Dynamic evolution of β-keratins in the archosaur lineage. This figure illustrates a proposed scenario of β-keratin evolution on the ancestral locus in archosaurs. The bottom row is the proposed locus of β-keratins in the ancestor of turtles, crocodilians and birds. The second row from the bottom indicates that the scale β-keratins have emerged since the divergence of turtles from crocodilians and birds. The origin of the feather β-keratins occurs after the divergence of crocodilians and birds. The order of the β-keratins subfamilies is based on our genomic data from the 48 birds and green sea turtle. The top row illustrates the dynamic changes of the proportions of β-keratin subfamilies in modern birds with aquatic and predatory lifestyles. Both aquatic and predatory birds have a larger proportion of keratinocyte β-keratins and smaller proportion of feather β-keratins in their genomes. Additionally, predatory birds have a larger proportion of claw β-keratins. The divergence times are in millions of years ago (MYA). The divergence estimates of the turtle – crocodilian/bird split and the crocodilian – bird split are from Shedlock and Edwards . The divergence time estimates for birds is from Jarvis et al.  and is the range starting with the divergence of the Palaeognathae and Neognathae (~100 MYA) and the subsequent divergences of most ordinal groups by ~50 MYA. Jon Fjeldså produced the images of the birds (emperor penguin on the left and peregrine falcon on the right).