1,720,997 research outputs found
New records of Miocene fossil birds of prey from western Kenya
No full textWe describe new fossil records of three diurnal birds of prey and an owl from four Miocene sites in western Kenya. All four new records are very similar to recent species present today in Kenya and include a vulture (cf. Aegypius monachus), a Goshawk (cf. Accipter tachiro) and a Chanting Goshawk (cf. Melierax metabates/canorus) as well as a small owl (cf. Otus senegalensis). All four new fossil taxa may represent the earliest known records for these genera
New records of fossil birds from the Pliocene of Kallo, Belgium
No full textWe present new records of fossil birds from the Pliocene deep marine deposits of the Kattendijk and Kallo Sands Formations of Belgium. Hitherto the only bird formally described from these deposits is the giant flying alcid Alca stewarti. Now we note the presence of two more named fossil species within the genus Alca (A. ausonia, A. antiqua), along with a fragmentary record of a taxon even larger than Alca stewarti. In addition to these seabirds, new records of a puffin (Fratercula sp.), a skua (Stercorarius sp.), and a small passerine (Allotacilla sp.) are presented. This collection of fossil birds comprises part of the first Pliocene avifauna to be described from Belgium and appears to be remarkably consistent in its composition to deposits of the same age in North America
Large euenantiornithine birds from the Cretaceous of southern France, North America and Argentina
No full textWe review historical approaches to the systematics of Enantiornithes, the dominant birds of the second half of the Mesozoic, and describe the forelimb remains of a new Cretaceous euenantiornithine. This taxon is known on the basis of fossil specimens collected from southern France, Argentina and the United States; such a wide geographical distribution is uncharacteristic for Enantiornithes as most taxa are known from single localities. Fossils from the Massecaps locality close to the village of Cruzy (Hérault, southern France), in combination with elements from New Mexico (USA) and from the Argentine locality of El Brete (Salta Province) testify to the global distribution of large flighted euenantiornithine birds in the Late Cretaceous. We discuss the systematics and taxonomy of additional isolated bones of Enantiornithes that were collected from the Argentine El Brete locality in the 1970s; the presence of these flying birds in Cretaceous rocks on both sides of the equator, in both northern and southern hemispheres, further demonstrates the ubiquity of this avian lineage by the latter stages of the Mesozoi
New specimens of a fossil ostrich from the Miocene of Kenya
No full textFossilised hind limb bones from the late Middle Miocene (approximately 14 million-year-old [MYA]) Fort Ternan, Kadianga West and Ngorora localities in Western Kenya indicate the presence of a new representative of the ostrich genus Struthio. These new fossils represent some of the oldest known records for Struthio yet described, slightly younger than Struthio coppensi, from the Lower Miocene of Namibia. Because the four sub-species of the modern-day ostrich (Struthio camelus camelus, Struthio camelus australis, Struthio camelus massaicus, and Struthio camelus molybdophanes) inhabit the plains of Africa, and as recently as the 1940s, a fifth sub-species was also present in the Middle East and Saudi Arabia (Struthio camelus syriacus), records of Struthio from Kenya and Namibia testify to the much wider distribution of these cursorial birds in the relatively recent past. This is further supported by the very high frequency of ostrich eggshell fragments found across Africa and Eurasia, which vastly outweighs the amount of skeletal material uncovered over the last century
A new species of large auk from the Pliocene of Belgium
No full textA new species of fossil auk, Alca stewarti from the Kattendijk Sands Formation (early Pliocene) of Belgium is described. Preserved elements of this new species include humeri and ulnae, all of which are longer than those of the largest auk currently known, the recently extinct Great Auk (Pinguinus impennis). The relative proportions and structure of these wing elements, together with our estimates of body mass and wing loading suggest that this new species was capable of flapping flight. We consider the biomechanical implications for a large flighted auk, and speculate on the lifestyle and appearance of this new species. We also estimate the likely flight speed and flapping frequency of Alca stewarti
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
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