Sinosaurus in Yunnan
Sinosaurus (meaning “Chinese lizard”) was a tetanuran theropod dinosaur which lived during the Early Jurassic Period. It was a bipedal carnivore approximately 5.6 metres (18 feet) in length. Fossils of the animal were found at the Lufeng Formation, in the Yunnan Province of China.
Description
According to Carrano et al. (2012) D. sinensis, now considered to be at least congeneric with Sinosaurus triassicus, can be distinguished based on the fact that a vertical groove is present on the lateral premaxilla adjacent to contact with the maxilla. Sinosaurus is the only “dilophosaurid” known from a complete braincase. Cryolophosaurus, Dilophosaurus, Zupaysaurus and Coelophysis kayentakatae are all known from partial braincases. Two partial braincases were found before 2012, and are probably mostly complete, except that large sections are obscured by sediments. In 2011, an exceptionally well-preserved braincase was found, only missing the frontal bones and orbitosphenoid.
Discovery and naming
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, finding it to be quite similar to Dilophosaurus sinensis. As Sinosaurus was named earlier, by Young in 1948, “Dilophosaurus” sinensis became its junior synonym. 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 1948.
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.
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 a 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.
Shaojin Hu (1993) assigned specimen KMV 8701 to Dilophosaurus sinensis. In 2013, a study by Currie et al., confirmed that D. sinensis was the same animal as Sinosaurus 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 525 mm), and is nearly complete. The specimen KMV 8701 is about 5.6 m (18 ft) long, meaning Sinosaurus was about that length. KMV 8701 has been assigned now to Sinosaurus, but the specimen still lacks sufficient description and preparation. In 2012, a new specimen of Sinosaurus was described, and was found to represent a new species.
Description
According to Carrano et al. (2012), D. sinensis, now considered at least congeneric with Sinosaurus triassicus, can be distinguished by a vertical groove on the lateral premaxilla adjacent to the maxilla. Sinosaurus is the only “dilophosaurid” known from a complete braincase. In contrast, Cryolophosaurus, Dilophosaurus, Zupaysaurus, and Coelophysis kayentakatae are known from partial braincases. Two partial braincases were found before 2012, obscured by sediments, but an exceptionally well-preserved braincase missing only the frontal bones and orbitosphenoid was found in 2011.
Discovery and Naming
The specimen KMV 8701, discovered in 1987, was initially identified as a new species named Dilophosaurus sinensis. In 1994, a more complete specimen was found and assigned to the same species. Dong Zhiming studied the material in 2003, finding it similar to Sinosaurus triassicus, which had been named earlier by Young in 1948, making “Dilophosaurus” sinensis its junior synonym. The composite term Sinosaurus comes from “Sinae” (Latin for Chinese) and “sauros” (Greek for lizard), thus “Chinese lizard.” The specific name “triassicus” refers to the Triassic, the period initially thought to date the fossils.
Paleontologists referred additional specimens to D. sinensis, now assigned to Sinosaurus. Dong (2003) referred specimen LDM-LCA10, consisting of a skull and an incomplete skeleton. In 2012, Xing referred two individuals, ZLJ0003 (partial skull and incomplete skeleton) and ZLJT01 (juvenile with various fragments), to Sinosaurus.
The holotype, IVPP V34, was found in the Lower Lufeng Formation and consists of maxillary fragments, teeth, and a lower jaw fragment. Over the years, other fossils referred to Sinosaurus included postcrania and sauropodomorph material. Some fossils were reassigned to Jingshanosaurus.
Shaojin Hu (1993) assigned specimen KMV 8701 to Dilophosaurus sinensis. Currie et al. (2013) confirmed that D. sinensis was the same as Sinosaurus triassicus, while Wang et al. (2017) suggested further investigation, tentatively assigning D. sinensis to Sinosaurus but as a distinct species. Specimen KMV 8701 consists of a nearly complete skull and skeleton, measuring about 5.6 meters long, but lacks sufficient description and preparation.
Classification
Initially thought to be a coelophysoid related to Dilophosaurus and Cryolophosaurus, Oliver Rauhut (2003) showed Sinosaurus to be a more advanced theropod. Carano (2013) agreed, classifying Sinosaurus as a theropod. Despite being considered a nomen dubium in some works, the referral of “Dilophosaurus” sinensis to Sinosaurus confirmed its validity.
Sinosaurus is possibly closer to the Antarctic theropod Cryolophosaurus. The anterior end of the jugal does not participate in the internal antorbital fenestra, and the maxillary tooth row is entirely in front of the eye socket. D. sinensis was exhibited at Dinofest in 1998 in Philadelphia. Although it features large nasolacrimal crests like D. wetherilli, other skeletal features suggest a closer relation to tetanuran theropods. Rauhut (2003) regarded D. sinensis as a basal tetanuran most closely related to Sinosaurus and Cryolophosaurus.
In 2007, the Lufeng Dinosaurian Museum discovered a new specimen of Sinosaurus (ZLJT01), consisting of an incomplete skull and postcranial fragments. Phylogenetic analysis of this specimen demonstrated that Sinosaurus is a more derived theropod.
Crest Function
Sinosaurus and Dilophosaurus both possess dual crests. However, these crests were not used in combat.
Feeding
The skull of Sinosaurus has a deep notch between the premaxilla and maxilla. Dong (2003) proposed that this notch housed jaw muscles, giving Sinosaurus a powerful bite. Sinosaurus might have been a carnivore or a scavenger. Dong suspected the premaxilla was covered in a narrow, hooked beak used to rip open skin and abdominal flesh, and that the crest helped hold open the abdominal cavity while feeding. The feet of Sinosaurus, resembling those of modern vultures, were likely adapted for feeding on large-bodied animals.
Paleopathology
A study by Xing et al. (2013) examined the effect of traumatic tooth loss on the dental alveolus in dinosaurs. Sinosaurus is the first dinosaur where remodeling of the alveolus was observed, suggesting that theropods were highly resilient to traumas and diseases.
Paleoecology
Provenance and Occurrence
The type specimen of Sinosaurus triassicus (IVPP V34) was recovered in the Zhangjiawa Member of the Lufeng Formation, Yunnan, China, from the Sinemurian stage of the Jurassic period (approximately 196-183 million years ago). Other discoveries in the Zhangjiawa Member include several IVPP specimens and FMNH CUP specimens discovered by M. Bien, C.C. Young, E. Oehler, and Hu.
Specimen IVPP V504, referred to Sinosaurus, was collected by Lee in the 1940s in the Shawan Member of the Lufeng Formation, dating to the Hettangian stage of the Jurassic period (approximately 201-199 million years ago). Additional discoveries include parts of two skeletons attributed to Sinosaurus and various IVPP specimens discovered by C.C. Young and Sou.
The D. sinensis remains (KMV 8701) were recovered in the Shawan Member of the Lufeng Formation, discovered in 1987 in the Dull Purplish Beds from the Hettangian stage of the Early Jurassic.
Fauna and Habitat
In the Lufeng Formation, Sinosaurus shared its paleoenvironment with therapsids like Morganucodon, Oligokyphus, and Bienotherium; archosaurs like Pachysuchus; diapsids like Strigosuchus; crocodylomorphs like Platyognathus and Microchampsa; the early mammal Hadrocodium; and other early reptiles. Contemporary dinosaurs included indeterminate sauropods; early thyreophorans Bienosaurus lufengensis and Tatisaurus oehleri; the supposed chimeric ornithopod “Dianchungosaurus lufengensis”; prosauropods like Gyposaurus sinensis, Lufengosaurus huenei, L. magnus, Jingshanosaurus xinwaiensis, Kunmingosaurus wudingensis, Chinshakiangosaurus chunghoensis, Yunnanosaurus huangi, “Y.” robustus, and an unnamed taxon; and theropods like Lukousaurus, Eshanosaurus, and Coelophysis sp.
Changpeipus footprints have been found in the Lufeng Formation. In 2009, a study led by Li-Da Xing found that these footprints, named Changpeipus pareschequier, were unique among ichnogenera and hypothesized to be produced by a coelophysoid, possibly Sinosaurus or Coelophysis sp.
