Original Article- Zhao Xijin, 1985. The Jurassic Reptilia. In Wang Si-en, Cheng Zhengwu and Wang Neiwen (eds.). The Jurassic System of China. Stratigraphy of China. 11, 286-289, 347, plates 10 and 11.

Translation by Leo W Sham, January 3, 2011.

(6) Jurassic Reptilian Fauna

The Jurassic period was a time of profuse development of reptiles, especially dinosaurs. For convenience of description, [we will] now separate our analysis into the following three stages.

Early Jurassic The Early Jurassic was an early stage of dinosaur evolution. Dinosaurs and other Mesozoic reptiles then were largely primitive. Fossils are not only few but also relatively poorly preserved. These primitive bauplans dictate the paucity of difference between genera; it is more difficult to determine the identity of fossils compared to later times. The Early Jurassic was the starting stage of dinosaur evolution. Exposed strata were most developed [ sic ] in southwestern China, for example, Lower Lufeng Group (alas Fengjiahe Formation) of Yunnan, Lower Ziliujing Group of Sichuan, and Daye Group of Tibet. The large amount of dinosaurian and other reptilian fossils preserved in these strata provided strong evidence to determine the chronology these terrestrial strata. Here, we first analyze the fauna of the representative Lower Lufeng Group to demonstrate their primitiveness. Sauropods and prosauropods coexisted in the Lower Lufeng Group. In general, sauropods appeared at the beginning of the Jurassic; thus the existence of sauropod fossils in a stratum would point to its earliest Jurassic age because prosauropods, evolving since the Late Triassic, had much declined with lineages lingering into the Early Jurassic. This phenomenon is particular in Lufeng, Yunnan, where the prosauropod Lufengosaurus described by Professor CC Young coexisted with the primitive sauropod Dachongosaurus yunnanensis , which also showed certain advanced characteristics. In addition to this was Sinosaurus triassicus Young. The holotype teeth were theropodan but referred postcranial skeletal elements were sauropodan. Thus, Sinosaurus was a valid genus, but the specific epithet was inappropriately named. All in all, the coexistence of prosauropods and sauropods makes it reasonable to infer an Early Jurassic age. In addition, the tritylodontid age corroborated [this inference]. Recent research by Cui showed that Yunnania brevirostre was from the Early Jurassic, some characters of which were more advanced than Oligokyphus . Other reptilian fossils of the Lower Lufeng Group include Lukosaurus yini , Tatisaurus oehleri , heterodontosaurs, crocodylomorphs; which had a long temporal range from the Late Triassic to Early Jurassic in general. Accordingly, the Lower Lufeng Group where they were found could be regarded as Early Jurassic. Although the protorosaurid Neotrilosaurus [ sic ] could also be found in the Lower Lufeng Group, protorosaurs were most proliferative in the Permian and Triassic with a few extending to the Jurassic and Cretaceous. Moreover, the Lower Lufeng fossil did not belong to Trilophosaurus , but Neotrilophosaurus , such that its age could definitely be put at Early Jurassic. Similar condition [of coexistence] in Yunnan include that of the primitive sauropod Chinshakiangosaurus zhonghonensis [ sic ] in the Lower Lufeng group above the Daching Group (Yongren) and Lufengosaurus found in the same stratum near Yongren; the primitive sauropod Kunmingosaurus wudingi found in the Lower Lufeng Group at Wuding; and Lufengosaurus and the primitive sauropod Oshanosaurus youngi with the heterodontosaur Dianchungosaurus elegans in the Lower Lufeng Group at Dianchung, Oshan. In the “Pearl deposit” of the Ziliujing Group in Sichuan and Guizhou, primitive sauropods referable to Brachiosauridae were also found together with prosauropods and plesiosaur fossils, for example, Bishanopliosaurus youngi in the Dongyuemiao Group, Bishan, Sichuan. Similar condition [of coexistence] was recently found in the Early Jurassic Daye Group of Changdu, Tibet, where not only the prosauropod Lufengosaurus changduensis was discovered, but also the primitive sauropod Damalasaurus magnus , Megalosaurus tibetensis , Scelidosaurus sp , and at the bottom of the Daye Group, the marine Plesiosaurus changduensis , Ichthyosaurus changduensis and Steneosuchus microobtusidens etc. In summary, Early Jurassic reptilian fauna of China is characterized by the following: (1) the appearance of sauropods marked the beginning of the Jurassic; (2) Early Jurassic prosauropods were an unsuccessful branch of saurischians evolving from the Late Triassic; (3) all carnosaurs were primitive megalosaurs; (4) heterodontosaurs were relatively primitive ornithischians, only existing in the Late Triassic and Early Jurassic; (5) tritylodontids were highly developed in the Early Jurassic; (6) coelurosaurs, plesiosaurs and some mesosuchians were characteristic of Early Jurassic forms. The Early Jurassic terrestrial stratigraphy of China, their degree of development and fossil appearance, is totally correlative to that in other countries, for example, the Red Bed and Cave Sandstone layers of South Africa (Stromberg series), Kota formation of India, Liassic formation of England, Kayenta formation of North America. Except for the controversial age of the South African strata, the others are all Early Jurassic deposits in view of their reptilian, especially dinosaurian, fossils. Since these contemporary fossils are similar to or even co-generic with ours, it is reasonable to place the Lower Lufeng Group and Daye Group etc at Early Jurassic. Middle Jurassic The Middle Jurassic was a transitional period of dinosaur evolution. The most remarkable difference compared with earlier times was the non-existence of prosauropods. Primitive sauropods evolved new characters and became more advanced, but in general retained their primitive appearance, resulting in obviously transitional forms. By this time carnosaurs showed obvious advances: enlarging teeth, reducing forelimbs and stronger vertebral columns; while for coelurosaurs, narrowing of teeth and pneumatization and lightening of the postcranial skeleton. Changes in ornithischians were even more marked, especially that in hypsilophodonts. One quite obvious change in sauropods was that, after certain developments of spatulate teeth, peg-like teeth evolved, the latter being major marker of the beginning of the Middle Jurassic. Stegosaur evolution was quite remarkable in the Middle Jurassic, by when dorsal armor and appendicular bones similar to later forms had evolved. Carnosaurs and coelurosaurs had evolved new forms processing some characteristics present in Late Jurassic forms. Middle Jurassic crocodylomorphs had also evolved, especially the disappearance of primitive “long-snout forms” of the Early Jurassic (with sharper teeth, more flattened and robust torso etc). Observation of fossils revealed that some major characters of Middle Jurassic dinosaurs were different from Late Jurassic forms as well: (1) Middle Jurassic coelurosaurs had smaller teeth; carnosaurs had narrower teeth with more sparse serrations but broader skulls and highly developed forelimbs; (2) sauropods had highly developed vertebral indentations, but “honeycomb septa” had not formed; the neural spines of posterior cervical and dorsal vertebrae were not divided; the fourth trochanter of the femur was still proximally positioned; the pubic notch of ilium was not centrally placed, but more anterior; the ischial notch of ilium was relatively long; the forelimbs [ ?] were not reduced; (3) hypsilophodonts were rare in the Middle Jurassic, but a few iguanodontids had been preserved; (4) stegosaurs evolved relatively quickly and processed obvious transitional characters, as exemplified by the Middle Jurassic stegosaurs in Tibet (plates thin and broad, femoral fourth trochanter unobvious, ischia flat etc). The Middle Jurassic was a time of exchange between primitive and advanced reptiles. New dinosaurs appeared while some early reptiles became extinct, as did the last lineages of tritylodontids. The distribution of Middle Jurassic reptilian fossil-bearing strata in China is regionally restricted, of which the more significant include: (1) Dabuka Group of Tibet – carnosaurs ( Megalosaurus dapukaensis ), coelurosaurs ( Ngexisaurus dapukaensis ), sauropods ( Lancangjiangosaurus cachuensis ), sauropods with primitive peg-like teeth (Microdontosaurus dayensis ), and stegosaurs ( Changdusaurus laminaplacodus ); (2) Hopingxiang Group of Yunnan – Peloneustes kiangchenensis ; (3) Lufeng Group of Yunnan – Plesiochelys oshanensis , Sauropoda indet., Chelonia indet., (4) Lower Shaximiao Group and Upper Ziliujing Group of Sichuan – sauropods ( Bothropodidae indet., Homalosauropodidae indet.), coelurosaurs (Coeluridae indet.), carnosaurs (Megalosauridae indet.) and mesosuchians (Teleosuchidae indet.). The Middle Jurassic reptilian fossils of China are similar to those from the Bajocian, Bathonian and Calovian Stages of England, with some fitting into the same genus and even species. Megalosaurus from China and the English Inferior Oolite Series, for example, are of the same genus, though of different species; while Cetiosaurus form the Great Oolite Series is similar to Lancangjiangosaurus . Anyhow, though the [Middle Jurassic] fossiliferous strata of China are less widely distributed than that of the Late Jurassic, their geologic age is reliably accurate since they could be cross compared with foreign strata. Late Jurassic The Late Jurassic was a time of rapid development for Mesozoic reptiles and the middle to late stages of dinosaurian evolution, the more remarkable of which being sauropod evolution in its heyday. Both lineages of sauropods (spatulate-teeth and peg- like teeth) enjoyed great development, with the latter in particular. Fossils of the latter were abundant in any typical Late Jurassic strata in Sichuan, like Mamenchisaurus hochuanensis , Mamenchisaurus constructus , Zigongosaurus fuxiensis and Omeisaurus changshouensis . Similar founds exist in Xinjiang ( Tienshanosaurus chitaiensis ). Great changes occurred in carnosaurs and coelurosaurs. Late Jurassic carnosaurs had highly serrated teeth with robust areolae, reduced forelimbs, thick hind limbs and tails, flat ilia and fused metatarsals etc. Representatives include: Youngchuanosaurus [ sic ] shangyouensis , Szechuanosaurus campi and cf. Szechuanosaurus campi etc. Contemporary coelurosaurs had further narrowing of teeth and lightening of the post-cranial skeleton, e.g. Sinocoelurus fragilis . Ornithischian evolution in the Late Jurassic should receive special attention, whence they dropped their sluggish evolution pace. Large bipedal iguanodons were an example. They had many advanced characters like increased body size, robust skulls, loss of enamel on one side of tooth crown, ophisthocoelous cervical vertebrae, loss of pre-maxillary teeth, a radial-humeral ratio of circa 2/3, broad anterior pubic notch with short posterior notch, tibia shorter than femur, distal phalanges in semi-hoofed shape etc. Sanpasaurus yaoi and Yandusaurus hongheensis of Sichuan are two typical examples. The appearance of advanced nodosaurid ankylosaurs is a marker of the Late Jurassic. These ankylosaurs probably evolved from Scelidosaurus and retained certain degree of primitiveness with small homogenous scales. They were restricted to Xinjiang. Stegosaur evolution is another characteristic of the Late Jurassic. Represented by Tuojiangosaurus multispinus and Chialingosaurus kuani in Sichuan, stegosaurs shared synapomorphies like sharp robust plates, forward pointing iliac blade etc, which characterize late stegosaurs. Evolved from Dianchungosaurus , Chaoyoungosaurus liaosiensis and Xuanhuasaurus niei were prototype psittacosaurs appearing in the early Late Jurassic. They were characterized by the presence of maxillary canine, early trilobate teeth and non-elevated but laterally expanded jugals. They paved the way for psittacosaur evolution but further finds of Late Jurassic chaoyoungosaurids is waiting. Besides dinosaurs, crocodylomorphs were regarded as the most conservative [archosaurs]. Even so, their fossils exhibited marked changes in the Late Jurassic. Pholidosauridae mesosuchians showed this clearly: enlarged skulls, lengthened snouts, elliptical tooth cross-section, carinae meeting at tip of teeth, generally curved or even conical teeth etc. They were represented by Peipehsuchus teleorhinus and Sunosuchus miaoi . Hsisosuchidae was another rapid evolving branch, being more abundant in the Late Jurassic e.g. Hsisosuchus chungkingensis . They were characterized by high and narrow skulls, deep facies, forward extending snouts, reduced tooth number and laterally compressed teeth with anterior and posterior serrations. Late Jurassic chelonids, especially [amphibious turtles] and plesiochelids, took a great step in evolution with elongated skulls and necks that could not or could scarcely retreat inside the carapace. Plesiochelys radiplicutus and Teinfuchelys tsuyangensis are examples. It must also be mentioned that, the terrapins, which lost the keratinous shield but retained a visible bony carapace, probably evolved from side-necked turtles in the Late Jurassic. Though mostly from the Cretaceous, Tertiary to Modern, the ancestry of terrapins could be traced back to the Late Jurassic e.g. Sinospideretes wimani . The Late Jurassic lepidosaruian record is scarce, limited to individual lizard specimens e.g. Changisaurus microrhinus , which may belong to Gekkonidae. Although sparsely found in the Late Jurassic, pterosaurs evolved significantly; most remarkably, teeth were reduced from the back of jaw forwards. By the Late Jurassic, specimens showed only a few small, light teeth at the tip of snout. Lately, edentate specimens were found in the Late Jurassic strata of the Shaanxi-Gansu- Ningxia basin. Lastly, an important class of vertebrates evolved from reptiles in the Late Jurassic – the birds. Currently their ancestry remains unclear, but two possibilities – from ornithischians and from saurischians – worth further study. With the accumulation of fossils, this question will settle; however, to date no complete and convincing bird fossils have been found in China. There are only fragmentary remains. Reptile fossil-bearing strata of Late Jurassic age were highly developed and widespread in China, in particular southwest regions: Upper Shaximiao Group, Lower Penglaizhen Group, Kenzuoga Group, Yantang Group, Lower Zhidan Group, Qugu Group, Kalaza Group, Houcheng Group, Tuchengzi Group, Caiyang Group etc. Correlative foreign strata include the North American Morrison Formation, East African Tendagura [ sic ] Formation and the European Oxfordian and Kimmeridgian [stages].

Plate 10 1. Lancangjiangosaurus cachuensis Zhao Teeth (field, in situ ) ×1/10. Dabuka village, Daye, Changdu, Tibet. Dabuka Group, Middle Jurassic. 2. Yunnania brevirostre Cui Skull in lateral view ×1. Zhangjiawa, Dali village, Lefeng, Yunnan. Lower Lufeng deep red beds, Early Jurassic. 3. Chinshakiangosaurus zhongheensis Zhao Femur in anterolateral view ×1/6. Fenghe village, Zhonghe, Yongren, Yunnan. Fengjiahe Group, Early Jurassic. 4. Damalasaurus laticostalis Zhao Dorsal ribs (field, in situ ) ×1/13. Daye, Changdu, Tibet. Upper Daye Group, Early Jurassic.

Plate 11 1. Mamenchisaurus hochuanensis Young et Zhao 19 th cervical vertebra and 1 st dorsal vertebra in lateral view ×1/40. Taihe town, Hochuan, Sichuan. Upper Shaximiao Group, early Late Jurassic. 2. Kunmingosaurus utingensis Zhao Right pelvic girdle and hind limb with partial caudal series ×1/11. Foxiaofeng, Wuding, Yunnan. Lower Lufeng Group, Early Jurassic. 3. Neotrilophosaurus petilus Young Skull in dorsal view ×2. Dachungxi, Lufeng, Yunnan. Lower Lufeng dark purple beds, Early Jurassic. 4. Dachungosaurus yunnanensis Zhao Postcranial skeleton (field, in situ ) ×1/25. Dafongtian, Lufeng Yunnan, Early Jurassic.