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Re: Some thoughts on AVES



----- Original Message -----
From: <NJPharris@aol.com>
To: "Demetrios M Vital" <vita0015@tc.umn.edu>; <dinosaur@usc.edu>
Sent: Friday, November 02, 2001 2:00 PM
Subject: 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?<

If you're asking how "we" labor to fill the amount of knowledge we have, the
simple answer is by digging up new species.  In the end though, it was a
vague statement that has no meat behind it.

> 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.<

Yes, but that ability exists for very few features.  Classification can't
stop in the present.

> 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.<

That presumes that ability to pinpoint every adaptation to its exact gene
source.  We can't do that reliably, now or with fossils.

> > 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.

That's a pretty arbitrary statement.  Whose choice is it when that happens?
What percentage of the population must have the adaptation before it can be
used for a character-based system?  Not to mention the difficulties of a
practical definition of "population"...

> 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_?<

Velociraptor didn't evolve into, or is an example of, birds.  As to why
Confusciornis isn't used, I don't know.  That's not an area that I can argue
for or against.  And don't get me wrong, I know that every system has a huge
chunk of subjectivity to it, but some more than others.  Tell me, are you
arguing for a hierarchical system, or just character-based classifications?

-Demetrios Vital