An old controversy solved: bird embryos have five fingers

New studies by Larsson and Wager, and by Feduccia and Nowicki of the embryogenesis of birds undisputedly show Anlagen for five fingers. This has important implications. First, the early presence of digit I, and its later disappearance, indicate that the evolutionary reduction of digits occurred via developmental arrest followed by degeneration. Second, it shows that the digits in the wings of birds develop from Anlagen II–IV. This suggests that the hypothesized descent of birds from theropods might be problematic, because theropods are assumed to have digits I–III.