The Research And Quantitative Phylogenetic Analysis Of A New Sauropod From The Lower Jurassic Of Huili, Sichuan, China

Sauropods are most popular and attractive sample in museum because of their colossal bodies,and they also are most important dinosaur for extensive distributing both geological and geographical distribution.These fossils include about 20 vertebrae, a complete right pectoral girdle and right forelimb, the distal end of a left scapula, a pair of complete ischia, a complete right hindlimb, the proximal and distal ends of a left femur, right metatarsals (mt. I, II, III and V), a right pedal ungual, and ten neural spine and rib fragments. The third cervical and anterior caudals are most similar in shape to those of the mamenchisaurid Omeisaurus (from the Middle Jurassic, Sichuan Basin), and quite different from those of other sauropod. The material was therefore assigned to the Family Mamenchisauridae Young & Chao, 1972 and a new genus and species were established. This represents the first discovery of a sauropod in the Lower Jurassic of China since Gongxianosaurus was found in Sichuan Basin. The Tonganosaurus material is of great importance for understanding the phylogenetics of the early Sauropoda.Diagnosis of the new genus Tonganosaurus are as fellows: Pleurocoels are developed in all presacral vertebrae, and the bone texture is solid. Pleurocoels are large and deep. Cervical centra are slender. A ventral keel is present on each cervical centrum. Posterior cervical centra have well developed laminae and cavities. Both laminae and pleurocoels are well developed in the dorsal vertebrae. Cervical and anterior dorsal centra are opisthocoelous, middle dorsal centra are platycoelous, posterior dorsal and anterior caudal centra are amphicoelous. Centra lack a cancellous structure. Forelimb length is 80% of hindlimb length. Humerus is straight and robust, and deltopectoral crest is well developed. Femur is straight and robust with a well developed 4th trochanter. Tonganosaurus, which comes from the Early Jurassic of Sichuan Basin and belong to long-neck sauropods, have fill up big vacancy both of geography and geohistory.Tonganosaurus bear both progressive and primitive characteristics of sauropod dinosaurs. Its progressive characteristics are described as fellows: firstly, thin and long cervical vertebrae, centrum parameters of the third cervical is 2.91; Secondly, Pleurocoels are developed in all presacral vertebrae, and the pleurocoels are big and deep;Thirdly, Posterior cervical centra and anterior dorsal centra have well developed laminae and cavities; Fourthly, forelimb is long, its length is 80% of hindlimb length. Primitive characteristics of Tonganosaurus are described as fellows: firstly , the bone texture of centra is solid , and has no honeycomb structure ; Secondly, structure of pleurocoel on presacral is simple, there is no any clapboard; Thirdly, neural spines of posterior cervical and anterior dorsal are not bifurcate. Fourthly, humerus and femur are straight and robust, horizontal cross section of diaphysis are round in shape.Tonganosaurus is different from all other sauropods currently known from the Late Triassic to the Late Jurassic, both in China and abroad. Among the sauropods mentioned above, Omeisaurus from the Middle Jurassic of Sichuan is most similar to Tonganosaurus. The similarities are as follows: they both bear thin and long cervical vertebrae, their centrum parameters of the third cervical are both bigger than 2.50, their anterior cervical centra have low and long neural spines , well developed ventral keels and parapophyses on the cervical vertebrae, well developed pleurocoels on the presacral centra, the presacral centra are constricted near the mid-point, extremely well-developed laminae and cavities in the posterior cervical and dorsal vertebrae, a forelimb to hindlimb length ratio of 0.80, and a straight and robust humerus and femur. However, Tonganosaurus has simply constructed presacral centra, while Omeisaurus has complex presacral centra. Furthermore, the ratio of humeral length to femoral length in Tonganosaurus is 0.75, compared to 0.80 in Omeisaurus. Dong and Tang (1984), He et al. (1988), Li (1998a) and others have attributed Omeisaurus to the Family Mamenchisauridae Young & Chao, 1972, so we attribute Tonganosaurus to this family as a newly established genus. This new genus is more primitive than Omeisaurus in its characteristics.On Sichuan Basin, almost primitive sauropods are discovered on the Lower Jurassic and the lower member of the Middle Jurassic. Where progressive sauropod, which are take for long-neck sauropods, are discovered on the Middle Jurassic and the Upper Jurassic. Tonganosaurus, which bear both progressive and primitive characteristics of sauropod dinosaurs, are discovered on the Lower Jurassic. Therefore, fossils of Tonganosaurus are important for researching on phylogenetic relationship of sauropods from southwest, China.We thought that Tonganosaurus and Omeisaurus have close relationship, Tonganosaurus may be Omeisaurus ancestor, and Mamenchisaurus may be Omeisaurus'inherit and developmental offspring, this three long-neck sauropods bear clear phylogenetic evolvement. Their evolvemental direction showed:the bodily form becoming more and more bigger, centra structure becoming more and more complexer, the bone texture of centra becoming poriferous from solid.We research on the phylogenetic position of Tonganosaurus on the sauropods by Quantitative Phylogenetic Analysis. The process of Tonganosaurus'Quantitative Phylogenetic Analysis are as fellows: We incorporated Tonganosaurus'morphologyi- cal characters into the data matrix of Upchurch (1998), Wilson (1998) and Lii (2010) respectively. The data matrix of Upchurch (1998) has 205 characters for one sauropod dinosaurus, of Wilson (1998) has 109 characters and of Lii (2010) has 91 characters. The phylogenetic analysis was conducted using Colour-compare Method and TAD v1.0. Lii (2010) matrix, Colour- compare method and TAD v1.0 are compiled especially in order to researching phylogenetic relationship of Tonganosaurus and sauropods from Sichuan Basin, those are original method of sauropods at home. Being straightforward and clear are outstanding characteristic of Colour- compare method. Analysing and comparing fleetly between sauropods come true by TAD. The result of Quantitative phylogenetic analysis showed that Tonganosaurus and Omeisaurus have close relationship. The result also showed Tonganosaurus may be Omeisaurus ancestor, and Mamenchisaurus may be Omeisaurus'inherit and developmental offspring, this three long-neck sauropods bear clear phylogenetic evolvement .