β-keratin or beta-keratin (not to be confused with β-carotene) is rich in stacked β pleated sheets, in contrast to alpha-keratin, a fibrous protein rich in alpha helices.
β-keratin is found in reptiles. It adds much more rigidity to reptilian skin than alpha-keratin does to mammalian skin.
β-keratin is impregnated into the stratum corneum of the reptilian skin, providing waterproofing and the prevention of desiccation.
In birds, scales, beaks, claws and feathers also contain β-keratin of the avian family. Phylogenetic studies of β-keratin sequences show that feather β-keratins evolved from scale β-keratins . The scale β-keratins form the basal group in avians. Duplication and divergence events then led to claw β-keratin genes, and further recombination resulted in new feather and feather-like avian β-keratin genes. Evidence for these duplication events comes from the correlation of feather β-keratin clade structure with their genomic loci .
Changes in β-keratins may have also influenced the development of powered flight. A recent study using molecular dating methods to link the evolution of β-keratin genes to that of feathers reveals that the avian β-keratin family began diverging from the crocodile family about 216 million years ago . But 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 . Thus, the feathered ancestors of birds including Anchoirnis and Archaeopteryx, whose flight capabilities have been questioned, would have had avian, but not feather β-keratins.
The small alvarezsaurid dinosaur Shuvuuia deserti showed evidence of a featherlike skin covering. Analysis by Schweitzer et al. (1999) showed that these featherlike structures consisted of beta-keratin.