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Re: Some thoughts on AVES
Nicke Pharris (NJPharris@aol.com) wrote:
<<... 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.>>
Demetrios Vital (firstname.lastname@example.org) wrote:
<Yes, but that ability exists for very few features. Classification can't stop
in the present.>
As Nick's example went, it doesn't. There are numerous completely definable
features found only in selective groups of extant mammals, including descended
testicles (not in
Afrotheria or Xenarthra+Pholidota, or even "insectivores"; it is an advanced
even if afrotheres reversed the polarity to the basal condition in their
ancestry rather than
inheriting it forthwith). Nick's statement of an actual observance of a
selective, inclusive gene
expression does in fact state that a genetic and morphological feature can be
used to define
<That presumes that ability to pinpoint every adaptation to its exact gene
source. We can't do
that reliably, now or with fossils.>
We have been gaining progress in pinpointing genes responsible for
Time goes on. The presumption here is that we may _not_ have thw ability to
pinpoint gene sources.
Nick also wrote:
<<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"...>
Didn't we already go through this? A percentage is uncessesary and arbitrary
to a degree when in
fact we can do entirely without it. We can define a population easily, just
take the species
concept of genetic isolation and use it to refer to populations where this
occurs. Fin. And it
can be quite an interesting practice if, when more than two people agree on
something, some things
can actually be done. The choice is the naming, not the population viability.
<<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 didn't evolve into, or is an example of, birds.>
Well, of course not. Velociraptor never had the features of a "bird" as seen
through the public
mind's eye. That wasn't what Nick said, however. He said Aves. The assumption
is that Aves and
bird are synonymous, a statement which has led to previous discussions (and
before. One can, logically, define Aves as :Velociraptor + Passer}.
Unfortunately, the node
Eumaniraptora already occupies that node.
<As to why Confusciornis isn't used, I don't know.>
At the time Confuciusornis was described, Archaeopteryx was a much better,
popular taxon. The choice was easy, as I see it.
Jaime A. Headden
"When the state sends someone to the electric chair, it's called murder; when
the state sends someone to prison, they sanction a gay dungeon."
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