Guanling Formation
Introduction The '''Guanling Formation''' is a Middle Triassic (Anisian or Pelsonian in the regional chronostratigraphy) geologic formation in southwestern China.
Geology The formation encompasses two members. The first member is primarily calcareous mudstone and dolomite, indicative of a coastal environment. The second member is a thicker marine sequence of dark micritic limestone with some dolomite. Two distinct fossil assemblages are found in the second member. The older '''Luoping biota''' preserves abundant arthropods along with fossils from other invertebrates and vertebrates, which are rare but well-preserved. The slightly younger '''Panxian fauna''' has a more diverse and common assortment of marine reptiles such as sauropterygians.A tuff bed in the Luoping biota has been dated to 244.5 ± 2.2 Ma via U-Pb SHRIMP dating. The Luoping biota as a whole was deposited over a period of 340 ± 71 kyr. This estimate is justified by cyclostratigraphic evidence, as indicated by fluctuations of terrestrial proxy metals.
Fossil content Among others, the following fossils were reported from the formation:===Ichthyopterygia===+ '''Ichthyosauria''' Genus  Species  Member  Notes  Image''Barracudasauroides'' ''B. panxianensis''  Upper Member  A small mixosaurid ichthyosaur, either a memeber of its own genus or a species of ''Mixosaurus''. ''Phalarodon'' ''P''. cf. ''fraasi''  Upper Member  Known from a skull of a small mixosaurid ichthyosaur with durophagous dentition. ''P. atavus'' Upper Member  A small mixosaurid ichthyosaur known from a complete skeleton. Might represent a member of its own genus, ''Contectopalatus''. ''Xinminosaurus''  ''X. catactes''  Upper Member  A medium-sized early ichthyosaur with durophagous dentition, possibly a member of Cymbospondylidae. ===Sauropterygia===+ Placodontiformes Genus  Species  Member  Notes  Image ''Atopodentatus''  ''A. unicus''  Upper Member A bizzare, likely herbivorous sauropterygian with possible placodontiform affinities, known from several well-preserved specimens. ''Placodus''  ''P. inexpectatus''  Upper Member A medium-sized placodontid placodont, known from a complete specimen. + Saurosphargidae Genus  Species  Member  Notes  Image''Largocephalosaurus'' ''L. polycarpon''  Upper Member   A mid-sized basal saurosphargid sauropterygian. ''L. qianensis''  Upper Member   A mid-sized basal saurosphargid sauropterygian. ''Sinosaurosphargis''  ''S. yunguinensis''  Upper Member  A small armoured saurosphargid sauropterygian. * ''Austronaga''* ''Diandongosaurus''* ''Dianopachysaurus''* ''Dinocephalosaurus''* ''Gracilicollum''* ''Honghesaurus''* ''Kyphosichthys''* ''Luopingosaurus''* ''Luoxiongichthys''* ''Luxisaurus''* ''Pectodens''* ''Qianosuchus''* ''Sanchiaosaurus''* ''Sinosaurichthys''* ''Wumengosaurus''
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