A developmental phase shift moved digits 1, 2 and 3 of the dinosaurian hand to positions 2, 3 and 4 in birds

Some say it's the last holdout for a handful of scientists still not convinced that birds evolved from dinosaurs. The fingers of the two groups of animals, they say, just don't match up. As embryos, birds seem to develop the equivalent of our middle three fingers, but theropods—two-legged, primarily carnivorous dinosaurs from which birds are thought to have evolved—sport the equivalent of our thumb, index, and middle fingers. Now, a study of chick embryos shows thatbirds do indeed have thumb, index, and middle "fingers" in their wings. The rest here.