Embryological evidence that bird fingers are I, II, III

[David Marjanovic <david.marjanovic@gmx.at>]

Matthew Towers, Jason Signolet, Adrian Sherman, Helen Sang & Cheryll 
Tickle (9 August 2011): Insights into bird wing evolution and digit 
specification from polarizing region fate maps, Nature Communications 2, 
article number 426

Abstract and figures here: 
http://www.nature.com/ncomms/journal/v2/n8/full/ncomms1437.html

Abstract:

>>
The proposal that birds descended from theropod dinosaurs with digits 2, 
3 and 4 was recently given support by short-term fate maps, suggesting 
that the chick wing polarizing region -- a group that [sic] Sonic 
hedgehog-expressing cells -- gives rise to digit 4. Here we show using 
long-term fate maps that Green fluorescent protein-expressing chick wing 
polarizing region grafts contribute only to soft tissues along the 
posterior margin of digit 4, supporting fossil data that birds descended 
from theropods that had digits 1, 2 and 3. In contrast, digit IV of the 
chick leg with four digits (I--IV) arises from the polarizing region. To 
determine how digit identity is specified over time, we inhibited Sonic 
hedgehog signalling. Fate maps show that polarizing region and adjacent 
cells are specified in parallel through a series of anterior to 
posterior digit fates -- a process of digit specification that we 
suggest is involved in patterning all vertebrate limbs with more than 
three digits.
<<

<Spock>Fascinating.</Spock>

Anterior to posterior? I can't wait to read the paper and ponder its 
implications for salamanders, temnospondyls, anthracosaurs, 
colosteids... :-)