the Middle Triassic, high sea levels enabled shallow water to cover much of the South China Block, a tectonic plate that today consists of the stable Yangtze Craton and the less stable South China Fold Belt. A mountain-building event known as the Indosinian orogeny uplifted Precambrian rocks to form four major landmasses on the South China Block: Khamdian to the west, Jiangnan in the centre, Yunkai to the south, and Cathaysia to the east. Island chains also stretched between Yunkai and Cathaysia in the east. Located between Khamdian and Jiangnan was a deep oceanic basin known as the Nanpanjiang Basin. Along the western edge of this basin, fossil-bearing sediments were laid down to become what are now the Lagerstätten (sedimentary deposits characterized by exemplary preservation) of Panxian, Luoping, and other localities. At Panxian, there appears to have been a transition in the endemic marine reptile fauna, possibly caused by volcanism. This volcanism is indicated by the presence of a bentonite layer between the Middle and Upper Reptile Horizons. From lower in the Upper Reptile Horizon, fossils have also been found of the ubiquitous mixosaurian ichthyosaur Mixosaurus panxianensis (which occurs in all layers), the pachypleurosaurs Keichousaurus sp. and Wumengosaurus delicatomandibularis, and fish, although fossils of the latter are fragmentary. The lower Middle and Lower Reptile Horizons also include the mixosaurian Phalarodon cf. fraasi, the primitive ichthyosaur Xinminosaurus catactes, the placodont Placodus inexpectatus, the nothosaurs Lariosaurus hongguoensis and Nothosaurus yangjuanensis, and the archosaur Qianosuchus mixtus, alongside bivalves and saurichthyid fish. The fauna of Luoping appears to have been preserved in a small intraplatform basin instead of the surrounding open water, judging by the anoxic sediments present at the site. Out of 19,759 specimens, 93.7% of the fossils found at Luoping are arthropods: decapods, isopods, crab-like cycloids, shrimp-like mysidaceans, clam shrimp, and ostracods, as well as rare millipedes and horseshoe crabs. By comparison, only 0.07% of specimens come from marine reptiles, which include Dinocephalosaurus and Pectodens alongside the mixosaurians Mixosaurus cf. panxianensis and Phalarodon atavus; the pachypleurosaurs Dianmeisaurus gracilis and Dianopachysaurus dingi; the saurosphargids Largocephalosaurus polycarpon and Sinosaurosphargis yunguiensis; the nothosaurs Nothosaurus zhangi and a species of Lariosaurus; other sauropterygians Atopodentatus unicus, Dawazisaurus brevis, and Diandongosaurus acutidentatus; and an archosaur related to Qianosuchus. Otherwise, fish including saurichthyids, palaeoniscids, birgeriids, perleidids, eugnathids, semionotids, pholidopleurids, peltopleurids, and coelacanths have been found at Luoping, forming 3.66% of fossils with 25 taxa in 9 families. Molluscs such