A NEW SPECIES OF OMEISAURUS FROM THE MIDDLE JURASSIC OF ZIGONG,SICHUAN

记述了产自四川自贡大山铺中侏罗世峨眉龙属一新种——焦氏峨眉龙（Omeisaurusjiaoisp.nov.）。新种为大型蜥脚类恐龙，以如下特征区别于其他蜥脚类：前、中部背椎为典型的后凹型，后部背椎为双平型，背椎神经棘呈高大棒状，不分叉；尾椎为弱双凹型，第一尾椎不具扇形尾肋；第一脉弧短小且与第一尾椎关联；锁骨长大；肱骨和股骨细长而圆实；肱骨与股骨长度之比为0.83，尺骨与肱骨长度之比为0.72，胫骨与股骨长度之比为0.63。

Omeisaurus jiaoi, a new species of giant sauropod is described in this paper. Tile specimen （ZDM 5050） was discovered from the Xiashaximiao Formation of the Middle Jurassic of ZigongDinosaur Museum, Sichuan. ZDM 5050 is a nearly complete skeleton. Its main features can be summarized as follows： dorsal vertebrae are tall and large. The anterior dorsal vertebrae （dorsals 1 to 6） are opistho- coelous. The pleurocoels of the dorsal vertebrate are well developed except on the 1^st dorsal. The neural spines are club-like and the neural spines of the anterior dorsal vertebrae are not bi- furcated. Caudal vertebrae are relatively short and thick. The anterior caudal vertebrae are slightly amphicoelous. The chevron of the 1^st, caudal vertebrae is connected with the 1st caudal and is shallow and small. Whereas the ^st caudal vertebrae of Omeisaurus tianfuensis have no chevron. The rib of the 1^st caudal vertebrae are laterally directed, while the first caudal rib of the other species of Omeisaurus are prominently enlarged distally, being slightly fan-shaped. Humerus is long and straight, with slightly expanded proximal end and greatly expanded distal end. The dehopectoral crest is well-developed and relatively low. Femur is slender in shape, with greatly expanded proximal and distal ends. The fourth trochanter is well-developed. The ratio of the humerus to femur length is approximately 0. 83, the ratio of the ulna to humerus length is approximately 0.72, and the ratio of the tibia to femur length is approximately 0.63.