Feathers evolved in dinosaurs and are a key characteristic of birds today. They are arranged in a precise hexagonal pattern in a bird’s skin, but it has been unclear how this happens. According to a new study published February 21 in the open-access journal PLOS Biology, led by Dr. William Ho and Denis Headon of the University of Edinburgh, and collaborative colleagues, the patterning of bird feathers relies on signaling through ectodysplasin (EDA) and its receptor EDAR—the same signaling pathway known to be crucial for the formation of hair follicles, teeth and scales in fish, lizards and mammals.