Xinjiangtitan
Xinjiangtitan ) is an extinct genus of mamenchisaurid sauropod known from the Middle Jurassic Qiketai Formation in Piqan County of Xinjiang, northwestern China. Estimates of body length for the holotype are approximately in length, making "Xinjiangtitan" one of the longest sauropods known. In 2016 Gregory S. Paul gave a length of 30 meters (100 feet) and a weight of 40 tonnes (44 short tons). In 2020 Molina-Perez and Larramendi gave a lower estimation of 27 meters (88.6 ft) and 25 tonnes (27.5 short tons), with a total height of 17 meters (56 ft) making it one of the tallest  known dinosaurs. Discovery. "Xinjiangtitan" was first described and named by Wu Wen-hao, Zhou Chang-fu, Oliver Wings, Toru Sekiha and Dong Zhiming in 2013 and the type species is "Xinjiangtitan shanshanesis". The generic name is derived from Xinjiang where the bones were discovered in 2012, and from "titan", giant in Greek mythology. The specific name, "shanshanesis", is derived from an alternative name for the county where it was found, Shanshan, named after the ancient Shanshan Kingdom. The specific name is occasionally misspelled as "shanshanensis" or "shashaensis", which are invalid spellings even though the correct form would indeed have been  shanshanensis rather than "shanshanesis", as the Latin suffix "-ensis" meaning "from", was used to create the name. "Xinjiangtitan" is known solely from the holotype SSV12001, a partial but, apart from some erosion, well preserved in situ postcranial skeleton including the first two caudal vertebrae, all cervical vertebrae, and all dorsal (12) and sacral vertebrae (5), as well as several cervical, dorsal and sacral ribs, a partial left leg (including the femur, tibia, fibula and a metatarsal), left and right pubic bones and right ischium. While in the describing paper it was said to be from the Qigu Formation, this is  incorrect, and it is actually in layers belonging to the Qiketai Formation. Description. "Xinjiangtitan" was diagnosed based on the following traits: the presence of a ventral keel on the penultimate cervical centrum that forms a small semicircular process under the distal articular facet; both cervical vertebrae are relatively elongated; the sacricostal yoke excepts the first sacral rib; and an extremely robust femur. The series of dorsal vertebrae has a length of 372 centimetres. The thighbone is 165 centimetres long, and the tibia is 98 cm. Phylogeny. Among sauropods, a phylogenetic analysis places "Xinjiangtitan" as the sister taxon of "Mamenchisaurus", the  only other mamenchisaurid included. "Xinjiangtitan" shares several derived characters with diplodocids, including prominent ambiens process of pubis, relatively short hind limb and fourth trochanter on the femur that is caudomedially developed.