Discovery of large neosauropod vertebrae from the earliest Middle Jurassic of China

Sauropod dinosaurs were the largest terrestrial animals to have ever lived on Earth. However, in the initial evolutionary stages of sauropod gigantism, few fossils are known. In China, most non-sauropod sauropodomorphs from the Early Jurassic Lufeng Formation of southwestern China do not exceed 10 m in length, while all sauropods from the Middle Jurassic (Bajocian-Bathonian) Dashanpu quarry in the Sichuan Basin do exceed 10 m in length, with its largest member (Omeisaurus) around 20 m long. Here, we report two large middle-posterior dorsal centra from dorsal vertebrae (the largest and most complete measures 142 mm in length, 201 mm in height and 230 mm in width at its posterior articular surface) and other associated elements of a large sauropod recovered from the earliest Middle Jurassic (Aalenian) Xintiangou Formation in the Sichuan Basin of China. Cladistic and anatomical analyses clarify the affinities of the Xintiangou specimen and early sauropod gigantism. This early-diverging eusauropod may represent a basal neosauropod and ranks among the largest Middle Jurassic early giant sauropods known from China. This discovery also provides further support for eusauropod-dominated assemblages that could have existed in East Asia at the beginning of the Middle Jurassic.