A large-sized caudal fin of the actinopteryigan Birgeria, from the Middle Triassic (Pelsonian, Anisian) Panxian Fauna in the Upper Member of the Guanlin Formation, Panxian County, Guizhou Province, China is described. It is the first report of Birgeria in the Panxian Fauna and represents the earliest fossil record of Birgeria in China. There are some specialized characters for this specimen in accordance with Bigeria: the speculated large size, narrow scales without ganoine ornament merely covering the posterodorsal portion of the caudal peduncle and the axial lobe of the caudal fin, single neural spine and haemal spine in caudal region, fulcra scales developed on the dorsal margin of the caudal fin, etc, which support the assignment of the current specimen to the genus Birgeria. Moreover, it distinguish from all known Birgeria species in its relatively large size (speculated total length over 2 m), a higher number of hypural (9), fulcras of the ventral margin of the caudal fin more developed and a bigger angle between the posterior margin of upper lobe and that of the lower lobe (>70º), but, a Birgeria sp. instead of a new species of Birgeria is assigned herein due to limited material. Birgeria is a kind of large carnivorous fish exsisting only in the Triassic ocean, which can be found from the Anisian Panxian Fauna to the Carnian Guanlin Fauna. The first appearance of Birgeria in China is later than that in West Tethys in Smithian, Early Triassic.

An almost complete Nothosaurus specimen is described in particular from the Upper Member of the Guanling Formation (Pelsonian, middle Anisian, Middle Triassic) of the Xinmin District, Panxian County, Guizhou Province, Southwestern China. The specimen provides new information on the postcranial osteology of the species. The diagnosed features of the species are revised by the following characters: four premaxillary fangs followed by one small conical premaxillary tooth and five to six small maxillary conical teeth followed by paired maxillary fangs, no posterior process in the interclavicle, four carpals, four sacral vertebrae and hyperphalangy in both manus and pes. In some aspects of its postcranial morphology, GMPKU-P-3014 appears to approach Lariosaurus more closely than Nothosaurus, such as no posterior process in the interclavicle, four carpals, four sacral vertebrae and hyperphalangy in both manus and pes, which provides the important characters to reevaluate the phylogenetic relationships of Nothosaurus and Lariosaurus within the Sauropterygia. GMPKU-P-3014, GMPKU-P-1080 and IVPP V 14294 are different from all other nominal species of Nothosaurus by their size, dentition and the skull future pattern. In addition they have the most similar shape and important proportions of the skull, as well as the same location and stratigraphic level. Thus, they are the same species and indicates that N. rostellatus is a junior synonym of N. yangjuanensis and should be abandoned.

The conodonts biostratigraphy from the Upper Member of the Guanling Formation to the basal Yangliujing Formation in Yangjuan-Chupiwa Section was re-analysed and the conodont Neogondolella constricta cornuta, Neogondolella constricta longa, Neogondolella constricta balkanica, Neogondolella alpina alpina, Neogondolella cf. Neogondolella acuta, Paragondolella excelsa, Paragondolella torna?sis were described. Based on the stratigraphical distribution and morphological variations of these conodonts, five conodont zones were re-established and the relevant biostratigraphic comparisons were made. The results reveal that: 1) From the Upper Member of the Guanling Formation to the basal Yangliujing Formation, five conodont zones can be investigated. In ascending stratigraphical order, they are Nicoraella germanica Zone (the bottom undefined), Nicoraella kockeli Zone, Neogondolella bifurcata Zone, Neogondolella constricta Zone, and Neogondolella constricta cornuta Zone (the top undefined); 2) These conodont zones are comparable to the same-named conodont zones of the Upper Longtou Formation at Qingyan Section (platform-margin slope) and of the Guandao wedge at Guandao (2) Section (basin-margin facies) in Guizhou Province, and these conodonts are also present in the ammonoid binodosus Zone, trinodosus Zone, and reitizi Zone in the West Tethys; 3) It further proves that the studied strata can be considered as the Pelsonian-Illyrian substages of the Anisian stage (Middle Triassic), not going into the Ladinian of the Middle Triassic.

A new species of Qianichthyosaurus Li, 1999 from the Zhuganpo Member of the Falang Formation (Ladinian, Middle Triassic), Wusha Town, Xingyi City of Guizhou is described here, namely Qianichthyosaurus xingyiensis sp. nov. The recognition of the new species revises the diagnosis of the genus: tooth size relative to the skull width slightly below 0.1; ulna peripheral “shaft” notched or largely reduced; hindlimb nearly equal or longer than forelimb; tibia peripheral “shaft” notched or largely reduced. Qianichthyosaurus xingyiensis sp. nov. differs from the type species in having relatively longer snout (snout length/skull length over 60%); humerus radial facet being prominently larger than ulnar facet; unenclosed obturator foramen on pubis; fibula posterior process on the posterior margin and the ischium sub-triangular lacking shaft. The new species is stratigraphically older than Q. zhoui, the specimens of which were exclusively known from the Wayao Member of the Falang Formation (Carnian, Late Triassic). Along with askeptosaurid thalattosaur Anshunsaurus and shastasaurid ichthyosaur Guizhouich- thyosaurus, the occurrence of Q. xingyiensis sp. nov. in Xingyi Fauna suggests a closer relationship between Xingyi Fauna (late Ladinian, Middle Triassic) and Guanling Biota (Carnian, Late Triassic).

On the basis of detailed morphological description and anatomy comparison of two specimens of Keichousaurus hui, the diagnostic characters of Keichousaurus hui have been reconfirmed: small upper temporal fenestra, large orbits, thickened proximal end of ribs and extremely broad ulnae; and more morphological information of Keichousaurus hui is added. The sexual dimorphism of three adults and the ontogenetic stage of a juvenile have been identified through the measurement of different bones. Furthermore, from the paleogeographic information and observation of the embryos, it’s inferred that the reproduction mode is most likely viviparous, but the possibility of ovoviviparity cannot be totally ruled out.

The present study is based on ammonoids collected from the strata above the ammonoid Trachyceras multituberculatum zone of Wayao Member of “Falang Formation” (Late Triassic) at the Niubudai Section in Luoping County, Eastern Yunnan Province. Eight species of four genera, including one conform species and three indeterminate species were recognized, among which Trachyceras aonoides, Simonyceras simonyi are firstly found in China. According to their assemblage and stratigraphic distribution, two ammonoid zones were recognized in ascending order: Trachyceras aonoides Zone, Austrotrachyceras triadicum Zone, corresponding to the middle-late Early Carnian of Late Triassic in age.

Here the true tailbends are reported in two complete skeletons of Guanlingsaurus from the late triassic of Guizhou Province, southwestern China after accurate observations, measurements and comparisons with Ichthyosaur of early jurassic. They have acquired the wedge-shaped centra and the angles in these tailbends are around 15°while those in jurassic types are around 60°. This study shows for the first time that wedge-shaped tailbend centra already existed in merriamosaurs as early as late triassic time, probably being a result of coevolution between ichthyosaurs and the environment. The occurrence of the true tailbend connected triassic and jurassic ichthyosaurs that used to be considered as separate groups in previous literature. The present finding also suggests the monophyly of ichthyopterygia.

The crania of Xinpusaurus sp. from the Carnian Wayao Formation of Guanling, Guizhou Province is studied in detail and then compared with other two species of Xinpusaurus. The new specimen shows following similarities to other two species: the lateral view looks like a right-angled triangle when the mouth is closed; the frontage of the dentary forms a platform as a result of its bending; a significant curve exists at the end of the premaxilla; the posterior process of the rasal extends far away from the external naris; the post-lateral process of the premaxilla extends beyond the external naris. So it is assigned to be a Xinpusaurus. However, the specimen is still significantly different to other two species: the adult size is relatively larger; the tooth at the end of the premaxilla inclines posteriorly; the premaxilla is not excluded from the formation of the external naris; no tooth on the pterygoid; the prefrontal contacts with the nasal; no tooth on the maxilla and the back of the dentary. Because of the ill preservation of the specimen, the characters of the temporal region and the post cranial can not be identified, and it's assigned to an undefined species of Xinpusaurus.

Chemo-stratigraphic analysis will help to solve the problem of the Ordovician-Silurian Boundary, which might locate in the bed of mudstone intercalated with dolostone from the top part of the Lower Member to the basal part of the Middle Member of the Kepingtage formation at the Dawangou Section in the Keping County. Systematically collected seventy two samples were measured by ICP, and data were compared and emended. The w(Ce)/w(La) chemo-stratigraphic analysis indicates that this bed can be subdivided into three chemo-beds. The chemo-fluctuation might reflect the fluctuation of oxidation-deoxidation, and can be correlated with the changes of fossils. The chemo-spike might be corresponding with the anomaly around the boundary of the Ordovician-Silurian at the east Yangtze Gorger.

The Panxian Fauna is mainly characterized by well-preserved and articulated skeletons of Middle Triassic (Anisian) marine reptiles with high diversity, associated with abundant invertebrate fossils, such as bivalves, brachiopods as well as cephalopods, and some as yet undescribed taxa. Stratigraphically, it is occurred at the Upper Member of the Guanling Formation, ascribed to the conodont Nicoraella kockeli Zone, which indicates that the age of this fauna is Pelsonian (Middle Anisian). Therefore, the Panxian Fauna is older than the Grenzbitumenzone fauna at Besano/Monte San Giorgio area of Italy/Switzerland border (near Anisian/Ladinian boundary), and represents the oldest marine reptile fauna of the Middle Triassic throughout the world. Such a rich, diversified and perfectly preserved paleontological assemblage with the exact stratigraphic horizon and definitive age not only provides abundant materials for exploring the taxonomy, evolution, and origin of the marine reptiles, but also has great significance for developing the study of paleoecology and biogeographic provincialism. So far, five genus and five species, including the oldest mixosaurid ichthyosaurs, the oldest lariosaurs and the first true aquatic protorosaur(Dinocephalosaurus orientalis), have been reported from the Panxian Fauna. Most of them are adapted to epicontinental environment or shallow sea, and show a strong West Tethyan affinity. The strata bearing the Panxian fauna consists of four or five tuff beds and seven volcanicities were recognized, which might be caused the extinction of these marine reptile animals directly.

The Guanling Biota, stratigraphically from the basal Wayao Member of the Falang Formation (the Early Carnian: Late Triassic), is remarkable for its completely articulated and well preserved large ichthyosaur fossils. A precise description in detail of the large ichthyosaurs will be of great significance to the understanding of their taxonomic status, evolution and phylogenic history. So far, five taxonomic names have been erected and published for these large ichthyosaur, namely Guizhouichthyosaurus tangae, Typicusichthyosaurus tsaihuae, Guanlingsaurus liangae, Cymbospondylus asiaticus, and Panjiangsaurus epicharis. However, most of them still need to be re-studied and confirmed their taxonomic status. On the basis of the field investigation and the preparation, observation, comparison, the revised and amended diagnostic description on Guizhouichthyosaurus tangae is given, and Cymbospondylus asiaticus and Panjiangsaurus epicharis are the synonyms of Guizhouichthyosaurus tangae.

Petrological samples collected from the Upper Triassic Wayao Formation bearing t he Guanling Fauna,located in Xinpu area of Guanling County, Guizhou rovince, were observated under microscope. Three kinds of lithology can be distinguished on the basis of the bio-abundance. Considering the bio-assemblage of the Guanling Fauna, its taphonomic environment characteristics can be concluded as follows: the sea water was relatively deep, lower energy, peachful and anoxic condition with normal paleosalinity and warmer climate. In addition, the distributions of the conodontParagondolella and the bivalve Halobia confirm the taphonomic environment and indicate the occurrence of the anoxic event as well. The study of paleoredox markers and fossil diversity finds two main significant factors. One is the fine grain and compact texture of marly lime stone bearing the Guling Fauna, which makes the remains deposit nearly intact. The other is the layer of reptile and crinoid fossils coincide well with w(Ce)/w(La) value over 2.0 and increasing positively, which reveals a high anoxic condition just like a protecting cover which keep the remains out of the oxygen.

Samples collected from the Wayao Formation, which yields the Guanling Fauna, and the underling formation, the Zhuganpo Formation, were treated for conodont analysis. The study result shows that two conodont zones, Paragondolella polygnathiformis-P.tadpole Assemblage Zone and the P. polygnathiformis Zone can be recognized. Comparing with the international and domestic related information, a conclusion can be drawn that their epoch should belong to the Middle or Late Carnian of the Late Triassic. So the final result indicates that the age of the Guanling Fauna belong to the middle Carnian of the Late Triassic, maybe the late Carnian, not to the Ladinian of the Middle Triassic.