Guanling Formation Research Articles

Youngest ambient inclusion trails from Middle Triassic phosphatized coprolites, southwestern China: New insights into an old intriguing phenomenon

Copious microtubular structures are reported, for the first time, from the coprolites of early Middle Triassic Guanling Formation in Luoping, Yunnan Province, southwestern China. Multiple salient characteristics of these microtubes, including curved to coiled grooves with longitudinal striations, angular turns, cross-cuttings, and a terminal rounded pitting at one end of a groove, support their strong affinities with ambient inclusion trails (AITs) that are more commonly found in pre-Ediacaran sedimentary rocks. These newly found microtubular structures are here interpreted to represent the youngest occurrence of AITs in the geological record. A review of all AITs and similar microtubular structures reveals their common occurrences in Ediacaran phosphorite and Phanerozoic phosphatized fossil substrate. Similar to the AITs found from the post-Ediacaran strata, the AITs from the Luoping coprolites are also preserved in a phosphatized substrate. We suggest that a microbial-induced process might have contributed to the phosphogenesis of faeces and AITs formation. This process is interpreted to have involved the precipitation of phosphate minerals by microbial communities, and the movement of pyrite through and within phosphatized substrate gel driven by fluid pressure. This new interpretive model differs from the existing scenario invoked to explain the formation mechanism of pre-Ediacaran AITs, in which pyrite propulsion is thought to be more likely driven by metamorphism-induced fluid pressure. We thus hypothesize that the transformation in AITs' formative substrate, from chert to phosphate, as well as their formation mechanism, might have been triggered by a significant change in ocean biogeochemistry linked to a phosphogenic event in the Neoproterozoic.

A new diapsid from the Middle Triassic of southern China

AbstractThe Middle and early Late Triassic of southern China is well known for a remarkable diversity of marine vertebrates, particularly reptiles, including an abundance of intriguing new forms (e.g., Jiang et al., 2005; Hu et al., 2011; Li et al., 2016). Here we describe a new diapsid from Yunnan Province. It possesses an elongate neck that exhibits a remarkable similarity to that of many Protorosauria, yet in other respects the skull and postcranium are much less derived.The new taxon is part of the so-called Panxian-Luoping Fauna and the deposits correspond to the Upper Member of the Guanling Formation, comprising thin to medium bedded, gray to dark-gray laminated marly limestone and limestone, with several layers of bentonite intercalated in the fossil level at Panxian (Wan, 2002; Motani et al., 2008; Jiang et al., 2009). Their age is Pelsonian (middle Anisian, Middle Triassic) as is indicated by the conodont Nicoraella kockeli Zone (Sun et al., 2006; Zhang et al., 2009). A recent U-Pb study indicates the absolute age of these middle Anisian beds to be close to 244 Ma (Wang et al., 2014).

The origin of high hydrocarbon groundwater in shallow Triassic aquifer in Northwest Guizhou, China.

Original high hydrocarbon groundwater represents a kind of groundwater in which hydrocarbon concentration exceeds 0.05mg/L. The original high hydrocarbon will significantly reduce the environment capacity of hydrocarbon and lead environmental problems. For the past 5years, we have carried out for a long-term monitoring of groundwater in shallow Triassic aquifer in Northwest Guizhou, China. We found the concentration of petroleum hydrocarbon was always above 0.05mg/L. The low-level anthropogenic contamination cannot produce high hydrocarbon groundwater in the area. By using hydrocarbon potential, geochemistry and biomarker characteristic in rocks and shallow groundwater, we carried out a comprehensive study in Dalongjing (DLJ) groundwater system to determine the hydrocarbon source. We found a simplex hydrogeology setting, high-level water-rock-hydrocarbon interaction and obviously original hydrocarbon groundwater in DLJ system. The concentration of petroleum hydrocarbon in shallow aquifer was found to increase with the strong water-rock interaction. Higher hydrocarbon potential was found in the upper of Guanling formation (T2g3) and upper of Yongningzhen formation (T1yn4). Heavily saturated carbon was observed from shallow groundwater, which presented similar distribution to those from rocks, especially from the deeper groundwater. These results indicated that the high concentrations of original hydrocarbon in groundwater could be due to the hydrocarbon release from corrosion and extraction out of strata over time.

Dawazisaurus Brevis, A New Eosauropterygian From the Middle Triassic of Yunnan, China

AbstractDawazisaurus brevis (gen. et sp. nov.) is a newly discovered Triassic marine reptile, represented by a complete skeleton from Member II of the Guanling Formation of Luoping, Yunnan Province, China. This paper aims to (1) present a thorough description of the species, (2) make a detailed comparison to demonstrate if the species can be referred to any known sauropterygian taxa, and (3) conduct phylogenetic analyses to establish the internal relationships of the species with other sauropterygians. In addition, the discovery of Dawazisaurus provides a chance not only to test the phylogenetic patterns of the Sauropterygia obtained by previous studies but also to evaluate the previous hypotheses on the origin of the sauropterygian groups at different levels. D. brevis is an eosauropterygian, characterized by a unique combination of derived features such as a pair of large nasals joining in the formation of the internarial septum, a short trunk with 16 dorsal vertebrae; the zygapophyses of the trunk vertebrae very small or weakly developed; the posterior margin of the skull roof deeply V‐shaped, and an ossified distal carpal 5. Phylogenetic analysis indicates that D. brevis appears to be more closely related to the Nothosauroidea than the Pistosauroidea within the Eosauropterygia.

Integrated biochronology for Triassic marine vertebrate faunas of Guizhou Province, South China

The Middle and Upper Triassic marine deposits of Guizhou Province, which yielded exceptionally well-preserved vertebrate faunas, are further investigated. New age-diagnostic conodonts and ammonoids from six measured sections, together with already published data, allow us to construct an integrated biochronology straddling strata from the upper Guanling Formation (Anisian, Middle Triassic) to the basal Xiaowa Formation (Carnian, Upper Triassic). Age constrains for those fossil Lagerstätten are now dated to the substage and zone levels: the Panxian Fauna, within the conodont Nicoraella kockeli Zone and broadly coexisted with the ammonoid ‘Schreyerites’ binodosus, is suggested as latest Pelsonian (middle Anisian) in age; the Xingyi Fauna is assumed to be not younger than the middle Longobardian (Late Ladinian) because the conodont Paragondolella inclinata with free-blade and the ammonoid Haoceras xingyiensis are recorded from slightly younger strata; the conodont Paragondolella auriformis and the ammonoid Trachyceras multituberculatum and Austrotrachyceras triadicum clearly indicate that the Guanling Fauna is not older than Julian (early Carnian) in age (time interval between Aon Zone or Aonoides Zone). With the new biostratigraphic data, a relative sequence and correlation of the Middle Triassic vertebrate faunas from Guizhou (South China) and Monte San Giorgio (Southern Alps, Switzerland/Italy) is proposed.

Spatial distribution of Crustacea and associated organisms in the Luoping Biota (Anisian, Middle Triassic), Yunnan Province, China: evidence of periodic mass kills

AbstractThe distribution of all recognized biotic elements was mapped on five extensive surfaces of the Middle Triassic Guanling Formation exposed in quarries near Luoping, Yunnan Province, China. A 0.5 m2 grid was overlain on the surfaces, and all recognizable fossils were located by placing them in one of nine quadrants within the grid. A total of 240 m2 were mapped, and each specimen observed was recorded as one of 15 categories, subsequently grouped as pelagic, benthic, and other (bone, trace fossils, algae). The pelagic component, fish, thylacocephalans, and mysidaceans, dominated all layers. The benthic component was sparse on all surfaces; epifaunal, vagrant organisms were the dominant forms, suggesting that the substrate was unsuitable for infaunal and sessile epifaunal organisms. Shrimp and bivalves dominated the benthic organisms. Two of the surfaces were overwhelmingly dominated by mysidaceans, and one was dominated by thylacocephalans, suggesting that their remains documented periodic mass kills of swarming, pelagic organisms. Scanning electron microscope analysis of the bedding surfaces revealed nothing remarkable about the sediment, suggesting that the cause of death of the organisms was likely due to an event within the water column, possibly an algae bloom, not recorded in the sediment record.

Discussion of ‘The Triassic U–Pb age for the aquatic long-necked protorosaur of Guizhou, China’

We thank Liu Jun for his comment on our recent paper (Wang et al. 2014) and are grateful for his calling our attention to this apparent contradiction, and we welcome the opportunity to reply. Based on the sensitive high-resolution ion microscope (SHRIMP) U–Pb zircon age for a volcanic tuff bed within the upper part of the Guanling Formation, we suggested in our study that the age of the fossil horizon of the Panxian fauna is 244 ± 1.3 Ma, which is 14 Ma earlier than the previously estimated age that Li, Rieppel & LaBarbera (2004) published in Science. However, Liu Jun argued that this conclusion is confused, that there is no 14 Ma difference and that there is agreement between the biostratigraphic data and the new radiometric age.

Early Middle Triassic stromatolites from the Luoping area, Yunnan Province, Southwest China: Geobiologic features and environmental implications

An early Middle Triassic stromatolite deposit is documented from the Guanling Formation of the Luoping area, Yunnan, SW China. The Luoping stromatolite shows five types of constructional microbial forms in various magnifications: 1) typical stratified columnar structures, up to 20cm high, with crinkled laminae. Dark coloured laminae, 1mm thick, are composed of upright filamentous tubes, averagely 29.4μm in diameter, showing a vertical growth fabric. 2) Laminoid fenestrae, 0.5–1mm wide, and 3) prostrate filaments, which are reflected by strong fluorescence in sharp contrast to dolomite cement in fluorescent images. 4) Rod-like aggregates, 4.6–18μm in diameter, composed of minute dolomite rhombs, are very common in stromatolitic laminae; they resemble present-day cyanobacterial trichome, and thus may represent putative fossilized cyanobacteria. 5) Moreover, small pits, coccoid-like spheroids, calcified biofilms, and fibrous structures are also common in stromatolitic laminae. The last two may represent calcified extracellular polymeric substances (EPS) that contributed to the development and lithification of stromatolites. Authigenic quartz grains are common and may also have involved biological processes in stromatolite formation. Of these microbial functional-groups driving accretion and lithification processes of stromatolite documented in literature, both lithified cyanobacteria/oxygenic phototrophs and possible sulfate-reducing bacteria (SRB), which induced microbial formation of dolomite and contributed to the accretion of the Luoping stromatolite, are suggestive of biogenic origin. The Luoping stromatolite differs from the Permian–Triassic boundary microbialites (PTBMs) in having abundant filamentous structures and growing in an oxic marine environment. Both sedimentary facies analysis and abundant fossilized cyanobacteria may indicate proliferation of oxygenic phototrophs in a normal, oxic habitat during the middle Anisian (early Middle Triassic), a period when hospitable environments, coupled with biotic diversification, prevailed in South China and set an agenda for the full recovery of marine ecosystems in middle–late Anisian. However, the post-extinction stromatolites and other anachronistic facies are not necessarily indicative of anoxic or oxic conditions, and their environmental settings are much more complex than previously thought.

First chirothere and possible grallatorid footprint assemblage from the Upper Triassic Baoding Formation of Sichuan Province, southwestern China

Trackways of archosaurs have recently been discovered in sandstones of the Upper Triassic (Norian–Rhaetian) Baoding Formation of Panzhihua City in southern Sichuan Province, China. Based on their overall-morphology, pes imprints are of characteristic chirotheriid shape showing a compact and symmetrical anterior group of digit traces II–IV with the trace of digit III being the longest, and a posterolaterally positioned, long and slender trace of digit V. Imprints of digit I and the manus are not preserved. This could be related to substrate conditions and the relatively shallow impressions, even if peculiarities in the gait such as overstep of the manus by the pes or bipedal movement cannot completely be excluded. Ichnotaxonomically, the imprints are assigned tentatively to cf. Chirotherium. There are some similarities with the type ichnospecies C. barthii from the Middle Triassic that has a global distribution and that was described also from the Guanling Formation (Middle Triassic) of adjacent Guizhou Province. However, the long and slender digit V that lacks a distinct large oval basal pad, the relatively short stride/step length, the low pace angulation, and the slight inward rotation of the imprints toward the midline are different. The peculiar shape of digit V and the lack of digit I in all imprints also preclude an assignment to the common Late Triassic ichnogenus Brachychirotherium or similar ichnotaxa such as Pseudotetrasauropus. An isolated tridactyl footprint on the same surface is different in shape from the chirotheriid ones by the stronger mesaxony and narrower digit divarication. It is considered here as a possible large grallatorid. This is the first occurrence of tetrapod footprints in the Baoding Formation of Sichuan Province and the second record of chirotheriids in the Triassic of China. The Baoding Formation has also yielded a characteristic Upper Triassic flora with cycads, filicopsids, gingkos, and conifers as well as bivalve fossils. The depositional environment can be designated as fluvial-lacustrine with occasional opening to marine areas. Considering biostratigraphic and palaeobiogeographic aspects, the late occurrence of chirotheriids cf. Chirotherium in China supports the view that basal crown-group archosaurs with a distinct tendency toward a functionally tridactyl pes developed and dispersed in parallel to typical tridactyl dinosaurs.

The Triassic U–Pb age for the aquatic long-necked protorosaur of Guizhou, China

AbstractThe ancient marine limestone beds of the upper part of the Guanling Formation, Panxian County, Guizhou Province, SW China, yielded a wide range of high-diversity well-preserved marine reptiles such as the fully aquatic protorosaur with an extremely long neckDinocephalosaurus orientalis, the oldest mixosaurid ichthyosaurs and lariosaurs. However, there is no precise isotopic age to study the intriguing origin, evolution and emigration history of the important fauna. We report a sensitive high-resolution ion microprobe (SHRIMP) U–Pb zircon age for a volcanic tuff bed within the upper part of the Guanling Formation. The result indicates that the age of the fossil horizon is 244.0±1.3 Ma, 14 Ma earlier than the previously estimated age based on conodont evidence. We consider that the marine reptiles had a relatively rapid evolution during Middle Triassic time, some 8 Ma after the end-Permian mass extinction.

CARBONATE RETICULATED RIDGE STRUCTURES FROM THE LOWER MIDDLE TRIASSIC OF THE LUOPING AREA, YUNNAN, SOUTHWESTERN CHINA: GEOBIOLOGIC FEATURES AND IMPLICATIONS FOR EXCEPTIONAL PRESERVATION OF THE LUOPING BIOTA

Exceptionally preserved carbonate reticulated ridge structures are documented from the lower Middle Triassic Guanling Formation of the Luoping area, eastern Yunnan Province, southwestern China. Macrostructures suggest these reticulated ridge structures are morphologically similar to the growth-related structures in ancient and modern microbial mats. Other such features as minute load structures and pyrite crystals beneath the reticulated layers on bedding surfaces are overlain by a black carbonaceous shale layer. Clay minerals in the reticulated layers are oriented parallel to bedding at the top, and they usually form wavy laminae. These characteristics indicate that these carbonate reticulated ridge structures share a similar microstructure to their siliciclastic analogs, and are also comparable with that of wrinkle structures. SEM imaging shows that many tiny objects—coccoid spheres, rod-like structures and filamentous fibrils—are distinct within those ultra-thin, wavy laminae, suggesting similar accretion and growth models to modern microbial mats. Accordingly, the Luoping reticulated ridge structures are of biogenic origin. These microbial mats are associated with the early Middle Triassic Luoping Biota and they are thought to have played a crucial role in the preservation of the fossils through sealing and microbial coats. An SEM-EDS analysis on fossil fragments and their surrounding matrix reveals that microbial mats also played an important role in the phosphatization of Luoping fossils.

A new shrimp (Decapoda, Dendrobranchiata, Penaeoidea) from the Middle Triassic of Yunnan, southwest China

A new penaeoid shrimp collected from the Middle Triassic Member II of the Guanling Formation in the vicinity of the city of Luxi, Yunnan, southwest China, is a new species,Aeger luxiin. sp. The new species possesses prominent spinose third maxillipeds, which is one of the typical characteristics ofAeger. The new species differs from the type species,Aeger tipulariusfrom the Jurassic Solnhofen Plattenkalk, in having a long, smooth rostrum with no subrostral spines. The new taxon increases the diversity of Chinese decapods, and further expands our knowledge of the phylogeny and evolution of the Mesozoic decapods. The find is the first complete specimen ofAegerin the Middle Triassic, and reveals a close biogeographic connection of the marine ecosystem between Eastern and Western Tethys.

Chirotherium Trackways from the Middle Triassic of Guizhou, China

Triassic tetrapod footprints from China are less well known than those from the Jurassic and Cretaceous. Archosaurian trackways of the ichnogenus Chirotherium were found in the Middle Triassic Guanling Formation in Zhenfeng County (Guizhou Province) at the southwestern edge of the Yangtze plate in the early 1960s but were not correctly identified and adequately described until 40 years later. Here we give a detailed re-description and review of the trackways, which are known from two localities near the villages of Niuchang and Longchang. They occur on the bedding surface of a mud-cracked argillaceous dolostone deposited in a near-shore, shallow-water environment. Their morphology and general trackway pattern indicate that they pertain to the ichnospecies Chirotherium barthii, well known from Middle Triassic track surfaces of Europe, North and South America, and northern Africa. A peculiarity of the trackways from China are the low pace angulation and stride length, reflecting slow-moving trackmakers, which were basal crown-group archosaurs, possibly early representatives of the dinosaur-bird line or, alternatively, stem-group crocodylians. These tracks constitute the only chirotheriid record known from Asia thus far and indicate a Pangea-wide distribution for this ichnotaxon. Biostratigraphically, assemblages with C. barthii are characteristic of the early Anisian, an age assignment already supported for the Guanling Formation based on conodont and bivalve biostratigraphy. In contrast, however, radiometric data from an interlayered ash bed indicate a Ladinian age.

Fuyuanperleidus dengi Geng et. al. 2012 (Osteichthyes, Actinopterygii) from the Middle Triassic of Yunnan Province, South China

Two well preserved specimens of Fuyuanperleidus dengi Geng et al., 2012 are described from the Upper Member of the Guanling Formation (Pelsonian, Anisian, Middle Triassic) in Luoping County, Yunnan Province, South China. The attribution to Perleidiformes is confirmed according to a combination of features such as the general skull pattern, with the large preoperculum showing a prominent infraorbital process, the maxilla with deep posterior region and a dentition made of long and stout peg-like teeth with an acuminate apex, the deep mid-lateral flank scales and the caudal fin with epaxial fin rays. However, this taxon shows an unique arrangement of the squamation (here considered as autapomorphy) given by the insertion of several scales in each vertical row posterior to the pelvic fin, just below the scales carrying the lateral line, when their depth decreases abruptly. Owing to this unique character, and in spite of the very recent description of this genus, the authors considered necessary the erection of a new family, Fuyuanperleididae offering also new insights on the evolutionary trends and morphological specializations of the “subholosteans”. A cladistic analysis of the well known perleidiformes, with this taxon included, supports a possible monophyly of the order, and matches well the paleobiogeographic relationships of the Gondwana fresh-water taxa. The specialized deep-bodied Gondwana and Tethyan perleidiformes are independently evolved, ascertained by the parsimony analysis.

Macrurous Decapoda from the Luoping Biota (Middle Triassic) of China

A large collection of macrurous decapod crustaceans is recorded from the middle–late Anisian (Middle Triassic) Guanling Formation in Yunnan Province, China. A remarkable assemblage of over 20,000 vertebrate, invertebrate, and plant fossils collectively referred to as the Luoping Biota has been collected from quarries in the vicinity of the city of Luoping. Among these, arthropods including the decapods are the most common element although articulated fish and reptiles are also common. The decapods represent new taxa, includingKoryncheiros luopingensisn. gen. n. sp. within Clytiopsidae, a newly elevated family within Erymoidea;Tridactylastacus sinensisn. gen. n. sp. within Glypheidae; andYunnanopalinura schramin. gen. n. sp. within Palinuridae. A single specimen has been referred to Palinuridae sp.Koryncheiros luopingensisexhibits a unique cheliped architecture and the second through fourth chelipeds are subchelate, an extremely rare configuration.Tridactylastacus sinensisalso exhibits subchelate closures of pereiopods 2–4, but it bears a distinctive subchelate first pereiopod with an intercalated spine between the fingers on the distal margin of the propodus.Yunnanopalinura schramirepresents the oldest occurrence of Palinuridae and Achelata. Collectively, these expand our knowledge of Chinese decapods significantly in that only six species of fossil decapods have been described previously from the country.

A New Basal Actinopterygian Fish from the Anisian (Middle Triassic) of Luoping, Yunnan Province, Southwest China

The new neopterygian fish taxon Luoxiongichthys hyperdorsalis gen. et sp. nov. is established on the basis of five specimens from the second member of the Guanling Formation (Anisian, Middle Triassic) from Daaozi Quarry, Luoping, Yunnan Province, Southwest China. The new taxon is characterized by the following characters: triangular body outline with a distinct apex located between skull and dorsal fin; free maxilla; slender preopercular almost vertical; three suborbitals; at least eight strong branchiostegals with tubercles and comb-like ornamentation on the anterior margin; clavicles present; two postcleithra; ganoid scales covered by tubercles and pectinate ornamentation on the posterior margin with peg-and-socket structure; hemiheterocercal tail slightly forked. Comparison with basal actinopterygians reveals that the new taxon has parasemionotid-like triangular symplectics, but a semionotid opercular system. Cladistic analysis suggests that this new genus is a holostean, and either a basal halecomorph...

A new species of Habroichthys Brough, 1939 (Actinopterygii; Peltopleuriformes) from the Pelsonian (Anisian, Middle Triassic) of Yunnan Province, South China

Habroichthys broughi n. sp. is described on the basis of eleven well-preserved specimens from the Luoping Biota, a newly discovered marine vertebrate fauna of the Pelsonian (Middle Anisian, Middle Triassic) in the Upper Member of the Guanling Formation of Luoping County, Yunnan Province, South China. The new taxon provides new insights to the anatomy of Habroichthys BROUGH, 1939: maxilla shorter than mandible and free from the pear-like preopercle; clavicle present; tail slightly asymmetrical, with a very small body lobe supporting few epaxial rays. Additionally, some Ladinian material of Habroichthys from the Zhuganpo Member of the 'Falang Formation' is investigated. In consequence, Habroichthys of the Triassic of the Eastern Tehtys (South China) greatly extends the temporal and spatial range of this small, enigmatic subholostean fishes.

A deep-bodied ginglymodian fish from the Middle Triassic of eastern Yunnan Province, China, and the phylogeny of lower neopterygians

The Ginglymodi are a group of ray-finned fishes that make up one of three major subdivisions of the infraclass Neopterygii. Extant ginglymodians are represented by gars, which inhabit freshwater environments of North and Central America and Cuba. Here, we report the discovery of well-preserved fossils of a new ginglymodian, Kyphosichthys grandei gen. et sp. nov., from the Middle Triassic (Anisian) marine deposits (Guanling Formation) in Luoping, eastern Yunnan Province, China. The discovery documents the first known fossil record of highly deep-bodied ginglymodians, adding new information on the early morphological diversity of this group. The studies of functional morphology of extant deep-bodied fishes indicate that Kyphosichthys is not a fast swimmer but has a good performance in precise maneuvering, representing a morphological adaptation to structurally complex habitats (e.g. thick macrophyte beds, rocky areas, or coral reefs), which differs from the other members of this group. A cladistic analysis with the new fish taxon included supports the hypothesis that the Ginglymodi are more closely related to the Halecomorphi than to the Teleostei. Represented by Felberia, Kyphosichthys, and Dapedium, a highly deep and short fish body type has independently evolved at least three times in the stem-group neopterygians, ginglymodians, and basal teleosts within the lower neopterygians of the Triassic.

New Saurichthyid Actinopterygian Fishes from the Anisian (Middle Triassic) of Southwestern China

A new genus Sinosaurichthys of the Saurichthyidae with three new species, S. longipectoralis, S. longimedialis, and S. minuta, are described and compared with Saurichthys. The new genus is represented by more than a hundred almost complete skeletons, collected from the strata corresponding to the Upper Member of the Guanling Formation (Pelsonian, Anisian, Middle Triassic) of two localities: Yangjuan of Panxian County, Guizhou Province, and Dawazi of Luoping, Yunnan Province, China. Sinosaurichthys differs from Saurichthys in having an unusual dermal pectoral girdle, high insertion of pectoral fin, relatively dorsally positioned axial skeleton in the abdominal region, and in the absence of branchiostegal rays. These differences are supposed to reflect the different life styles between the two genera. Sinosaurichthys, like the extant needlefish, probably has a better ability for cruising in surface water than Saurichthys. In addition, these species of Sinosaurichthys are compared, and their morphological differences also probably reflect individual adaptations for different habitats at the two localities.

A new pachypleurosaur (Reptilia: Sauropterygia) from the lower Middle Triassic of southwestern China and the phylogenetic relationships of Chinese pachypleurosaurs

ABSTRACT A new genus and species of Pachypleurosauria, Dianopachysaurus dingi, gen. et sp. nov., from a recently discovered Middle Triassic Lagerstätte in the Anisian Guanling Formation of Yunnan Province is described. The monophyly of Pachypleurosauria, including all potential Chinese pachypleurosaurs in this study, is supported by the rigorous cladistic analysis conducted here. Phylogenetic relationships of Chinese pachypleurosaurs are clarified. Wumengosaurus occupies the most basal position within Pachypleurosauria. Keichousaurus and Dianopachysaurus form the monophyletic Keichousauridae that is the sister group of all European pachypleurosaurs. Our cladistic analysis also supports a previously proposed paleobiogeographic hypothesis of an eastern Tethyan origin of pachypleurosaurs and their migration into the western Tethyan faunal province. The existence of a long ghost lineage as required by the paleobiogeographic hypothesis is greatly shortened by the discovery of Dianopachysaurus.