Shunosaurus, meaning "Lizard from Sichuan", is a genus of sauropod dinosaur from Late Jurassic (Oxfordian) beds in Sichuan Province in China, from 161 to 157 Million years ago. The name derives from "Shu", an ancient name for the Sichuan province.

Discovery and species

The first fossil of Shunosaurus was discovered in 1977 by a group of students, practising paleontological excavation at a road bank. The type species, Shunosaurus lii, was described and named by Dong Zhiming, Zhou Shiwu and Zhang Yihong in 1983. The generic name derives from "Shu", an ancient name for Sichuan. The specific name honours hydrologist Li Bing, the governor of Sichuan in the third century BC. The holotype, IVPP V.9065, was collected from the Lower Xiashaximiao Formation near Dashanpu, Zigong. It consists of a partial skeleton. Later about twenty more major specimens were discovered, including several complete or near-complete skeletons, skulls and juveniles, making Shunosaurus one of the best anatomically known sauropods, with 94% of all skeletal elements identified. Shunosaurus skeletons are on display at the Zigong Dinosaur Museum in Zigong, Sichuan Province, and the Tianjin Natural History Museum. A proposed second species, S. ziliujingensis, a name mentioned in the Zigong museum guide to indicate a smaller and older form, has never been formally described, and thus remains a nomen nudum. In 2004 a partial semi-articulated specimen from Jiangyi Township in Yuanmou County was described as the new species Shunosaurus jiangyiensis. It is known from nine cervicals, 15 dorsals, three sacrals, four caudals, both scapulae, the right coracoid and clavicle, the right forelimb lacking the hand, a pubis and ischium and the right hindlimb, found in the upper section of the Middle Jurassic Xiashaximiao Formation. The species was separated from Shunosaurus lii based on its unique pectoral girdle, but was described as otherwise very similar to both Shunosaurus lii and Kunmingosaurus.

Description

Shunosaurus was first estimated to be 11 m long; later and more complete finds indicated a somewhat smaller size. In 2010 Gregory S. Paul estimated the length at 9.5 m, the weight at 3 MT. Shunosaurus was very short-necked for a sauropod, comparable to certain members of Dicraeosauridae. The skulls found are mostly compressed or disarticulated and the interpretation of the head form has varied from broad, short and deep to extremely narrow and pointed. The upper and lower jaws were strongly curved upwards, allowing them to function as a pair of garden shears. The teeth were fairly robust but elongated with a crown length of up to 8 cm. They show a unique combination of a cylindrical body ending in a spatulate tip. Published in 1989 was the discovery that the tail ended in a club, equipped on its top with two successive spikes formed by cone-shaped osteoderms with a length of 5 cm. The club was probably used to fend off predators.

Classification

Shunosaurus was originally classified as a member of the Cetiosaurinae; in 1992 Dong assigned it to Shunosaurinae within the Cetiosauridae. Cladistic analyses have rendered conflicting results. In 1995 Paul Upchurch published a study in which Shunosaurus belonged to the Euhelopodidae together with other Jurassic Chinese sauropods. However, an analysis by Jeffrey Wilson in 2002 indicated it had a very basal position within the Eusauropoda. Shunosaurus is perhaps related to Rhoetosaurus from Queensland in Australia.

Paleobiology

Its neck length indicates that Shunosaurus was a low browser. The form of its jaws is well-adapted to processing large amounts of coarse plant material. Shunosaurus accounts for 90% of the fossils found in the Dashanpu fauna, showing it was a dominant and/ or common member of its habitat and environment. It shared the local Middle Jurassic landscape with other sauropods, Datousaurus, Omeisaurus and Protognathosaurus, the possible ornithopod Xiaosaurus, and the early stegosaur Huayangosaurus, as well as the carnivorous theropod Gasosaurus.