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Re: definition of dinosaur



I appreciate Tom and GO responding to my question.  Of course, I don't 
want to teach outmoded taxonomic thinking.  But a point Tom brought up 
has me back in my persistent cladistic haze:

[snip]

>We (i.e., phylogenetic taxonomists) WANT to
>leave behind grade-based thinking of taxa.  Taxa in this system are NOT
>defined by characteristics; they are soley defined by ancestry.

[snip]

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.?  Then, the Arctometatarsalia have: "elongate 
tibia and metatarsus; metatarsals deeper anteroposteriorly than 
mediolaterally;", etc. (from Tom Holtz's 1994 Jour. Paleo. paper).  Do 
those synapomorphies not represent grades, so that the taxa are 
recognizeable (within their clade) on the basis of the features 
mentioned?  It seems to me that "going up" the cladogram, more and more 
precise distinctions are added to those already specified, with each step 
analogous to a grade in the other taxonomic system.


*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*-*
Norman R. King                                       tel:  (812) 464-1794
Department of Geosciences                            fax:  (812) 464-1960
University of Southern Indiana
8600 University Blvd.
Evansville, IN 47712                      e-mail:  nking.ucs@smtp.usi.edu