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RE: Arctometatarsalia

On Tue, 26 Feb 2002, Williams, Tim wrote:

> Yep.  I think the tete-a-tete between Jaime and Mike superbly demonstrates
> (almost as well as Ken has) the problem with using apomorphy-based
> definitions.  Aside from the assumption of monophyly

I don't see how that's a problem if you specify that the trait must be
synapomorphic with that in a certain species or specimen.

> there's also the problem of differentiating incipient stages from
> secondary derivatives. This is especially acute in bird evolution - the
> semilunate carpal and sternal keel are good examples.

Now THAT I agree is a problem. (Not to mention the problem if you find a
basal avian that appears to go near the root of _Carinatae_ _sensu_
Gauthier & de Queiroz 2001, but it does not have the sternum preserved!
This sort of thing is actually a huge problem for their _Avifilopluma_,
which is based on presence of feathers.)

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