L’icnoassociazione a tetrapodi del Bletterbach (Trentino Alto-Adige) e le sue relazioni con gli ecosistemi terrestri di fine Permiano

In questo articolo viene proposta un’analisi aggiornata dell’associazione a impronte di tetrapodi rinvenuta a partire dagli anni ’70 del secolo scorso presso la Gola del Bletterbach (Alpi meridionali, Italia nord-orientale) e una sua contestualizzazione su scala globale basata sull’integrazione di dati paleontologici e climatici. Lo studio evidenzia l’importanza dell’associazione a tetrapodi del Bletterbach quale record eccezionale di un ecosistema terrestre di bassa latitudine durante il Lopingiano (Permiano superiore). I risultati dell’analisi a scala ecosistemica forniscono inoltre evidenza di una forte correlazione tra la distribuzione dei principali cladi di tetrapodi erbivori (dicinodonti, pareiasauri, captorinidi) e la zonazione climatica latitudinale.In this paper we provide an updated review of the tetrapod footprint association discovered in the Bletterbach Gorge (Southern Alps, NE Italy) from the ‘70s. We provide global-scale analysis integrating paleontological and climatic data highlight the importance of the Bletterbach ichnoassociation as key reference for low-latitude terrestrial ecosystems during the Lopingian (Late Permian). Our results provide evidence for a tight correlation between the distribution of the main herbivorous tetrapod clades (dicynodonts, pareiasaurs, captorhinids) and the latitudinal climatic zonation

Dinosaur diversification linked with the Carnian Pluvial Episode

Dinosaurs diversified in two steps during the Triassic. They originated about 245 Ma, during the recovery from the Permian-Triassic mass extinction, and then remained insignificant until they exploded in diversity and ecological importance during the Late Triassic. Hitherto, this Late Triassic explosion was poorly constrained and poorly dated. Here we provide evidence that it followed the Carnian Pluvial Episode (CPE), dated to 234–232 Ma, a time when climates switched from arid to humid and back to arid again. Our evidence comes from a combined analysis of skeletal evidence and footprint occurrences, and especially from the exquisitely dated ichnofaunas of the Italian Dolomites. These provide evidence of tetrapod faunal compositions through the Carnian and Norian, and show that dinosaur footprints appear exactly at the time of the CPE. We argue then that dinosaurs diversified explosively in the mid Carnian, at a time of major climate and floral change and the extinction of key herbivores, which the dinosaurs opportunistically replaced

Ordering of Ge quantum dots on silicon surfaces via bottom-up and top-down approaches

The nanoscale ordering of inorganic semiconductor quantum dots (QDs) is crucial to obtain reliable structures for novel nanotechnological applications such as nanomemories, nanolasers and nanoelectronic devices. We have directly grown Ge QDs by physical vapour deposition (PVD) on Si(111), Si(100) and some of its vicinal surfaces and studied innovative bottom up techniques to order such nanostructures. Specifically, we harnessed naturally occurring instabilities due to reconstruction and intrinsic anisotropic diffusion in Si bare surfaces, such as step bunching and natural steps occurring in silicon vicinal surfaces, to order the QDs both in one dimension and in the plane. We have also shown the use of controlled quantities of surfactants, like Sb, dramatically improves the desired ordering. Moreover, we have assisted these self-assembling processes using top-down approaches like Focused Ion Beam (FIB) milling and STM nanoindentation to control the nucleation sites and the density of the Ge QDs. Real-time study of growth and self-assembly has been accomplished using Scanning Tunneling Microscopy imaging in UHV. An explanation of the occurring processes is given, and a software routine is used to quantify the ordering of the QDs both in pre-patterned and bare surfaces. Applications, mainly in the field of Nanocrystal Nonvolatile Memories, are discussed

Archosauriform footprints in the Lower Triassic of Western Alps and their role in understanding the effects of the Permian-Triassic hyperthermal

The most accepted killing model for the Permian-Triassic mass extinction (PTME) postulates that massive volcanic eruption (i.e., the Siberian Traps Large Igneous Province) led to geologically rapid global warming, acid rain and ocean anoxia. On land, habitable zones were drastically reduced, due to the combined effects of heating, drought and acid rains. This hyperthermal had severe effects also on the paleobiogeography of several groups of organisms. Among those, the tetrapods, whose geographical distribution across the end-Permian mass extinction (EPME) was the subject of controversy in a number of recent papers. We here describe and interpret a new Early Triassic (?Olenekian) archosauriform track assemblage from the Gardetta Plateau (Briançonnais, Western Alps, Italy) which, at the Permian-Triassic boundary, was placed at about 11° North. The tracks, both arranged in trackways and documented by single, well-preserved imprints, are assigned to Isochirotherium gardettensis ichnosp. nov., and are here interpreted as produced by a non-archosaurian archosauriform (erytrosuchid?) trackmaker. This new discovery provides further evidence for the presence of archosauriformes at low latitudes during the Early Triassic epoch, supporting a model in which the PTME did not completely vacate low-latitude lands from tetrapods that therefore would have been able to cope with the extreme hot temperatures of Pangaea mainland

Phylogenetic stability, tree shape, and character compatibility: a case study using early tetrapods

Phylogenetic tree shape varies as the evolutionary processes affecting a clade change over time. In this study, we examined an empirical phylogeny of fossil tetrapods during several time intervals, and studied how temporal constraints manifested in patterns of tree imbalance and character change. The results indicate that the impact of temporal constraints on tree shape is minimal and highlights the stability through time of the reference tetrapod phylogeny. Unexpected values of imbalance for Mississippian and Pennsylvanian time slices strongly support the hypothesis that the Carboniferous was a period of explosive tetrapod radiation. Several significant diversification shifts take place in the Mississippian and underpin increased terrestrialization among the earliest limbed vertebrates. Character incompatibility is relatively high at the beginning of tetrapod history, but quickly decreases to a relatively stable lower level, relative to a null distribution based on constant rates of character change. This implies that basal tetrapods had high, but declining, rates of homoplasy early in their evolutionary history, although the origin of Lissamphibia is an exception to this trend. The time slice approach is a powerful method of phylogenetic analysis and a useful tool for assessing the impact of combining extinct and extant taxa in phylogenetic analyses of large and speciose clades