Origin of Bird Digits (IMAGE) Yale University Caption A genomic analysis shows that precursor cells pb that form index finger in five-fingered vertebrates can form the "thumb" (in orange) or first digit in three-digit bird wing Credit courtesy Yale University Usage Restrictions None License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.