Smithian (Early Triassic) ammonoids from Tulong, South Tibet

Intensive sampling of the Tulong Formation in South Tibet has facilitated the construction of a highly-resolved middle and late Smithian ammonoid succession. The new biostratigraphical sequence comprises the middle Smithian Brayardites compressus beds, Nammalites pilatoides beds, and the Nyalamites angustecostatus beds followed by the late Smithian Wasatchites distractus beds and Glyptophiceras sinuatum beds. This faunal succession correlates very well with that of other Tethyan sequences such as the Salt Range (Pakistan), Spiti (India), Oman and South China. The Smithian faunal sequence from Tulong contains several taxa with broad geographic distribution (e.g., Owenites, Paranannites spathi, Shigetaceras, Wasatchites), thus enabling correlation with faunal successions from areas outside the Tethys (e.g., USA, British Columbia, Arctic Canada, South Primorye, Siberia). Early Smithian ammonoid faunas are almost absent in Tulong because of a preservation bias (absence of carbonate rocks). Five new ammonoid genera (Brayardites, Nammalites, Nyalamites, Shigetaceras, Tulongites) and six new species (Brayardites crassus, Brayardites compressus, Prionites involutus, ?Subflemingites compressus, Tulongites xiaoqiaoi, Urdyceras tulongensis) are described.     

High-resolution biochronology and diversity dynamics of the Early Triassic ammonoid recovery: The Smithian faunas of the Northern Indian Margin

Based on new collections of abundant and well preserved material from the Salt Range (Pakistan), Spiti (Northern India) and Tulong (South Tibet), several recent studies focused on the taxonomic revision and detailed biostratigraphy of Smithian ammonoids. In this work, biochronological data for these three well-documented basins are analyzed by means of the Unitary Associations method, resulting in a biochronological scheme of unprecedented high-resolution for the Smithian of the Northern Indian Margin (NIM). Data for each basin are first processed separately, thus yielding three local biochronological zonations. Then, the three sequences are processed together as a regional three-section data set for the construction of an inter-basin sequence at the NIM level. The latter zonation comprises 16 Unitary Associations grouped into 13 zones for the entire Smithian. Analysis of ammonoid diversity dynamics based on this new highly resolved time frame highlights (i) a marked diversification during the early Smithian, (ii) a severe extinction during the late Smithian, and (iii) an overall very high turnover throughout the Smithian. At a global spatial scale and stage resolution, the diversity of Smithian ammonoid genera appears surprisingly high, as highlighted by a previous study. It is shown that at a smaller geographic scale and with the most highly resolved time frame, Smithian ammonoids of the NIM reached their explosive diversity peak essentially through extremely high turnover rates rather than through a classic diversification process of high origination rates coupled with low extinction rates. Based on recently published U/Pb ages, regional apparent total rates of origination and extinction of more than 100 species per My can be inferred for the Smithian ammonoids of the NIM.     

The biogeography of Early Triassic ammonoid faunas: Clusters, gradients, and networks

The aim of this paper is to quantitatively investigate the spatial and temporal biogeographical relationships of the recovery of ammonoid faunas after the Permian-Triassic mass extinction using three complementary numerical approaches among which is a new, non-hierarchical clustering strategy. The faunal data set consists of a taxonomically homogenised compilation of the spatial and temporal occurrences of ammonoid genera within 20 Early Triassic Tethyan and Panthalassic sites ranging from 40°S to 70°N in palaeolatitudes. In addition to hierarchical cluster analysis (hCA) and nonmetric multidimensional scaling (NMDS), we introduce a third, new non-hierarchical clustering technique allowing the visualisation of a nonmetric interassemblages similarity structure as a connected network constructed without inferring additional internal nodes. The resulting network, which we call a “Bootstrapped Spanning Network” (BSN), allows the simultaneous identification of partially or totally nested as well as gradational linear or reticulated biogeographical structures.The identified interlocalities relationships indicate that the very beginning of the Early Triassic (Griesbachian) corresponds to a very simple biogeographical context, representing a time of great cosmopolitanism for ammonoids. This context shifts rapidly to a more complex configuration indicative of a more endemic and latitudinally-restricted distribution of the ammonoids during the middle and late Early Triassic (Smithian and Spathian). From an evolutionary dynamic point of view, our results illustrate a very rapid (less than ca. 1.4 myr) Early Triassic recovery of the ammonoid faunas, in contrast to many other marine organisms. This recovery is linked with a marked increase in the overall biogeographical heterogeneity, and parallels the formation of a latitudinal gradient of taxonomic richness, which may be essentially controlled by the progressive intensification of the gradient of sea surface temperature. From a methodological point of view, we show that a BSN is a simple, intuitively legible picture of the nested as well as gradational taxonomic similarity relationships, hence providing a good synthesis (and additional insights) between hierarchical clustering and ordination in reduced space results.     

New trepostome Bryozoa from the Early Triassic (Smithian/Spathian) of Nevada

Two new bryozoan species of the trepostome family Dyscritellidae,Dyscritellopsis thaynesianus n. sp. andDyscritellopsis montelloensis n. sp., are described from the Early Triassic (Smithian/Spathian) Thaynes Limestone, Nevada (USA). The bryozoan fauna documents the survival of Paleozoic lineages into the earliest Triassic on northern open shelves outside the tropics. The fauna holds paleobiogeo-graphic connections to the Early Triassic bryozoan faunas of Spitsbergen.      

Ammonoid biostratigraphy of the Middle Triassic Latemar platform (Dolomites, Italy) and its correlation with Nevada and Canada

An extensive study of the ammonoid fauna occurring in the lagoonal facies of a Middle Triassic isolated carbonate platform (Latemar platform, Dolomites, Italy) has been undertaken, and ammonoids from selected coeval successions (Punta Zonia, Marmolada, Rio Sacuz) have been illustrated. Ammonoids from Latemar have been collected in 20 distinct horizons (storm deposits) within the ca. 500 m thick lagoonal succession of the platform, thus providing a biostratigraphy of a series which is unusually expanded for this time interval, close to the Anisian-Ladinian boundary. Contrary to general opinion, some ammonoids of the Latemar and other coeval carbonate platforms of the Dolomites (Marmolada, Cernera), in particular Aplococeras avisianum, Lecanites misanii, Celtites spp., and Paranevadites sp., are also present in nearby basinal series. The same taxa have been found in North American localities deposited at the opposite margin of Panthalassa. The homotaxis of these ammonoids in North America and Latemar allow to establish a global scale correlation between the Southern Alps and North America with the highest resolution to date possible. In the context of this study, Aplococeras transiens n. sp. and Esinoceras nerinae n. sp are established.     

Ammonoids and nautiloids from the earliest Spathian Paris Biota and other early Spathian localities in southeastern Idaho,USA

Intensive sampling of three earliest Spathian sites represented by the Lower Shale unit and coeval beds within the Bear Lake vicinity and neighboring areas, southeastern Idaho, yielded several new ammonoid and nautiloid assemblages. These new occurrences overall indicate that the lower boundary of the Tirolites beds, classically used as a regional marker for the base of the early Spathian, and therefore the regional Smithian/Spathian boundary, must be shifted downward into the Lower Shale unit and coeval beds. Regarding ammonoids, one new genus (Caribouceras) and two new species (Caribouceras slugense and Albanites americanus) are described. In addition, the regional temporal distribution of Bajarunia, Tirolites, Columbites, and Coscaites is refined, based on a fourth sampled site containing a newly reported occurrence of the early Spathian Columbites fauna in coeval beds of the Middle Shale unit. As a complement to ammonoids, changes observed in nautiloid dominance are also shown to facilitate correlation with high-latitude basins such as Siberia during this short time interval, and they also highlight the major successive environmental fluctuations that took place during the late Smithian–early Spathian transition.     

Taphonomy and palaeoecology of Late Triassic (Carnian) ammonoid concentrations from the Taurus Mountains,Turkey

The deposits of the Carnian Kas?mlar Formation within the Taurus Platform Units of south‐western Turkey represent an important archive of a Late Triassic ecosystem. New palaeontological information was obtained by analysing the Kasimlarceltites mass occurrence, located within the Kas?mlar Formation and named after the Lower Carnian (Julian) ammonoid genus Kasimlarceltites. This is the dominant taxon (> 94%) within the mass occurrence: nearly 775 million ammonoids and 50 million gastropods were extrapolated for the whole extension (at least 5 km²) of the Kasimlarceltites beds. This calculation is one of the main findings within this study, as it is the first time that such a fossil mass occurrence was quantified. Additionally, orientation measurements of the planispiral ammonoids and the helical gastropods enabled reconstructing the history of the mass occurrence and interpreting the underlying transport mechanisms. Further taphonomic aspects (e.g. biofabric, preservation, bioerosion or genetic classification) as well as comparisons with samples of the same acme zone from different localities near A?a?iyaylabel (AS IV, KA I‐II) point to a two‐phased genetic history. Accordingly, local mass mortality within the Kasimlarceltites fauna due to oxygen fluctuations or methane degassing may have initially led to a primary accumulation. These deposits were then reworked and redeposited basinward by gravity flows to create the present‐day secondary allochthonous concentrations.     

Late Smithian microbial deposits and their lateral marine fossiliferous limestones (Early Triassic,Hurricane Cliffs,Utah, USA)

Recurrent microbialite proliferations during the Early Triassic are usually explained by ecological relaxation and abnormal oceanic conditions. Most Early Triassic microbialites are described as single or multiple lithological units without detailed ecological information about lateral and coeval fossiliferous deposits. Exposed rocks along Workman Wash in the Hurricane Cliffs (southwestern Utah, USA) provide an opportunity to reconstruct the spatial relationships of late Smithian microbialites with adjacent and contemporaneous fossiliferous sediments. Microbialites deposited in an intertidal to subtidal interior platform are intercalated between inner tidal flat dolosiltstones and subtidal bioturbated fossiliferous limestones. Facies variations along these fossiliferous deposits and microbialites can be traced laterally over a few hundreds of meters. Preserved organisms reflect a moderately diversified assemblage, contemporaneous to the microbialite formation. The presence of such a fauna, including some stenohaline organisms (echinoderms), indicates that the development of these late Smithian microbial deposits occurred in normal-marine waters as a simple facies belt subject to relative sea-level changes. Based on this case study, the proliferation of microbialites cannot be considered as direct evidence for presumed harsh environmental conditions.     

滇西巍山地区上三叠统诺利阶三合洞组牙形石年代及沉积相分析*

滇西兰坪-思茅地块晚三叠世诺利期(Norian)发育一套海相碳酸盐岩沉积(三合洞组)。对巍山三合洞剖面进行了实测与采样, 分离了三合洞组碳酸盐岩中的牙形石, 经鉴定其种属为Epigondolella vialovi, Epigondolella uniformis和Epigondolella aff. triangularis, 时代为早诺利期(Lacian亚期)。通过野外剖面及室内显微薄片观察, 采用微相分析的方法对剖面三合洞组碳酸盐岩的微相类型和沉积环境进行研究, 将巍山三合洞剖面三合洞组沉积归纳为9种微相, 并根据微相特征结合野外宏观特征, 将三合洞剖面划分为3种沉积相类型, 即局限台地相、开阔台地相和台地边缘礁相。在剖面不同层位的碳酸盐岩中发现的热液矿物石榴子石及发黑的牙形石化石(CAI指数约为5), 表明该区曾遭受热液作用的影响, 可能与三合洞组沉积后大陆边缘裂谷下陷或板块拼合引起的热卤水上涌有关。     

Chondrichthyan teeth from the Early Triassic Paris Biota (Bear Lake County,Idaho, USA)

A new, diverse and complex Early Triassic assemblage was recently discovered west of the town of Paris, Idaho (Bear Lake County), USA. This assemblage has been coined the Paris Biota. Dated earliest Spathian (i.e., early late Olenekian), the Paris Biota provides further evidence that the biotic recovery from the end-Permian mass extinction was well underway ca. 1.3 million years after the event. This assemblage includes mainly invertebrates, but also vertebrate remains such as ichthyoliths (isolated skeletal remains of fishes). Here we describe first fossils of Chondrichthyes (cartilaginous fishes) from the Paris Biota. The material is composed of isolated teeth (mostly grinding teeth) preserved on two slabs and representing two distinct taxa. Due to incomplete preservation and morphological differences to known taxa, the chondrichthyans from the Paris Biota are provisionally kept in open nomenclature, as Hybodontiformes gen. et sp. indet. A and Hybodontiformes gen. et sp. indet. B, respectively. The present study adds a new occurrence to the chondrichthyan fossil record of the marine Early Triassic western USA Basin, from where other isolated teeth (Omanoselache, other Hybodontiformes) as well as fin spines of Nemacanthus (Neoselachii) and Pyknotylacanthus (Ctenachanthoidea) and denticles have been described previously.     

Late Paleozoic and Triassic bryozoans from the Tethys Himalaya (N India, Nepal and S Tibet)

New findings of Late Paleozoic and Triassic bryozoans from the Tethys Himalaya are reported. Fifteen species, including three undetermined, were described, while determinations at order, family or genus level were obtained on fragmentary material. The studied bryozoans were framed in a solid lithostratigraphic scheme spanning across the Tethys Himalaya for over 1500 km, from NW India (Zanskar and Spiti) through Nepal (Dolpo and Manang) to South Tibet; they are concentrated in correlatable stratigraphic intervals corresponding to the Upper Devonian-Tournaisian, Bashkirian, Sakmarian, Midian and Lower Norian. This study allowed us to integrate bryozoan occurrences reported from the literature, mostly referring to the Tournaisian, Bashkirian and Early Norian, and to refine the available biostratigraphic dates. Bryozoan-rich intervals are interpreted as associated to long-term transgressions, in turn driven by major climatic and/or tectonic events. Cosmopolitan genera which prevail in the Paleozoic, are replaced by provincial forms after the Triassic crisis.     

Battenizyga, a new Early Triassic gastropod genus with a discussion of the caenogastropod evolution at the Permian/Triassic boundary

Battenizyga, a new Early Triassic gastropod genus from the Moenkopi Formation of Utah, is described and the speciesAnoptychia eotriassica Batten & Stokes, 1986 is placed in it. The new genus has an axially ribbed planktonic larval shell and a teleoconch with an angulated periphery. This character combination is unknown from the Palaeozoic. Therefore,Battenizyga represents additional evidence that recovery from the end-Permian mass extinction was connected with a faunal turnover. Additionally, the extinction of diverse Palaeozoic groups of the Caenogastropoda in the Permian (e.g., the Pseudozygopleuridae) suggest a turnover. All caenogastropod genera that hold Early Triassic species, have post-Palaeozoic type species and most were not reported from the Palaeozoic. This corroborates the view that there was an intense faunal turnover within the Caenogastropoda.Battenizyga is probably a caenogastropod that is closely related to the superfamily Zygopleuroidea which is abundant in the late Palaeozoic and early Mesozoic.      

Plants of Leptostrobus Heer （Czekanowskiales） from the Early Cretaceous and Late Triassic of China, with Discussion of the Genus

Investigation of the Mesozoic seed plant Leptostrobus Heer from the Yangcaogou Formation of the Late Triassic and the Yixian Formation of the Early Cretaceous, Liaoning Province, China, provides new Insight Into Its general morphology and geographical distribution. The materials of L. cancer from the Yixian Formation described herein are later than all the past findings of this species and add to the record of L. cancer during the Early Cretaceous. Based on well-preserved specimens, the specific diagnosis Is slightly emended and the reconstructlon of L. cancer Is perfected. The materials from the Yangcaogou Formation of the Late Triassic are placed in L. spheericus, in addition, we review the history of investigation of the genus Leptostrobus since its establishment in 1876 and discuss the main characteristics of each species.     

Deciphering the exceptional preservation of the Early Triassic Paris Biota (Bear Lake County,Idaho, USA)

After the end-Permian mass extinction, the Early Triassic (∼251.9 to 247 Ma) is characterized by several biotic crises that particularly affected marine faunas; accordingly, marine ecosystems from this unstable interval have been often described as heavily depauperate. This assumption, however, may relate to a biased fossil record. The discovery of taphonomic windows, like Konservat-Lagerstätten, in the Early Triassic would help to better understand the composition and diversity of ecosystems at that time. The Paris Biota (Idaho, USA) is a highly diverse fossil assemblage from the earliest Spathian (early late Olenekian, ∼250.6 Ma), indicating a rapid rediversification for many groups after the end-Permian crisis and pointing toward a remarkably complex marine ecosystem ∼1.3 m.y. after the Permian-Triassic boundary. However, its detailed taphonomy has not yet been investigated. Here we present the mineral characterization of four of its most abundant taxa: discinoid and linguloid brachiopods, leptomitid sponges, and caridean shrimps. For this purpose, we combined data from Raman microspectroscopy, Fourier Transform InfraRed spectroscopy, and SEM-EDXS. Although all taxa were preserved in calcium phosphate, the morphology, structuring and size of crystals are highly dissimilar at a nano- to micrometric scale. In brachiopods, the ultrastructure of calcium phosphate shows unorganized bacillary-like crystals, while in crustaceans their size is considerably smaller and round-shaped. Similar small crystals are observed in sponges. However, the ultrastructure of calcium phosphate in sponges exhibits a well-defined preferential orientation. In addition, sponges show some compressed but preserved three-dimensional features, with an inner surface better preserved. Such analyses are essential to understand the taphonomic pathways enabling exceptional preservation. The further comprehension of preservation features would help to understand potential bias on observed diversity signals and their interpretation.     

Early Triassic bivalves from the Feixianguan Formation in Xingyi,Guizhou and the Ximatang Formation in Qiubei,Yunnan (southern China)

Based on newly collected materials from the Lower Triassic Feixianguan Formation of Xiongwu section in Xingyi, Guizhou and the Ximatang Formation of Ximatang section in Qiubei, Yunnan, southern China, nine species belonging to seven genera are described. Two bivalve assemblages are recognized and regionally correlated in South China. The bivalve assemblage from the Feixianguan Formation of Xiongwu exhibits a higher diversity including seven species belonging to seven genera: Claraia griesbachi, Leptochondria virgalensis, Entolium (Entolium) microtis, Towapteria scythicum, Bakevillia exporrecta, Bositra sp., and Unionites? fassaensis. In contrast, the bivalve assemblage from the Ximatang Formation of Ximatang has a much lower diversity, consisting of only two species, i.e., Claraia griesbachi and Claraia radialis. Additionally, C. griesbachi and C. radialis, as the most common species of Claraia in the Early Triassic, are revised.     

Early Miocene cricetids (Rodentia) from the Junggar basin (Xinjiang, China) and their biochronological implications

Among the 14 small mammal species from the early Miocene locality of the northern area of the Junggar basin (northern Xinjiang, China), four species are cricetids (Rodentia): unnamed species of Cricetodon and Eumyarion, and two new species, Karydomys debruijni nov. sp. and Megacricetodon beijiangensis nov. sp. Some aspects of the morphology of Cricetodon sp. are shared by Eucricetodon from the late Oligocene, suggesting that these specimens could be of intermediate form between Eucricetodon and Cricetodon. One tooth of Eumyarion sp. was found, making its determination uncertain, but its morphology is clearly differentiated from the one of Cricetodon sp. The species K. debruijni nov. sp. is established based on its primitive features compared to the species known in Europe and Anatolia, and its specific association of characters compared to Karydomys dzerzhinskii. M. beijiangensis nov. sp. shows many plesiomorphic features compared to the species already described in the middle Miocene of China. Based on both the whole assemblage of rodents and the species of cricetids, the biochronologic position and the age of the locality are discussed. The locality appears to be biochronologically very close to the fauna from the Chul’adyr Formation in Aktau Mountains, but we propose an age slightly older than the one proposed for this fauna, probably equivalent to the MN3 biozone in Europe.     

A diagenetic control on the Early Triassic Smithian–Spathian carbon isotopic excursions recorded in the marine settings of the Thaynes Group (Utah,USA)

In the aftermath of the end‐Permian mass extinction, Early Triassic sediments record some of the largest Phanerozoic carbon isotopic excursions. Among them, a global Smithian‐negative carbonate carbon isotope excursion has been identified, followed by an abrupt increase across the Smithian–Spathian boundary (SSB; ~250.8 Myr ago). This chemostratigraphic evolution is associated with palaeontological evidence that indicate a major collapse of terrestrial and marine ecosystems during the Late Smithian. It is commonly assumed that Smithian and Spathian isotopic variations are intimately linked to major perturbations in the exogenic carbon reservoir. We present paired carbon isotopes measurements from the Thaynes Group (Utah, USA) to evaluate the extent to which the Early Triassic isotopic perturbations reflect changes in the exogenic carbon cycle. The δ¹³C_carb variations obtained here reproduce the known Smithian δ¹³C_carb‐negative excursion. However, the δ¹³C signal of the bulk organic matter is invariant across the SSB and variations in the δ³⁴S signal of sedimentary sulphides are interpreted here to reflect the intensity of sediment remobilization. We argue that Middle to Late Smithian δ¹³C_carb signal in the shallow marine environments of the Thaynes Group does not reflect secular evolution of the exogenic carbon cycle but rather physicochemical conditions at the sediment–water interface leading to authigenic carbonate formation during early diagenetic processes.     

A late-surviving Triassic protomonaxonid sponge from the Paris Biota (Bear Lake County,Idaho, USA)

Protomonaxonid sponges are a major group of Cambrian and Ordovician fossils in exceptionally preserved (especially Burgess Shale-type) faunas, but are rare thereafter. Rare examples of apparent surviving lineages are known from the late Palaeozoic and Mesozoic, but by this time more derived groups of sponges have generally displaced them in at least shallow-water (shelf depth) ecosystems. The early Spathian (Early Triassic) Paris Biota includes abundant material of a new leptomitid protomonaxonid, Pseudoleptomitus advenus Botting nov. gen., nov. sp., distinguished by having an unbundled longitudinal skeleton and very weak transverse component. This is the first post-Ordovician leptomitid known, and indicates long-term survival of the group in unknown environments. Its occurrence near storm wave base is similar to the preferred environment of earlier examples of the family, suggesting either ecological rarity or taphonomic reasons for their ∼200-million-year absence from later Palaeozoic rocks.