1,721,044 research outputs found
Macroraptorial sperm whales (Cetacea, Odontoceti, Physeteroidea) from the Miocene of Peru
Full text linkThe three extant sperm whale species, the giant Physeter macrocephalus and the diminutive Kogia species, are relict members of the superfamily Physeteroidea, whose evolutionary history is traced back to the late Oligocene. Although well-preserved and diagnostic cranial remains are relatively scarce, the physeteroid fossil record reveals a considerable degree of morphological disparity (especially during the Miocene), suggesting that sperm whales occupied a broader range of ecological niches in the past. Here, we provide detailed descriptions and a (re)analysis of several new and established middle-late Miocene stem physeteroids from the Pisco Formation of southern Peru. In particular, we (1) further describe the holotype of Acrophyseter deinodon from the latest Tortonian-Messinian of Sud-Sacaco, with new information on previously unpublished portions of the skull (including the ear bones) and a discussion of its masticatory musculature; (2) diagnose a new species of Acrophyseter, A. robustus sp. nov., based on a finely preserved skull with some associated cranial remains from the late Serravallian-Tortonian (> 9.2 Ma) of Cerro la Bruja; (3) provisionally refer a skull from Cerro los Quesos, which has been radiometrically dated to the Messinian (6.9-6.7 Ma), to Acrophyseter sp.; and (4) further describe the skull of the giant raptorial sperm whale Livyatan melvillei from Cerro Colorado, recently re-dated to the Tortonian (9.9-8.9 Ma) based on the associated diatom fauna and Ar/Ar dating. A phylogenetic analysis based on 53 characters and 21 physeteroid species confirms the monophyly of Acrophyseter and groups this genus with the larger, middle to late Miocene macroraptorial stem physeteroids Brygmophyseter and Zygophyseter. With its unique supracranial basin morphology, Livyatan forms a separate, more crownward stem physeteroid lineage. Combined with biostratigraphic information, our cladistic hypothesis allows us to discuss the time of origin of the main physeteroid clades, as well as trends in the evolution of their body size, dentition, temporal fossa and supracranial basin
Physeteroids from the Miocene of Peru: new data on Acrophyseter and Livyatan supports macroraptorial feeding in several extinct sperm whales
No full textWith only three extant species, modern sperm whales (Odontoceti, Physeteroidea) are generally considered as relicts of a previously more diversified clade, originating
during the late Oligocene and reaching its maximum diversity in the Miocene. Displaying a spectacular size disparity, modern Kogia spp. (pygmy and dwarf sperm whales) and Physeter (giant sperm whale) share several morphological features (dental reduction, slender mandibles, and small temporal fossa) correlated to a specialized suction feeding technique on disphotic to mesopelagic prey. Although remaining scarce, the fossil record of sperm whales suggests a broader past ecological diversity; based on cranial and dental characters, several middle to late Miocene taxa (the medium size Acrophyseter, the large Brygmophyseter and
Zygophyseter, and the giant Livyatan) were tentatively interpreted as macroraptorial feeders, using massive teeth deeply embedded in robust upper and lower jaws to catch proportionally large prey. Together with the study of two new Acrophyseter skulls, a detailed description of the type material of A. deinodon and L. melvillei (both originating from Miocene levels of the Pisco Formation, Peru) provides new clues about their hypothetical feeding strategies.
The analysis of the specimens followed different lines: (1) basic craniomandibular anatomy and comparison; (2) reconstruction of the musculature for adduction/abduction of the mandibles; (3) bone pathology including the description of buccal maxillary exostoses in A. deinodon; and (4) tooth wear. Observations and resulting interpretations point to a feeding technique involving intense use of teeth via powerful bites, contrasting markedly with the capture technique in both Kogia and Physeter. Placed in a phylogenetic context, the morphology of the oral apparatus in these macroraptorial sperm whales is thought to represent a combination of plesiomorphic and derived characters. Finally, a detailed sedimentological and paleontological analysis of the fossil-rich localities of Cerro Colorado and Cerro los Quesos yielded a vast amount of data about the faunas associated to Acrophyseter and Livyatan; the mapping of several hundreds of marine vertebrate specimens, as well as their positioning along stratigraphic sections, provides valuable indications about potential prey of these extinct sperm whales
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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
Author-wise bibliometric analysis based on entropy.
No full textAuthor-wise bibliometric analysis based on entropy.</p
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