Re: Tetanurae

["T. Michael Keesey" <keesey@gmail.com>]

On 12/9/06, Tim Williams <twilliams_alpha@hotmail.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
> usage.

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
> qualifier.

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/