146 research outputs found
Guadalupian (Middle Permian) paleobiogeography of the Neotethys Ocean
No full textA matrix of presence/absence data of Guadalupian (Middle Permian) brachiopod genera from Sicily, Tunisia, Oman, Turkey, north Iran, central Afghanistan, Karakoram, Salt Range, and south Thailand has been analyzed by multivariate methods (cluster analysis, principal coordinate analysis, minimum spanning trees) and Parsimony Analysis of Endemicity. The application of these different and independent paleobiogeographical methods has led to the individuation of three bioprovinces: the Cathaysian (Sicily and Tunisia), Cimmerian (Oman, Turkey, north Iran, Salt Range, south Thailand) and Transhimalayan (Karakoram and central Afghanistan) provinces. These provinces have been placed on a paleogeographical reconstruction based on paleomagnetic data, which we used to decipher the principal factors that governed brachiopod distribution in the Neotethys Ocean during the Guadalupian. As a conclusion, the pattern of biotic provinces at this time resulted from the complex interplay between latitudinal thermal gradient, oceanic paleocurrents, and the continental drift of the Cimmerian terranes across zonal climate belts. (C) 2012 International Association for Gondwana Research. Published by Elsevier B.V. All rights reserved
Biomineralization and global change : A new perspective for understanding the end-Permian extinction
No full textWe investigated the kill mechanisms of the end-Permian mass extinction by analyzing patterns in biomineralization of marine invertebrates. The microstructures of Upper Permian brachiopod organocarbonate shells show the demise of the production of fabrics with a columnar layer-which has less organic matrix-in favor of more organic-rich shells at the end of Permian. Also, in the 100-120 k.y. interval prior to the Permian-Triassic boundary (PTB), the Rhynchonellata had small calcite structural units (fibers) and thus a higher shell organic content, whereas the Strophomenata were not able to produce smaller units. This suggests that the two classes had a different capacity to cope with environmental change, with the Rhynchonellata being more able to buffer against pH changes and surviving the PTB, whereas the Strophomenata became extinct. The observed trends in biomineralization are similar to the patterns in extant marine invertebrates exposed to increasing pCO2 and decreasing pH, indicating that ocean acidification could have been one of the kill mechanisms of the mass extinction at the PTB
Frost action and human occupation during the Late Pleistocene in the Italian Southern Alps : micromorphological evidences from the Caverna Generosa cave
No full textThe Late Pleistocene has been characterised by frequent and intense climatic oscillation, well recorded in the Caverna Generosa cave deposits. In this work, micromorphological analyses have been performed on samples from the cave where the stratigraphy is particularly well exposed and complete, in order to obtain temporal and spatial information on climate- and human-related processes during MIS3 and 4. The older layers (more than 50 ka BP - Before Present - old) record a very cold time interval, where ice did not melt during the warmer season, and with little or no vegetation outside the cave. During this cold stage, probably, humans spent a short period in the cave, using bones to light the fire and, later, cave bears dug their hibernation beds in the innermost room. Subsequently (between 50 ka BP and 40 ka BP) a relatively brief climatic amelioration should have occurred, leading to the onset of ice melting during the summer season. Between 40 ka BP and 30 ka BP, loess deposited in the cave entrance, indicating cold and arid conditions in the area. After loess deposition, recovered wet conditions have re-established with freeze and thawing processes influencing the sediments
Foreword - Proceedings of the 8th International Brachiopod Congress “Brachiopods in a changing planet: from the past to the future” (Milano, 10-14 September 2018)
No full textThe 8th International Brachiopod Congress took place in the prestigious venue of the Univer¬sity of Milano, Italy, in September 2018, after the previous edition held in Nanjing, China, in 2015. 150 participants from universities and re¬search institutes from all over the world attended the meeting, from Argentina, Armenia, Austria, Belgium, Canada, China, Czech Republic, Den¬mark, France, Germany, Hungary, Iran, Israel, It¬aly, Japan, New Zealand, Poland, Russia, Slovakia, Spain, Sweden, United Kingdom, and United States of America. Besides oral and poster scientific sessions, pico-presentations of young researchers, and two prestigious plenary lectures, the Congress was preceded and followed by three field trips (Spain, United Kingdom and Sicily), and by two mid-con¬gress day excursions at Castell’Arquato and Grigna Mountains. During the congress, all the topics and the re¬cent advances in the study of brachiopods, marine invertebrates that have dominated the Palaeozoic seas and had an important role in the Phaneorozo¬ic benthic communities, have been touched: from systematics and evolution to biostratigraphy, pala¬eoecology, palaeobiogeography, mass extinctions, and the biology of recent taxa. One of the novelties of this edition was a session dedicated to brachio¬pod shells as biomineral archives of fundamental importance to understand the evolution of marine calcifiers during climate and environmental changes in recent and deep time. So, also biomineralization and geochemistry were among the topics of the event. The high scientific level, activity and wide and interdisciplinary interests of the brachiopod re¬searchers’ community are testified by the numerous contributions received for the Proceedings of the 8th International Brachiopod Congress, 16 of which are published open access in issue 125/3 of Rivista Italiana di Paleontologia e Stratigrafia
Sovranità e reciprocità (potere e libertà)
No full textThe Essay deals with juridical and political sovereignty. The Author observes that modern scholars struggle to create an affordable theory on the relationship between power and individual or collective rights, especially on the link betwenn "compliance" and "protection", which was the core of the traditopnal doctrine on sovereignty. In this context, the Author recommends to reinterpret politics, law and constitutions from the point of view of a mutual exchange of good and evil, of rights and duties, between individuals, according to an ancient theory, which was not properly analysed in modern times
Le "autorità" alla ricerca dell' "indipendenza"?
No full textThe author offers an interpretation of the independent authorities which diverges from the one current in legal science and embraced both by those who regard the authorities as an means to renew and develop the protection of constitutional freedoms, and by those who regard them as a subversion of principle in the Italian organization of the public powers. The author contests in particular the utility of including provisions disciplining the independent authorities in the constitutional reform law. On the one hand, sanctioning the independence of the public power of the "authorities" would give fatal rigidity to a system of relationships whose principle quality is its flexibility and elasticity. On the other hand, if the independent authorities manifest a with-drawal from policy by the administration, the retreat from the principles and rules of administrative law should be regarded with suspicion, since it may attenuate the guarantees ordinarily afforded to citizens
The shell fabric of Palaeozoic brachiopods: patterns and trends
No full textunderstand the evolution and adaptations of marine calcifiers in time. Therefore, a
detailed study of the shell microstructure of Cambrian to Devonian brachiopods from
Iran is here presented. The shell of 38 brachiopod species, representatives of 22 families
and nine orders, has been analysed using scanning electron microscope (SEM), and a
database has been built, including macro‐ and micro‐morphological features used to
characterize the two‐ or three‐layered brachiopod shells. Two main microstructural
variants of the secondary layer have been analysed: fibrous and laminar fabrics. The
fibrous layer has a fabric comparable to that of recent brachiopods, whereas the laminar
fabric is more complex in its structural organization and has no recent analogue. In
cross‐section, the laminae are thinner than the fibres, and much less variable in size.
There is evidence that taxa with laminar microstructure have diverged from the
Billingsellida and then followed a trend implying a decrease in thickness of the laminae.
Our linear discriminant analysis (LDA) shows that shell fabric and shell thickness are
powerful predictors of shell shapes, which in turn approximate the brachiopod lifestyles
and ecological strategies. Taxa with a fibrous fabric are mostly biconvex, whereas
the groups with a laminar secondary layer are associated to a variety of shell shapes
and lifestyles. Even if the relations between shell fabric and shell thickness remain enigmatic,
as well as the metabolic cost they imply, shell fabrics, and the possible structural
and mechanical advantages conferred, could have played a role in the evolutionary success
of the Strophomenata during the Palaeozoic
Triassic stratigraphy in the island of Hydra (Greece)
No full textThe Triassic sedimentary succession, cropping out in the island of Hydra, is described. A typical passive continental margin succession is recorded in the Triassic of Hydra, suggesting its affinity with the Subpelagonian domain. -from Author
Hydrodynamic advantages in the free-living spiriferinide brachiopod Pachycyrtella omanensis: functional insight into adaptation to high-energy flow environments
No full textImmobile benthic organisms lacking attachment or cementation mechanisms are considered to be best adapted to quiet bottom environments. Since the free-living Lower Permian spiriferinide brachiopod Pachycyrtella omanensis inhabited a sandy substrate with high-energy water flow, flume experiments were performed to show the possible hydrodynamic advantages of shell morphology in postural stability and generation of feeding flows. Modelling indicates that a vertical position, with the commissure plane perpendicular to the seabed, was the most unstable, although it is considered to have been its original life position. On the other hand, the passive flow inside the model in vertical position exhibited vortex movement with constant degree of inhalent flow and exhalent flow, conferring advantages on the effective filtration of food particles using a spiral lophophore. The intensity and movement of the passive flow for feeding could have been adjusted through changes in the angle of opening of the valves. As the shoreface habitat was affected by oscillatory flows, a small-sized animal could have undergone a high risk of burial, while an increase in size would have led to easier removal from the sandy bottom. To avoid both physical risks, Pachycyrtella developed a thick shell with a high rate of growth, specifically increasing the weight of the ventral umbo without altering its morphofunction to generate passive feeding flows. Biomechanics, functional morphology, opportunistic species, Pachycyrtella, Spiriferinida, suspension feeder
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