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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.
Joy for skeptics! Very interesting indeed.
2011/8/10 David Marjanovic <firstname.lastname@example.org>:
> 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
> Abstract and figures here:
> 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.
> Anterior to posterior? I can't wait to read the paper and ponder its
> implications for salamanders, temnospondyls, anthracosaurs, colosteids...