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RE: Arctometatarsalia



Jaime Headden wrote:
 
> This is the problem of
>apomorphy-based definitions ... they only work if the phylogeny holds it
>to be true, and not convergent, and you have to be absolutely _sure_ the
>feature is part of a monophyletic group. 

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, 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.


Tim


------------------------------------------------------------ 

Timothy J. Williams 

USDA-ARS Researcher 
Agronomy Hall 
Iowa State University 
Ames IA 50014 

Phone: 515 294 9233 
Fax:   515 294 3163