Linking the Molecular Evolution of Avian Beta (β) Keratins to the Evolution of Feathers

Feathers of today's birds are constructed of beta (beta)-keratins, structural proteins of the epidermis that are found solely in reptiles and birds. Discoveries of feathered dinosaurs continue to stimulate interest in the evolutionary origin of feathers, but few studies have attempted to link the molecular evolution of their major structural proteins (beta-keratins) to the appearance of feathers in the fossil record. Using molecular dating methods, we show that before the appearance of Anchiornis (similar to 155 Million years ago (Ma)) the basal beta-keratins of birds began diverging from their archosaurian ancestor similar to 216Ma. However, the subfamily of feather beta-keratins, as found in living birds, did not begin diverging until similar to 143Ma. Thus, the pennaceous feathers on Anchiornis, while being constructed of avian beta-keratins, most likely did not contain the feather beta-keratins found in the feathers of modern birds. Our results demonstrate that the evolutionary origin of feathers does not coincide with the molecular evolution of the feather beta-keratins found in modern birds. More likely, during the Late Jurassic, the epidermal structures that appeared on organisms in the lineage leading to birds, including early forms of feathers, were constructed of avian beta-keratins other than those found in the feathers of modern birds. Recent biophysical studies of the beta-keratins in feathers support the view that the appearance of the subfamily of feather beta-keratins altered the biophysical nature of the feather establishing its role in powered flight. J. Exp. Zool. (Mol. Dev. Evol.) 316: 609-616, 2011. (C) 2011 Wiley Periodicals, Inc.