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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 (vita0015@umn.edu) 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 
morphological
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 
eutherian adaptation,
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
extant populations.

<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 
morphological expression.
Time goes on. The presumption here is that we may _not_ have thw ability to 
pinpoint gene sources.
Not so.

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.

Nick continued:

<<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.>

  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 
arguments) here
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, 
primitive, and
popular taxon. The choice was easy, as I see it.


=====
Jaime A. Headden

  Interesting Dichotomy:
  "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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