Omeisaurus (meaning "Omei lizard") is a genus of sauropod dinosaur from the Middle Jurassic Period (Bathonian-Callovian stage) of what is now China. Its name comes from Mount Emei, where it was discovered in the lower Shaximiao Formation of SichuanProvince.[1]
Like most sauropods, Omeisaurus was herbivorous and large. The species O. tianfuensis measured 20.2 metres (66 ft) long, and weighed 9.8 tonnes.[4]
Discovery
Omeisaurus was first described in 1939. It was named after the sacred mountain Omeishan, which is where the first fossil example of Omeisaurus was found.[1] Most skeletons of Omeisaurus were found in the 1970s and 1980s, during the great “Chinese dinosaur rush”. There have been eight species of Omeisaurus named so far: O. junghsiensis,[1]O. changshouensis,[2] O. fuxiensis, O. tianfuensis,[5] O. luoquanensis, O. maoianus, O. jiaoi, and O. puxiani.[6] All of these but the last two were named after the locations where they were found. O. fuxiensis was the smallest species, measuring around 35 feet (11 m) long. O. tianfuensis had the longest neck of the genus, around 30 feet (9.1 m) long. The only dinosaur with a longer neck was Mamenchisaurus. Tail clubs have in 1988/1989 been referred to Omeisaurus tianfuensis,[7]but Paul Upchurch in 2004 considered them possible Shunosaurus clubs.[8][9] In their paper on Qijianglong, Xing et al. (2015) considered O. maoianus more closely related to Mamenchisaurus than to O. tianfuensis, a proposal supported by the cladistic analysis of Ren et al. (2018).[10][11]
Mounted skeletons of Omeisaurus are on display at the Zigong Dinosaur Museum in Zigong, Sichuan Province and at Beipei Museum, near Chongqing, both in China.
Classification
It was once classified as a member of the family Cetiosauridae, which had long been a wastebasket taxon. The species O. fuxiensis is sometimes confused with Zigongosaurus, but the two are based on different material despite having the same species name.
Omeisaurus was formerly assigned to Euhelopodidae.[1] However, it and other Jurassic sauropods from Asia formerly assigned to Euhelopodidae are now placed in the separate family Mamenchisauridae.
The cladogram below shows a possible phylogenetic position:[12]
Paleoecology
Omeisaurus lived in dense forests. Different species of Omeisaurus sometimes shared habitats with each other (O. junghsiensis and O. tianfuensis, for example). In addition to other species of Omeisaurus, Shunosaurusand Datousaurus are also known from the Xiashaximiao Formation, while Mamenchisaurus is present in the Shangshaximiao Formation. Yangchuanosaurus is a large theropod from the Shangshaximiao, and it probably preyed on sauropods. The smaller Xuanhanosaurus was also present. In the Xiashaximiao, another theropod, Gasosaurus, was also present, as was the herbivorous stegosaurHuayangosaurus. The latter probably did not compete with sauropods for food.[9]
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