Omeisaurus

''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 Sichuan Province.

Like most sauropods, ''Omeisaurus'' was herbivorous and large. The largest species, ''O. tianfuensis'', measured long, and weighed . Other species were much smaller, as the type species ''O. junghsiensis'' reached a size of in length and in body mass, and ''O. maoianus'' reached a size of and .

Discovery and species

Initial discovery and ''O. changshouensis''

The initial discovery of ''Omeisaurus'' was in 1936 when Charles Lewis Camp and Yang Zhongjian collected a partial skeleton from strata of the Shaximiao Formation in Szechuan, China.Young, C. C. (1939)
On a new Sauropoda, with notes on other fragmentary reptiles from Szechuan
''Bulletin of the Geological Society of China'', ''19''(3), 279-315.Dong, Z. (1983)
The dinosaurian remains from Sichuan basin, China
''Palaeontologia Sinica, new series C'', ''23'', 1-145. The material was taken to and prepared in what is now the Institute of Vertebrate Paleontology and Paleoanthropology in Beijing. The skeleton was named ''Omeisaurus junghsiensis'' in 1939 by Yang Zhongjian, the skeleton consisting of a partial postcranial skeleton that included four cervical (neck) vertebrae. It was named after the sacred mountain Omeishan, which is near where ''O. junghsiensis'' was found, and the species name after the locality. The skeleton of ''O. junghsiensis'' was lost during WWII. In 1955, Xuanmin Li and colleagues collected several Sauropod remains from the same strata as ''O. junghsiensis'' in Changshou during construction of a reservoir. The IVPP sent Youling Su to conduct the excavation in Changshou, the crew finding eleven vertebrae and several appendicular elements (IVPP V930). The specimen was described later in 1958, also by Yang Zhongjian, as a new species, ''O. changshouensis''.

Discoveries at Wujiaba

During the construction of the Wujiaba Dam in Zigong during the mid-to-late 1970s, crews discovered many large Sauropod remains from strata of the Upper Shaximiao Formation. The amount of material was vast and was collected by the Chongqing Museum of Natural History over five years, and was prepped and briefly described. The material consisted of many partial skulls and skeletons, consisting of between thirteen and sixteen individuals and 2 composite skeletons were later mounted in Chongqing and Zigong. Wujiaba also saw the collection of a fragmentary partial skull of an additional species of ''Omeisaurus'', ''Omeisaurus fuxiensis,'' that was described by Zhiming Dong and colleagues in 1983.

Dashanpu Quarry finds

The next and most bountiful ''Omeisaurus'' discovery came in the 1980s when many dinosaur remains were found at Dashanpu in Zigong, these remains including a nearly complete skeleton, several skulls, and additional postcrania from several individuals.Li, K., & Cai, K. (1988). ''The Middle Jurassic dinosaur fauna from Dashanpu, Zigong, Sichuan: Omeisaurus tianfuensis. Sauropod dinosaurs (2)''. Sichuan Publishing House of Science and Technology. The best of these skeletons, a nearly complete and semi articulated postcranial skeleton (ZDM T5701), was selected as the holotype and described by He ''et al'' in 1984.X. He, K. Li, K. Cai and Y. Gao. (1984).
''Omeisaurus tianfuensis''—a new species of ''Omeisaurus'' from Dashanpu, Zigong, Sichuan
. ''Journal of Chengdu College of Geology'' 1984 (suppl. 2): 13-32 A nearly complete skull and partial postcranial skeleton (ZDM T5702) was selected as the paratype, and was is one of the few known ''Omeisaurus'' specimens with a well preserved skull. The several specimens were described in much detail later in 1988, with a skeleton mounted at the Zigong Dinosaur Museum sometime later. Interestingly, ''O. tianfuensis'' was discovered to have a tail club on the end of its caudal vertebrae based on a specimen from Dashanpu.Dong Zhiming, Peng Guangzhao and Huang Daxi. 1988. "The Discovery of the bony tail club of sauropods". ''Vertebrata PalAsiatica'' 27 (3): 219-224 A second new species was named in 1988, ''O. luoquanensis,'' in the osteology of ''O. tianfuensis'' off of a partial postcranial skeleton.

Recent discoveries

Several ''Omeisaurus'' species have been named since the 1980s, with the most complete of them coming in 2001 with ''Omeisaurus maoianus'' from the Shaximiao Formation in Jingyan.Tang F, Jin X S, Kang X M et al., 2001. Omeisaurus maoianus: a Complete Sauropoda From Jingyan, Sichuan. Beijing: China Ocean Press. 1–128 ''O. maoianus'' was collected by Jin Xingshen and Zhang Guojin during the 1990s and the remains consisted of a skull, partial vertebral column, and several additional postcranial elements (ZNM N8510). ''O. maoianus'' was mounted at the Zhejiang Natural History Museum with its holotype skull on display. ''O. maoianus generic assessment has been questioned, with several phylogenetic analyses finding it more closely related to ''Mamenchisaurus'' and ''Xinjiangtitan''. 10 years later in 2011, ''Omeisaurus jiaoi'' was named based on a well preserved and partially articulated postcranial skeleton, also from Zigong and is deposited at the Zigong Dinosaur Museum (ZDM 5050).江山, 李飞, 彭光照, & 叶勇. (2011)
A new species of Omeisaurus from the Middle Jurassic of Zigong, Sichuan.
''古脊椎动物学报'', ''49''(2), 185-194. The most recently named ''Omeisaurus'' species, ''O. puxiani'', was discovered in Yunyang and is one of the best preserved ''Omeisaurus'' species, with fossils from most of the vertebral column and girdles recovered.Tan, C., Xiao, M., Dai, H., Hu, X. F., Li, N., Ma, Q. Y., ... & You, H. L. (2021)
A new species of Omeisaurus (Dinosauria: sauropoda) from the Middle Jurassic of Yunyang, Chongqing, China.
''Historical Biology'', ''33''(9), 1817-1829. The specimen is deposited under CLGRP V00005 at the Chongqing Laboratory of Geoheritage Protection and Research.

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. However, it and other Jurassic sauropods from Asia formerly assigned to Euhelopodidae are now placed in the separate family Mamenchisauridae, which is more basal in Sauropoda. In 2021, John D'Angelo determined that all ''Omeisaurus'' species, besides ''O. maoianus,'' were valid and likely members of the same genus, with ''O. junghsiensis'' as the most basal species.

The cladogram from Tan et al., 2020 below shows a possible phylogenetic position:

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'', ''Shunosaurus'' and '' 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 stegosaur ''Huayangosaurus''. The latter probably did not compete with sauropods for food.

References

*
*Britt, Carpenter et al. (2002). Encyclopedia of Dinosaurs.. Publications international, Ltd., Lincolnwood Illinois..
*The Middle Jurassic dinosaur fauna from Dashanpu, Zigong, Sichuan. Volume 4. Sauropod dinosaurs (2). Omeisaurus tianfuensis. He, X., Li, K. and Cai, Sichuan Publishing House of Science and Technology, Chengdu ; 1-143 (1988).
*The dinosaurian remains from Sichuan Basin, China. Dong, Z., Zhou, S. and Zhang, Y. PALAEONTOLOGIA SINICA SERIES C (No. 23) i-iii; 1-145 (1983).

{{Portal bar, Dinosaurs, China

Middle Jurassic dinosaurs of Asia
Mamenchisaurids
Taxa named by Yang Zhongjian
Fossil taxa described in 1939
Paleontology in Sichuan