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Re: A few more...



In a message dated 95-10-03 08:48:27 EDT, Thomas_R_HOLTZ@umail.umd.edu (th81)
writes:

>I think that ornithologists and molecular biologists can strongly argue
>against such a position (presumably you mean the hoatzin diverged before the
>hesperornithoform-ichthyornithoform-neornithine clade evolved).  Or,
>alternatively, that the fingers were lost several times in the evolution of
>ornithurine birds.

All extant volant birds have three manual digits after hatching. They did not
_lose_ them, they fused them into a wing. Fusion usually takes place during
embryonic development, but in the hoatzin, fusion is delayed until maturity,
allowing the immature birds the use of free fingers for climbing around. It
is this delay in fusion that is the "reversal," not the "regaining" of "lost"
fingers. That's a really simple kind of reversal, and I have no problem
understanding how it could come about.