Identification of reptilian genes encoding hair keratin-like proteins suggests a new scenario for the evolutionary origin of hair. 2008. L. Eckhart. PNAS, Published online before print November 10, 2008
From the press release:
The origins of hair date back to an unknown reptile ancestor that lived more than 300 million years ago, in the Paleozoic era. The discovery was made by comparing human, chicken, and green anole lizard genomes. The genome of the lizard was found to contain six different genes for hair keratin, the protein from which mammal hair is made.
The genes were expressed most strongly in the lizard's toes, indicating that the first hair genes played a role in claw formation.
"At least two of these hair protein keratins are formed in the growth zones of the claws," Eckhart said. While the role of the anole lizard's four other hair genes remains unclear, they were likely related to the growth of scales, the study team said. The chicken genome revealed a single hair gene. It's unclear what that gene is for, if anything.
The finding suggests that modern birds, reptiles, and mammals—as well as dinosaurs—shared an early common ancestor that had claws built from hair keratin, Eckhart said.
