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Re: definition of dinosaur



Norm King (nking.ucs@smtp.usi.edu) asks:

> Have we really gotten away from grade-based taxa when we say that the 
> Maniraptora, for example, have: "ulna bowed posteriorly; metacarpal III 
> long and slender;", etc.?

You have to remember to make a distinction between *definition* of a
taxon and *diagnosis* of a taxon.  Diagnoses may change, but in
principle definitions do not.  What a phylogenetic taxonomist would
stress to you is that definitions of taxa do not refer to grades
because the definition is dependent only upon phylogeny (e.g. the most
recent common ancestor of _Iguanodon_ and _Megalosaurus_ and all of
its descendents).  Since the "scars" of phylogeny are character
states, we must fall back on character states (grades if you will) to
diagnose taxa.  For a good discussion of phylogenetic taxonomy I refer
you to:

 Author(s):      DEQUEIROZ K; GAUTHIER J
 Title:          PHYLOGENETIC TAXONOMY 
 
 Source:         ANNUAL REVIEW OF ECOLOGY AND SYSTEMATICS V0023  1992 pp. 449- 
                   480. 

As I previously said and contrary to George's claim, definitions of
taxa may be node based, stem based or even apomorphy based at least in
the system outlined by DeQueiroz and Gauthier.

-- 
Mickey Rowe     (rowe@lepomis.psych.upenn.edu)