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Re: Some thoughts on AVES

In a message dated Fri, 2 Nov 2001 11:30:40 AM Eastern Standard Time, Demetrios 
M Vital <vita0015@tc.umn.edu> (demetrios Vital) writes:

> > Fortunately, I don't have to.  We only have to classify the specimens we
> > actually discover.  For this reason, abstract apomorphy-based definitions
> > like the one I gave do not bother me overly much.
> Again, not only are you relying on a lack of knowledge (which we all labor
> to fill),

How so?

> but are setting up a system which inherently has limitations. 
> One of these limitations is the fact that you can only work with fossil
> taxa.  

Not at all.  If I wanted to define a group as all descendants of the first 
individual to carry the feline wire-hair gene (the first occurrence of which is 
historically documented), I would be free to do so.  It would be an odd thing 
to do, but I could do it, in principle.

> > Not necessarily (see above).  And besides, any adaptation, if defined
> > strictly enough, must indeed have been acquired overnight.
> I don't know if that's true.  

I do.  Any given heritable feature (again, if narrowly enough defined) will 
have a first occurrence, whether it is due to a novel mutation or to a novel 
shuffling of genes.

> We'd need a complete genomic understanding
> of every individual in the population that speciates, which we can't even
> define, and then a complete understanding of the future heredity patterns
> of those individuals.  That's not possible.

Yes, and therefore it would be unwise to name a group based on such a feature 
until it had fixed itself in a population.

> And aside from all the problems listed above, the system is _still_ more
> arbitrary that phylogenetic taxonomy!

Wrong.  Defining Mammalia based on auditory ossicles is no more arbitrary than 
defining Aves based on _Archaeopteryx_ and _Passer_.  Why not use 
_Confuciusornis_?  Why not _Velociraptor_?

--Nick P.