Parrotfish Scales

Photograph by Tim Laman, National Geographic

Snapped off the coast of Borneo, these iridescent green scales armor a parrotfish (Scarus sp.). The evolutionary link between feathers and scales is evident on developing bird embryos, which are scattered with disks of cells called placodes. Some of these cells grow into scales, such as the ones that cover a chicken's legs, while others turn into feathers.