Guanling Formation Research Articles

Mercury isotopes of the Late Ordovician to Middle Triassic tuff layers in South China link the fate of ancient volcanism and the mass extinction

Mercury (Hg) anomalies in sedimentary records are a newly developed proxy of large volcanism in the geological past. Tuff layers host abundant volcanic ash and record key information on the type of volcanic emission (e.g., arc volcanism and large igneous province eruptions). Here, we measured the Hg isotopic compositions of several tuff layers in South China. Tuff samples in the Late Ordovician Wufeng Formation and the Middle Triassic Guanling Formation mostly show positive Δ199Hg values of – 0.01 to 0.10‰ and – 0.06 to 0.16‰, respectively, suggesting arc volcanism occurred during these two periods. Tuff samples in the Middle Permian Dachang Layer mostly show near-zero Δ199Hg values (– 0.08 to 0.00‰), suggesting volcanism was driven by the Emeishan large igneous province eruption. Results of this study verify Hg isotopes as a useful proxy in revealing the type of volcanism in geological history.

A redescription of Trachelosaurus fischeri from the Buntsandstein (Middle Triassic) of Bernburg, Germany: the first European Dinocephalosaurus-like marine reptile and its systematic implications for long-necked early archosauromorphs

Some of the earliest members of the archosaur-lineage (i.e., non-archosauriform archosauromorphs) are characterised by an extremely elongated neck. Recent fossil discoveries from the Guanling Formation (Middle Triassic) of southern China have revealed a dramatic increase in the known ecomorphological diversity of these extremely long-necked archosauromorphs, including the fully marine and viviparous Dinocephalosaurus orientalis. These recent discoveries merit a reinvestigation of enigmatic Triassic diapsid fossils from contemporaneous European deposits housed in historical collections. Here, we provide a redescription of Trachelosaurus fischeri, represented by a single, disarticulated specimen first described in 1918. Due to its unique morphology, which includes short, bifurcating cervical ribs, and a high presacral vertebral count, this taxon has been referred to either as a “protorosaurian” archosauromorph or a sauropterygian. Our revision clearly shows that Trachelosaurus represents the first unambiguous Dinocephalosaurus-like archosauromorph known from outside the Guanling Formation. Our finding has important systematic implications. Trachelosauridae Abel, 1919 represents the senior synonym for the recently identified Dinocephalosauridae Spiekman, Fraser and Scheyer, 2021. Based on our phylogenetic analyses, which employ two extensive datasets, we also corroborate previous findings that tanystropheids and trachelosaurids represent two families within a larger monophyletic group among non-crocopodan archosauromorphs, which is here named Tanysauria (clade nov.). Trachelosauridae is minimally composed of Trachelosaurus fischeri, Dinocephalosaurus orientalis, Pectodens zhenyuensis, and Austronaga minuta, but one of our analyses also found a probably taxonomically broader clade that may also include Gracilicollum latens and Fuyuansaurus acutirostris. Trachelosaurus fischeri considerably expands the known spatial and temporal range of Trachelosauridae to the earliest Anisian and the Central European Basin. Our findings add to the growing evidence for the presence of a diverse group of fully marine reptiles during the Middle Triassic among Tanysauria. These trachelosaurids possess flipper-like limbs, high vertebral counts, and elongate necks, thus superficially resembling long-necked Jurassic and Cretaceous plesiosaurs in some regards.

A new pachypleurosaur (Reptilia: Sauropterygia) from the Middle Triassic of southwestern China and its phylogenetic and biogeographic implications

After the devastating Permo-Triassic Mass Extinction, several new groups of large reptilian predators invaded the sea in the early part of the Triassic. Among these predators, sauropterygians, consisting of placodonts, pachypleurosaurs, nothosaurs and pistosaurs (including the iconic plesiosaurs), displayed the greatest diversity at both the generic and species levels, and persisted from the Early Triassic to the Late Cretaceous. Here, we report a new species of Pachypleurosauria, Dianmeisaurus mutaensis sp. nov., from a recently discovered Lagerstätte in the Upper Member of the Anisian Guanling Formation. The only known specimen of the new species was collected from a quarry near Muta village, Luxi County, Yunnan Province, South China. Our new phylogenetic analysis based on a novel data matrix recovered the new taxon as a sister group to Dianmeisaurus gracilis—a small pachypleurosaur from the Middle Triassic Luoping biota. The new phylogenetic analysis also collapsed the monophyly of the traditionally recognized Eusauropterygia. Pistosauroidea, Majiashanosaurus, and Hanosaurus comprise the consecutive sister groups to a new clade including Pachypleurosauria and Nothosauroidea. A monophyletic Pachypleurosauria, within which the clade consisting of Dianmeisaurus and Panzhousaurus occupies the basal-most position, is recovered by this study. The clade consisting of Dawazisaurus and Dianopachysaurus forms the sister group to the remaining pachypleurosaurs included in this study. Since Dianmeisaurus, Panzhousaurus, Dawazisaurus, and Dianopachysaurus are all exclusively known from South China, our study provides further evidence to the hypothesis that pachypleurosaurs had a palaeobiogeographic origin in the eastern Tethys.

Dinocephalosaurus orientalis Li, 2003: a remarkable marine archosauromorph from the Middle Triassic of southwestern China

ABSTRACTThe non-archosauriform archosauromorph Dinocephalosaurus orientalis was first described from the Upper Member of the Guanling Formation (late Anisian, Middle Triassic) of Guizhou Province by Li in 2003 on the basis of a complete articulated skull and the first three cervical vertebrae exposed in dorsal to right lateral view. Since then, additional specimens have been discovered in southwestern China. Here, five newly discovered specimens are described for the first time, and redescriptions of the holotype IVPP V13767 and another referred specimen, IVPP V13898, are provided. Together, these permit the description of the complete skeleton of this remarkable long-necked marine reptile. The postcranial skeleton is as much as 6 metres long, and characterised by its long tail and even longer neck. The appendicular skeleton exhibits a high degree of skeletal paedomorphosis recalling that of many sauropterygians, but the skull and neck are completely inconsistent with sauropterygian affinities. The palate does not extend back over the basisphenoid region and lacks any development of the closed condition typical of sauropterygians. The arrangement of cranial elements, including the presence of narial fossae, is very similar to that seen in another long-necked archosauromorph, Tanystropheus hydroides, which at least in part represents a convergence related to an aquatic piscivorous lifestyle. The long and low cervical vertebrae support exceptionally elongate cervical ribs that extend across multiple intervertebral joints and contribute to a ‘stiffening bundle of ribs’ extending along the entire ventral side of the neck, as in many other non-crocopodan archosauromorphs. The functional significance of the extraordinarily elongate neck is hard to discern but it presumably played a key role in feeding, and it is probably analogous to the elongate necks seen in pelagic, long-necked plesiosaurs. Dinocephalosaurus orientalis was almost certainly a fully marine reptile and even gave birth at sea.

A new long-necked archosauromorph from the Guanling Formation (Anisian, Middle Triassic) of southwestern China and its implications for neck evolution in tanystropheids.

A long neck is an evolutionary innovation convergently appearing in multiple tetrapod lineages, including groups of plesiosaurs, non-archosauriform archosauromorphs, turtles, sauropodomorphs, birds, and mammals. Among all tetrapods both extant and extinct, two Triassic archosauromorphs, Tanystropheus and Dinocephalosaurus, have necks that are particularly elongated relative to the lengths of their trunks. However, the evolutionary history of such hyper-elongated necks in these two archosauromorph clades remains unknown, partially because known close relatives such as Macrocnemus and Pectodens possess only moderately elongated necks. Here, we describe a newly discovered early diverging archosauromorph, Gracilicollum latens gen. et sp. nov., based on a specimen comprising a partial neck and an incompletely preserved skull. The long neck is composed of at least 18 cervical vertebrae. The dentition suggests that this new taxon most likely represents an aquatic piscivore, similar to Dinocephalosaurus and Tanystropheus hydroides. Despite possessing a high number of cervical vertebrae, Gracilicollum gen. nov. is recovered as a tanystropheid in an evolutionary grade between Macrocnemus and Tanystropheus rather than as a close relative of Dinocephalosaurus, a result that is primarily attributable to the presence of palatal teeth and the anatomy of the cervical vertebrae in Gracilicollum gen. nov. Considering the information provided by the new specimen, we provide a detailed discussion of the cervical evolution in dinocephalosaurids and tanystropheids, which is shown to be highly complex and mosaic in nature.

A new tanystropheid (Diapsida: Archosauromorpha) from the Middle Triassic of SW China and the biogeographical origin of Tanystropheidae

Tanystropheidae is a clade of early archosauromorphs with high morphological disparity and a wide geographical distribution. The origin and early radiation of Tanystropheidae are still incompletely understood. Here we report Luxisaurus terrestris gen. et sp. nov., a new archosauromorph collected from the marine Upper Member of Guanling Formation (Pelsonian substage, Anisian, Middle Triassic) in Luxi County, Yunnan Province, China, and phylogenetically recovered as a tanystropheid. The morphology of Luxisaurus is consistent with a terrestrial lifestyle. This is the first occurrence of a tanystropheid found from the Anisian Guanling Formation in SW China and also the earliest tanystropheid from the eastern Tethys. Phylogenetic analysis shows that Dinocephalosauridae forms the sister group of Tanystropheidae, Fuyuansaurus occupies the most basal position in Tanystropheidae, and Luxisaurus forms the sister group to a clade consisting of all other tanystropheids. Considering that Fuyuansaurus and Luxisaurus are found exclusively in South China, we hypothesize that Tanystropheidae originated in the Early Triassic of South China and then dispersed globally. The discovery of Early Triassic tanystropheids in South China is needed to further support this hypothesis. The discovery of Luxisaurus expands the stratigraphical and geographical distribution of Tanystropheidae, and provides new insights into the origin and early radiation of the clade. http://zoobank.org/urn:lsid:zoobank.org:pub:07DE12AC-8AE7-48F0-8BAD-0B73F04C0858

High productivity promoted exceptional fossil preservation of the early Middle Triassic Luoping biota of Yunnan Province, China

The early Middle Triassic (Anisian) Luoping biota is representative of marine ecosystems following their full recovery after the Permian-Triassic mass extinction; however, its exceptional preservation remains poorly understood. In this paper, we report multiple geochemical proxies (TOC, TN, P/Al, Cuxs, Nixs, Baxs, δ13Ccarb, and δ13Corg) from Member II of the Middle Triassic Guanling Formation at the Xiangdongpo section in Luoping County, Yunnan Province, China, to assess the relationship between primary productivity and exceptional preservation of the Luoping biota. Variations in TOC, TN, P/Al, Cuxs, and Nixs values show that exceptional preservation coincides with two intervals of high productivity. Relatively low C/N ratios and distributed Δ13Ccarb-org values indicate that primary productivity was dominated by eukaryotic algae and prokaryotic microbes. Based on geochemical analyses and regional correlations, we conclude that, following sea level rise, nutrients were supplied to the Luoping area by upwelling from the open ocean and facilitated the blooming of marine communities in an open platform setting. In the intra-platform depression, increased nutrients supply also fueled high primary productivity in surface waters and oxygen consumption in the water column, causing bottom water anoxia. The lack of oxygen in the bottom water reduced the rate of biomass degradation and bioturbation, promoting growth of microbial mats, leading to the exceptional preservation of macrofauna. This study highlights the important role of elevated primary productivity in exceptional fossil preservation by triggering anoxia of bottom waters. Our findings confirm the widespread development of anoxic conditions during the middle Anisian (Pelsonian), from the eastern Tethys to the Panthalassa, and also reveal the interactions between organisms and the environment after Permian-Triassic mass extinction.

A new morphotype of nothosaurs (Sauropterygia: Nothosauridae) from the Middle Triassic of South China

ABSTRACT A new morphotype of nothosaurs collected from the Upper Member of Anisian Guanling Formation in the Muta village, Luxi County, Yunnan Province, China is reported here. The new morphotype is represented by a single specimen that can be distinguished from other nothosaurs in the combination of the following features: premaxilla partly fused, jugal positioned forward in the cheek, pineal foramen in a deep trough and close to the middle of the skull table, quadratojugal present, distinctly long internal naris. The right lower jaw of the new specimen is completely exposed in medial view, providing hereto unknown information about the medial morphology of the lower jaw for nothosaurid sauropterygians, including the large splenial forming half of the inner wall of the lower jaw, the slender and elongate coronoid located in the middle of the mandible, and the Meckelian foramen located within the adductor fossa bounded by surangular and prearticular. Morphological comparison with other Triassic eosauropteygians reveals previously unrecognised characters that may be used for reconstructing the phylogeny of sauropterygians in the future.

Anisian (Middle Triassic) stromatolites from Southwest China: Biogeological features and implications for variations of filament size and diversity of Triassic cyanobacteria

This study documents new stromatolite deposits from the Anisian succession of the Guanling Formation in the Boyun section of eastern Yunnan Province, southwestern China. The Boyun stromatolites are characterized by undulating laminations, which yield a variety of biostructures and abiotic grains, such as cyanobacteria Bevocastria and Renalcis, microclots, fecal pellets, coccoid-like spheroids, and authigenic quartz. Filamentous cyanobacteria Bevocastria are likely the major builder constructing the Boyun stromatolite build-ups. Stromatolites in the Boyun section likely grew in an open, oxic marine environment, differing from the Lower Triassic stromatolites that were mostly formed in relatively oxygen-poor conditions of shallow marine settings, strengthening the view that stromatolites are not necessarily indicative of harsh environments. In addition, the global dataset of cyanobacteria filament sizes through the Triassic deciphers that a pronounced increase in the diameter of filamentous cyanobacteria through the Early-Middle Triassic, followed by a decline during the Late Triassic. The developments of marine deoxygenation in the Early Triassic and Rhaetian broadly coincided with the reduction in cyanobacteria filament diameter, suggesting a possible causal link between the two. Our data also show that the diversity of cyanobacteria does not show a significant correlation relationship with any modeled estimates of CO2, indicating that their might be more complex when CO2 levels below ∼2800 ppm (10 times present atmospheric level).

A large osteoderm-bearing rib from the Upper Triassic K\xf6ssen Formation (Norian/Rhaetian) of eastern Switzerland

An important component of the Alpine vertebrate record of Late Triassic age derives from the Kössen Formation, which crops out extensively in the eastern Alps. Here, we present an isolated and only partially preserved large rib, which carries an osteoderm on a low uncinate process. Osteological comparison indicates that the specimen likely belongs to a small clade of marine reptiles, Saurosphargidae. Members of the clade are restricted to the western (today Europe) and eastern margins of the Tethys (today China) and were so far known only from the Anisian stage of the Middle Triassic. The assignment of the new find to cf. Saurosphargidae, with potential affinities to the genus Largocephalosaurus from the Guanling Formation of Yunnan and Guizhou Provinces, China, would extend the occurrence of the clade about 35 million years into the Late Triassic.

Astronomically forced changes in chemical weathering and redox during the Anisian (Middle Triassic): Implications for marine ecosystem recovery following the end-Permian mass extinction

The timing and pattern of ecosystem recovery following the end-Permian mass extinction are still highly controversial, and a potential influence from orbital climate forcing is often not considered. To investigate this issue, a cyclostratigraphic analysis of an Anisian (Middle Triassic) marine platform succession (Guanling Formation, Yongning section, South China) using elemental proxies and lithofacies has been carried out. Spectral analysis of proxies for terrestrial flux (Fe/Al and Zr/Al) indicate significant cycles. Based on available age constraints and sedimentation rate modelling, the recognized cycles include 405-kyr long eccentricity, 100-kyr short eccentricity and ~ 20-kyr precession cycles. Anchoring these signals to a dated and widespread “green bean” volcanic ash layer (246.6 Ma) and tuning to stable 405-kyr long-eccentricity cycles yields an astronomical time scale spanning ~4.2 + 0.3/−1.4 Myr (246.7 to 242.5 + 0.3/−1.4 Ma) in the Anisian. This time scale constrains the ages of the Luoping biota (which marks the earliest complex Mesozoic marine ecosystem in South China) and the Panxian marine vertebrate biota to 243.8 + 0.3/−1.4 and 243.4 + 0.3/−1.4 Ma, respectively. The early Anisian is characterized by intercalated claystone and marls with high values in terrestrial flux proxies, indicating an intensified hydrological cycle due to a humid climate in the study area. This was followed by a long-term cooling trend into the late Anisian, as indicated by declining terrestrial flux proxy values. Seawater redox conditions were assessed using V/Al, Mo/Al and lithofacies analyses, and these data reveal possibly two putative deoxygenation events during the Anisian. Our new high-resolution redox data can also be correlated with results on Anisian ocean redox changes elsewhere. Our new astronomical timescale and high-resolution geochemical data provide key constraints on the timing of marine ecosystem recovery after the end-Permian mass extinction. Orbital forcing seems to have played an important role in modulating chemical weathering and seawater chemistry dynamics that impacted the timing of ecosystem recovery.

The link between exceptional fossil preservation and palaeo‐redox conditions in the Middle Triassic Luoping Biota from South China

The Luoping Biota represents of the recovery of marine ecosystems after the Permian–Triassic Mass Extinction. To better understand the palaeoenvironmental background of the Luoping Biota, sedimentary analysis and multi‐geochemical proxies (Mo, U, V, V/Cr, MoEF, UEF, and VEF) were assessed in Member II of the Middle Triassic Guanling Formation of the Xiangdongpo section in Luoping County, Yunnan Province. According to the facies characteristics and redox‐sensitive elemental proxies, in combination with macrofossil and bioturbation evidence, five intervals (I, II, III, IV, and V) were recognized. The exceptional preservation of the fossils is related to two anoxic intervals (II and IV) sandwiched by three suboxic intervals (I, III, and V). Based on this study and regional correlation, it is concluded that anoxia in the water‐column increased the preservation potential of macrofauna fossils and inhibited the survival of trace‐making organisms. In addition, microbial mats could produce local anoxic and restricted micro‐environments, preventing the disarticulation of the carcasses by water turbulence. Therefore, we demonstrate that anoxic conditions played a key role in the exceptional fossil preservation of the Luoping Biota.

Panzhousaurus rotundirostris Jiang et al., 2019 (Diapsida: Sauropterygia) and the recovery of the monophyly of Pachypleurosauridae

ABSTRACT Panzhousaurus rotundirostris Jiang, Lin, Rieppel, Motani and Sun, 2019, is restudied on the basis of a second specimen from the Upper Member of the Guanling Formation near Panzhou City, Guizhou Province, China. The second specimen offers hitherto unknown or unconfirmed information regarding the dermal palate, the ventral aspect of the cervical vertebrae, and the hind limbs, thus permitting a refinement of the diagnosis. Newly added or modified diagnostic characters include paired frontals with no posterolateral process, elongated and slender phalanges in the manus and pes, and a phalangeal formula of 3-4-5-4-3 for the manus, and 2-3-4-5-3 for the pes. A new phylogenetic analysis of Eosauropterygia demonstrates that Pachypleurosauridae is the sister taxon of Eusauropterygia, and the monophyly of these groups as traditionally upheld is confirmed. Panzhousaurus is most closely related to Dianopachysaurus and Keichousaurus within Pachypleurosauridae. In this study, the monophyletic Pistosauroidea excludes Corosaurus and Cymatosaurus. The latter two genera are found to form a monophyletic clade that represents the basal-most members of Eusauropterygia, which is in accordance with their stratigraphic distribution.

Studies on the chronology and geochemistry of the green pisolites at the bottom of the Middle Triassic Guanling Formation in Yanjin area, northeastern Yunnan Province

Studies on the chronology and geochemistry of the green pisolites at the bottom of the Middle Triassic Guanling Formation in Yanjin area, northeastern Yunnan Province

Footprints of marine reptiles from the Middle Triassic (Anisian-Ladinian) Guanling Formation of Guizhou Province, southwestern China: The earliest evidence of synchronous style of swimming

Subaqueously-registered trackways of marine tetrapods are only rarely preserved; some of the best examples so far come from the Shizishan Member (Member II) of the Guanling Formation (Middle Triassic, Anisian-Ladinian) of Yunnan Province in southwestern China. The unit is well-known for the Luoping Biota including abundant skeletons of marine reptiles. The described footprints consist of impressions of fin-like autopodia comprising numerous broad trackways that have been named Dikoposichnus luopingensis and interpreted as having been made by foraging nothosaurs. Morphologically identical tracks and trackways have now been discovered near the city of Anshun in Guizhou Province, in slightly older strata and on a large surface of argillaceous dolostone belonging to the Songzikan Member (Member I) of the Guanling Formation. Additionally, a second morphotype is abundant on the same surface, with long trackways that show semi-plantigrade to plantigrade foot imprints with four distinct digit impressions. All tracks are similar in shape and positioned symmetrically, in broad trackways on either side of the trackway midline. Based on several unique features this morphotype is assigned here to the new ichnotaxon Anshunpes aquacursor ichnogen. nov. ichnosp. nov. It is interpreted as the trackway of a buoyant and punting tetrapod, using its forefeet only. The trackmaker is inferred to be similar to some diapsid placodonts and saurosphargids whose skeletons have been found in the Guanling Formation (Middle Triassic, Anisian-Ladinian) and in the overlying Falang Formation (Middle–Upper Triassic, Ladinian–Carnian). Comparative measurements of trackways and skeletons support this. Additional associated ichnofossils are enigmatic traces such as isolated large oval impressions and cord-like knobby structures. The palaeoenvironment was a shallow near-coast marine habitat, possibly a lagoon. The ichnofauna from Anshun is important, because it is the first record of subaqueous progression activity by marine diapsid placodonts and/or saurosphargids, and also indicates the early adoption of a synchronous style of swimming by marine reptiles.

Reprint of: “Gondolelloid multielement conodont apparatus (Nicoraella) from the Middle Triassic of Yunnan Province, southwestern China”

The morphology and position of elements in the apparatus are keys to resolving the taxonomy, homology, evolutionary relationships, structure, function and feeding patterns among conodont taxa. Fused clusters preserving natural associations between elements provide direct information on element morphology, the positions of elements within the apparatus, and even their original three-dimensional arrangement. Here, we report 41 fused conodont clusters from Member II of the Guanling Formation in Luoping County, Yunnan Province, southwestern China, which provide a basis for inferring the multielement composition of the apparatus of the early Middle Triassic Nicoraella. The apparatus is composed of 15 elements (a single S0 element, two pairs of S1–4, M and P1–2 elements) like other apparatuses in Gondolellidae, i.e. the genera Novispathodus and Neogondolella. These Luoping Biota clusters are significant because (a) they permit a positional homology-based comparison of multielement Novispathodus with form genera such as Cypridodella (S1), Enantiognathus (S2), and Hindeodella (S3 and S4), (b) they facilitate a review of apparatus composition within superfamily Gondolelloidea, (c) they provide direct insight into apparatus architecture currently interpreted largely in light of distantly related Carboniferous polygnathacean ozarkodinins, and (d) these clusters, along with collections of discrete conodont elements, provide a model for inferring the multielement composition of closely related species known only from discrete element collections.

Chirotherium and first Asian Rhynchosauroides tetrapod trackways from the Middle Triassic of Yunnan, China

ABSTRACT The Middle Triassic (Anisian) Guanling Formation in Yunnan and Guizhou provinces, southwestern China, is well-known for its marine-reptile fauna with numerous well-preserved skeletons. Tetrapod footprints from this unit have been reported of both terrestrial and marine forms documenting a marginal marine environment in the eastern Tethys region. In particular Chirotherium barthii, an ichnospecies that is characteristic of the Middle Triassic (Anisian), was formerly described from the Guanling Formation of Guizhou Province. Recently chirotheriid tracks were also reported from deposits of this unit in Yunnan Province. Here we provide the first detailed documentation of this tracksite. Furthermore, we assign these trackways to the ichnospecies Chirotherium barthii, based on identical features in footprint morphology. Additionally, from the same surface, we describe the first tracks and trackways of the lacertoid ichnogenus Rhynchosauroides from the Asian continent. Trackmakers of C. barthii are non archosaurian archosauriforms or members of the archosaur crown-group, while Rhynchosauroides can be attributed either to lepidosauromorph or archosauromorph diapsids. The environment was a coastal area along the eastern Tethys, with marine, semi-aquatic and terrestrial tetrapods leaving their footprints in the carbonatic sediment of mudflats and lagoons when searching for food, that possibly consisted of small marine invertebrates or the small lacertoid forms being the prey of the larger archosaurs.

Erratum to: Palaeoecological Analysis of Trace Fossil Sinusichnus sinuosus from the Middle Triassic Guanling Formation in Southwestern China

The original version of this article unfortunately contained a mistake. The title was incorrect. The corrected one is given below. Palaeoecological Analysis of Trace Fossil Sinusichnus sinuosus from the Middle Triassic Guanling Formation in Southwestern China

Palaeoecological Analysis of Trace Fossil Sinusichnus sinuosus from the Middle Triassic Guanling Formationin Southwestern China

The Luoping Biota discovered from the early Middle Triassic (Anisian) Guanling Formation of southwestern China represents a fully recovered shallow marine ecosystem, marking the end point of Early Triassic biotic recovery following the end-Permian mass extinction. Contemporaneously preserved are prolific trace fossils, which offer good opportunities to understand the palaeoecology of marine invertebrates from a fully recovered shallow marine ecosystem. Here we present a newly discovered sinuous branching burrow from the fossil-bearing unit in Member Ⅱ of the Guanling Formation. Several features, including the horizontal regular sinuous nature, the branching pattern, typical H-junction, and the small wavelength/amplitude ratio of these sinuous structures within the burrow systems justify assignment of these traces as Sinusichnus sinuosus, a trace possibly produced by decapod crustaceans. Close association of S. sinuosus with Rhizocorallium commune suggests a deposit-feeding strategy of these trace makers. The newly reported Anisian material from the Guan-ling Formation in Luoping represents first report of Sinusichnus from South China. The global record of Sinusichnus occurrence suggests that these burrows might have an older history than Early Middle Triassic.

Gondolelloid multielement conodont apparatus (Nicoraella) from the Middle Triassic of Yunnan Province, southwestern China

The morphology and position of elements in the apparatus are keys to resolving the taxonomy, homology, evolutionary relationships, structure, function and feeding patterns among conodont taxa. Fused clusters preserving natural associations between elements provide direct information on element morphology, the positions of elements within the apparatus, and even their original three-dimensional arrangement. Here, we report 41 fused conodont clusters from Member II of the Guanling Formation in Luoping County, Yunnan Province, southwestern China, which provide a basis for inferring the multielement composition of the apparatus of the early Middle Triassic Nicoraella. The apparatus is composed of 15 elements (a single S0 element, two pairs of S1–4, M and P1–2 elements) like other apparatuses in Gondolellidae, i.e. the genera Novispathodus and Neogondolella. These Luoping Biota clusters are significant because (a) they permit a positional homology-based comparison of multielement Novispathodus with form genera such as Cypridodella (S1), Enantiognathus (S2), and Hindeodella (S3 and S4), (b) they facilitate a review of apparatus composition within superfamily Gondolelloidea, (c) they provide direct insight into apparatus architecture currently interpreted largely in light of distantly related Carboniferous polygnathacean ozarkodinins, and (d) these clusters, along with collections of discrete conodont elements, provide a model for inferring the multielement composition of closely related species known only from discrete element collections.