Like the closely related "Pteranodon", "Nyctosaurus" also had relatively long forelimbs compared to other earlier genera. Most of the tendons of the upper arm and forearm were mineralized within, this is a unique feature only seen in nyctosaurids, another of which was the related "Muzquizopteryx". Another distinctive feature seen in "Nyctosaurus" was that it only had three phalanges instead of four, as seen in other pterodactyloids, this trait is rarely seen in other pterosaurs, and perhaps may have been an autapomorphy only found in "Nyctosaurus".