1,720,988 research outputs found
Macroevolutionary patterns in cranial and lower jaw shape of ceratopsian dinosaurs (Dinosauria, Ornithischia): phylogeny, morphological integration and evolutionary rates.
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Mechanical performance of ceratopsian lower jaws: New insight revealed by finite element analysis
No full textIs Torosaurus Triceratops? Geometric morphometrics evidences of late Maastrichtian ceratopsid dinosaurs
No full text"Background: Recent assessments of morphological changes in the frill during ontogeny hypothesized that the late Maastrichtian horned dinosaur Torosaurus represents the “old adult” of Triceratops, although acceptance of this finding has been disputed on several lines of evidence.. Methodology\/Principal Findings: Examining the cranial morphology of 28 skulls in lateral view and 36 squamosals of Nedoceratops hatcheri, Triceratops spp. and Torosaurus spp. by means of landmark-based geometric. morphometrics, we compared ontogenetic trajectories among these taxa. Principal Component Analysis and cluster. analysis confirmed different cranial morphologies. Torosaurus shape space is well separated from Triceratops, whereas Triceratops horridus and Triceratops prorsus partially overlap within Triceratops shape space. Linear. regressions between shape and size suggest different ontogenetic trajectories among these taxa. Results support the “traditional” taxonomic status of Torosaurus. We hypothesize that ontogeny drives cranial morphology with different patterns between Torosaurus and Triceratops.. Conclusions\/Significance: Torosaurus is a distinct and valid taxon. Whether looking at entire skulls, skulls without the frill, frills alone, or squamosals, Torosaurus has different morphologies and distinct allometric trajectories. compared to Triceratops. This new approach confirms the taxonomic status of Torosaurus as well as the. comparatively low diversity of ceratopsids at the end of the Maastrichtian in North America.
Males resemble females: Re-evaluating sexual dimorphism in Protoceratops andrewsi (Neoceratopsia, Protoceratopsidae).
No full textBackground
Protoceratops andrewsi(Neoceratopsia, Protoceratopsidae) is a well-known dinosaur from the Upper Cretaceous of Mongolia. Some previous workers hypothesized sexual dimorphism in the cranial shape of this taxon, using qualitative and quantitative observations. In
particular, width and height of the frill as well as the development of a nasal horn have been hypothesized as potentially sexually dimorphic.
Methodology/Principal Findings
Here, we reassess potential sexual dimorphism in skulls of Protoceratops andrewsiby applying two-dimensional geometric morphometrics to 29 skulls in lateral and dorsal views. Principal Component Analyses and nonparametric MANOVAs recover no clear separation between hypothetical “males” and
“females” within the overall morphospace. Males and females
thus possess similar overall cranial morphologies. No differences in size between
“males” and “females” are recovered using nonparametric ANOVAs.
Conclusions/Significance
Sexual dimorphism within Protoceratops andrewsiis not strongly supported by our results, as previously proposed by several authors. Anatomical traits such as height and width of the frill, and skull size thus may not be sexually dimorphic. Based on PCA for a data set focusing on the rostrum and associated ANOVA results, nasal horn height is the only feature with potential dimorphism. As a whole, most purported dimorphic variation is probably primarily the result of ontogenetic cranial shape changes as well as intraspecific cranial variation independent of sex
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
The evolution of squamosal shape in ceratopsid dinosaurs (Dinosauria, Ornithischia)
No full text""Ceratopsidae represents one of the last and best-known radiations of non-avian dinosaurs. Interspecific variation is well documented qualitatively with linear measurements, but little has been done to quantify shape differences in the frill that may indicate functional or evolutionary signals. In order to investigate shape change in the squamosal across Chasmosaurinae and Centrosaurinae, we applied geometric morphometrics to the outline of the squamosal for 155 specimens representing. 27 ceratopsid species and Protoceratops spp. A Mantel test suggests that the shape of ceratopsid squamosals is highly constrained by phylogeny. MANOVA, ANOVA, and their phylogenetic versions suggest that an evolutionarily significant allometric signal exists between the two clades, but not within clades. Principal component analysis indicates that centrosaurines have a uniform squamosal shape, with the exceptions of Spinops and Diabloceratops. Even when accounting for phylogeny,. the relationship between squamosal shape and size is significant. Mapping shape onto the phylogeny, we estimated ancestral shapes at nodes. The transition from the non-ceratopsid to ceratopsid condition is characterized by a squamosal with a wider angle between the infratemporal process and the caudoventral margin, and a more dorsoventrally elongated and caudally expanded blade. From root to tips, centrosaurine squamosals were found to be conservative, but exhibit a slight dorsoventral. expansion and a narrow angle between the infratemporal process and the caudoventral margin in more derived taxa. Chasmosaurines, compared with centrosaurines, show a derived morphology, with a trend towards a blade that is strongly expanded dorsoventrally and with a narrower angle between the infratemporal process and the caudoventral margin."
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