A. G. Sennikov

Disruption of playa-lacustrine depositional systems at the Permo-Triassic boundary: evidence from Vyazniki and Gorokhovets on the Russian Platform

Abstract: Permo-Triassic sections at Vyazniki and Gorokhovets provide evidence on terrestrial events at, or close to, the Permo-Triassic boundary, the time of the largest ever mass extinction. The sedimentary succession records the overrun of a muddy playa–lacustrine depositional system by major channel belts transporting sand-grade sediments. Biostratigraphy of sections at Vyazniki and Gorokhovets (Zhukov Ravine) shows that this event occurred either at the very end of the Permian or 8 m above in the sections. The timing and nature of this event, which records increased sediment flux from the Ural Mountains, is closely comparable with that from the Southern Uralian Foreland Basin. The Vyazniki and Gorokhovets sections are 800 km from the mountain front and in a separate depositional basin, which strengthens the case that increased sediment flux from the Urals at the Permo-Triassic boundary is related to devegetation of upland catchments (increasing sediment yield) and a switch toward low-frequency but high-magnitude discharge events (increasing sediment delivery). The interbedding of fluvial and aeolian deposits provides further evidence for climatic instability and extremes in the Early Triassic. Supplementary material: Detailed reports on the ostracodes and fossil fish remains from the Zhukov Ravine sections are available at http://www.geolsoc.org.uk/SUP18402.

Evolution of the Permian and Triassic tetrapod communities of Eastern Europe

Abstract The Permo-Triassic terrestrial and freshwater tetrapod communities of Eastern Europe are reconstructed as food-webs. The Late Permian theriodont-dinocephalian community (Ocher, Mezen, Isheyevo) changes to a latest Permian theriodont-pareiasaur community (North Dvina, Vyazniki). After a major extinction, the Triassic thecodontian-dicynodont communities appear, a lystrosaurid one in the Early Triassic (Lower and ?Upper Vetluga), and a kannemeyerid one in the later Early Triassic (?Yarenga) and the Mid Triassic (Donguz, Bukobay). Similar stages are represented in the evolution of aquatic communities: the Late Permian temnospondyl community (Ocher, Isheyevo), the latest Permian chroniosuchian one (North Dvina, Vyazniki), the Lower and Middle Triassic new temnospondyl one (from Vetluga to Bukobay). The faunal changes in Eastern Europe are mirrored in other parts of the world, although there are some endemic Russian forms.

Vyazniki biotic assemblage of the terminal Permian

A new unique and diverse biotic assemblage of the terminal Permian has recently been discovered in the town of Vyazniki (Central Russia). The Vyazniki terrestrial community is transitional between Permian and Triassic ones and represents the last, so far unknown stage of the global ecological crisis of the continental biota at the Permian-Triassic boundary. The successive development of land biotic crisis in the Late Permian, which was followed by mass extinction at the Permian-Triassic boundary, and long, successive postcrisis development and specialization of new Triassic groups as well as rearrangement and diversification of the biotic assemblage composition and community structure suggest predominance of intrinsic, biotic causes of this crisis, realized in destabilization, alteration, and new stabilization of continental communities and ecosystems.

Upper Permian Vertebrate Coprolites from Vyazniki and Gorokhovets, Vyatkian Regional Stage, Russian Platform

Abstract Numerous coprolites have been found in the Vyazniki and Gorokhovets localities of European Russia. Five identified coprolite-bearing horizons occur in the upper Permian deposits of the Vyatkian Regional Stage. Coprolites were collected from mudstone with a coprolite breccia-like layer and also from intraformational conglomerates that were deposited in a floodplain and overbank environment. Two coprolite morphotypes (A and B) are recognized from size and shape analysis of 32 specimens. Morphotype A has long, nonsegmented feces. Smaller, cylindrical or tubular-shaped coprolites of morphotype B are commonly segmented. SEM images of the coprolite matrix show spheres and thin-walled vesicles with diameters 0.5–4 µm. Electron Micro Probe (EMP) analyses of polished thin sections show microcrystalline carbonate-fluoride-bearing calcium phosphate with small amounts of calcium replaced in the crystal lattice. Optical microscopy and EMP investigations show that iron and manganese oxides are responsible for elevated iron and manganese concentrations in the bulk mass of coprolites. Other metals (V, Ni) can be associated with oxides forming spheroids with diameters 3–10 µm. REEs (rare earth elements, U, and other trace element concentrations suggest significant eolian sediment input to the burial environment of the coprolites. The scats contain fish scales and bones of tetrapods (amphibians or reptiles). In one large-sized coprolite, a small fragment of therapsid bone was also found. Both morphotypes are matched to carnivorous taxa within the Archosaurus rossicus zone of the Eastern Europe. The size and shape of the best-preserved specimens suggest that they were possibly produced by a large therapsid, anthracosaur, or early archosauromorph predator.

On a Typical Jurassic Sauropterygian from the Upper Triassic of Wilczek Land (Franz Josef Land, Arctic Russia)

A new elasmosaurid genus and species, Alexeyisaurus karnoushenkoi, from the Lower-Middle Norian (Wilczek Formation) of the Upper Triassic of the island of Wilczek Land (Franz Josef Land) is described based on an incomplete skeleton. The new form combines characters of typical late plesiosaurs and structural features unique to this form. It is probably the earliest representative of typical late sauropterygians (plesiosaurs).

Differentiation of Tetrapod Communities and Some Aspects of Biotic Events in the Early Triassic of Eastern Europe

The patterns of spatial differentiation of the Early Mesozoic terrestrial biota in Eastern Europe and Australia-Tasmania demonstrate that the tetrapod faunal recovery following the Permian extinction was characterized by both global and regional heterogeneity. Local distinctions observed in the development of Early Triassic tetrapod assemblages of European Russia allow the recognition of the following realms: (1) the central and northern regions of the East European Platform (Moscow-Mezen Syncline) and the Timan-North Ural Region; (2) the southern Fore-Urals, including the Obshchii Syrt Plateau; and (3) the southern regions of the East European Platform (the slope of the Voronezh Anticline). Climatic conditions at the initial stage of the development of local communities were characterized by an increase in aridity and seasonal contrasts of climate. Therefore, terrestrial assemblages mostly concentrated in the aquatic and coastal biotopes. Accordingly, vertebrate assemblages of the region were dominated everywhere by aquatic amphibians and semiaquatic reptiles, while the accompanying palynomorph assemblages show the predominance of hygrophilous vegetation indicative of swampy mangrove setting. With respect to amphibians, a peak of local biogeographic differentiation falls on the onset of the Early Triassic and, in the case of reptiles, on the end of this time span. This change conforms to the increasing role of reptiles in the overall taxonomic diversity with time. Among the three main biogeographic units of the region, the Southern Fore-Ural Realm is distinguished by the maintenance of distinct faunal links with Gondwanan regions. The Southern Realm shows a connection with the Germanic Basin and more western Euramerican areas, which is documented for the Late Olenekian and occurred under influence of coastal marine conditions.

On the faunal verification of the Permo-Triassic boundary in continental deposits of eastern Europe: 1. Gorokhovets-Zhukov ravine

A reference section of the Permian and Triassic continental deposits of the Zhukov ravine near the town of Gorokhovets (Vladimir Region) is described and new tetrapod localities are characterized. The position of the Permian-Triassic boundary in this section is recognized and its faunal substantiation based on vertebrates is provided for the first time. The Zhukov ravine section is unique in the fact that it shows a thick stratigraphically continuous succession of the Permo-Triassic boundary beds, with three successive tetrapod zones: the terminal Permian Chroniosuchus paradoxus and Archosaurus rossicus zones and the Early Triassic Tupilakosaurus wetlugensis Zone.

New tanystropheids (Reptilia: Archosauromorpha) from the Triassic of Europe

A new prolacertilian species and genus, Augustaburiania vatagini gen. et sp. nov. (Reptilia: Archosauromorpha), from the Lower Triassic of the Don River Basin is described. It is the first representative of the Tanystropheidae in the Eastern Europe and the world oldest member of this family. Another new genus (Protanystropheus gen. nov.) from Central and Western Europe is also established. The diversity, systematics, phylogeny, evolution, and stratigraphic and geographical distribution of prolacertilians are discussed. The ecological role of prolacertilians in Early Triassic communities and adaptation to marine environments are analyzed.

A New Species of Garjainia Ochev, 1958 (Diapsida: Archosauriformes: Erythrosuchidae) from the Early Triassic of South Africa

A new species of the erythrosuchid archosauriform reptile Garjainia Ochev, 1958 is described on the basis of disarticulated but abundant and well-preserved cranial and postcranial material from the late Early Triassic (late Olenekian) Subzone A of the Cynognathus Assemblage Zone of the Burgersdorp Formation (Beaufort Group) of the Karoo Basin of South Africa. The new species, G. madiba, differs from its unique congener, G. prima from the late Olenekian of European Russia, most notably in having large bony bosses on the lateral surfaces of the jugals and postorbitals. The new species also has more teeth and a proportionately longer postacetabular process of the ilium than G. prima. Analysis of G. madiba bone histology reveals thick compact cortices comprised of highly vascularized, rapidly forming fibro-lamellar bone tissue, similar to Erythrosuchus africanus from Subzone B of the Cynognathus Assemblage Zone. The most notable differences between the two taxa are the predominance of a radiating vascular network and presence of annuli in the limb bones of G. madiba. These features indicate rapid growth rates, consistent with data for many other Triassic archosauriforms, but also a high degree of developmental plasticity as growth remained flexible. The diagnoses of Garjainia and of Erythrosuchidae are addressed and revised. Garjainia madiba is the geologically oldest erythrosuchid known from the Southern Hemisphere, and demonstrates that erythrosuchids achieved a cosmopolitan biogeographical distribution by the end of the Early Triassic, within five million years of the end-Permian mass extinction event. It provides new insights into the diversity of the Subzone A vertebrate assemblage, which partially fills a major gap between classic ‘faunal’ assemblages from the older Lystrosaurus Assemblage Zone (earliest Triassic) and the younger Subzone B of the Cynognathus Assemblage Zone (early Middle Triassic).

The first gliding reptiles from the upper Permian of Russia

Two new gliding reptiles from the Late Permian Kul’chumovo-A locality (Orenburg Region), Rautiania alexandri gen. et sp. nov. and R. minichi sp. nov., are described and assigned to the family Weigeltisauridae. These finds substantially expand the knowledge of the morphology of this group and suggest the climax state of terrestrial tetrapod communities of eastern Europe in the pre-Triassic Time, which resulted in the development of ecological niches not typical of earlier terrestrial vertebrate faunas.