The first dromaeosaurid (Dinosauria: Theropoda) from the Early Cretaceous Bayan Gobi Formation of Nei Mongol, China

The first dromaeosaurid theropod from the Early Cretaceous Bayan Gobi Formation is identified based on an incompletely preserved partially-articulated left leg, increasing the known diversity of its understudied ecosystem. The leg belongs to specimen IVPP V22530 and includes a typical deinonychosaurian pedal phalanx II-2 with a distinct constriction between the enlarged proximal end and the distal condyle as well as a typical deinonychosaurian enlarged pedal phalanx II-3. It possesses a symmetric metatarsus and a slender and long MT V that together suggest it is a dromaeosaurid. Two anatomical traits suggest the leg is microraptorine-like, but a more precise taxonomic referral was not possible: metatarsals II, III and IV are closely appressed distally and the ventral margin of the medial ligament pit of phalanx II-2 is close to the centre of the rounded distal condyle. This taxonomic status invites future efforts to discover additional specimens at the study locality because - whether it is a microraptorine or a close relative - this animal is expected to make important contributions to our understanding of dromaeosaurid evolution and biology. IVPP V22530 also comprises of an isolated manual ungual, a proximal portion of a right dorsal rib and an indeterminate bone mass that includes a collection of ribs. However, these specimens cannot be confidently referred to Dromaeosauridae, although they may very well belong to the same individual from whom the left leg belongs.