Giant alatoform bivalves in the Upper Triassic of western North America

ABSTRACT. Large, alatoform bivalves, Wallowaconcha raylenea gen. et sp. nov., from the Upper Triassic of north-eastern Oregon, are described and placed in a new family, Wallowaconchidae, within the Megalodontoidea, which also contains the families Megalodontidae and Dicerocardiidae (herein transferred). Major character innovations of wallowaconchids are the internal partitioning of wings and development of non-articulating thin vanes on the hingeplate. The wallowaconchid hinge, which changed during ontogeny, differs greatly from the hinge of other bivalves. Wallowaconchids probably evolved from a species of the megalodontid Triadomegalodon . Although wallowaconchids are homeomorphs of the alate Permian alatoconchid bivalves, hinge structure shows that these two groups are unrelated.
Large wings on wallowaconchids were used for snowshoe support. They may have utilized elaborate vanes and wing chambers to culture microbial symbionts, either microalgae or bacteria. These bivalves are endemic to displaced island arc terranes in western North America, occurring in Yukon, Canada (Stikine terrane), Oregon, USA (Wallowa terrane), and Sonora, Mexico (Antimonio terrane). They occupied environmental niches similar to those of large megalodontid bivalves of Triassic tropical provinces.     

Sedimentary facies from Upper Triassic reefal limestone of the Sambosan accretionary complex in Japan: mid-ocean patch reef development in the Panthalassa Ocean

Microfacies of the Early to Middle Norian reefal limestone of the Sambosan Accretionary Complex (SAC) at Kamase locality, southwest Japan, are classified into seven major facies types in stratigraphic order: peloidal grainstone-packstone, unfossiliferous lime-mudstone, tubular problematica-rich wackestone, sponge-coral floatstone, sponge bafflestone, coral rudstone, and peloidal-bioclastic packstone-grainstone. The SAC records patch reef development on a mid-oceanic seamount in the Panthalassa Ocean. Because most examples of Triassic reefs come from the former Tethys, counterparts such as those from the SAC are pivotal in resolving paleogeographic issues as well as clarifying the depositional patterns between the eastern Tethys and adjacent western Pacific (Panthalassa). We also reveal that the primary stratigraphy of the reefal limestone was disrupted by submarine landslides of the seamount in an open-ocean realm during the late Middle to Late Jurassic time.     

High diversity dinoflagellate cyst assemblages from the Late Triassic of southern England: new information on early dinoflagellate evolution and palaeogeography

Abundant and diverse dinoflagellate cyst assemblages from the Rhaetian of southern England are characterized by the occurrence of a new species of Rhaetogonyaulax, some undescribed taxa and numerous forms with Arctic and Australasian affinities. The dinoflagellate cyst assemblages permit a discussion of the palaeogeographic distribution of dinoflagellate cysts in the Late Triassic. The hypothesis on a Late Triassic migration event of organic walled microplankton from higher latitudes to the Boreal domain is presented.     

Pangea Megasequences of Tethyan Gondwana-margin reflect global changes of climate and tectonism in Late Palaeozoic and Early Triassic times—A review

The maximum concentration of continental crust at the Pangea stage is characterized by a specific depositional sequence generally referred to as the Pangea Megasequence. Extending in time from the Late Carboniferous to the middle of the Triassic, the succession exhibits similar trends across the whole of Gondwana. Invariably, the sequence was initiated by Late Carboniferous to Early Permian glacial and periglacial deposits. Deglaciation occurred in Early Sakmarian time, evidenced by a typical, commonly transgressive facies. The succeeding formations comprise, in ascending order, coal measures, redbeds, some more coal measures and again redbeds with an intercalation of fluviatile sands in the Early Triassic.After deglaciation the basic depositional theme was modified, depending on postglacial adjustments of climate and on the type of regional tectonic regimes. Extension of the tropical climatic belt after deglaciation was one factor that governed the resulting sediment facies. Coal deposition that prevailed in central Gondwana in the Early Permian gave way to dominance of redbeds in the Middle and Late Permian and, in more distal positions, evaporitic deposits were laid down, following deglaciation. Within marine realms, coralline limestones were formed.Within Gondwana the depositional period of the Pangea Megasequence was governed by three distinctive tectonic regimes: collision dominated the Panthalassa margin, transpressional sag controlled the interior basins, and extension and rifting was experienced along the entire Tethyan margin. In the Early Permian, large and complex graben structures commenced to develop between Africa and India (Malagasy Trough) and between India and Australia (West Australian Trough), giving access to Tethyan waters during deglaciation, commencing in the late Early Sakmarian.Rifting along the Tethyan margin commenced in the Early Permian and was associated with active volcanism between Cashmere and Yunnan and in north-western Australia. Spreading of Neo-Tethys and the formation of oceanic crust, leading to the separation of the Cimmerian Blocks from Gondwana, commenced in the late Early Permian and continued into the Triassic. Thus two facies realms developed, an intracratonic rift facies comprising the Cashmere, Lhasa and Baoshan blocks and a facies controlled by detachment, comprising more distal blocks, such as Tengchong, Malay and Sumatra. The present distribution of individual blocks was governed by fold movements of the Himalayan Orogeny, complicated by transpression along the eastern Himalayan Syntaxis.     

Bivalves and evolutionary resilience: old skills and new strategies to recover from the P/T and T/J extinction events

Diversity dynamics among bivalves during the Triassic and Early Jurassic provides the opportunity to analyse the recovery patterns after two mass extinctions: Permian/Triassic and Triassic/Jurassic (T/J). The results presented here are based on a newly compiled worldwide genus-level database and are contrasted to the main morphological characters of the different taxonomical (orders and their constituent families and genera) and ecological groups. Many of such morphological characters are innovations appearing during the time span considered. Diversity and evolutionary rates were assessed and compared between these groups. During the Early Triassic there was a slow recovery, dominated by epifaunal taxa, the order Pectinida being the most diverse. The major post-Permian radiation took place during the Anisian, with several morphological and ecological innovations appearing and/or diversifying. The Late Triassic was a time of great diversification and ecological specialisation. Although the T/J was a true mass extinction for bivalves, it was not indiscriminate as its impact was stronger on specialised orders and not all ecological categories were equally affected. Recovery during earliest Jurassic was fast, confirming the high-evolutionary resilience of bivalve molluscs, except for groups with thick shells and tropical distribution, probably because of a biocalcification crisis.     

Strontium isotope stratigraphy of Cretaceous hippuritid rudist bivalves: rates of morphological change and heterochronic evolution

Strontium isotope stratigraphy of 17 localities of rudist formations in the region of the former Mediterranean Tethys has provided a reliable and precise stratigraphical frame for the evaluation of morphological change in hippuritid rudist bivalves during the Coniacian–Campanian. The phyletic lineage Vaccinites cornuvaccinum (Bronn)–Vaccinites chaperi (Douvillé) evolved from the Early Coniacian until the Early Campanian and is characterized by phyletic size increase and allometric growth, as shown by morphometrical measurements of 102 shells. These chronospecies intergrade in the Late Coniacian so that V. cornuvaccinum is considered to be a reliable marker species for the Coniacian. The taxonomy of Vaccinites alpinus (Douvillé) is discussed and the species is recognized as a senior synonym of Vaccinites ultimus (Milovanovi ). It appears first in the Late Santonian and the last appearance is probably in Late Campanian. Both lineages are characterized by phyletic size increase and peramorphic evolution involving hypermorphosis. A doubling of the length of the mantle margin occurred within 5 m.y. in both lineages. The results demonstrate that the combination of morphometric analyses and stratigraphical precision provides an important tool for the delineation of tempo and mode of evolution in rudist bivalves. Strontium isotope stratigraphy resulted in a considerable revision of the ranges of the species investigated. As the stratigraphy of many Tethyan carbonate platforms relies on the distribution of rudist bivalves, and the species investigated are abundant in many rudist formations, the history of many Late Cretaceous carbonate platforms must be re-evaluated.     

Early Jurassic shell beds from marginal marine environments in southern Mendoza, Argentina

External estuarine facies in Late Sinemurian beds from the base of the Puesto Araya Formation in the Atuel river region, Mendoza Province, Argentina, contain concentrations of a new species of Cardinioides (a shallow burrowing suspension-feeding Pachycardiidae bivalve) and a low diversity benthic fauna. These bivalves appear in tidal inlet facies of a wave-dominated estuary (environment similar to lagoon-barrier island systems), forming bioclastic lags at the channel bases. The taphonomic attributes (such as shell articulation, degree of fragmentation and abrasion, bioclast size, orientation) change from North to South, from monospecific concentrations of nearly complete large Cardinioides shells with low degree of fragmentation and abrasion, through beds with smaller Cardinioides shells associated with a few bivalves from marine environments, to only isolated fragmented specimens associated with a fully marine biota including not only other bivalves but also brachiopods and ammonoids. This, together with different palaeoecologic, sedimentologic and stratigraphic attributes at the studied localities are evidence of southwards changing environmental conditions from marginal marine (brackish) to fully marine on the eastern margin of the Neuquén basin at that time. From detailed analysis of taphonomic features, size distribution of shells, and the associated fauna at the different localities, the new species is regarded as a brackish water endemic, possibly a low salinity euryhaline species, which inhabited well oxygenated waters. Salinity, turbulence levels and food supply were the main limiting factors in the distribution of the species.     

New Late Triassic gastropods from the wallowa Terrane (Idaho) and their biogeographic significance

Summary Two characteristic new species and one new genus are described from the Late Triassic of Idaho (Wallowa Terrane):Brochidiella idahoensis n. gen., n. sp. andPtychostoma ornata n. sp.Brochidiella is only known from western North America.Ptychostoma is present in the Carnian of the European Alps (Tethys) and is widespread in the western part of the North American continent (Panthalassa). Late Triassic gastropod faunas from the accreted terranes of North America are poorly known but hold a great potential for future palaeobiogeographic reconstructions.     

Strontium isotope stratigraphy of the Gabbs Formation (Nevada): implications for global Norian–Rhaetian correlations and faunal turnover

The Luning and Gabbs formations in west‐central Nevada, USA represent a Late Triassic shallow marine sedimentary succession with global significance (the Gabbs Formation was a candidate for the basal Jurassic GSSP). Typically, the Norian–Rhaetian stage boundary is placed at the contact between the formations, and the Rhaetian–Hettangian boundary (the Triassic–Jurassic boundary) is within the Müller Canyon Member of the Gabbs Formation. However, the use of different biostratigraphical index‐species schemes in Norian–Rhaetian successions between Tethys and Panthalassa, the two largest ocean basins at the time, makes precise correlation problematic. Here, we compare ⁸⁷Sr/⁸⁶Sr measurements of well‐preserved carbonate shell material from Nevada to the well‐known and biostratigraphically constrained ⁸⁷Sr/⁸⁶Sr record from Tethys, where a negative excursion in ⁸⁷Sr/⁸⁶Sr is noted across the Norian–Rhaetian boundary. Our new ⁸⁷Sr/⁸⁶Sr data from the Luning and Gabbs formations reveal a comparable trend, with a sharp drop in ⁸⁷Sr/⁸⁶Sr within the Nun Mine Member of the Gabbs Formation, suggesting the position of the Norian–Rhaetian boundary is higher in the succession, and not between the Luning and Gabbs formations as previously defined. Relating the stage boundary using global isotopic signals is a useful tool for biostratigraphical correlation of successions between Tethys and Panthalassa, and for estimating the rate of faunal turnover at the Norian–Rhaetian stage boundary in comparison with the succeeding Late Triassic mass extinction. If correct, this biostratigraphical–chemostratigraphical correlation suggests that the current index groups for the Panthalassic stage boundary should be changed.     

A primitive ornithischian dinosaur from the Late Triassic of South Africa, and the early evolution and diversification of Ornithischia

Although the group played an important role in the evolution of Late Mesozoic terrestrial ecosystems, the early evolutionary history of the ornithischian dinosaurs remains poorly understood. Here, we report on a new primitive ornithischian, Eocursor parvus gen. et sp. nov., from the Late Triassic (?Norian) Lower Elliot Formation of South Africa. Eocursor is known from a single specimen comprising substantial cranial and postcranial material and represents the most complete Triassic member of Ornithischia, providing the earliest evidence for the acquisition of many key ornithischian postcranial characters, including an opisthopubic pelvis. A new phylogenetic analysis positions this taxon near the base of Ornithischia, as the sister taxon to the important and diverse clade Genasauria. The problematic clade Heterodontosauridae is also positioned basal to Genasauria, suggesting that an enlarged grasping manus may represent a plesiomorphic ornithischian condition. This analysis provides additional phylogenetic support for limited ornithischian diversity during the Late Triassic, and suggests that several major ornithischian clades may have originated later than generally believed. There are few morphological differences between Late Triassic and Early Jurassic ornithischians, supporting previous suggestions that the Early Jurassic ornithischian radiation may simply represent the filling of vacant ecological space following Late Triassic terrestrial extinctions.     

First report of dinosaurian claws from the Late Triassic of India

The Late Triassic Tiki Formation has yielded five isolated nearly complete claws or ungual phalanges from a fossil locality, which are described in detail and compared with other Late Triassic tetrapods. Of these, four ungual phalanges are slender, asymmetric, ventrally recurved, transversely compressed, and contain deep collateral grooves on either side, a low median keel on the proximal articular surface and a prominent proximoventral flexor tubercle showing their high similarity to the theropod dinosaurs. The remaining claw is unlike that of any theropods in terms of high robusticity and near symmetry. However, as in dinosaurs it is ventrally recurved and contains deep lateral grooves, a small flexor tubercle, lateromedially extended proximal articular surface with a distinct median keel and is considered as belonging to an indeterminate dinosaur. Although it is not possible to ascertain whether the unguals belong to a single taxon or multiple taxa, this new find points towards the presence of small dinosaurs in the Late Triassic Tiki fauna.     

OSTRACODS AS MARKERS OF THE PERMIAN/TRIASSIC BOUNDARY IN THE KHUFF FORMATION OF SAUDI ARABIA

Abstract:  Ostracods are described for the first time from Permian–Triassic shallow marine sediments of the Khuff Formation of central Saudi Arabia. They were collected using a modified acetolysis technique for releasing calcareous shells from limestones that is described herein. Thirty-four species belonging to 17 genera are recognized. Two new species are described: Arqoviella arabica sp. nov. and A. khartamensis sp. nov. The ostracod fauna supports a Late Permian age for the lower Khartam Member and a probable Early Triassic age for the upper Khartam Member of the Khuff Formation of central Saudi Arabia. This suggests that the Permian/Triassic boundary is located within the Khartam Member, rather than at the major lithological break between the Midhnab and Khartam members. Palaeoecological analysis suggests that the palaeoenvironment of the Khuff Formation was shallow marine (between 1 and 50 m deep) on an internal shelf.     

青藏高原白垩纪双壳类生物地理

青藏高原白垩纪沉积见于６条东西向延伸的条带内。双壳类主要发育于这些条带的Ｂｅｒｒｉａｓｉａｎ,Ａｐｔｉａｎ－Ａｌｂｉａｎ,Ｃｅｎｏｍａｎｉａｎ－Ｔｕｒｏｎｉａｎ,Ｃｏｎｉａｃｉａｎ－Ｓａｎｔｏｎｉａｎ和Ｃａｍｐａｎｉａｎ－Ｍａａｓｔｒｉｃｈｔｉａｎ５个时期的地层。雅鲁藏布江缝合线为白垩纪双壳类地理分布的主要控制界线。早白垩世期间,雅鲁藏布江缝合带以南的喜马拉雅地区的双壳类Ｐｅｔｒｏｃｅｒａｍｕｓ,     

川西,藏东晚三叠世有孔虫及海参骨片

金沙江上游两岸为川西、藏东地区。此区的四川省白玉县、西藏贡觉县及江达县的晚三叠世诺利期沉积中发现了有孔虫１８属２１种,海参骨片５属８种。三叠纪海参在中国为首次报道：白玉县及贡觉县的三叠世有孔虫也为首次发现。这一动物群在区域地质史及古地理研究上具有一定意义。     

Pathologies of non‐marine bivalve shells from the Late Triassic of Poland

Gorzelak, P., Nied?wiedzki, G. & Skawina, A. 2010: Pathologies of non‐marine bivalve shells from the Late Triassic of Poland. Lethaia, Vol. 43, pp. 285–289. Shells of Late Triassic non‐marine bivalves from Lisowice (Lipie ?l?skie clay pit, southern Poland), which co‐occur with remains of several vertebrate taxa (mammal‐like reptiles, carnivorous dinosaurs, pterosaurs, temnospondyl amphibians, hybodont sharks, dipnoan and ganoid fish), bear evidence of pathologies. Distribution, dimension and shape of some of these injuries (radiate tooth marks) closely match the dental morphology of lungfish (here probably represented by the genus Ceratodus). Thus, we interpret these pathologies as evidence of unsuccessful predatory attack on bivalves by this fish. This interpretation is also consistent with modern examples of such behaviour among lungfish. The feasibility that other culprits caused other pathologies (shell scarring and wedges) on the bivalves analysed is also discussed. Discovery of these traces constitutes important evidence of predator–prey interaction, which provides ‘fingerprints’ of trophic structure within this Late Triassic freshwater ecosystem. □Freshwater bivalves, lungfish, pathologies, predation, Triassic.     

QUALITY OF THE TRIASSIC–JURASSIC BIVALVE FOSSIL RECORD IN NORTHWEST EUROPE

Abstract: The quality of the Triassic–Jurassic bivalve fossil record in northwest Europe has been measured using the Simple Completeness Metric (SCM). The SCM has been applied to the fossil record of total bivalve diversity and to the records of different ecological guilds. The Westbury and Lilstock Formations record high SCM values for most ecological groups. The ‘Pre‐Planorbis Beds’ of the lower Lias Group, however, witness a precipitous decline in the completeness of most guilds and emigration of taxa due to localized marine anoxia is a likely cause. Neither variation in lithofacies, shell mineralogy, sedimentary rock outcrop area, nor sequence architecture can convincingly explain the observed patterns of completeness. Our SCM data reveal that the Early Jurassic fossil record of infaunal suspension‐feeding bivalves is significantly poorer than that of epifaunal bivalves. Any differences in the apparent Rhaetian extinction rates between these two guilds should therefore be viewed with caution. Analyses of selectivity during the Late Triassic mass extinction based on studies of global databases appear robust in light of our SCM data. Nevertheless, future investigations of the Triassic–Jurassic benthic marine ecosystem undertaken at a finer‐resolution, may need to account for the poor quality of the Early Jurassic fossil records of certain ecological guilds, such as the infaunal suspension‐feeding taxa.     

Rib fabrication in Ostreoidea and Plicatuloidea (Bivalvia,Pteriomorphia) and its evolutionary significance

Ribs of Ostreoidea and Plicatuloidea are defined as antimarginal, that is, perpendicular to the margin throughout growth. Morphogenetically, these ribs are unique, since, unlike radial ribs, they are secreted by a homogeneous mantle margin. Based also on the reconstructed shell secretion cycle in Bivalvia, we propose that ribs of Ostreoidea and Plicatuloidea are formed by a mantle margin which, upon extension from the shell margin, stretches and folds by taking the preformed ribs as templates. In extending perpendicular to the margin (as in all Bivalvia growing isometrically), such a mantle extends the rib pattern antimarginally. Ribs of this kind are purely mechanical structures, as their arrangement depends on the mechanical properties of the mantle and on the environmental conditions. This explains the high irregularity of such ribbing patterns. The presence of antimarginal ribs in both the Ostreoidea and Plicatuloidea sheds light on their origin. The first known oyster, Actinostreon cristadifformis, probably derived from an antimarginally ribbed Prospondylidae gen. indet. in the Late Permian or Early Triassic. Antimarginally ribbed Triassic species formerly included in Placunopsis originated both the Dimyidae Atreta in the Late Triassic and Enantiostreon in the Mid Triassic, which was transitional to Plicatulidae. Therefore, Dimyidae and Plicatulidae are closely connected and grouped under Plicatuloidea, to which Ostreoidea is phylogenetically unrelated.     

Tethyan uppermost Permian (Dzhulfian and Dorashamian) foraminiferal faunas and their paleogeographic and tectonic implications

The foraminiferal faunas and biostratigraphic correlation of the Tethyan uppermost Permian (Dzhulfian and Dorashamian) provide important paleogeographic and tectonic data for the interpretation of the Palaeofusulina-bearing terranes in East and Southeast Asia. These interpretations have a significant bearing on understanding Japanese pre-Cretaceous tectonostratigraphic and micropaleontologic data, as well as the geodynamic evolution of the Japanese Palaeofusulina-bearing terranes. The Tethyan foraminiferal fauna in the uppermost Permian is characterized by the occurrence of provincial and endemic schubertellid genera, and the absence of neoschwagerinids and verbeekinids which had characterized the rapidly evolving Middle Permian Tethyan marine faunas until their extinction at the end of the Midian. Difficulties in world-wide correlation of the uppermost Permian have resulted because of different geographic faunal compositions and the geographic patterns of extinction of Permian marine faunas. The Palaeofusulina fauna is one of the most reliable indicators of the uppermost Permian. Its presence or absence serves as paleogeographic constraints on East and Southeast Asian terranes. For example, the absence of Palaeofusulina fauna and the presence of late Midian Lepidolina multiseptata faunas in the Lhasa Terrane in Tibet and the Wolya Terrane in Sumatra (the third continental sliver north of Gondwana) are important, particularly, for identifying the rift–drift–collision process of the Gondwana-affinity terranes. They suggest a Late Permian separation of the two terranes from Gondwana. Tethyan Palaeofusulina occur in the latest Permian tropical to subtropical latitudinal belt and along with other geologic data assist in paleogeographic reconstructions and in interpreting the possible movement and emplacement of the Palaeofusulina-bearing terranes such as the Maizuru, South Kitakami–Kurosegawa and Chichibu terranes in Japan. They reveal that: (1) the Upper Permian Maizuru Group was deposited on the eastern continental margin of South China; (2) the occurrence of the Lower Permian Cathaysian flora and a number of geologic data in the South Kitakami–Kurosegawa suggest an arc–trench system setting and the Late Permian deposition in a shallow open-marine environment in proximity to South China; (3) foraminiferal biogeograpic data and the reconstructed oceanic plate stratigraphy in the Chichibu Terrane constrain the location of the Chichibu Seamount Chains to the western part of the Panthalassan domain, as they moved westwards against the Cathaysian Continent until their Jurassic accretion.