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Strength, timing, setting and cause of mid-Palaeozoic extinctions
No full textMuch has been written over the last 20 yr on the Upper Kellwasser Event (Frasnian/Famennian or F/F boundary) as the major extinction event of the Middle Palaeozoic (Devonian) and as the fifth largest extinction event in the Phanerozoic; this opinion was based on analysis of family range data. These views are misleading. A current analysis of family extinction data, largely based on The Fossil Record 2, but updated in some respects, supersedes the data base of Raup and Sepkoski (1982) and shows that the Famennian has the highest total family extinction of marine taxa, with the Givetian in second and Frasnian in third place. If these new data are related to current (unreliable) estimated length of stages, then the severest extinction rates are: first, the Givetian at 14.2 family extinctions per Ma, secondly the Frasnian at 11.2 and thirdly the Eifelian at 6.8. Many short-term 'events' have been named for the Devonian based on short-term distinctive sedimentary and/or faunal perturbations. A review of these shows how they are often transgression/regression couplets, many with an association of anoxia and poor in benthos, or spreads of pelagic faunas, and some are phased and complex. Evidence is presented to suggest that the transgressive pulses correspond to warm temperatures which are terminated by cooling. Possible links with orbitally forced patterns are considered. A common explanation seems required, not just for the Kellwasser Event, but for all these events. The relation of the family stage extinctions, especially the Kacak, Taghanic, Kellwasser and Hangenberg Events, which are of much more limited duration, is discussed particularly in relation to new and more precise data of the extinction events known within these stages. In the absence of detailed studies for many groups, those that have been well documented may serve as a temporary proxy for other
Late Devonian biotic crisis: ecological, depositional and geochemical records: foreword
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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
Variations on the Author
Get PDF“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
Get PDFWe 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
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