A new specimen (CAGS V 382)(Figs. 1～2) was described and a new species, Parakannemeyeria chengi , was erected based on this specimen. This material was found in the lower part of the Kelamayi Formation (Middle Triassic) of Jimusar, Xinjiang by Professor Cheng Zhengwu. It was identified as Parakannemeyeria by: skull curved, long, narrow and high; preorbital length more than 45% of skull length; the width between orbits less than 40% of the skull length; occipital plate high and narrow. But it also has some characters used to be thought as the diagnosis of Sinokannemeyeria such as broad intertemporal region, reduced nasal middle ridge; these two characters are enough to distinguish this specimen from all other Parakannemeyeria . A cladistic analysis was done for the phylogenetic relationship of Parakannemeyeria chengi among all known species of Sinokannemeyeria, Parakannemeyeria and Xiyukannemeyeria using the characters and data matrix of Liu and Li (2003), only adding the character states of P. chengi (Table 1). A shortest tree was obtained, it is nearly the same as the tree of Liu and Li (2003), other than P. chengi is the sister group of P. shenmuensis . The autopomorphies of P. chengi are indistinct mid nasal ridge, wide intertemporal region mainly formed by parietal (and interparietal), the posterior part of jugal arch nearly triangular in cross section.
The Olenekian Stage of the Lower Triassic is named from the Boreal Realm, but the stage has never been properly defined, nor has it been applied in the low-latitude Tethyan Realm, with exception of North Caucasus and Mangyshlak. This paper proposes a stratotype for the In-duan-Olenekian boundary in the low-latitude Tethyan Realm. South China is one of the main regions in the Tethyan Realm with well-developed Lower Triassic sequences and abundant fossils. According to the basic stratigraphic records and various accumulated data, we believe that the West Pingdingshan Section in Chaohu, Anhui Province is one of the best sequences to define the Induan-Olenekian boundary. The first appearance datum (FAD) of conodont Neospathodus waageni is the preferred index to define the boundary. This datum lies 26 cm below the FAD of the ammonoids Flemingites and Euflemingites, and is located slightly prior to the top of the second Triassic normal magnetozone, and the peak of the first Triassic positive excursion of carbon isotope σ13C.
Studies on three Lower Triassic sections located on the shallow water platform, the deep water slope and in the deep water basin in the Lower Yangtze Region, South China, show the similar trend of carbon isotope evolution. Biostratigraphic correlations among the Lower Triassic sections on the basis of standard conodont zones indicate that three negative shifts occurred in the Griesbachian, the Smithian and the late Spathian stages respectively, and one distinctly positive shift occurred in the early Spathian stage. Trend of carbon isotope evolution of the Lower Triassic reflects some significant changes in the global carbon cycle. Moreover, δ 13C background values are intensively controlled by palaeogeographic environment. In general, δ 13C values from deep-water slope carbonates are lighter than those from carbonate platform and heavier than those from deep-water basin carbonates. The positive carbon isotope excursion may be induced by a significant amount of organic carbon burial in marine sediments and increase in primary productivity. The large negative carbon isotope excursions during the Early Triassic in Lower Yangtze Region are interpreted to relate to volcano eruptions based on tuffaceous claystone interlayers observed near the Permian-Triassic boundary, the Induan- Olenekian boundary and the Lower Triassic-Middle Triassic boundary.
ZUO Jingxun1,2, TONG Jinnan3, QIU Haiou4 & ZHAO Laishi3 1. Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, Nanjing 210008, China
