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A fossil of Tianyuraptor was seen in a database scene

Tianyuraptor is a genus of short-armed dromaeosaurid dinosaur ('running lizard'; a type of small dinosaur considered to be closely related to birds) that lived during the Early Cretaceous, about 122 million years ago. Its remains have been found in western Liaoning, China. It was similar to other dromaeosaurids found in Liaoning, with the exception of being somewhat more primitive. The type specimen, formally named in 2010, shows features not seen in previously known Northern Hemisphere (Laurasian) dromaeosaurids, but present in Southern Hemisphere (Gondwanan) species and early birds. Because of this, the scientists who first studied Tianyuraptor described it as a "transitional species", bridging the gap between northern and southern types of dromaeosaurid. Tianyuraptor also differs from previously known dromaeosaurids in that it possesses a relatively small furcula ("wishbone"), and unusually short forelimbs.[1]

Etymology Edit

The generic name of Tianyuraptor combines Tianyu, referring to the Shandong Tianyu Museum of Nature where the holotype specimen is stored, with raptor, the Latin word for 'robber', referring to the action of grabbing prey, often used in naming dromaeosaurids. The specific epithet, ostromi, is in honor of John Ostrom,[1] who contributed greatly to the study of dromaeosaurid fossils, including Deinonychus and feathered dinosaurs.[2][3]

Description Edit

Artist's restoration

Tianyuraptor is a medium-sized dromaeosaurid that has several derived features that separate it from other dromaeosaurids. These include the length of the middle caudal (tail) vertebrae being more than twice that of the dorsal (back) vertebrae, a small and extremely slender furcula, and an unusually long hindlimb that is roughly three times as long as the entire series of dorsal vertebrae. As in other dromaeosaurid fossils discovered in Liaoning,[4] the tail is relatively long at 960 millimetres (38 in), nearly 4.8 times as long as the femur.[1]

The type specimen is STM1–3, a nearly complete and fully articulated skeleton that is only missing the extreme distal end of the tail. A total of 25 fully articulated caudal vertebrae are preserved and at the end three at most are estimated to be missing. The fossil was discovered in the Dawangzhangzi Bed of the Yixian Formation (Jehol Group), located in Lingyuan in western Liaoning, China.[1] The Yixian Formation is an Early Cretaceous rock unit, dated to between approximately 129.7 and 122.1 million years old, in the Barremian and Aptian faunal stages.[5] The Dawangzhangzi Bed specifically has been dated to about 122 million years ago.[6] STM1–3 is believed to be a sub-adult, with features including the incomplete fusion of skeletal parts during ontogeny. The holotype of Tianyuraptor preserves no soft tissues, unlike many other theropod specimens from the Jehol Group.[1]

Limbs Edit

The forelimbs are comparatively short, being only 53% of the hindlimbs' length. This differs greatly from the known skeletal elements of other dromaeosaurids, most of which have relatively long forelimbs that are more than 70% of the hindlimbs' length.[1]

While Tianyuraptor is larger in size than all other known microraptorines, it also has relatively elongated lower hindlimbs, like other microraptorines. In this regard, it is different from most other dromaeosaurids, which have relatively short lower legs.[7] For example, Tianyuraptor has a tibiotarsus/femur length ratio of greater than 1.30, while Velociraptor mongoliensis, a creature of similar size, exhibits a ratio of less than 1.10.[8] Aside from elongate hind limbs, Tianyuraptor is different from other members of Microraptorinae in regards to the relative lengths of the forelimb elements. The forelimbs of Tianyuraptor are proportionally much shorter than those of larger dromaeosaurids. For example, a similar-sized Velociraptor specimen shows an arm/leg length ratio of approximately 0.75., while Tianyuraptor has an arm/leg ratio of 0.53.[1]

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