Allain & Aquesbi, Citation2008 Mannion et al., Citation2013 Pol et al., Citation2020 Tan et al., Citation2021 Upchurch, Citation1995, Citation1998 Wilson, Citation2002 Xing et al., Citation2015). This analysis provided the first quantitative support for the oft-cited close kinship of Mamenchisaurus and Omeisaurus (e.g. hochuanensis (Young & Zhao, Citation1972). Anatomical data derived from Mamenchisaurus sinocanadorum were included in the first published cladistic analysis of sauropods (Russell & Zheng, Citation1993), in a genus-level Mamenchisaurus operational taxonomic unit (OTU) that also incorporated information from M. Wang et al., Citation2019, Klamelisaurus gobiensis Zhao, Citation1993 and Mamenchisaurus sinocanadorum Russell & Zheng, Citation1993, the latter being one of only a few currently recognized occurrences of the genus Mamenchisaurus from outside the Sichuan Basin of south-western China (Upchurch et al., Citation2004, Citationin press).Ĭhinese sauropods in general, and several of those from the Shishugou Formation in particular, have played a central role in the development of key phylogenetic, biogeographical and biomechanical hypotheses relating to the Jurassic evolution of Eusauropoda, and are central to a number of ongoing debates. To date, four additional species of sauropod have been named from the Shishugou Formation: Bellusaurus sui Dong, Citation1990, Fushanosaurus qitaiensis X.-R. Since that time, numerous fossil discoveries in the Shishugou Formation have revealed a diverse vertebrate fauna composed of fishes, brachyopoid temnospondyls, turtles, mammaliamorphs, squamates, crocodylomorphs, pterosaurs and dinosaurs, including a particularly rich record of neotheropods (Clark et al., Citation2006 Dong, Citation1993 reviewed by Xu et al., Citation2022). Yuan and the Sino-Swedish Expedition, which yielded its first recorded dinosaur fossil, the sauropod Tienshanosaurus chitaiensis (Sullivan et al., Citation2012 Young, Citation1937 Xu et al., Citation2022). Palaeontological exploration of the Shishugou Formation began in 1927, by Professor F. The Middle–Upper Jurassic Shishugou Formation is extensively exposed in the Junggar Basin of the Xinjiang Uyghur Autonomous Region, in north-western China (Clark et al., Citation2006 Dong, Citation1993 Eberth et al., Citation2001 Xu et al., Citation2022). Given that extent of pneumaticity responds dynamically to a bone’s habitual loading, we propose that long cervical ribs – and other structural modifications that limited flexibility – promoted the evolution of increasingly long necks by producing a more predictable biomechanical milieu amenable to increased pneumatization. sinocanadorum stabilized the neck by limiting its mobility. Previous work has suggested that the elongated cervical ribs of particularly long-necked sauropods such as M. sinocanadorum that is comparable to that of the largest sauropods, and updated scaling analyses imply a neck over 14 m long, rivalling estimates for other exceptionally long-necked sauropods. Finally, computed-tomography reveals extensive vertebral pneumaticity in M. Analyses that score ontogenetically variable characters ambiguously recover Bellusaurus and Daanosaurus as juvenile mamenchisaurids, a hypothesis supported by several features that are unique to mamenchisaurids or exhibit little homoplasy, including anteriorly bifurcate cervical ribs. We recover all species of Mamenchisaurus as part of a radiation of predominantly Middle–Late Jurassic East Asian eusauropods, but the genus is non-monophyletic, underscoring the need for further systematic revision of mamenchisaurid taxonomy. We incorporate new data into a phylogenetic character matrix that also includes Bellusaurus and Daanosaurus, both of which are known only from juvenile material and are often hypothesized to be neosauropods (or close relatives thereof). Although the original diagnosis is no longer adequate, we identify several autapomorphies that support the validity of this species, including an elongate external mandibular fenestra and distinctive pneumatic structures on the cervical centra. Here, we re-describe the holotype and only specimen of M. Although included in the first cladistic analysis of sauropods, only recently has the monophyly of Mamenchisaurus, and the anatomical diversity of the many penecontemporaneous East Asian eusauropods, been evaluated critically. The sauropod genus Mamenchisaurus, from the Late Jurassic–Early Cretaceous of East Asia, has a convoluted taxonomic history.
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