New Basal Sauropodomorph Materials From The Lower Jurassic Fengiiahe Formation In Yimen,Yunnan

The basal sauropodomorph dinosaurs lived in the Late Triassic to the Early Jurassic(230-190 million years ago).They were completely extinct in the late Early Jurassic and replaced by sauropods.Their fossil records are widely distributed in all continents except Oceania,but in China 7 valid genera have been reported in Yunnan presently.The research on the basal Sauropodomorpha in Yunnan started relatively late.There are some problems such as specimen mismatch and loss,unstable classification position and so on.The study of new material not only provides new information on the sauropodomorph morphological characteristics from Yunnan,but also helps to further explore the evolutionary relationship between the basal sauropodomorph forms in Yunnan.Here we report the new basal sauropodomorph material excavated from the Lower Jurassic Fengjiahe Formation in Jiaojiadian,Yimen,including five continuous vertebrae with the complete sacrum and a pair of incomplete ilia.The specimen was organized and prepared,photographed and reconstructed by 3D scanning.Then we described and compared it with other basal sauropodomorph specimens in China.It was found that it has obvious variation from other specimens from China in morphology,such as huge and robust sacrum,more complex and developed transverse process and sacral rib,presence of caudosacral,etc.This specimen may present a new species.And the fusion degree between centrums shows that it is an adult.The results of phylogenetic analysis not only show the relationship between the specimen and other Chinese basal sauropodomorphs,but also show that it is closer to sauropods,which is also consistent with the morphological performance of the specimen in this paper.In addition,the body mass of the basal sauropodomorph individuals in China are calculated by the formula.The new material not only retains some plesiomorphies of the basal sauropodomorph,but also shows the morphological characters similar to the sauropod,such as the reduction of the ischial peduncle of the ilium,which indicates that the individual is likely to be in the transitional stage of the evolution of the basal sauropodomorph into the sauropod.In addition,the huge sacrum indicates that it may be quadrupedal to support the huge body better.Therefore,the new material may represent the new basal sauropodomorph quadrupedal adult species discovered in China.It makes a transition to the giant sauropods.Also,it infers that the evolution from basal Sauropodomorpha to Sauropoda began in the early Jurassic.