The Research And Phylogenetic Analysis Of A New Materials For Yimenosaurus From Jiaojiadian District,Yimen County,Yunnan Province,China

Lufeng basin,Yunnan Province,is the most important source of dinosaur fossils in early Jurassic in China.The discovery of a large number of basic sauropods provides an important basis for the study of the evolution of this group.The discovery of Yimen-Eshan dinosaur fauna in Yuxi area,Yunnan Province,has expanded the distribution of Lufeng sauropod fauna.This paper describes in detail the new materials of basic sauropod type which are produced in Yimen County,Yunnan Province.It is considered as Yimenosaurus cf.youngi,and on this basis,the phylogenetic analysis of Yimenosaurus and other basic sauropods in Yunnan Province is carried out,which is helpful to understand the early evolution mechanism of basic sauropods and the origin of sauropods.The main characteristics of Yimenosaurus cf.youngi include: long and thin cervical vertebrae,all of which are biconcave;short dorsal vertebrae,and biconcave anterior dorsal vertebrae,The posterior dorsal vertebra is of flat concave type,and the change trend of nerve spine becomes higher and narrower from the front to the back;the anterior two parts of the sacral vertebra heal and the third one is free;the coccygeal vertebra is short,without lateral concave development and slightly contracted in the middle,both of which are of double concave type;the forelimb is shorter than the hind limb;the scapula is thick,and the proximal and distal parts are significantly expanded;the sternum is larger,showing a nearly round diamond shape;the humerus is shorter than the femur,The proximal part is strongly expanded,the triangular ridge is developed,the shaft of ulna is thicker than that of radius,and the radius is thin,It is slightly longer than the ulna;the central part of the ischial shaft contracts strongly,and the proximal part expands significantly,showing a "Y" shape;the pubis and Ischia are nearly the same length;the length of the ischial stalk of the ilium is slightly shorter than that of the pubic stalk;the femoral shaft is thick,the right shaft is "s" shaped bent,the small turning joint is not developed,and the fourth rotor is fertile;the length of the tibia is 0.68 of the length of the femur,and the fibula is smaller than the tibia,slightly shorter than the tibia.Compared with other basic stem lizards,Yimen specimen has many similarities with Lufengosaurus magnus.In phylogenetic analysis,based on the characteristic matrix of Mc Phee et al.,the author determined the taxonomic position of Yimenosaurus among the genera and species of Sauropoda and the relationship between them.It is shown in the tree diagram that the Yimenosaurus youngi and Jingshanosaurus xinwaensis form a sister group,while the comparison shows that the Yimenosaurus youngi is very similar to Lufengosaurus magnus and Jingshanosaurus xinwaensis,so the author thinks that the three species of Yimenosaurus youngi,Lufengosaurus magnus and Jingshanosaurus xinwaensis may be the same thing and different names.