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S. L. Utschenko, Ciceron e il suo tempo, Biblioteca di storia antica, I. A cura di M. Mazza. Prefazione di Filippo Cassola , 1975
No full textAchard Guy. S. L. Utschenko, Ciceron e il suo tempo, Biblioteca di storia antica, I. A cura di M. Mazza. Prefazione di Filippo Cassola , 1975. In: Revue des Études Anciennes. Tome 78-79, 1976, n°1-4. pp. 280-281
Revision of the conodonts of key Upper Triassic Tethyan sections: A step forward in definition of the Carnian/Norian boundary and new correlation options
No full textThe need to find a biomarker to define the Carnian¬Norian boundary resulted in appreciable revision of the taxonomy of the Upper Triassic P1 conodont elements in recent years. Pizzo Mondello (Sicily, Italy) is a GSSP candidate for the Norian and provides the most continuous and valuable conodont record for the Tethys: in 2004 seven species were recognized for the Upper Carnian-Lower Norian interval at Pizzo Mondello, whereas today 42 have been identified. Among these, seven new species are defined here. Since the Pizzo Mondello record could make it the world reference for Late Triassic conodont biostratigraphy, its correlation potential with other sections is fundamental. For this purpose, the conodont faunas of the Tethyan key sections Silická Brezová (Slovakia), Bölücektasi Tepe and Erenkolu Mezarlik (Turkey) were revised. This revision enabled recording the occurrence of newly established species in much of the Tethys. Species that are potentially useful for definition of the C/N boundary were discriminated in all these sections: Epigondolella quadrata Orchard, E. rigoi Noyan & Kozur, Carnepigondolella gulloae Mazza & Rigo and species of the Metapolygnathus communisti Hayashi group. The same succession of conodont bioevents were identified in all investigated sections, confirming that the Pizzo Mondello conodont record is representative for the entire Tethys. These results open the possibility of new correlation options throughout the Tethyan realm, solving some biostratigraphic discrepancies raised in past years, and laying the groundwork for discriminating a truly reliable biovent for definition of the C/-N boundary
Why generic turnovers in Carnian/Norian conodonts?
No full textConodont biostratigraphy around the Carnian/Norian boundary is rather problematic because of the apparent provincialism of most of the conodont species. New biostratigraphic data from Pizzo Mondello, Western Sicily, Italy (a 400 m thick succession of hemipelagic limestones, belonging to the Cherty Limestone), point out clear relationships among the three most widespread conodont genera Carnepigondolella, Metapolygnathus, Epigondolella and allow to identify particular trends in the genera turnovers which affected the real conodonts stratigraphic distribution.
The first 48 meters of the section are largely dominated by the genus Carnepigondollella, with some Paragondolellae, only sporadic Metapolygnathids (M. mersinensis along with transitional forms P. noah - M. communisti) and few representatives of Epigondolella orchardi. In the overlaying 17 meters, the genus Carnepigondolella and transitional forms P. noah - M. communisti disappear, replaced by the genus Epigondolella (several E. quadrata). The genus Metapolygnathus is still rare. In the following 10 meters, a mass occurrence of the M. communisti group along with M. primitius is present, while the genus Epigondolella disappears. Another genera overturning takes place in the last 30 meters of the section, where advanced Epigondolellae (triangularis group) almost replace Metapolygnathids (only few M. parvus still occur). After comparisons with sedimentological data (Nicora et al., 2007) and geochemical variations (d13C or d18O; Muttoni et al., 2004), at Pizzo Mondello section, the turnovers of conodont genera around the Carnian/Norian boundary might be likely explained by competition of Carnepigondolella versus Metapolygnathus and, subsequently, of Epigondolella versus Metapolygnathus, or by invasions of conodont species from other domains (North America; see Noyan and Kozur, 2007 and references herein)
Taxonomy and phylomorphogenesis of the Carnian/Norian conodonts from Pizzo Mondello section (Sicani Mountains, Sicily)
No full textCARNIAN/NORIAN CONODONTS FROM THE PIZZO MONDELLO SECTION (MONTI SICANI, WESTERN SICILY), GSSP CANDIDATE FOR THE BASE OF THE NORIAN: INTEGRATED BIOSTRATIGRAPHY, PHYLOGENY AND STABLE ISOTOPE ANALYSES.
No full textPizzo Mondello section (Sicani Mountains, Western Sicily, Italy), is one of the best localities for the definition of the Carnian/Norian boundary (CNB). The section is a 430 m thick continuous succession of marine limestones, characterized by uniform facies, ranging from Late Carnian to Rhaetian (Upper Triassic), named Calcari con selce. The section is entirely exposed and it shows high sedimentation rates of 20-30 m/m.y. (Muttoni et al., 2004). Pizzo Mondello section is not affected by diagenetic overprint and it thus preserves the original paleomagnetic and geochemical record and, moreover, it yields several biostratigraphically significant fossil groups. The conodont and radiolarian records are in fact very rich and, furthermore, the Calcari con Selce of the Western Sicily, and especially of the Sicani Mountains, are well known all over the world for the exceptionally rich and well preserved Late Carnian to Early Norian ammonoid faunas studied by G.G. Gemmellaro (1904) and for the very rich halobiid record (Gemmellaro, 1882; Montanari & Renda, 1976; Cafiero & De Capoa Bonardi, 1982; De Capoa Bonardi, 1984; Levera, 2009: PhD Thesis in progress). At present conodonts are considered the most useful tool to define the CNB.
Thus, in order to find the most suitable conodont bioevent as primary biomarker for the CNB and to solve some problematic issues concerning the biostratigraphy and phylogeny of some Upper Triassic conodonts, the first 143 m of the section, where the CBN interval is located, were sampled in detail to conduct integrated taxonomic, biostratigraphic, phylogenetic and ecological studies on the conodont populations.
The five most widespread Upper Triassic conodont genera (Paragondolella, Carnepigondolella, Metapolygnathus, Epigondolella and Norigondolella) have been revised in detail: this revision allowed to make very accurate biostratigraphic correlations of Pizzo Mondello with the other most complete Upper Triassic sections in the world, and to recognize some discriminating morphological features for the separation of these five genera and many others for the classification of the species. The changes in the conodont platform morphology observed through the section provided the following trends in the evolution of the pectiniform elements: a) the forward-shifting of the pit; b) the shortening of the platform; c) the gradual posterior prolongation of the keel end and d) the appearance of nodes on the platform margins and the evolution of nodes into denticles. Species belonging to the five studied genera have been thus assigned to two separate monophyletic lineages: i) the Paragondolella-Metapolygnathus lineage and ii) the Carnepigondolella-Epigondolella lineage.
Nevertheless, the phylogenetic relationships of some species remained still problematic. In order
to solve these problems, numerical cladistic analyses have been applied to the studied species. The morphological characters used to classify conodont species have been thus codified to generate numerical matrices and then analyzed by PAUP software (Swofford, 2002) under the parsimony criteria. The cladograms evidenced morphological relationships among genera and species, showing that the evolutionary trends identified are supported by the most parsimonious character states distribution among taxa, confirming the importance of the considered characters for the conodont systematic and revealing also other new important diagnostic characters. The cladistic analyses clarified thus the phylogenetic relations between the studied taxa: Paragondolella resulted the most probable forerunner genus of all the other Upper Carnian/Norian genera and Norigondolella is strictly related to it; Metapolygnathus and Epigondolella are recognized as two monophyletic groups while Carnepigondolella as a polyphyletic group; the two lineages have been confirmed and the systematic positions of problematic (e.g. Carnepigondolella nodosa and “Metapolygnathus communisti B”) and key species (e.g. Epigondolella quadrata and Metapolygnathus communisti) for the definition of the CNB have been better delineated.
Given the richness of the conodont populations, a statistical approach was also applied. The quantitative curves of the absolute abundances for each genus showed potential ecological competition between Paragondolella-Carnepigondolella and later between Metapolygnathus-Epigondolella (and partially between Epigondolella-Norigondolella). This ecological behaviour supports the phylogenetic relationships among Norigondolella, Paragondolella and Metapolygnathus, and between Epigondolella and Carnepigondolella. Furthermore, cross checks of the quantitative curves evidenced the presence of three major turnovers, named T1, T2 and T3: at event T1 Carnepigondolella is replaced by its descendant Epigondolella in an evolutionary step; at event T2 Epigondolella is substituted by the mass occurrence of Metapolygnathus and at event T3 Metapolygnathus is succeeded by more evolved Epigondolellae and by Norigondolella. Looking for environmental explanations to these biological events, the conodont assemblages were compared to coeval δ18O and δ13C isotopic curves, based on new data from Pizzo Mondello. From the comparison, a correspondence appeared between higher 13C/12C ratios and the interval between events T2-T3, but not with event T1, in accordance with the interpretation of event T1 as an evolutionary turnover. In more detail, we observe the possible influence of environmental conditions on the absolute abundances of all the studied genera: while Epigondolella proliferates when seawater δ13C ranges between 2.1‰ and 2.5‰, Carnepigondolella proliferates in the range between 1.6‰ and 2.1‰; Metapolygnathus instead appears to be limited to environmental conditions related to higher δ13C values in the seawater.
Given the results provided by the phylogenetic and ecological studies, the FAD of Epigondolella quadrata results the best primary biomarker for the definition of the CNB: this species is worldwide spread, its phylogenetic lineage is, it is globally recognized and its FAD (coinciding with event T1) is not triggered by any ecological perturbation. The FAD of Metapolygnathus communisti in sample NA35 is another possible biomarker, but its FAD, coinciding with event T2, is ecologically controlled and till now not found in North America and, thus, not a good species for global correlations
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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