Source: Hairs, feathers and scales have a lot in common

The potential evolutionary link between hairs in mammals, feathers in birds and scales in reptiles has been debated for decades. Today, researchers demonstrate that all these skin appendages are homologous. On the basis of analyses of embryonic development, the biologists evidenced molecular and micro-anatomical signatures that are identical between hairs, feathers and scales at their early developmental stages. These observations indicate that the three structures evolved from their common reptilian ancestor.