[D] Graciliraptor lujiatunensis [sG] [T]
Xu and Wang, 2004
Saurischia Theropoda Tetanurae Coelurosauria Dromaeosauridae
Yixian Formation (Jiufotang Formation) of Liaoning, China
Genus - Typespecies
Fragmentary maxilla with some teeth, a few caudals, almost complete fore limbs, and partial hind limbs
Distinctive characteristics of Graciliraptor lujiatunensis include a laminal structure connecting the postzygapophyses of middle caudals, middle caudals extremely long and slender, small manual ungual I, proximal end of metacarpal III strongly expanded, proximal tibiotarsus shaft rectangular in cross section, astragalar medial condyle significantly expanded posteriorly, metatarsal II distally much wider than other metatarsals and long and slender pedal phalanx III-1.
Graciliraptor lujiatunensis displays a few features similiar to those of basal birds, such as caudals significantly elongated, semilunate carpal small and primarily contacting metacarpal II, and manual digit I short, providing further evidence for a close relationship between the Dromaeosauridae and the [Aves] Avialae; on the other hand, it is similiar to troodontids in some features on the caudals. The discovery of Graciliraptor lujiatunensis also indicates a high diversity of the Dromaeosauridae in the Early Cretaceous Jehol Biota. Combined with other lines of evidence, it is inferred that the Dromaeosauridae rapidly diversified taxonomically but remained relatively stable morphologically in the early evolution of the group.
Being the earliest definitive dromaeosaurid species known to date, Graciliraptor lujiatunensis provides new information important for understanding the early evolution of the group.