Mammals, birds and reptiles inherited key cell structures that give rise to their fur, feathers and scales from a shared reptilian ancestor.
Scientists have long debated whether these skin appendages evolved independently or had a single origin. To find out, Nicolas Di-Poï and Michel Milinkovitch at the University of Geneva in Switzerland studied skin development in embryos of Nile crocodiles (Crocodylus niloticus; pictured right), corn snakes (Pantherophis guttatus) and bearded dragons (Pogona vitticeps). They found that reptilian scales, like feathers and mammalian hair (mouse embryo pictured left), develop from a group of cells called the anatomical placode (pictured as dark blue spots). These appear only briefly during development in snakes and lizards, and were previously not detected and so thought to be missing in these animals.
These cells express the same developmental genes as bird and mammalian placodes, suggesting a common origin for modern hair, feathers and scales.