| Sauropod is the largest terrestrial vertebrates appeared in the history of the earth,and Mamenchisauridae is a large sauropod with East Asian characteristics. This paperresearch Mamenchisauridae mainly produced in the southwest region of China,analysis skeletal evolution characteristics of Mamenchisaurus in the Mesozoic Jurassic,and the cladistics method is used to analyze the phylogenetic relationship ofMamenchisauridae.Mamenchisauridae have4genera and16species.4genera are respectivelyTonganosaurus, Abrosaurus, Omeisaurus and Mamenchisaurus.16species arerespectively Tonganosaurus hei Li et al.,2010, Abrosaurus dongpoi Ouyang，1989, O.junghsiensis Young，1939, O. changshouensis Yong,1958, O. tianfuensis He et al.，1984, O. luoquanensis Li，1988, O. maoiaus Tang et al.，2001, O. jiaos，et at.，2011,M. constructus Young，1954, M. hochuanensis Young et Zhao，1972, M.guangyuanensis Zhang，1981, M. anyueensis He et al.，1996, M. youngi Pi et al，1996,M. jingyanensis Zhang et al，1998, M. sinocanadorum Russell，1993, M. yunnanensisFang et al.，2004。In addition to M. sinocanadorum, M. yunnanensis and M. hochuanensis fromYongdeng, Gansu, the rest of the genera and species are all excavated in Sichuan basin.Mamenchisauridae has the obvious characteristics of the times, mainly reflected ingeological and geographical distribution, the number of fossils sites, the number ofgenera and species and so on. In the early Jurassic, Mamenchisauridae has only1genera and1species of fossils, only one fossil site is located in the south of Sichuan. Inthe middle Jurassic, Mamenchisauridae have3genera,9species of fossils, and about15fossils sites. All of fossils sites belong to the Shaximiao formation. Limestonecontaining conchostraca fossil as a bounded, the Shaximiao formation is divided intotwo sections, the lower section and the upper section.The fossils sites belonged to the lower section of Shaximiao formation are mainlydistributed in the southeast of Sichuan Basin, the rest are located in the west and north,including Sichuan Basin, Gansu and Xinjiang. In the late Jurassic, Mamenchisauridaehave1genera,2species and4fossils sites, distributed throughout the southwest, including Dianzhong basin in Yunnan province and Sichuan basin.The most original of Mamenchisaurus member is Tonganosaurus hei, the fossilssites horizon is the Yimen formation(J1y) belonged to the early Jurassic.The latest is M.anyueensis and M. yunnanensis, the fossils sites horizons are respectively thePenglaizhen formation (J3p), the Suining formation (J3s) and Anning formation (J3a).The Shaximiao formation (J2s) is the main Mamenchisauridae fossils bearing horizons.The geological distribution of Mamenchisaurus from early to late are as follows:Tonganosaurus hei (J1)，Abrosaurus dongpoi (J2)，O. tianfuensis (J2)，O. jiaos (J2)，O. maoiaus (J2)，O. junghsiensis (J2)，O. changshouensis (J2)，M. youngi (J2)，M.hochuanensis (J2)，M. constructus (J2)，M. jingyanensis (J2)，M. sinocanadorum (J2)，M. anyueensis (J3)，M. yunnanensis (J3).Fossils of M. hochuanensis (two individuals from Hechuan of Chongqing,Huidong of Zigong)，M. youngi，O. tianfuensis (holotype) and O. jiaos are relativelyintact, most of fossils are contact with each other according to the joint position, sothose individuals are buried in situ. Abrosaurus dongpoi has only skull, and this skull isnearly complete.The fossils of the remaining Mamenchisauridae individuals are not so good, suchas fewer fossils quantity, lower the complete degree, fewer the number of associatedfossils and so on. Their buried type is heterochthonous burial after a certain distance ofmovement. The four heterochthonous burial individuals, Tonganosaurus hei, O.junghsiensis, O. changshouensis and M. constructus had been moved longer distance,the distance between the deathplace and burial place are relatively further than otherheterochthonous burial individuals.Mamenchisauridae is medium to large sauropod dinosaur. The skull of moderateheight. In the lateral view, antorbital, orbital narial and other fossa are well-developed.The teeth is spoon-shaped. The neck is long, the longitudinal ratio of the longest neckand the axial skeleton is close to0.5. Cervical vertebra is thin and long, the number ofcervical vertebra are between15and19. Cervical vertebra has low neural spines. Thepleurocoels of dorsal vertebrae are developed in different degree.The primitive character of original individual are:1) the posterior cervical andanterior dorsal vertebrae‘s neural spines are unbranched in anterior and caudal view.2)meanwhile anterior caudal vertebrae is weak amphicoelous or platycelous.Aorresponding, the progressive character of late ascensive individual are:1) theposterior cervical and anterior dorsal vertebrae‘s neural spines are bifurcate.2) anterior caudal vertebrae are procoelous, the shallow or degree of the anterior concave are asindividuals vary. The tail is short, pulse arc of middle caudal vertebrae are bifurcate.The lower end of the front scapula significantly is inclines upward. The pubic processof iliac are special developed. The ratio of forelimb and hindlimb length is0.75~0.8.According to the traditional method of fossil‘s morphological comparativeanalysis, Mamenchisauridae‘s skeletal evolutive characteristics are as follows:I. Tooth size has diminished, number of teeth has increased, the number ofmaxillary teeth has increased from11to19, and the mandibular teeth from14to23.While the number of marginal tooth denticles has decreased, especially the marginaltooth denticles in the back edge of tooth crowns are almost disappeared.II.All bones of skeleton‘s volume have increased except tooth.III. The ratio of skull‘s height and length become larger. Depth of rostral end ofdentary ramus has increases in dorsoventral height and robustness rostrally. Orbitalfossa, nostril and other fossa becomes larger, and led to the head looks very light andhandy.IV. In vertebral column, the cervical evolutive characteristics are most obvious：1）The increase in the number of cervical vertebra, from about15to19.2）The increase inthe length of cervical vertebrae.3) Pleurocoel‘s form, from a simple concave structureand undivided to becoming complex, divided by bony septa.3) Construction of neuralarch and diapophysis, from with fewer lamina, ridged, cavity structure to with more andcomplex this structure.4) The shape of neural spine in the posterior cervical andanterior dorsal vertebrae，from a simple rod become a plate, final to bifurcated plate,and each lateral side edge present a triangle plate. Secondly, anterior caudal vertebraetype, from amphicoelous or platycelous to Procoelous. The height of neural arch hasincreased and move backward.V. The coracoid becomes small. The coracoid articulation of scapular has becomecrooked, and make joint substantial between scapular and coracoid, and thischaracteristic may be matters to firmness and flexibility of forelimb.VI. Limbs become thick, deltopectoral crest and fourth trochanter become moreobvious. The change of manus is tiny, while the number of metatarsal III and V hasslightly changes, metatarsal III is increased, metatarsal V is decreased.The cladistic analysis showed that four pairs of Mamenchisauridae, O. jiaos and O.luoquanensis, O. tianfuensis and M. youngi, M. jingyanensis and M. constructus, twoindividuals of M. hochuanensis from Hechuan and Zigong, are respectively form four sister groups. While Tonganosaurus hei and Abrosaurus dongpoi located respectivelyin the relatively independent branch.The results of the analysis proved that the four genera of Mamenchisauridae are inan continuous evolutionary line, and two genera, Omeisaurus and Mamenchisaurus hasclosely genetic relationship. The results of two analysis, the traditional method offossil‘s morphological comparative analysis and the quantitative cladistics method iscoincident. |
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