New information on Shanshanosaurus huoyanshanensis, a juvenile tyrannosaurid (Theropoda, Dinosauria) from the Late Cretaceous of China

Shanshanosaurus huoyanshanensis from the Subashi Formation (Upper Cretaceous) of Xinjiang in northwestern China has long been thought of as a distinctive genus of small theropod. Although usually assigned to its own family, it has generally been included in the tyrannosaurid subfamily Aublysodontinae in recent years. Restudy and description of the only known specimen reveal that it is not a small species, but is a juvenile tyrannosaurine, possibly Tarbosaurus. With a total estimated length of 2.3 m, it is the smallest tyrannosaurid skeleton known. Shanshanosaurus provides the best information available on ontogenetic changes in these enormous carnivores and reveals that young tyrannosaurids had long, low skulls, huge pubic boots, and well-developed limb joints. Evidence suggesting that young tyrannosaurs had relatively longer forelimbs than the adults is not supported by Shanshanosaurus.