Mamenchisaurus (/məˌmʌntʃiˈsɔːrəs/ mə-MUN-chee-SOR-əs,[1] or spelling pronunciation /məˌmɛntʃɪˈsɔːrəs/) is a genus of sauropod dinosaur known for their remarkably long necks which made up nearly half the total body length. Numerous species have been assigned to the genus; however, many of these might be questionable. Fossils have been found in the Sichuan Basin and Yunnan Province in China. Several species are from the Upper Shaximiao Formation whose geologic age is uncertain. However, evidence suggests that this be no earlier than the Oxfordian stage of the Late Jurassic. M. sinocanadorum dates to the Oxfordian stage (158.7 to 161.2 mya) and M. anyuensis to the Aptian stage of the Early Cretaceous around 114.4 mya. Most species were medium- to large-size sauropods 15 to 26 meters (49 to 8