[D] Xixiasaurus henanensis [sG] [T]
Lü, Xu, Liu, Y, Zhang, Jia, & Ji Q. 2010
Cretaceous Late \\\"Coniacian Santonian\\\" Campanian
Saurischia Theropoda Tetanurae Coelurosauria Maniraptora Troodontidae
Majiacun Formation, Xixia County, China
A new troodontid dinosaur, Xixiasaurus henanensis gen. et sp. nov., from the Upper Cretaceous Majiacun Formation of 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.
A partial skull, an anterior portion of the lower jaw, and central portions of the ulna and radius, and a partial right manus with a complete first digit. The specimen (41HIII-0201) is housed in the Henan Geological Museum.
Xixiasaurus refers to the theropod dinosaur found in the Chinese administrative unit Xixia County of Henan Province. / The specific name refers to Henan Province, in which the holotype site in Xixia County is found.
Type locality and horizon
Songgou Village, Zhangying of Wuliqiao Town, northeast region of Xixia County. Mid-lower part of Majiacun Formation (Coniacian-Campanian) (Wang et al. 2006; Chen et al. 2007; Pan et al. 2007).
Differs from other troodontids by having fewer maxillary teeth (which total 22) than Byronosaurus ( > 30; Makovicky et al. 2003) and Mei (24; Xu and Norell 2004), but more than Sinornithoides youngi (18; Makovicky and Norell 2004), Saurornithoides junior (20; Makovicky and Norell 2004), and Saurornithoides mongoliensis (19; Makovicky and Norell 2004).
It also has a distinct opening on the lateral surface of the base of the nasal process of the premaxilla, the rostral end of the upper jaw shows a more tapered U-shape than in Byronosaurus, and the mandibular symphyseal region is slightly inflected medially. Like Byronosaurus, Mei, Urbacodon, and Anchiornis, this new taxon has unserrated teeth, and like Byronosaurus it has a heterodont dentition and an extensive secondary bony palate. An extensive palate is also scored for Saurornithoides mongoliensis and Troodon formosus (see Varricchio 1997).