1,721,303 research outputs found
The Middle Triassic vertebrate levels in the Western tethys: are fossil fishes useful for biostratigraphy?
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Feeding specialization in Late Triassic fishes
No full textThe ichthyofauna of the Zorzino Limestone represents an important proof of the richness and variety
reached by bony fishes during the Norian and, at the same time, it testifyies the beginning of the faunal
transition which will be realized during the Jurassic. The thousands of specimens and the extraordinary quality
of preservation found in the fossiliferous levels of this unit allowed, in the last years, not only to follow such a
crucial moment in the evolution of vertebrates, but also to reconstruct the mode of life and the trophic
adaptations reached by the different groups, living in the depositional basins. As evidence of this peculiar
evolutionary period, the large predators at the highest trophic levels are still represented by ’primitive’ basal
actinopterygians; on the contrary, the most derived neopterygians specialized in durophagy, a trophic niche
previously almost unexploited by actinopterygians. Within the main trophic categories, anyway, we can find
different morphological specializations, which probably allowed the fishes to exploit most of the available
trophic resources
A new basal actinopterygian fish from the Late Ladinian of Monte San Giorgio (Canton Ticino, Switzerland)
No full textA new taxon of Late Ladinian basal actinopterygian is described on the basis of a single specimen from the Meride Limestone (Kalkschieferzone) of Meride (Canton Ticino, Switzerland). The species is characterized by a single plate-like branchiostegal, a suboperculum larger than the operculum, a maxillary fixed and posteriorly expanded, a large and rectangular dermopterotic and a large triangular dermosphenotic; the scales are rectangular to rhomboidal, the lepidotrichia of median fins are segmented from their base and the caudal fin shows epaxial rays. These features resemble the condition of the Redfieldiiformes, a freshwater fish group, whose presence in Europe is still controversial, owing to poor preservation of specimens found so far
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
A proposito di Harrison
No full textEsistono davvero le “persone”? E cosa dire del “linguaggio”, del “discorso” o della “cultura”? Fino a che punto le reti sociali hanno determinato la specie umana in quelli che consideriamo come i suoi tratti costitutivi? Cosa unisce matematica e sociologia? Domande tanto ambiziose e originali trovano risposte altrettanto innovative in questo volume, in cui si propone la traduzione italiana di due saggi di uno degli ultimi maestri della sociologia americana. Muovendosi con eleganza tra ambiti concettuali e metodologici differenti, Harrison C. White analizza i fondamenti logici ed epistemologici di un approccio attualmente tanto utilizzato quanto raramente compreso in profondità: la social network analysis. I numerosi neologismi appositamente coniati – “forchette bayesiane”, “commutazioni”, “netdom”, “nodi del futuro”, “soluzioni d’angolo” – vengono inquadrati e presentati dai curatori attraverso una guida introduttiva alla lettura
New perleidiforms from the Triassic of the Southern Alps and the revision of Serrolepis from the Triassic of Würtemberg (Germany)
No full textA new actinopterygian genus, Felberia gen. nov., is described on the basis of a few, well-preserved specimens from the Ladinian Kalkschieferzone of Meride (Canton Ticino, Switzerland), and of some fragmentary remains from the Carnian localities of Oltre il Colle (BG) and Raibl-Cave del Predil (UD). The new genus, belonging to Perleidiformes, is characterized by a deep body covered with narrow and high, strongly ornamented, but thin scales. The head is deep as well. It shows a preoperculum with equal-sized dorsal and ventral regions, an operculum larger than the suboperculum, and a small gape with teeth that are long, pencil-like and protruding on the oral margin, and stout and acuminate on the palatal bones. The fins are long and delicate. Dorsal and anal fins are located close to the tail, which is characterized by seven epaxial rays and a ventral lobe slightly larger than the dorsal. The morphology of the new genus, with its deep, laterally compressed body and its peculiar dentition, suggests a specialized feeding habit, such as preying on small crustaceans on a rough bottom: the prey could have been seized with the marginal protruding teeth and then crushed by the strong palatal ones.
The systematic position of the genus Serrolepis Quenstedt from the Lettenkohle of Württemberg, is also discussed, based on comparisons of part of the original material with these new well-preserved specimens. Due to the morphology of both scales and palatal teeth, Serrolepis is moved from the order Semionotiformes to the order Perleidiformes
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