1,720,967 research outputs found
“Haliterium” bellunense Zigno, 1875 from the Chattian of Cavarzano (Belluno Northern Italy): systematic review and paleobiogeographic considerations
No full textEvolution of Sirenian Pachyosteosclerosis, a Model-casefor the Study of Bone Structure in Aquatic Tetrapods.
No full textOsteosclerosis, or inner bone compaction, and
pachyostosis, or outer hyperplasy of bone cortices (swollen
bones), are typical features of tetrapods secondarily adapted
to life in water. These peculiarities are spectacularly
exemplified by the ribs of extant and extinct Sirenia. Sea
cows are thus the best model for studying this kind of bone
structural specializations. In order to document how these
features differentiated during sirenian evolution, the ribs of
15 species, from the most basal form (Pezosiren portelli) up
to extant taxa, were studied, and compared to those of other
mammalian species from both morphometric and histological
points of view. Pachyostosis was the first of these
two specializations to occur, by the middle of the Eocene,
and is a basal feature of the Sirenia. However, it subsequently
regressed in some taxa that do not exhibit hyperplasic
rib cortices. Osteosclerosis was only incipient in
P. portelli. Its full development occurred later, by the end
of the Eocene. These two structural specializations of bone
are variably pronounced in extinct and extant sirenians, and
relatively independent from each other, although frequently
associated. They are possibly due to similar heterochronic
mechanisms bearing on the timing of osteoblast activity.
These results are discussed with respect to the functional
constraints of locomotion in water
Peri-Messinian dwarfing in Mediterranean Metaxytherium (Mammalia: Sirenia): evidence of habitat degradation related to Mediterranean desiccation?
No full textPeri-Messinian Dwarfing in Mediterranean Metaxytherium (Mammalia: Sirenia): Evidence of Habitat Degradation Related to the Messinian Salinity Crisis
No full textOne lineage of dugongid sirenians (Metaxytherium spp.) inhabited Old World waters
throughout the Miocene and Pliocene. During the Early to Late Miocene (M. krahuletzi,
M. medium) and the Early and Middle Pliocene (M. subapenninum), these animals were
consistently large; however, the earliest Pliocene member of this lineage, M. serresii,
was distinctly smaller, as shown by the population sample from Montpellier, France. In
1987 Domning and Thomas interpreted this as ecophenotypic dwarfing and attributed it
to suboptimal foraging habitat in the wake of the Messinian Salinity Crisis (MSC). This
explanation implied that the reduction in body size should have first occurred near the
onset of the MSC, and should have been reversed after its end, or whenever adequate
seagrass resources again became available. Recent discoveries of Late (post-M. medium)
Miocene M. serresii in Calabria, Italy and the attribution to the latest Miocene of the M.
serresii records from As Sahabi, Libya, previously referred to the Early Pliocene,
support the hypothesis of peri-Messinian dwarfing. This decrease in size is well
evidenced in this study where we have analysed the pattern of body size change from
the Early Miocene to the Middle Pliocene of these and other diagnostic European and
Libyan fossils of Metaxytherium. We have also observed an increase in tusk size of
these sirenians beginning with M. serresii that could be related to a shift to a diet richer
in rhizomes due to the degradation of food resources
Peri-Messinian dwarfing in Mediterranean Metaxytherium (Mammalia: Sirenia): evidence of habitat degradation related to the Messinian Salinity Crisis
No full text
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
- …
