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Earth Science Frontiers, Vol. 17, Special Issue, Aug. 2010 ISSN 1005-2321 232 The Evolvement of Long-necked Sauropods of Sichuan Basin Chunyan Yang 1 , Kui Li 1 , Jian Liu 1 , Tao Jiang 2 , Zhiguang Li 2 1. The Museum of Chengdu University of Technology, Chengdu 610059, China (E-mail: ycy-y@163.com) 2. Institute of Sedimentary Geology of Chengdu University of Technology, Chengdu 610059, China Lots of sauropod fossils, including long-necked type and short-necked type, had been discovered in the Jurassic of Sichuan Basin. There are three genera of long-necked sauropods: Tonganosaurus from the Early Jurassic, Omeisaurus from the Middle Jurassic, Mamenchisaurus from the Middle and Late Jurassic. The Early Jurassic sauropod Tonganosaurus from Yimen Formation in Huili (in the south of Sichuan Province) is among the earliest known long-necked sauropod dinosaur in the Sichuan Basin. Tongano- saurus hei Li et al., 2010 is the only species of this genus. According to the original description by Li et al. (2010), Tonganosaurus is a moderate sauropod (its length is approximately 12 m), Pleurocoels are developed in all presacral vertebrae, and the bone texture is solid. 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 4 th trochanter (Li et al.,2010). The Middle Jurassic sauropod Omeisaurus have six species, they are Omeisaurus junghsiensis Young, 1939 (Young, 1939) from Rongxian County, Omei- saurus fuxiensis Dong et. al., 1983 (Dong et al., 1983) from Zigong County,Omeisaurus tianfuensis He et. al., 1984 (He et al.,1984)from Dashanpu of Zigong County, Omeisaurus luoquanensis Li, 1988 (He et al., 1988) from Luoquan of Zizhong County,Omeisaurus changshouensis Young , 1958 (Young, 1958) from Changshou County of Chongqing Municipality, Omei- saurus maoianus Tang et al., 2001 (Tang et al., 2001) from Huangshikang of Jingyan County . Above all six species of Omeisaurus have been discovered in the Shaximiao Formation. Their geographic positions extend from south to east of Sichuan Basin. Omei- saurus are middle, 18-m-long sauropods, their skull moderately high. Teeth spatulate and robust. The denticles well developed on the anterior edge of the teeth, poor or absent on its posterior edgr. The vertebral formula: 17 cervicals, 12 dorsals. Posterior cervical and anterior dorsal spine simple and not bifurcated, anterior caudals slightly amphicoelous; first caudal rib more less fan-shaped (He et al., 1984). Genus Mamenchisaurus had been established in 1954 on the basis of sauropod fossils from the Sha- ximiao Formation of Yibin County. Mamenchisaurus constructus Young, 1954 is the type species (Yang, 1954). Beside, there are four species of Mamen- chisaurus had been found in Sichuan Basin, they are: Manenchisaurus hochuanensis (Young and Zhao, 1972) from the Shaximiao Formation of Taihe Town of Hechuan County (Yang and Zhao, 1972), Manen- chisaurus anyueensis (He et al.,1996) from the Penglai- zhen Formation (Late Jurassic) of Longqiao Town, Anyue county (He et al., 1996), Manenchisaurus youngi (Pi et al., 1996) from the Shaximiao Formation of Zigong County, Manenchisaurus jingyanensis (Zhang et al., 1998) from the Shaximiao Formation of Jingyan County (Zhang et al., 1998). Mamenchi- saurus are large size sauropods (their length approximately 24m long) with exteremely small skull. Occipital crest is well developed. Mandible slender with a hight symphyseal region. External mandiblular foramen is present. Teeth arranged closely. The wear facets of teeth prominent, and denticles on the posterior carinae degenerate. Vertebral formula: 18-19 cervicals, 12 dorsals, 4-5 sacrals and more than 50 caudals. Presacrals are opsithocoelous with cacell- ous structure in varying degree. Posterior cervical and anterior dorsal spine bifurcated, Cervicals elongated with long cervical ribs. Anterior caudals are procoelous, the middle-posterior ones amphicoelous,and distal caudals fused and expanded. There are typical diplodocoid forked chevrons in the middle tail region. Scapula is longer than femur with a expanded distal blade. Sternum small and subcircular. The length ratio of forelimb and handlimb about 0.75 to 0.80 (Ouyang and Ye, 2002). Those three long-necked sauropods bear many homology characteristics: 1) their cervical centra are slender, the ratio of centrum length to posterior width in the 3 rd cervical are more than 2.90; They have or more 15 cervical centra; 2) Anterior dorsal centra, in which both laminae and pleurocoels are well developed, are opisthocoelous; 3) Forelimb length is 0.75~0.80 of hindlimb length. Owing to the above resemble characteristic, we considered that Tonganosaurus,
Earth Science Frontiers, Vol. 17, Special Issue, Aug. 2010 ISSN 1005-2321 Omeisaurus and Mamenchisaurus have close relation- ships with each other. In other words, Tonganosaurus may be Omeisaurus, ancestor, and Mamenchisaurus may be Omeisaurus’ descendant and developmental offspring, they bear clear phylogenetic evolvement. The evolutionary direction of those three long- necked sauropods showes as fellows: Firstly, the bodily form becomes more and more big; Secondly, centra structure become more and more complex. We take pleurocoels of the presacral centra as example. Tonganosaurus’ pleurocoels are large and deep, but simple in structure; Every pleurocoel of Omeisaurus is divided into many parts by clapboards; There are too many ridges or clapboards in pleurocoel of Mamen- chisaurus to find the pleurocoel’ shape; Third, the bone texture of centra become poriferous from solid. Key words: Sichuan Basin; Long-necked sauropod; Evolvement References: Dong Z.M., Zhou S.W., Zhang Y.H. The dinosaurian remains from Sichuan Basin, China. Palaeont Sin, 1983, New Ser C (23): l-145 (in Chinese with English summary). He X.L., Li K., Cai K.J., et al. Omeisaurus tianfuensis: A new species of Omeisaurus from Dashanpu, Zigong, Sichuan. Journal of Chengdu Institute of Geological, 1984, supplement: 13-32 (in Chinese with English summary). He X.L., Li K., Cai K.J. The Middle Jurassic Dinosaur Fauna from Dashanpu, Zigong, Sichuan. Vol. 4, Sauropod Dinosaurs (2), Omeisaurus tianfuensis. Chengdu: Sichuan Publishing House of Science and Technology, 1988: 1-143 (in Chinese with English summary). He X.L, Yang S.H, Cai K.J. New discovery of Mamen- chisaurus (Dinosaur: Sauropoda), Symposium of Geological Science. Beijing: China Economy Publishing Company, 1996: 83-86. Li K., Yang C.Y., Liu J., et al. A New Sauropod from the Lower Jurassic of Huili, Sichuan, China. Vert PalAsiat, 2010, 48(3): 185-202 (in Chinese with English summary). Ouyang H., Ye Y. The First Mamenchisaurian Skeleton with Complete Skull, Mamenchisaurus youngi. Chengdu: Sichuan Publishing House of Science and Tech- nology, 2001: 1-111 (in Chinese with English summary). Peng G.Z., Ye Y., Gao Y.G., et al. Jurassic Dinosaur Faunas in Zigong. Chengdu: Sichuan People’s Publishing House, 2005: 69-98 (in Chinese). Tang F., Jin X.S., Kang X.M., et al. Omeisaurus, a Complete Sauropoda from Jingyan, Sichuan. Bei- jing: China Ocean Press, 2001: 1-112 (in Chinese with English summary). Young C.C. On a new Sauropoda, with notes on other fragmentary reptiles from Szechuan. Bulletien of the Geological Society of China, 1939, 19: 279- 316. Young C.C. On a new sauropod from Yiping, Szechuan, China. Acta Scientia Sinica, 1954, 3(4): 481-503. Young C.C. New sauropods from China. Vertebrata PalAsiatica, 1958, 2(1): 1-28. Yang Z.J., Zhao X.J. Mamenchisaurus hochuanensis. Institute of Vertebrate Paleontology and Palaeon- thropology Monographs, 1972, Series A, 8: 1-30 (in Chinese). Zhang Y.H., LiK., Zeng Q.H. A new species of sauropod dinosaur from the Upper Jurassic of Sichuan Basin, China. Journal of Chengdu University of Technology, 1998, 25(1): 61-68 (in Chinese with English summary). 233
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