| Darwinopterus, a medium-sized pterosaur, was found in the Middle Jurassic Tiaojishan Formation of Linglengta, Jianchang County, western Liaoning Province. It is the only known transitional form from basal pterosaurs to pterodactyloids, and shares both primitive and derived characteristics. The primitive characteristics include long tail with more than 20 caudal vertebrae, which are surrounded by thin rod-like extensions of the zygapophyses and chevrons, and the fifth toe bearing two long digits, whereas the derived characteristics (pterodactyloid characteristics) include an elongated skull with antorbital and nasal openings fused into a large nasoantorbital fenestra, long cervical vertebrae with reduced or absent cervical ribs. The length ratio of the wing metacarpal to the humerus is between the basal pterosaurs and pterodactyloids. The discovery of Darwinopterus is highly significant, because it fills the gap between non-pterodactyloids and pterodactyloids and provides evidence of biological macroevolution mechanism (modular evolution theory), i.e., the entire modules, or groups of body features, evolved together within a relatively short period of time. In terms of the fundamental restructuring of the pterosaur bauplan, the high diversity of food sources from the air (such as feathered dinosaurs, gliding mammals, small pterosaurs and insects) might have been one of the causes responsible for the first evolution of the skull and neck. The discovery of Darwinopterus may challenge the traditional and simple classification of pterosaurs into two groups. |