A new troodontid dinosaur, Xixiasaurus henanensis gen. et sp. nov., from the Upper Cretaceous Majiacun Formation of the Xixia Basin, Henan Province, is erected, based on a partial skull. It is characterized by bearing 22 maxillary teeth, a distinct opening on the lateral surface of the base of nasal process of the premaxilla, the rostral end of the upper jaw forming a tapered U−shape, and the mandibular symphyseal region slightly inflected medially. Xixiasaurus is most closely related to the Mongolian Byronosaurus among troodontids. Byronosaurus, Urbacodon, and Xixiasaurus may form a new clade, suggesting an endemic radiation of troodontids across Asia, including multiple taxa without dental serrations. The discovery of Xixiasaurus in the Xixia Basin may imply that the Xixiasaurus−bearing Majiacun Formation is Campanian in age.

Key words: Theropoda, Troodontidae, Xixiasaurus, Late Cretaceous, Henan Province, China.

Juanchang Lü [Lujc2008@126.com], Yongquing Liu [liu_cags@126.com], and Qiang Ji [jirod@cags.net.cn], Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China; Li Xu [zhzhxuli@sina.com], Xingliao Zhang [zhxliao@sina.com], and Songhai Jia [jiasonghai@163.com], Henan Geological Museum, Zhengzhou 450016, Henan Province, China.