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The biogeography of the late Paleozoic floras of India
No full textThis paper reviews the biogeography of Paleozoic floras in India and addresses some of the important biogeographic questions that have been raised regarding the distribution of floras and faunas on the subcontinent. Little is known about the Silurian and Devonian floras. Plants of this age have been reported sparingly from the extra-peninsular Panjab-Kashmir Himalaya region. On the basis of the available evidence, land plants comprised a cosmopolitan world flora until the end of the Early Carboniferous. The beds above the Lower Carboniferous strata of Gondwanaland record a sudden large-scale extinction of plants due to widespread glaciation. The Gondwana glaciation is believed to have ranged from the Upper Carboniferous to the Upper Permian in different parts of the supercontinent. The earliest post-glacial fossiliferous strata of Upper Carboniferous/Lower Permian age in India are found in the Talchir Series which has been divided into two stages, the Talchir and the Karharbari. Talchir floras are depauperate and appear to have lived under unfavorably cold conditions. Approximately 20 Talchir taxa are reported. The floras are dominated by Gangamopteris. Conditions during the Karharbari in peninsular India favoured the development of diverse floras and extensive, thick peat accumulations. On the basis of floral evidence, climatic conditions are interpreted to have been milder and warmer than during the Talchir Stage. Gangamopteris still dominated but other glossopterids were becoming abundant and the pre-conifers first emerged. The Talchir series is overlain by the Damuda Series. The time during which the Damuda strata were being deposited is divided into three stages, the Barakar, Barren Measures (Kulti or Ironstone Shales), and the Raniganj. These stages are characterized by the increased diversification of Glossopteris and the waning of Gangamopteris. The tectonic movement of Gondwanaland northward away from its southern polar position resulted in gradually ameliorating temperatures during the Permian period. By the beginning of the Triassic, northward plate movement had positioned the subcontinent within an arid realm. Except for some rare occurrences of Glossopteris and Sphenophyllum, the glossopterids became extinct by the Triassic and were replaced by the Dicroidium floras. Some of the important biogeographic problems relating to the distribution of the late Paleozoic floras of India are concerned with the location of the northern, northeastern, and northwestern boundaries of Gondwanaland. The occurrence of non-Gondwanan forms at these localities could be interpreted as an indication that paleoecotones developed in the border areas between biogeographic provinces. However, an alternative hypothesis suggests that the areas of mixed floras constitute evidence that a microcontinent lay between the Eurasian plate and Gondwanaland. The occurrence of marine strata in the middle peri-Tethys region in the Salt Range and the Himalayan localities in Kashmir has long been established. However, the discovery of shelled faunas and smooth-walled acritarchs interpreted to be of marine origin throughout peninsular India indicates that the possibility of widespread marine transgressions into Lower Gondwana strata situated far from the Tethys will have to be considered
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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