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I'm sorry if I'm answering to a question not made
to me.
anyway ,philidor11 wrote: <<Go far enough back in any group you choose
to distinguish and the
differences from an ancestral group will be small, by definition.>> ..sure
<<And,
because the whole list of differences between the two groups appear over time, you also have to choose how many of those differences have to be present to say that a specific animal is part of one group or the other.>> ok, but if you consider Archaeopteryx to be part of
Aves, then you've to consider the presence of the characters you've
previously chosen (having observed them in an animal thought to be derived
enough to be considered a bird, which is a purely arbitrary choice ),in Archie
too, and you surely won't find many of them, because they would have been
recognized in animals considered to be "different enough" from , say, a dromie
which is, however very similar to Archie.
Then you would have to consider Archie, and all the
animals more "birdy" than a dromie, but not "birdy" enough to be considered
a true bird, as something between a bird and a dinosaur, but ....
<<The difference in approach being considered
is: are you emphasizing the end
result (bird/dinosaur) or the beginning of the separation between the two groups? Doesn't it seem most reasonable to emphasize the end result when deciding when differences are large enough to distinguish a group?>> no, i think it's more reasonable to consider the
group as a whole; in this case you have to arbitrarily choose to consider one
branch of the tree as a different group, which it is , based on few characters
seen only in the components of this group, but _in ALL_ of them. Many
derived featurs will be present in some taxa, but this isn't important(well, at
least as long as you don't think they're enough to estabilish another
group).
ths is only a matter of human perspective as it has
been pointed out many times on the list.
bye
FC
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