Phylogenetic Tree Reconstruction of all β-keratin Sequences Located on the Genomes of both G. gallus and T. guttata: Three nile crocodile (Crocodylus niloticus) β-keratin genes are constrained as the out group  with all 219 β-keratin genes found in the two avian genomes. The BS (bootstrap values) from the Neighbor-Joining method are listed for each major branch when they are above 70 percent. The bootstrap values from the Maximum Likelihood method, are listed in parenthesis for each major branch when they are above 70 percent (see Methods) [56, 60]. All individual taxa names have been removed and instead only the names of major groups are displayed. The subfamilies are colored with the following scheme: GGA25_Keratinocyte = red, scale β-keratin genes = blue, claw β-keratin genes = yellow, feather β-keratin genes = green and feather-like β-keratin genes = magenta. Please refer to Additional File 5, Figure S2 to view all bootstrap values and taxa labels for the Neighbor-Joining phylogeny and Additional File 6, Figure S3 to view all bootstrap values and taxa labels for the Maximum Likelihood phylogeny.