.phylonames.org/forum/