Study On Basal Sauropodomorph Dinosaurs From The Early Jurassic Lufeng Basin Of Yunnan

Lufeng Basin of Yunnan Province is the most important place yielding Early Jurassic dinosaurs fossils in China.Numerous basal sauropodomorphs specimens have been recovered from Lufeng,providing important information on studying the evolution of this taxon.In this dissertation,a new basal sauropodomorph from Lufeng Basin is described in detail,and some debated Lufeng basal sauropodomorph taxa are descriped and revised.Furthermore,a phylogenetic analysis is carried out to investigate the interrelationships of basal sauropodomorphs from Lufeng Basin.The research on basal sauropodomorphs will increase our understanding on the early evolution of dinosaurs during the Late Triassic to the Early Jurassic and on the origin as well as the gigantism of sauropods.The material of Xingxiulong chengi includes three partial skeletons buried together with overlapping elements,thus representing a new basal sauropodomorph taxon that almost completely preserved.Xingxiulong possesses a number of autapomorphies including transversely expanded plate-like summit on top of the neural spine of posterior dorsal vertebrae,four sacral vertebrae,robust scapula,ilium with ventral margin of postacetabular process strongly concave,elongated pubic plate approximately 40% of the total length of the pubis,posterolateral process of distal tibia much narrower anteroposteriorly and extended more laterally and distally than anterolateral process,a median bulge present on the dorsoposterior margin of the astragalus,and metatarsal V with strongly expanded proximal end.Although being relatively primitive,Xingxiulong displays some derived features normally occurred in advanced sauropodiforms including sauropods,such as a four sacral-sacrum,a robust scapula,and a pubis with elongated pubic plate,which indicates a more complicated scenario in the early evolution of sauropodiforms.“Gyposaurus” sinensis was reported in 1941 and represents the most questionable Lufeng basal sauropodomorph taxon.The taxonomic status of this taxon has long been debated ever since.The remained holotype of“Gyposaurus” sinensis is restudied here.Both the unfused dorsal vertebrae and the bone histology of the fibula suggest that“Gyposaurus” sinensis was a young juvenile.In addition,the morphology of the holotypespecimens of “Gyposaurus” sinensis strongly resembles that of Lufengosaurus huenei.In addition,the taxonomic status of Lufengosaurus magnus is preliminarily studied.Lufengosaurus magnus differs from Lufengosaurus huenei in morphology,whereas it is more similar to Jingshanosaurus xinwaensis.Two phylogenetic analyses were performed in order to investigate the interrelationships of basal sauropodomorphs.The first analysis was based on a data matrix that consisis of 55 taxa and 356 characters,in which Xingxiulong chengi was added,and the second analysis was based on 56 taxa that includes Xingxiulong chengi and“Gyposaurus” sinensis.The strict consensus tree is poorly resolved within basal sauropodomorphs given the complex evolution of these taxa in which numerous convergent features exists.Reduced strict consensus tree resolves Xingxiulong as one of the basalmost sauropodiforms,suggesting that there were two evolutionary clades among Lufeng basal sauropodomorphs: one as a member of Massospondylidae,and all others on the Sauropodiformes clade,especially at its base,and shows that “Gyposaurus” sinensis has a close relationship with Lufengosaurus huenei,which is consistent with their similarity in morphology,indicating that “Gyposaurus” sinensis is probably a junior synonym of Lufengosaurus huenei.