A New Dromaeosaurid Dinosaur From The Early Cretaceous Of Yujingzi Basin,Jiuquan Area,Gansu Province,China

The Yujingzi Basin and its neighboring areas in Gansu Province are famous for its diversity of Lower Cretaceous dinosaur fauna. Excavation in 2007 uncovered a new dromaeosaurid specimen from the Lower Cretaceous Zhonggou Formation (Early Cretaceous, Aptian?-Albian) at the "Baichengzi" locality in the Yujingzi basin (Jiuquan area). The specimen consists of a single left frontal, an isolated partial axial skeleton and some appendicular elements.The specimen is unique among dromaeosaurids in that:the ulnar condyle of humerus is subdivided into a strongly bulbous lateral facet and a small clove-shaped medial one; the pedal phalanx III-1 bears a distinctive sigmoid curvature in dorsal aspect; the grooves for claw sheath on manual unguals distinctively extend from the top of articular facets; the transverse process on either side of the proximal caudal vertebra merges with the prezygapophysis forming a forward-swept, wing-like structure, and the zygapophyseal facets of proximal caudal vertebra are completely planar. In order to determine the phylogenetic position of the specimen, I conduct a phylogenetic analysis at species-level within the larger context of Coelurosauria based on a published coelurosaurian phylogeny data matrix.The discovery of this new dromaeosaurid adds to the diversity of Lower Cretaceous dinosaur fauna in Yujingzi Basin. According to my phylogenetic analysis, the specimen is a basal member of the subfamily Velociraptorinae. Morphological and functional analysis of the unique proximal caudal vertebra shows that the proximal tail segment of the specimen bears much more flexibility in lateral movement than any other dromaeosaurids, which may have been an evolutionary adaptation to an unusual need for forceful and energetic activity.