1,720,998 research outputs found
A leafcutter bee trace fossil from the middle eocene of patagonia, Argentina, and a review of Megachilid (Hymenoptera) ichnology
Full text linkThe ichnospecies Phagophytichnus pseudocircus isp. nov. is described to include trace fossils characterized by leaf-margin excisions showing eccentricity values of 0.35-0.65 and more than 270 degrees of an arc, a non cuspate margin and vein stringers or necrotic flaps of tissue along the margin. A method for determining ellipse eccentricity was performed on leaf discs obtained from the nests of the modern leafcutter bee Megachile rotundata (Hymenoptera: Megachilidae), which provided objectively obtained values comparable to the trace fossil from the middle Eocene of Argentina and other world-wide ichnological records, historically and subjectively considered to be 'circular' trace fossils and attributed to leafcutter bees. The material described herein represents the first evidence for fossil Megachilidae from the Southern Hemisphere.Fil: Sarzetti, Laura Cristina. Museo Paleontológico Egidio Feruglio; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Nacional Patagónico; ArgentinaFil: Labandeira, Conrad C.. National Museum of Natural History; Estados Unidos. University of Maryland; Estados UnidosFil: Genise, Jorge Fernando. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Nacional Patagónico; Argentina. Museo Paleontológico Egidio Feruglio; Argentin
Rapid recovery of Patagonian plant–insect associations after the end-Cretaceous extinction
Full text linkThe Southern Hemisphere may have provided biodiversity refugia after the Cretaceous/Palaeogene (K/Pg) mass extinction. However, few extinction and recovery studies have been conducted in the terrestrial realm using well-dated macrofossil sites that span the latest Cretaceous (late Maastrichtian) and early Palaeocene (Danian) outside western interior North America (WINA). Here, we analyse insect-feeding damage on 3,646 fossil leaves from the latest Maastrichtian and three time slices of the Danian in Chubut, Patagonia, Argentina (palaeolatitude approximately 50° S). We test the southern refugial hypothesis and the broader hypothesis that the extinction and recovery of insect herbivores, a central component of terrestrial food webs, differed substantially from WINA at locations far south of the Chicxulub impact structure in Mexico. We find greater insect-damage diversity in Patagonia than in WINA during both the Maastrichtian and Danian, indicating a previously unknown insect richness. As in WINA, the total diversity of Patagonian insect damage decreased from the Cretaceous to the Palaeocene, but recovery to pre-extinction levels occurred within approximately 4 Myr compared with approximately 9 Myr in WINA. As for WINA, there is no convincing evidence for survival of any of the diverse Cretaceous leaf miners in Patagonia, indicating a severe K/Pg extinction of host-specialized insects and no refugium. However, a striking difference from WINA is that diverse, novel leaf mines are present at all Danian sites, demonstrating a considerably more rapid recovery of specialized herbivores and terrestrial food webs. Our results support the emerging idea of large-scale geographic heterogeneity in extinction and recovery from the end-Cretaceous catastrophe.Fil: Donovan, Michael P.. State University of Pennsylvania; Estados UnidosFil: Iglesias, Ari. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto de Investigaciones en Biodiversidad y Medioambiente. Universidad Nacional del Comahue. Centro Regional Universidad Bariloche. Instituto de Investigaciones en Biodiversidad y Medioambiente; ArgentinaFil: Wilf, Peter. State University of Pennsylvania; Estados UnidosFil: Labandeira, Conrad C.. Smithsonian Institution; Estados Unidos. University of Maryland; Estados Unidos. Capital Normal University; ChinaFil: Cúneo, Néstor Rubén. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Museo Paleontológico Egidio Feruglio; Argentin
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
Atlas of Plants and Animals in Baltic Amber. By W. WEITSCHAT and W. WICHARD (2002). Verlag Dr. Friedrich Pfeil, Munich (Germany). 256 pages, 92 color plates, 124 figures; 29 x 21.7 cm, hardcover; ISBN 3-931516-94-6; Euro 75,00, US$ 98.00.
No full textAppropriate 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
Book Reviews
Full text linkObra ressenyada: W. WEITSCHAT and W. WICHARD, Atlas of Plants and Animals in Baltic Amber. Munich: Verlag Dr. Friedrich Pfeil, 2002
Book Reviews
No full textObra ressenyada: W. WEITSCHAT and W. WICHARD, Atlas of Plants and Animals in Baltic Amber. Munich: Verlag Dr. Friedrich Pfeil, 2002
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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