From scales to feathers to fur, vertebrates clothe themselves in a dazzling variety of textures and hues. But scientists have shown that many of those coverings emerge from the same anatomical hardware.
Biologists have long known that feathers and hairs both start as structures called placodes. In reptiles, however, biologists had found distinct skin areas that yielded scales but no placodes. The absence proved puzzling, since birds are more closely related to reptiles than to mammals. Had birds and mammals evolved placodes independently? Or had today’s reptiles discarded them?
Then University of Geneva biologist Michel Milinkovitch visited an Italian animal fair, found scaleless, “naked” bearded dragons for sale—and a third scenario emerged. When he compared the naked lizards and their scaly kin, he saw to his shock placode-like bumps dotting the skin of scaled embryos. Naked embryos, however, stayed smooth.