Foreground: Drawing of a pterosaur wing showing the short digits I, II, and III that would have made "wing prints" when the pterosaur walked on all fours. Drawing by Arthur Weasley (CCA BY 3.0). Background: Artist's reconstruction of Nyctosaurus, a pterosaur from the Cretaceous Period, walking quadrupedally. The animal that left the Pteraichnus tracks above may have been walking in a similar fashion. Image by Matthew Martyniuk (CCA BY 2.5).