Sedimentological evidence suggests an Early Jurassic age for Yunnanosaurus youngi (Dinosauria: Sauropodomorpha) in Yunnan Province of China

The age of Yunnanosaurus youngi, a non-sauropod basal sauropodomorph, was reported as the Middle Jurassic. However, no basal sauropodomorphs have been reported worldwide in the Middle Jurassic previously, and only one clade of sauropodomorphs, Sauropoda, existed in the Middle Jurassic and became extinct by the end of the Cretaceous. Here, we further investigated the locality and its horizon of Yunnanosaurus youngi in Jiangyi, Yuanmou County, Yunnan Province, China. We found the species horizon is actually from the Lower Jurassic Fengjiahe Formation, and its age is probably Pliensbachian. Furthermore, the three known Yunnanosaurus-bearing horizons in Chuxiong, Yunnan can be correlated lithostratigraphically. Abbreviations FJHF: Fengjiahe Formation; LFF: Lufeng Formation; P: profile; TJB: Triassic-Jurassic boundary; YNOQ: quarry of Yunnanosaurus youngi; ZHF: Zhanghe Formation.