Four specimens of the pterosaur Pteranodon exhibit patterns of irregular alternating light and dark bands on the lateral surfaces of the upper jaw anterior to the nasoantorbital fenestra. Examinations reveal that the maxilla and premaxilla of Pteranodon consisted of two thin sheets of bone interconnected by regularly spaced septa with the spaces contained within presumably pneumatized, resulting in a structure analogous to modern honeycomb sandwich panels. The alternating light and dark bands resulted from waves of bone deposition moving anteriorly along the external surface of the lateral sheet of bone and laying down thin laminae of new bone while...