Guido Roghi

High-precision U-Pb zircon age from the Triassic of Italy : Implications for the Triassic time scale and the Carnian origin of calcareous nannoplankton and dinosaurs

The Triassic time scale is poorly constrained due to a paucity of high-precision radiometric ages. We present a 206 Pb/ 238 U age of 230.91 ± 0.33 Ma (error includes all known sources) for zircon from an ash bed in the upper Carnian (Upper Triassic) of southern Italy that requires a major revision of the Triassic time scale. For example, the Norian stage is lengthened to more than 20 m.y. The section containing the ash bed is correlated with other Tethyan sections and, indirectly, with the Newark astronomical polarity time scale (APTS). The dating provides also a minimum age for some important climatic and biotic events that occurred during the Carnian. We note a coincidence between these events and the eruption of the large igneous province of Wrangellia, but the possible link between volcanism and climatic and biotic events requires further scrutiny.

Arthropods in amber from the Triassic Period

The occurrence of arthropods in amber exclusively from the Cretaceous and Cenozoic is widely regarded to be a result of the production and preservation of large amounts of tree resin beginning ca. 130 million years (Ma) ago. Abundant 230 million-year-old amber from the Late Triassic (Carnian) of northeastern Italy has previously yielded myriad microorganisms, but we report here that it also preserves arthropods some 100 Ma older than the earliest prior records in amber. The Triassic specimens are a nematoceran fly (Diptera) and two disparate species of mites, Triasacarus fedelei gen. et sp. nov., and Ampezzoa triassica gen. et sp. nov. These mites are the oldest definitive fossils of a group, the Eriophyoidea, which includes the gall mites and comprises at least 3,500 Recent species, 97% of which feed on angiosperms and represents one of the most specialized lineages of phytophagous arthropods. Antiquity of the gall mites in much their extant form was unexpected, particularly with the Triassic species already having many of their present-day features (such as only two pairs of legs); further, it establishes conifer feeding as an ancestral trait. Feeding by the fossil mites may have contributed to the formation of the amber droplets, but we find that the abundance of amber during the Carnian (ca. 230 Ma) is globally anomalous for the pre-Cretaceous and may, alternatively, be related to paleoclimate. Further recovery of arthropods in Carnian-aged amber is promising and will have profound implications for understanding the evolution of terrestrial members of the most diverse phylum of organisms.

A microworld in Triassic amber

Amber provides an effective medium for conservation of soft-bodied microorganisms, but finds older than 135 million years are very rare and have not so far contained any microbial inclusions. Here we describe 220-million-year-old droplets of amber containing bacteria, fungi, algae and protozoans that are assignable to extant genera. These inclusions provide insight into the evolution and palaeoecology of Lower Mesozoic microorganisms: it seems that the basal levels of food webs of terrestrial communities (biocoenoses) have undergone little or no morphological change from the Triassic to the Recent.

THE PRATI DI STUORES/STUORES WIESEN SECTION (DOLOMITES, ITALY): A CANDIDATE GLOBAL STRATOTYPE SECTION AND POINT FOR THE BASE OF THE CARNIAN STAGE

The Prati di Stuores/Stuores Wiesen section (Dolomites, Italy) is proposed as a candidate Global Stratotype Section and Point for the base of the Carnian Stage. In addition to being a famous, richly fossiliferous locality, it includes the type-section of the Cordevolian substage. The section is located near Pralongia, along the southern slope of the crest separating the Badia/Abtei and Cordevole valleys. Below the levels with Trachyceras aon , the section contains a rich ammonoid fauna that chacterizes the lower part of the Regoledanus Subzone and subsequently records the first appearances of the mid-high latitude genus Daxatina ( Daxatina sp., D. cf. canadensis ) and of traditional Trachyceras with species different from T. aon . Moreover, the Daxatina cf. canadensis Subzone is recognised above the Regoledanus Subzone. Very rare conodonts of the Budurovignatus group and species of Gladigondolella from the diebeli Assemblage Zone occur. Gondolella polygnatyformis, already known from the Aon Subzone, is absent. Palynomorphs, foraminifers, gastropods, bivalves, brachiopods, microcrinoids and holothurian sclerites were studied. Variations in frequency and taxonomic diversity of these faunas suggest anaerobic-disaerobic bottom conditions for the lower-middle part of the section (0-105 m), followed by a more stable oxygen content in the upper portion. Magnetostratigraphy showed four intervals with normal polarity and three intervals with reversed polarity. The Daxatina cf. canadensis Subzone falls close to the normal polarity interval S2n. The present study proposes the FAD of the cosmopolitan genus Daxatina as a marker of the base of the Carnian Stage, placing it at a lower stratigraphic level than previously indicated in the Stuores area. The Prati di Stuores section is proposed as GSSP of the Ladinian-Carnian boundary.

Cretaceous African life captured in amber.

Amber is of great paleontological importance because it preserves a diverse array of organisms and associated remains from different habitats in and close to the amber-producing forests. Therefore, the discovery of amber inclusions is important not only for tracing the evolutionary history of lineages with otherwise poor fossil records, but also for elucidating the composition, diversity, and ecology of terrestrial paleoecosystems. Here, we report a unique find of African amber with inclusions, from the Cretaceous of Ethiopia. Ancient arthropods belonging to the ants, wasps, thrips, zorapterans, and spiders are the earliest African records of these ecologically important groups and constitute significant discoveries providing insight into the temporal and geographical origins of these lineages. Together with diverse microscopic inclusions, these findings reveal the interactions of plants, fungi and arthropods during an epoch of major change in terrestrial ecosystems, which was caused by the initial radiation of the angiosperms. Because of its age, paleogeographic location and the exceptional preservation of the inclusions, this fossil resin broadens our understanding of the ecology of Cretaceous woodlands.

Discovery of a major negative δ13C spike in the Carnian (Late Triassic) linked to the eruption of Wrangellia flood basalts

Major climate changes and mass extinctions are associated with carbon isotope anomalies in the atmosphere-ocean system and have been shown to coincide with the onset of large igneous provinces (LIPs) and, by association, their emissions of greenhouse gases and aerosols. However, climatic and biological consequences of some known LIP eruptions have not yet been explored. During the Carnian (Late Triassic) large volumes of flood basalts were erupted to form the so-called Wrangellia LIP (western North America). This huge volcanic province is similar in age to a major climatic and biotic change, the Carnian Pluvial Event (CPE), but no evidence of a causal relationship exists other than timing. Here we report a sharp negative δ 13 C excursion at the onset of the CPE recorded in organic matter. An abrupt carbon isotope excursion of ∼−4‰ occurs in terrestrial and marine fossil molecules, whereas total organic carbon records an ∼−2‰ shift. We propose that this carbon isotope negative shift was caused by an injection of light carbon into the atmosphere-ocean system linked to the eruption of Wrangellia flood basalts. This carbon-cycle perturbation occurs slightly before two major evolutionary innovations: the origin of dinosaurs and calcareous nannoplankton.

Classification of amber based on thermal analysis

The present study considered a possible way of classifying fossil and sub-fossil resins by means of thermal analysis, by using thermogravimetric (TG) and differential thermogravimetric (DTG) profiles. We used samples of resins of different origin and ages, ranging from present-day to Triassic (225 million years ago (Ma)), in order to extend the knowledge of thermal patterns of very ancient resins. Under differential thermogravimetric analysis, all the samples presented a main exothermal event, whose temperature varied among resins of different age. The increasing value of the main exothermal peak varies with the increase of the age of the specimen and a significant linear correlation was found (r=0.701, P<0.01) with a slope of 0.216. Additional information came in relation to paleobotanical origin, lithology and diagenesis of the fossil samples. Thermal analysis of fossil resins appears therefore as a useful method that may improve the characterization of fossil resins and well correlates with the maturation grade.

Triassic Amber of the Southern Alps (Italy)

Abstract The Heiligkreuz-Santa Croce Formation (also known as Dürrenstein Formation, Upper Triassic) in the Dolomites contains one of the most ancient and substantial Triassic amber deposits in the world. The amber is found in sandstones and paleosols. It has an affinity to the conifer family Cheirolepidiaceae, and amber samples from the Julian and Carnic Alps (Southern Alps) also show an affinity to this family. Physico-chemical investigations of the amber from the Dolomites by solid-state Fourier-transform infrared analysis (FTIR), nuclear magnetic resonance (NMR), pyrolysis-gas-chromatography/mass-spectrometry (pyr-GC/MS), thermogravimetry (TG), differential thermogravimetry (DTG), and automatized elemental analysis yielded a complete characterization of the amber, and allowed comparison with other ambers and younger resins (copals). FTIR revealed absorption bands typical of all fossil resins, and the spectrum region from 8–10 μm provided a fingerprint of the Triassic amber that differs from other known resins. The NMR spectrum also shows a typical pattern for fossil resins, but peculiar peak abundances permitted further characterization of the Triassic amber, both in the saturated (10–70 ppm) and unsaturated carbon region (100–160 ppm). The amber also lacks exomethylene resonances found in younger resins at 110 and 150 ppm. Pyrolysis-gas-chromatography/mass-spectrometry (pyr-GC/MS) experiments showed the amber was of class II, with some components of Class I. Thermogravimetric (TG) and differential thermogravimetric (DTG) analyses of combustion behavior of Triassic amber indicated a main exothermal event near 437°C, higher than that of other known resins. The elemental composition of Triassic amber is consistent with well-known constituents of natural resins, although the sulfur content was higher, likely due to high sulfur content in the embedding sediment. Triassic amber from the Dolomites appears to be a new kind of fossil resin with unique stratigraphical and physico-chemical characteristics.

Mass spectrometry in the characterization of ambers. I. Studies of amber samples of different origin and ages by laser desorption ionization, atmospheric pressure chemical ionization and atmospheric pressure photoionization mass spectrometry.

Amber is a fossil resin constituted of organic polymers derived through complex maturation processes of the original plant resin. A classification of eight samples of amber of different geological age (Miocene to Triassic) and geographical origin is here proposed using direct mass spectrometric techniques, i.e. laser desorption ionization (LDI), atmospheric pressure chemical ionization (APCI) and atmospheric pressure photoionization (APPI), in order to obtain a fingerprint related to the amber origin. Differences and similarities were detected among the spectra with the four methods, showing quite complex spectra, full of ionic species in the mass range investigated (up to m/z 2000). The evaluation required statistical analysis involving multivariate techniques. Cluster analysis or principal component analysis (PCA) generally did not show a clear clustering with respect to the age of samples, except for the APPI method, which allowed a satisfying clustering. Using the total ion current (TIC) obtained by the different analytical approaches on equal quantities of the different amber samples and plotted against the age, the only significant correlation appeared to be that involving APPI. To validate the method, four amber samples from Cretaceous of Spain were analyzed. Also in this case a significant correlation with age was found only with APPI data. PCA obtained with TIC values from all the MS methods showed a fair grouping of samples, according to their age. Three main clusters could be detected, belonging to younger, intermediate and older fossil resins, respectively. This MS analysis on crude amber, either solid or extract, followed by appropriate multivariate statistical evaluation, can provide useful information on amber age. The best results are those obtained by APPI, indicating that the quantity of amber soluble components that can be photoionized decreases with increasing age, in agreement with the formation of highly stable, insoluble polymers.

Plant-feeding mite diversity in Triassic amber (Acari: Tetrapodili)

Carnian-aged amber (c. 230 Ma) from north-eastern Italy contains the first pre-Cretaceous inclusions of arthropods, plant remains and microorganisms. Here, we report further recovery of mites from this Late Triassic amber, supporting the prediction of a diversity of arthropods to be found in this oldest known fossiliferous resin. Two new genera and species of the Tetrapodili lineage, Minyacarus aderces and Cheirolepidoptus dolomiticus, are described. They indicate, along with the two previously described taxa of these mites, Triasacarus fedelei and Ampezzoa triassica, from the same source, a quite flourishing group of already highly specialized, four-legged, phytophagous mites in those remote times. The diversity of character states found in these Triassic mites challenges some conceptions of polarities inferred from modern four-legged mites. A hierarchical distinction is made between the Tetrapodili as a higher category of mites, and two constituent superfamilies, the Eriophyoidea embracing c. 300 extant genera and 3500 species, and the new superfamily Triasacaroidea, accommodating the four Triassic taxa. Varied forms and sizes of bodies and mouthparts amongst these Triassic mites indicate different feeding strategies in adapting to specialize on the same host plant of the Cheirolepidiaceae, for which we first report entire shoots from this amber outcrop. The cheliceral stylets of Triasacaroidea are generally blunt, indicating that, unlike extant Eriophyoidea, they were less able to pierce surface plant cells. Rather, we suggest that they may have fed on mesophyll cells by access through leaf stomata, whose density and appropriate dimensions are revealed by our study of plant cuticles. Further findings of small arthropods from this source of amber are increasingly probable and of great potential interest in adding knowledge about their early evolution. http://zoobank.org/urn:lsid:zoobank.org:pub:279BE1F3-8667-48D9-BEE8-F7F22C5DEF7D