The title stunned me as I was surfing the Yahoo News. At some evolutionary phase, birds really did have thumbs. So what happened to them? Researches at Yale University and the University of Wisconsin propose that it shifted its position after studies made on the gene expression in crocodiles, as published in PLoS ONE.

Going back now, birds have only three fingers, which until very recently where believed to be the 2nd, 3rd, and 4th respectively. The only problem this faced was that fingers in the early birds such as Archaeopteryx correspond to number 1, 2, and 3 “thumb, forefinger, and middle finger”. Fossil records clearly indicate that finger 4 and 5 “ring and pinky finger” were lost in the flying dinosaur ancestors of birds.

To end this debate, researchers began to focus on the expression of HoxD11 gene. In mice, digit 1 had no expression for this gene, which also held true for the 1st digit in birds, which suggests that in reality, it is actually a thumb. But to test this, it was compared to crocodiles, the closest living relatives to birds. The findings did in fact support what they suspected. The expression, as in mice, was absent only in finger one “the thumb”

So, birds at one time had thumbs. And the fact remains because they still do. It chose to develop at a different position in the body, that’s all.