Objective The Early Cretaceous Mazongshan Dinosaur Fauna from the Mazongshan region (including Gongpoquan and Yujingzi basins) in western Gansu Province, northwestern China contains several types of the fossil dinosaurs, crocodiles and turtles. This study gives the definite evidence of pterosaur existence from the Lower Cretaceous Xiagou Formation in the Yujingzi Basin for the first time, and further discusses the significance on its supplement to the Mazongshan Dinosaur Fauna.

Methods Detailed description and comparison on the fossil bone’s anatomy are used for identifying the systematic position of the fossil. Confirmation of the fossil reptile groups is the basis of analyzing the components of the Mazongshan Dinosaur Fauna.

Results An incomplete piece of fossil bone collected from the Lower Cretaceous Xiagou Formation in the Yujingzi Basin has been identified as the proximal end of the first wing phalanx and fused extensor tendon process of a pterosaur. It should be included within Order Pterosauria. This pterosaur would be estimated to be a large flying reptile with the wing span around 4 meters according to the morphology and size of the bone.

Conclusions This finding represents the first definite record of pterosaurs from the Lower Cretaceous in western Gansu Province, which adds a new reptile group for the Mazongshan Dinosaur Fauna. It fills the gap of the pterosaur distribution in Mazongshan region and Beishan sedimentary area. This material further enriches the ecological niches of the Mazongshan Dinosaur Fauna, therefore provides new fossil evidence of understanding the components and distributions of the Early Cretaceous dinosaur faunae across the different regions in northern China.