Re: Dino Birds (was Re: Dinosaur = extinct animal)

[Dinogeorge@aol.com]

In a message dated 7/12/99 10:50:51 AM EST, cbrochu@fmppr.fmnh.org writes:

<< Dinogeorge@aol.com wrote:
 > 
 > In a message dated 7/12/99 9:00:56 AM EST, cbrochu@fmppr.fmnh.org writes:
 > 
 > << The overall point is that paraphyletic assemblages, above the species
 >  level, are subjective, have no biological reality, and are not
 >  recognized in modern systematics. >>
 > 
 > Paraphyletic taxa certainly have "biological reality," whatever that is. If
 > monophyletic taxon A and included monophyletic taxon B are "biologically
 > real," then so is the paraphyletic taxon A-B, the set of organisms that are
 > in A but not in B. 
 
 No, it isn't, because we're subjectively deciding what to subtract from
 A. >>

Not to be misunderstood: If A is >any< monophyletic taxon and B is >any< 
monophyletic taxon included in A, then the taxon A-B is as "real" as A or B. 
Deciding which B to subtract from A has nothing to do with the "reality" of 
A-B. It has only to do with the >utility< of formally declaring A-B a taxon. 
You can form a perfectly real and well-defined taxon by removing, say, the 
genus Tyrannosaurus from Theropoda (or at least as perfectly well-defined and 
real as Tyrannosaurus and Theropoda are), but is it useful to do so? I'd say 
that virtually nobody would think so, and so we don't have a taxon called 
"Nontyrannosauria." But if A is the monophyletic Dinosauria and B is the 
monophyletic Avialae, then there certainly is great utility in retaining a 
taxon A-B for "nonavian dinosaurs." Taxonomies have other uses than merely 
being phylogenetic mirrors.