The Phylogenetic Evolution Of Titanosauriform Sauropod Dinosaurs In The Lanzhou-Minhe Basin Of Gansu Province

Titanosauriformes is a large clade of sauropod dinosaurs whose members were present and common in most Mesozoic ecosystems,but their inter-relationships remain poorly understood.In particular,the study of phylogenetic evolution of Titanosauriforms in China has not been consistent with that in the world.This paper research Huanghetitan liujiaxiaensis,Daxiatitan binglingi and Yongjinglong datangi produced from the Lower Cretaceous Hekou Group of Lanzhou-Minle Basin,Gansu Province,China,and analysis skeletal evolution characteristics of Titanosauriforms.The cladistics method is used to analyze the phylogenetic relationship of Titanosauriforms.The results will provide a good basis for the study of environmental evolution of dinosaur fossil geological remains in Gansu Province.Titanosauriformes from Hekou Group is distinct each other and has numerous autapomorphies.Huanghetitan had extremely low sacral neural spines and transversely expanded distal ends of the neural spines.The anterior articular surface of the cervical Vertebra of the Daxiatitan moves backward,and the distal margin of the scapular shaft is obliquely crossed with the long axis,femoral distal condyles beveled ~10° dorsolaterally with respect to femoral shaft.Yongjinglong is characteristic of low,unbifurcated neural spine fused with the postzygapophyses to form a cranially-pointing and very deep lateral pneumatic foramina on the lateral surfaces of the cervical.All of them have very obvious skeletal features of the Somphospondyli.However,Daxiatitan and Yongjinglong share more characters in Titanosauria,such as the ventral of the cervical vertebra extended the parapophysis,the posterior of the ventral part of the Cervical Vertebra was medial concave,and the Dorsal Vertebra had lateral foramina.Compared with Sauropod dinosaurs from Jiuquan area of Gansu Province,Euhelopus and Opisthocoelicaudia,Titanosauriformes from Hekou Group is more derived Somphospondyli while Sauropod dinosaurs from Jiuquan area were basel titanosauriforme.The highest average elongation index value(a EI)of Cervical centra of Titanosauriformes from Hekou Group is less than 3 while Euhelopus more than 4.Euhelopus has no concave Fossa on the lateral surface of the posterior cervical vertebra,and the nerve spines of the Middle Dorsal Vertebra did not bifurcate.The sacrum of Huanghetitan is composed of five coossified vertebrae,but six in Euhelopus.At the same time Titanosauriformes from Hekou Group has a lot of defferenc from Opisthocoelicaudia.Dorsal centra not deeply cavernous.Dorsal spines divided into two low metapophyses.Caudals without pleurocoels.Scapula little expanded distally.Coracoid subquadrangular.The three key femoral characters deemed responsible for wide-gauge locomotion of Opisthocoelicaudia were the outwardly angled femora,eccentric femoral midshaft cross-section,and dorsomedially beveled femoral distal condyles.Only first two are present in Daxiatitan.Huanghetitan liujiaxiaensis is recovered as a non-titanosaurian somphospondylan,just basal to the titanosaur radiation.Daxiatitan was recovered as a non-lithostrotian titanosaur,forming the sister clade of Yongjinglong + Savannasaurus+(Diamantinasaurus+AODF 836).