Zigongosaurus

• Sichuan, People's Republic of China ( Lower Shaximiao Formation)

• Zigongosaurus fuxiensis

Zigongosaurus is a little known genus of sauropod dinosaur from the Middle Jurassic of China. The validity of this genus is controversial - as many researchers assume that the only way Zigongosaurus fuxiensis, in fact, whether or Mamenchisaurus Omeisaurus must be assumed.

Research History and Description

The only known fossils were recovered in 1974 by employees of the Chungking Museum of Natural History from the Wujaiba Dam reference in Zigong in Sichuan Province, China. The site closes on rocks of the Lower Shaximiao formation, which can be dated to the Bathonian to Callovian. Among the finds are bones of the skull and bones of the rest of the skeleton, which belonged to several different individuals. Under time pressure, only the most important fossils for preparation and subsequent description could be selected - 1976 were these fossils by paleontologists Hou, Zhao and Chao in a brief description in the Chinese language as a new genus and species, Zigongosaurus fuxiensis, scientifically described. According to these researchers, the fossils resemble those of Omeisaurus, differ from them but by the anterior caudal vertebrae, the vertebral body procoel (on the front and concave at the rear convex) and the spinous processes were less pronounced.

Dong ( 1983) provided the largest number of fossils junghsiensis to the type Omeisaurus. However, some skull fragments ( jaw bone and basioccipital ) and a cervical vertebra (axis ), he wrote to a new way - Omeisaurus fuxiensis. A single upper jaw but was Dong is the only fossil of the material originally described as Zigongosaurus not assign Omeisaurus, but led him further than fuxiensis Zigongosaurus. According to Dong Thus were three sauropods in the Wujaiba Dam reference available: Omeisaurus junghsiensis, Omeisaurus fuxiensis and Zigongosaurus fuxiensis. McIntosh (1990 ) holds Zigongosaurus fuxiensis identical with Omeisaurus junghsiensis - so that would be Zigongosaurus a junior synonym of Omeisaurus.

Zhang and Chen (1996 ) studied the fossils again and came to an opposite result. As these researchers note, the posterior cervical and anterior dorsal vertebrae slightly forked spinous on - this feature, although less pronounced, typical of Mamenchisaurus, but absent in Omeisaurus. Consequently, these researchers write the Sauropodenmaterial of the reference of the genus to Mamenchisaurus - as Mamenchisaurus fuxiensis. According to these researchers M. fuxiensis was a medium to large sauropod, who distinguished himself in comparison with other types of Mamenchisaurus by a relatively high skull with a poorly developed muzzle. The spatula-shaped teeth were medium in size, in the premaxilla sat on each side 4 teeth in the upper jaw, respectively 12-14 and 15-17 in the lower jaw.

Another study by Martin -Rolland (1999) holds Zigongosaurus however, for a valid genus. Thus, the fossils would be significantly different from Mamenchisaurus, among others in the diminished degree of bifurcation of the vortex. However, a recent study by Upchurch and colleagues ( 2004) follows the interpretation of Zhang and Chen and leads Zigongosaurus fuxiensis within the genus Mamenchisaurus.