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Re: Feduccia's allegations



--- Jeff Hecht <jeff@jeffhecht.com> wrote:
> Remember that Microraptor is at least 20 million
> years after 
> Archaeopteryx, so the fossils Xu et al found cannot
> be ancestral. 
> Either it's an evolutionary throwback (living
> fossil), or it's an 
> evolutionary dead-end. It's fascinating in either
> case, but it can't but it can't  provide a
definitive >proof of how flight originated in birds.

We should keep in mind that primitive and derived
forms often coexist together. For example knuckle
walking great apes coexist with the erect humans, the
brachiating lesser apes, the old world monkeys, the
tarsiers and lemurs. One cannot deny that many of
these forms retain primitive characters and are good
approximations for reconstructing of the various
ancestral states leading to humans. Hence the Sinitic
fossils do provide good approximations for the
ancestral states in the emergence of birds, though
they may be co-eval or later than A'pteryx.

An early Jurassic fossile would surely be great but
there is little doubt that the Yixian forms greatly
clarify the actual steps in the emergence of birds.

Another point is that one should very cautious in
interpretting the mosaicism of derived characters in
organisms coming from major transition zones in
evolution. They mosaicism is most likely to result
from reversal rather than independent gains. I
interpret this a arising from the following:
evolutionary phenomenon: 1) There is very rapid
colonization of a niche with all derived characters
associated with the transition arising quick
succession. 2) There is heavy competition in the new
niche and hence selection for some forms that can
exploit both the new niche and their old original
niche more effectively. The forms that do this gain
greater access to resources. This effect selects for
certain reversals. 3) These reversal occur in parallel
in different lineages resulting in mosaicism.

EA

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||>>>>>               .....   =+--------> Amidst
||                   /     \  =+-------->
||>>>               | O   O | =+--------> the
||                   \  0  /  =+-------->
||>>>>>Katerina       |||||   =+--------> shamans
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