1,721,073 research outputs found
THE ORAL APPARATUS OF MARSUPIALS IS MORE INTEGRATED BUT NOT LESS MORPHOLOGICALLY DIVERSE THAN THAT OF PLACENTAL CARNIVORES
No full textDifferent clades can display extremely different levels of morphological, taxonomical, and
ecological variability. Understanding the factors promoting or decreasing organismal
variability is a central question for paleobiologists. To answer this question, researchers
have focused on identifying the key innovations that have determined patterns of radiation
in specific clades. In this context, developmental constraints can have a major impact on
morphological variability (e.g., disparity) and the evolutionary trajectories of shape change.
Phenotypic integration, or covariation among traits, has been shown to play an important
role in shaping organismal disparity at both micro- and macro-evolutionary scales. A
longstanding proposition in the field of mammalian evolution has been that morphological
variability among marsupials was limited by developmental constraints, in particular,
constraints on the marsupial oral apparatus linked to the need for the embryo to access the
mother’s teat early in its ontogeny. In this study, we apply a recently proposed Geometric
Morphometric approach (i.e., global integration) to investigate phenotypic integration
intrinsic to a particular structure, in order to compare morphological disparity in the oral
apparatus of marsupial and placental carnivores. Our results show that the marsupial oral
apparatus is significantly more integrated than that of placentals; however, at least when
fossil specimens are included, morphological disparity among marsupials was not
significantly different to that found in placentals. Our findings underscore the importance
of including fossil material in evolutionary studies and show that phenotypic integration
alone cannot explain the lower morphological variation of extant marsupials. We suggest
that extrinsic variables, such as habitat fragmentation, are likely to have played a key role in
limiting marsupial disparity
THE ORAL APPARATUS OF MARSUPIALS IS MORE INTEGRATED BUT NOT LESS MORPHOLOGICALLY DIVERSE THAN THAT OF PLACENTAL CARNIVORES
No full textDifferent clades can display different levels of morphological, taxonomical and
ecological variability. Understanding the factors promoting or decreasing organismal
variability is a central question for paleobiologists. To answer this question researchers
have focused on identifying the key innovations that determined the patterns of radiation
in specific clades. In this context developmental constraints can have a major impact on
the evolution of morphological variability (e.g. disparity). Phenotypic integration, or
covariation among traits, has been shown to play an important role in shaping
organismal disparity at macro-evolutionary scale. A longstanding proposition about
mammalian evolution has been that morphological variability among marsupials was
limited by developmental constraints, in particular, constraints on the marsupial oral
apparatus linked to the need for the embryo to access the mother’s teat early in its
ontogeny. In this study we apply a recently proposed Geometric morphometric
approach, i.e., Global Integration, to investigate integration intrinsic to a particular
structure to compare the degree of oral apparatus morphological disparity between
marsupial and placental carnivores. Our results show that marsupial oral apparatus is
significantly more integrated than that of placentals, however, at least when fossil
specimens are included, morphological disparity among marsupials was not significantly
different to that found in placentals
Marsupial Functional Morphology, Biomechanics, and Feeding Ecology
No full textResearchers have sought to infer the relationships between animal form and function for centuries. The study of biomechanics has become an increasingly important tool with which to quantify such relationships. Together analyses of shape and biomechanics can greatly inform our understanding of how animals interact with their environments and allow us to predict ecology in extinct species. They can also provide a sound basis from which we can gain insight into broader macroevolutionary processes. Because the acquisition and processing of food is clearly key to survival, the vertebrate feeding apparatus has received particular attention. Although clearly far less speciose than placental mammals, marsupials, and the broader metatherian clade to which they belong, are characterized by a long fossil history and considerable diversity. Consequently, they have been of critical importance in the study of evolutionary convergence. Assessments of convergence with placentals and predictions of feeding behavior in extinct species, such as the Thylacine (Thylacinus cynocephalus), Marsupial Lion (Thylacoleo carnifex), and the metatherian sabertooth (Thylacosmilus atrox), have generated particularly long-run controversy and debate. Here the study of form, function, and biomechanics in the feeding ecology of marsupials is reviewed, from nineteenth-century observation-based inference, through increasingly quantitatively founded studies incorporating two-dimensional shape analysis, lever mechanics, and beam theory in the twentieth century, to increasingly sophisticated recent investigations based on finite element analysis and three-dimensional morphometrics
Morphological integration affects the evolution of midline cranial base, lateral basicranium, and face across primates
No full textObjectives The basicranium and face are two integrated bony structures displaying great morphological diversity across primates. Previous studies in hominids determined that the basicranium is composed of two independent modules: the midline basicranium, mostly influenced by brain size, and the lateral basicranium, predominantly associated with facial shape. To better assess how morphological integration impacts the evolution of primate cranial shape diversity, we test to determine whether the relationships found in hominids are retained across the order. Materials and methods Three-dimensional landmarks (29) were placed on 143 computed tomography scans of six major clades of extant primate crania. We assessed the covariation between midline basicranium, lateral basicranium, face, and endocranial volume using phylogenetically informed partial least squares analyses and phylogenetic generalized least squares models. Results We found significant integration between lateral basicranium and face and between midline basicranium and face. We also described a significant correlation between midline basicranium and endocranial volume but not between lateral basicranium and endocranial volume. Discussion Our findings demonstrate a significant and pervasive integration in the craniofacial structures across primates, differing from previous results in hominids. The uniqueness of module organization in hominids may explain this distinction. We found that endocranial volume is significantly integrated to the midline basicranium but not to the lateral basicranium. This finding underlines the significant effect of brain size on the shape of the midline structures of the cranial base in primates. With the covariations linking the studied features defined here, we suggest that future studies should focus on determining the causal links between them
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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