Do birds have a thumb or an index finger?

Using chickens, researchers investigating whether the innermost digit of a bird’s three-pronged wing is a index finger or thumb is in fact a bit of both.

The first digits from the wings and feet both occur from the same genetic coding. However, the digit in the wing develops in the area reserved for the index.

Researchers were also able to reveal a lack of homology (that is, an evolutionary connection) between the other two digits buried in the bird wing and those found in the foot.