Xinjiangtitan is an extinctgenus of mamenchisauridsauropod 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 and a weight of 40 tonnes. In 2020 Molina-Perez and Larramendi gave a lower estimation of 27 meters and 25 tonnes, with a total height of 17 meters 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 ancientShanshan 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 preservedin situpostcranial skeleton including the first two caudal vertebrae, all cervical vertebrae, and all dorsal and sacral vertebrae, as well as several cervical, dorsal and sacral ribs, a partial left leg, left and rightpubic 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. Xinjiangtitanshares several derived characters with diplodocids, including prominent ambiens process of pubis, relatively shorthind limb and fourth trochanter on the femur that is caudomedially developed.
