Re: Strange thoughts on PN - was Re: BAD vs. BADD

[Martin Baeker <martin.baeker@tu-bs.de>]

> > Everybody here agrees that group A=(Megalos.+Iguanodon) is useful, as
> > is B=(Passer+Archaeopteryx) - where () denotes MRCA - despite the fact
> > that these are also quite arbitrary - there will be a critter looking
> > *almost* like the first member of A that is not a member of it (like
> > Lagosuchus), but still, the concepts are useful, albeit arbitrary.
> > 
> > Why is then A\B (A without-B) such a big no-no?
> 
> Ah, but you've just answered your own question.  If B is treated as a subgroup
> of A, then we can recognize groups like (B+_Deinonychus_), to include B and
> "critters that look *almost* like the first member of B but are not members of
> B".
> 
> However, if A and B are recognized as separate and coequal groups, then we do
> not have this option, unless we want to have a highly confusing system of
> overlapping groups.

Probably I did not made myself clear: what I would like to have is a system
where I can say:

Dinsauria=(Megalos+Iguanodon)
Aves=(Archaeo+Passer)
Classicodinosauria (or whatever) = Dinosauria without Aves

just because this grouping is so useful...


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