New magnetostratigraphy from the Punta Grohmann section (Dolomites, NE Italy): an improvement of the Geomagnetic Polarity Time Scale around the Ladinian/Carnian boundary

<p>The Ladinian/Carnian boundary (LCB) is defined at Prati di Stuores (GSSP of the Carnian Stage) with the First Appearance Datum (FAD) of ammonoid <em>Daxatina canadensis</em> and approximated by the FAD of conodont <em>Paragondolella polygnathiformis</em>. The age of the Carnian is currently estimated at ca. 237 Ma using the composite magnetostratigraphy of the main late Ladinian basinal sequences from literature, calibrated with a U-Pb radiometric age of 237.77±0.14 Ma from the Rio Nigra section in Alpe di Siusi (Dolomites, NE Italy). In the attempt to improve the precision of the Geomagnetic Polarity Time Scale (GPTS) around the LCB we investigated for magnetostratigraphy the Punta Grohmann section in the Dolomites. The Punta Grohmann section is calibrated with ammonoids (the FAD of <em>Zestoceras</em> cf. <em>lorigae</em> is considered a proxy of the LCB) and is chronologically constrained by two U-Pb radiometric ages from zircons (237.58±0.04 Ma; 237.68±0.05 Ma). The magnetostratigraphy of the Punta Grohmann section has been successfully correlated to other Ladinian-Carnian magnetostratigraphic sections (Prati di Stuores, Mayerling, Rio Nigra) and compared to the most recent version of the Triassic Geomagnetic Polarity Time Scale (GPTS). The LCB at Prati di Stuores is calibrated through magnetostratigraphy with the U-Pb radiometric datings of Punta Grohmann, obtaining an age of the LCB of ca. 237.4 Ma. Therefore, the Ladinian should be ca. 4 Myr long and the Carnian ca. 10.4 Myr long.</p>

Ammonoids of the Genus Yakutosirenites from the Carnian Stage of Northeast Asia

A revision of ammonoids of the genus Yakutosirenites (Sirenitidae) from the Carnian deposits of Northeast Asia have been carried out. Based on the study of the morphogenesis of the most important structures of the shell, a division of the genus Yakutosirenites into two subgenus is proposed: Yakutosirenites with the type species Sirenites pentastichus Vozin, 1964 and Vozinites with the type species Sirenites armiger Vozin, 1965. A description of the genus and its subgenera and species is given. The significance of the species of these subgenera for the biostratigraphic subdivision and correlation of the Lower/Upper Carnian boundary interval is substantiated. The boreal-thethyan correlation of the Yakutosirenites pentastichus zone have been refined. For the first time, taking into account the data of the revision of the genus Yakutosirenites, the upper part of the pentastichus Zone is compared only to the Arctosirenites canadensis Beds of the Arctic Canada and to the lower Subzone of the Tropites welleri Zone of British Columbia, wich are an equivalent to the lower part of the Tropites subbullatus Zone of the Alpine standard.

The Carnian Humid Episode of the late Triassic: a review

From 1989 to 1994 a series of papers outlined evidence for a brief episode of climate change from arid to humid, and then back to arid, during the Carnian Stage of the late Triassic Epoch. This time of climate change was compared to marine and terrestrial biotic changes, mainly extinction and then radiation of flora and fauna. Subsequently termed, albeit incorrectly, the Carnian Pluvial Event (CPE) by successive authors, interest in this episode of climatic change has increased steadily, with new evidence being published as well as several challenges to the theory. The exact nature of this humid episode, whether reflecting widespread precipitation or more local effects, as well as its ultimate cause, remains equivocal. Bed-by-bed sampling of the Carnian in the Southern Alps (Dolomites) shows the episode began with a negative carbon isotope excursion that lasted for only part of one ammonoid zone (A. austriacum). However, that the Carnian Humid Episode represents a significantly longer period, both environmentally and biotically, is irrefutable. The evidence is strongest in the European, Middle Eastern, Himalayan, North American and Japanese successions, but not always so clear in South America, Antarctica and Australia. The eruption of the Wrangellia Large Igneous Province and global warming (causing increased evaporation in the Tethyan and Panthalassic oceans) are suggested as causes for the humid episode.

The roles of herbivory and omnivory in early dinosaur evolution

ABSTRACTHerbivorous and omnivorous dinosaurs were rare during the Carnian stage of the Late Triassic. By contrast, the succeeding Norian stage witnessed the rapid diversification of sauropodomorphs and the rise of the clade to ecological dominance. Ornithischians, by contrast, remained relatively rare components of dinosaur assemblages until much later in the Mesozoic. The causes underlying the differential success of ornithischians and sauropodomorphs remain unclear, but might be related to trophic specialisation. Sauropodomorphs replaced an established herbivore guild consisting of rhynchosaurs, aetosaurs and basal synapsids, but this faunal turnover appears to have been opportunistic and cannot be easily attributed to either competitive interactions or responses to floral change. Consideration of diversity patterns and relative abundance suggests that the ability to eat plants might have been a major factor promoting sauropodomorph success, but that it was less important in the early evolution of Ornithischia. On the basis of current evidence it is difficult to determine the diet of the ancestral dinosaur and scenarios in which omnivory or carnivory represent the basal condition appear equally likely.

Evidence of oribatid mite herbivory in the stem of a Late Triassic tree fern from Arizona

Small coprolite-bearing borings occur in the stem of the filicalean tree fern Itopsidema vancleaveii Daugherty from the Chinle Formation of Late Triassic Age (Carnian Stage) in Petrified Forest National Park, Arizona. These borings are restricted to parenchyma within the leaf petioles and among the adventitious roots of the root mantle. Although they are not lined by wound tissue, some of the borings in the leaf petioles contain small discontinuous masses of wound-tissue at a few places along some of the walls, indicating that the plant was alive when it was attacked. Coprolites within the borings generally are small (mostly about 40–50 μm in diameter and 85–100 μm in length) and oval in longitudinal section and round to weakly hexagonal in transverse section; they consist of very small particles of unidentifiable plant matter. Although the weakly hexagonal coprolites are similar to those produced by termites but they are an order of magnitude smaller. Furthermore, the borings are much smaller than those produced by known extant termites. It is likely that oribatid mites produced the coprolite-bearing borings and coprolites. This occurrence is significant because it bridges the Late Permian to Early Jurassic gap in the geologic record of endophagous mites and also contributes new data on arthropod activity during the Late Triassic in southwestern North America.

Middle Triassic cnidarians from the New Pass Range, Central Nevada

We describe three scleractinian corals and one species of hydrozoan from the New Pass Range, central Nevada, which together constitute the oldest Triassic cnidarian assemblage from North America. They occur in carbonate rocks tentatively correlated with the Augusta Mountain Formation, Star Peak Group. At generic and higher levels, these cnidarians seem representative of early Mesozoic Tethyan faunas and carbonate lithofacies, but they indicate some endemism. Although the original aragonitic skeletons and microstructure are destroyed by recrystallization, the corals still yield important details allowing their correct taxonomic assignment. They contain the minitrabecular cerioid coral,Ceriostella variabilisnew genus and species, the thick-trabecular, thamnasteroid coralMesomorpha newpassensisnew species, and an undeterminable cuifastreid coral tentatively assigned toCuifastraea.The discovery ofMesomorphamarks the first occurrence of this genus outside the Jurassic and Cretaceous seas. Also discovered is a remarkably corallike hydrozoan,Cassianastraea reussi(Laube), already known from the Carnian stage of the western Tethys. This is the first occurrence of this species outside the western Tethys.