News flash: Bird fingers

"Embryological Evidence Identifies Wing Digits in Birds as Digits 1, 2, 
and 3"

Koji Tamura, Naoki Nomura, Ryohei Seki, Sayuri Yonei-Tamura, and Hitoshi

Science 11 February 2011:
Vol. 331 no. 6018 pp. 753-757
DOI: 10.1126/science.1198229


The identities of the digits of the avian forelimb are disputed. Whereas
paleontological findings support the position that the digits correspond 
to digits one, two, and three, embryological evidence points to digit 
two, three, and four identities. By using transplantation and 
cell-labeling experiments, we found that the posteriormost digit in the 
wing does not correspond to digit four in the hindlimb; its progenitor 
segregates early from the zone of polarizing activity, placing it in the
domain of digit three specification. We suggest that an avian-specific 
shift uncouples the digit anlagen from the molecular mechanisms that 
pattern them, resulting in the imposition of digit one, two, and three 
identities on the second, third, and fourth anlagens.