Beta-keratin (β-keratin) is a member of a structural protein family found in the epidermis of reptiles and birds.
A recent study using molecular dating methods to link the evolution of avian β-keratin genes in general to that of feathers specifically reveals that the avian β-keratin family began diverging from the crocodile family about 216 million years ago.
[6] It also found that the feather β-keratin family did not begin diverging until 125 million years ago, a date consistent with the adaptive radiation of birds during the Cretaceous.
β-keratins found in modern feathers have increased elasticity, a factor that may have contributed to their role in flight.
[8] This has since been refuted by Saitta et al., finding that the fibers analyzed instead consisted of inorganic calcium phosphate as evidenced by fluorescence under cross polarised light.