A new mamenchisaurid sauropod dinosaur from the Upper Jurassic of Southwest China reveals new evolutionary evidence from East Asian eusauropods

East Asian non-neosauropodan eusauropods have been central to the study of the evolution of Middle to Late Jurassic sauropod dinosaurs. Despite their remarkable diversity, the fragmentary condition of many taxa and the insufficiency of phylogenetic data for many specimens have hindered the study of continental-scale paleobiogeographic relationships. We described a new mamenchisaurid, Mamenchisaurus sanjiangensis sp. nov., based on a single partial skeleton from the early Oxfordian fossil site of Chongqing (Southwest China). M. sanjiangensis phylogenetically recovered as a diverged mamenchisaurid, shares a relatively near relationship with most other Mamenchisaurus. This new taxon is supported by an exclusive combination of characters that highlights strong convergences with members of the neosauropods. That indicates the niche overlap further enhances the competition between mamenchisaurids and neosauropods. Mamenchisaurids potentially developed a strategy to maintain dominance in East Asia before the recoupling of the East Asian and European sub-plates in the Early Cretaceous.