Mamenchisaurus

Mamenchisaurus ( , or spelling pronunciation ) is an extinct genus of sauropod dinosaurs known for their remarkably long necks, which made up nearly half the total body length. Numerous species have been assigned to the genus; however, the validity of these assignments has been questioned. Fossils have been found in the Sichuan Basin and Yunnan Province in China. Several species from the Upper Shaximiao Formation, whose geologic age is uncertain, have been described. However, evidence suggests this formation to be no earlier than the Oxfordian stage of the Late Jurassic. M. sinocanadorum dates to the Oxfordian stage (161.2 to 158.7 mya), and M. anyuensis to the Aptian stage of the Early Cretaceous (around 114.4 mya). Most species were medium-large to large sauropods, measuring roughly in length—possibly up to , based on two undescribed vertebrae.

==History and species== left|thumb|Mounted M. hochuanensis skeleton, Field MuseumMamenchisaurus was first discovered in 1952 on the construction site of the Yitang Highway in Sichuan Province, China. The fossil site belonged to the Upper Shaximiao Formation, dating to at least the Late Jurassic. The partial skeleton fossil was later studied and named Mamenchisaurus constructus in 1954 by the renowned Chinese paleontologist Professor C. C. Young.