Yangchuanosaurus

Yangchuanosaurus is an extinct genus of metriacanthosaurid theropod dinosaur that lived in China from the Middle Jurassic to Late Jurassic periods (Bathonian to Tithonian stages), and was similar (although slightly larger) in size and appearance to its North American and European relative, Allosaurus. Yangchuanosaurus hails from the Upper Shaximiao Formation and was the largest predator in a landscape that included the sauropods Mamenchisaurus and Omeisaurus and the stegosaurs Chialingosaurus, Tuojiangosaurus and Chungkingosaurus. This theropod was named after the area in which was discovered, Yongchuan, in China.

==Discovery and species== thumb|left|Mounted skeleton of Y. zigongensis, Delaware Museum of Natural History Dong et al. (1978) named Yangchuanosaurus shangyouensis on the basis of Municipal Museum of Chongqing 00215, a complete skull and skeleton which was collected from the Shangshaximiao Formation, near Yongchuan, Yongchuan District, Sichuan. It dates to the Oxfordian stage of the Late Jurassic period, about 161.2 to 157.3 million years ago. It was discovered in June 1977 by a construction worker during the construction of the Shangyou Reservoir Dam. A second species from the same locality, Y. magnus, was named by Dong et al. (1983) on the basis of CV 00216, another complete skull and skeleton. A detailed revision of tetanuran phylogeny by Carrano, Benson & Sampson (2012) revealed that both species are conspecific. Dong et al. (1978) and Dong et al. (1983) differentiated these species primarily on the basis of size. In addition, Dong et al. (1983) noted that the maxilla of Y. magnus has an additional fenestra within the antorbital fossa, whereas Y. shangyouensis possessed only a fossa in this location. However, it is considered to be an intraspecific, possibly ontogenetic, variation. Furthermore, the apparent difference in cervical vertebral morphology can be explained by comparing different positions within the column. Hence, the holotypes of the two species of Yangchuanosaurus are effectively identical, and their codings are identical in Carrano et al. (2012) matrix. Gregory S. Paul (1988) regarded this genus as a synonym of Metriacanthosaurus, but this has not been supported.