Tianyuraptor, meaning “Tianyu thief,” is a genus of dromaeosaurid dinosaur from the Barremian and Aptian stages of the Early Cretaceous Period (129 to 122 million years ago). It was discovered in western Liaoning, China in the Dawangzhangzi Bed of the Yixian Formation. While similar to other dromaeosaurids that have been discovered in Liaoning, it is somewhat more primitive. The type specimen, which was described in 2009, shows features not previously known in Northern Hemisphere dromaeosaurids, but present in Southern Hemisphere species. Scientist who first studied Tianyuraptor described it as a transitional species, bridging the gap between northern and southern dromaeosaurids.
The holotype is housed at the Shandong Tianyu Museum of Nature. The type species, T. ostromi, honors John Ostrom, who contributed greatly to the study of dromaeosaurid fossils, including Deinonychus and feathered dinosaurs.
Phylogenetic analysis of Tianyuraptor showed it to be a primitive member of a group containing Laurasian dromaeosaurids. Tianyuraptor possesses several features that are not seen in other Laurasian dromaeosaurids, but which are found in primitive birds and Gondwanan dromaeosaurids, including Austroraptor, Buitreraptor, Neuquenraptor, Rahonavis, and Unenlagia. The discovery of Tianyuraptor sheds new light on the early evolution of dromaeosaurs.
There are several features that separate Tianyuraptor from other dromaeosaurids. These include the length of the middle tail vertebrae being more than twice that of the back vertebrae, a small, slender wishbone, and an unusually long hind limb that is about three times as long as the entire series of back vertebrae. In contrast to other dromaeosaurids discovered in Liaoning, the tail is relatively long at 38 inches, almost 4.8 times as long as the femur.
The type specimen consists of a nearly complete skeleton that is only missing the very end of the tail vertebrae. It is believed to be a sub-adult, with features including the incomplete fusion of skeletal parts during development.
The forelimbs of Tianyuraptor are relatively short, being only 53 percent the length of the hindlimbs’ length. This feature differs significantly from known skeletons of other dromaeosaurids, most of which have relatively long forelimbs in relation to the hindlimbs.
The clear difference in arm length compared to other dromaeosaurids suggests that the function of the arms in Tianyuraptor was different from that of other dromaeosaurids. Being a sub-member of the Microraptorinae family, some scientists believe that it may have been aerodynamic and able to glide. But, microraptorines are usually noted for their long and robust forelimbs and large, asymmetrical flight feathers, and, as such, the shortened forelimbs, small wishbone, and wide coracoid in Tianyuraptor suggest that it was not suited for aerodynamic gliding or flight.