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Re: Embryological evidence that bird fingers are I, II, III



 It appeared that the enemies of the Frame Shift had lost their
 battle.

That's debatable, but in any case the paper, which I'm reading right now, _destroys_ the the frameshift hypothesis.

-- Frameshift: digits I and V disappear, digits II to IV assume the anatomies of digits I to III. -- Observation I: the Sonic-hedgehog-expressing "polarizing region" in hands and feet grows into digit IV. -- Observation II: in the chicken foot, that's exactly what happens, but in the chicken hand, the polarizing region does not grow into a digit at all. -- Observation III: "However, it has been suggested that bird wing digits arise in the embryo in digit positions 2, 3 and 4 because all vertebrate limbs are thought to have a 'primary axis' of cartilage condensation running through cells that give rise to digit 4 (ref. 6; Fig. 1b, red line). In addition, transient digit condensations have been reported in putative digit 1 and 5 positions^6, although it is debated whether the digit 1 condensation is a true digit primordium, and an additional posterior condensation has also been detected^7." -- Conclusions: there is no frameshift in birds (other than probably some kiwi individuals), and the primary axis* is a much weaker hypothesis than many people used to think. The authors call their model "axis-shift hypothesis".

* Or rather the idea that it continues beyond the ulnare/fibulare into the distal carpals/tarsals and the digits.

References:
6: A. C. Burke & A. Feduccia (1997): Developmental patterns and the identification of homologies in the avian hand. Science 278: 666 -- 668. 7: M. C. Welten, F. J. Verbeek, A. H. Meijer & M. K. Richardson (2005): Gene expression and digit homology in the chicken embryo wing. Evolution & Development 7: 18 -- 28.