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Re: A sure sign you're launching an unscientific discussion (was Re: Taxonomic philosophy)

Ken Kinman wrote (and Tracy Ford posed similar sentiments):

Well, I suspect this is the first time on this list that there has been
a serious discussion of whether Aves should be given Class status (correct
me if I am wrong).

...and Chris Brochu responded quite well, but never summarily stated the heart of this issue, which is: "What is a Class?" That is, what features of a group make it a class? What features make an Infraclass, or and Order, or a Phylum? Is it number of members? Clearly not, as others pointed out that, in Linnaean systematics, there are many "orders" (etc.) with only one member and others with thousands. Essentially, it boils down to "degree of difference." Well, if so, then we need to have explained the criteria by which those "degrees" are calculated. As explained previously by many persons, character possession becomes problematic for this as new taxa with varying character possession are found. Dr. Kinman (unless I am grossly misinterpreting him here) believes that "Class" can be applied to Aves, so I ask "why?" What features of Aves make it a "Class?" Why not an Infraclass, Order, Phylum, Subkingdom, or any other rank? If you can argue that Aves deserves the rank of class, then we need to know what Aves has that makes them worthy of that one, but not other, ranks. Following that, of course, we need to know precisely which taxa get put into Aves and which don't (as they do or do not possess whatever "degrees" of difference may exist to define the "Class" rank).

  This is why ranks are pointless and should be abandoned.

Jerry D. Harris
Dept of Earth & Environmental Science
University of Pennsylvania
240 S 33rd St
Philadelphia PA  19104-6316
Phone: (215) 898-5630
Fax: (215) 898-0964
E-mail: jdharris@sas.upenn.edu
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