Sinosaurus (meaning "Chinese lizard") is an extinct genus of basal theropod dinosaur which lived during the Early Jurassic (Hettangian-Sinemurian). Fossils of the animal have been found in the Lufeng Formation, in the Yunnan Province of China. The type species, S. triassicus, was named by Chung Chieng Young in 1940. A second species, S. sinensis, was originally assigned to Dilophosaurus, but was later reassigned to Sinosaurus. Sinosaurus is morphologically similar to Dilophosaurus including the presence of a similarly shaped cranial crest, though its precise taxonomic position is uncertain, and the two genera may not be closely related.
Discovery and naming The composite term Sinosaurus comes from Sinae, the Latin word for the Chinese, and the Greek word sauros (σαυρος) meaning "lizard"; thus "Chinese lizard". The specific name, triassicus, refers to the Triassic, the period that the fossils were originally thought to date from. Sinosaurus was described and named by Chung Chien Young, who is known as the 'Father of Chinese Vertebrate Paleontology', in 1940.
The holotype, IVPP V34, was found in the Lower Lufeng Formation, and consists of two maxillary (upper jaw) fragments, four maxillary teeth, and a lower jaw fragment with three teeth. The teeth are laterally compressed, and feature fine serrations both at their anterior and posterior edges. The teeth are also variable in size and are curved backwards. This material is too fragmentary to determine the length and weight of this dinosaur. Over the years, other fossils were referred to Sinosaurus, some of which were material that was shown to belong to two sauropodomorphs. The fossils include postcrania, with a sacrum with three preserved sacral vertebrae. The material assigned to "Sinosaurus postcrania" includes a mix of plateosaurid and melanorosaurid elements. All the material from the Red Beds block has now been reassigned to Jingshanosaurus.
KMV 8701 was originally discovered in 1987. The specimen was identified as a new species, and was named Dilophosaurus sinensis. Then in 1994, during a field expedition, a more complete specimen was found, and was assigned to the same species. In 2003, Dong Zhiming studied the material of Sinosaurus triassicus, finding it to be quite similar to Dilophosaurus sinensis. As Sinosaurus was named earlier, "Dilophosaurus" sinensis became its junior synonym. In 2013, a study by Currie et al., confirmed that D. sinensis was the same animal as S. triassicus On the other hand, Wang et al. (2017) stated that it needs to be further investigated whether D. sinensis is indeed a junior synonym of S. triassicus, and noted that the two species are different at least in the anatomy of the premaxilla. The authors tentatively assigned D. sinensis to the genus Sinosaurus, but retained it as a species distinct from Sinosaurus triassicus. Specimen KMV 8701 consists of a skull, measuring 52.5 cm (20.7 in), and is nearly complete. Dong claimed that animal was about 5.6 m (18 ft) long. It has been assigned now to Sinosaurus, but the specimen still lacks sufficient description and preparation. Over the years, paleontologists referred additional specimens to D. sinensis which are now assigned to Sinosaurus. Dong (2003) referred specimen LDM-LCA10 which consists of a skull and an incomplete skeleton. In 2012, Xing referred two individuals, ZLJ0003 which consists of a partial skull and an incomplete skeleton, and ZLJT01 which is a juvenile individual that consists of a premaxillary fragment, an incomplete maxilla, a maxillary fragment, a lacrimal, both frontals, both parietals, an incomplete braincase, an incomplete dentary, an atlantal intercentrum, two dorsal rib fragments, and a partial proximal caudal neural arch, to Sinosaurus. In 2012, a new specimen of Sinosaurus was described, and was found to represent a new species. The species Shuangbaisaurus anlongbaoensis, discovered and named in 2017, has later been considered a synonym of Sinosaurus triassicus. A complete skull with a preserved mandible and 11 cervical vertebrae was described for Sinosaurus in 2023, after it was discovered near the locality where the holotype was found. The specimen also suggests three autapomorphies are unique to this theropod, all regarding crest development and the various fenestrae of the skull.
Description
Size Sinosaurus was a relatively large theropod by the standards of the Early Jurassic. With the use of virtual skeletal mount, Liang et al. (2024) estimated that Sinosaurus was a large theropod around 5.85 metres (19.2 ft) long with a maximum body mass of 895 kilograms (1,973 lb). The authors suggested that since the phylogenetic position of Sinosaurus is not well understood, previous estimations based on extant scaling approaches derived from femur length and circumference are unreliable.
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