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FIGURE 1. Locality and stratigraphy. A in New discovery of rhyncholites and conchorhynchs (cephalopod jaw elements) from the Upper Cretaceous Mount Laurel Formation of Delaware
No full textFIGURE 1. Locality and stratigraphy. A, collection locality of rhyncholites and conchorhyncs. B, stratigraphic column of an adjacent locality including the Mount Laurel Formation from which our specimens were collected (modified after Kennedy and Cobban, 1994).Published as part of Tajika, Amane, Landman, Neil H., Koyasu, Hiromichi, Broussard, Amy, Anderson, Lian, Ikuno, Kenji & Ikuno, Kenji, 2023, New discovery of rhyncholites and conchorhynchs (cephalopod jaw elements) from the Upper Cretaceous Mount Laurel Formation of Delaware, pp. 1-20 in American Museum Novitates 2023 (3998) on page 3, DOI: 10.1206/3998.1, http://zenodo.org/record/800615
FIGURE 10 in New discovery of rhyncholites and conchorhynchs (cephalopod jaw elements) from the Upper Cretaceous Mount Laurel Formation of Delaware
No full textFIGURE 10. Results of principal component analysis using the six parameters L, W, H, Ls, Ws, Lh, and β. The original data are from preciously published papers (Till, 1909; Van Der Tuuk, 1985; Riegraf and SchmittRiegraf, 1995; Komarov, 2005a, 2005b; Košťák et al., 2010; Weaver et al., 2012)Published as part of Tajika, Amane, Landman, Neil H., Koyasu, Hiromichi, Broussard, Amy, Anderson, Lian, Ikuno, Kenji & Ikuno, Kenji, 2023, New discovery of rhyncholites and conchorhynchs (cephalopod jaw elements) from the Upper Cretaceous Mount Laurel Formation of Delaware, pp. 1-20 in American Museum Novitates 2023 (3998) on page 17, DOI: 10.1206/3998.1, http://zenodo.org/record/800615
Ecology and Variation of Cretaceous and Recent Cephalopods
Full text linkPalaeodiversity, palaeoecology and organismic evolution are essential disciplines in palaeontology. Although major trends and changes in biodiversity through the Phanerozoic are more or less well known, much more work is needed to understand ecological details as well as all the involved biases linked with biodiversity analyses. As far as evolution is concerned, variation produces the raw material for selection, and thus is of great importance. Within this work, questions of evolutionary processes, morphological intraspecific variation and palaeoecology of cephalopods have been addressed because cephalopods are excellent model organisms to study such fields due to their abundance and morphological diversity. The first part of this (Chapter I and II) thesis documents cephalopod associations and their ecology from the Alpstein massif in Switzerland. It is based on remains of over 1000 macrofossil taxa. Although this region has been sedimentologically and geologically studied in great detail, the fossil associations are much less well-known. To fill this gap, all available cephalopod fossils from the Alpstein were examined comprehensively. In total, at least 100 ammonite taxa, 6 nautilid taxa and 4 coleoid taxa occurred in the Alpstein region. Macrofossil associations of various ages from the Alpstein were also examined in order to assess palaeoecological and environmental changes through the Cretaceous. To quantify these changes, two diversity indices of taxonomic richness and ecological disparity were employed. Results show that taxonomic richness and ecological disparity are decoupled, i.e., taxonomic richness did not show a strong fluctuation with around 20 families through time, whereas ecological disparity fluctuated strongly. These results imply that, when environmental changes occur, ecological disparity is more susceptible than taxonomic richness at family level. In the second part (Chapter III and IV), phenotypic intraspecific variation of cephalopods and its ontogenetic trajectories were investigated. Knowledge of intraspecific variability is a prerequisite to study diversity, palaeobiogeography and chronobiostratigraphy because these can be only carried out correctly with accurate taxonomic assignments. Ammonoids are extinct externally shelled cephalopods (ectococh-leates), which had high evolutionary rates and occur worldwide in great numbers. If complete, ammonoid conchs record their entire ontogeny because of their accretionary growth and thus are, like many other mollusks, ideal to study ontogeny. However, ammonoid intraspecific variation is often underestimated or ignored when a new taxon is introduced, which resulted in oversplitting in many cases. To understand intraspecific variation in ammonoids, Recent Nautilus was used as a reference since fossil materials introduce a set of additional biases (e.g., taphonomy, time averaging). A quantitative approach using 3D morphometry was employed to analyze the phenotypic intraspecific variation of three conch parameters of three geographically separated Nautilus populations through ontogeny. Results illustrate that there are
commonalities in the pattern of ontogenetic change of intraspecific variation between the three populations: In early ontogenetic stages, variation is higher and decreases until it shows an increase again before maturity. This pattern was compared with that of some ammonoids and belemnites, which revealed that this ontogenetic pattern of intraspecific variation is common among some groups of cephalopods.The second part of this thesis (Chapter III and IV) also included applications of (destructive and non-destructive) tomography technique to fossil cephalopods. As in the above mentioned study on intraspecific variation of Nautilus,3D morphometry was carried out to examine several ammonoid species in order to understand ontogenetic patterns of phragmocone chamber volume increase and its intraspecific variation. When the results of ammonoids and Nautilus are compared, the ammonoids show a much stronger ontogenetic variation of chamber volumes than nautilids. The driving factors behind this variation will be part of my postdoctoral study. In the last part of this thesis (Chapter V), the roles of ammonoids in the marine food web and their incumbent replacement after their extinction at the end of the Cretaceous are discussed. Globally, Cretaceous ammonites occur in great numbers. This stresses the importance for the question for the
post-Cretaceous re-occupation of this ecospace. First, reproductive rates of large Cretaceous ammonoids
were reconstructed, which yielded numbers of up to 100 million eggs (hatchling size 0.5 to 1 mm) for an
adult female ammonite with two meters conch diameter. Combining that large ammonites with a diameter exceeding half a meter are abundant globally, this implies a key role of ammonite (and also belemnite) hatchlings in the plankton of Mesozoic seas. With the end-Cretaceous mass-extinction, this ecospace became available. Remarkably, holoplanktonic gastropods resembling ammonite and belemnite hatchlings in form, size and habitat originated early in the Palaeogene and subsequently provided the ecological prerequisites for the evolution of large filter feeders such as mantas, whale sharks and baleen 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
How many ontogenetic points are needed to accurately describe the ontogeny of a cephalopod conch? A case study of the modern nautilid Nautilus pompilius
Full text linkRecent advancements in tomographic techniques allow for detailed morphological analysis of various organisms, which has proved difficult in the past. However, the time and cost required for the post-processing of highly resolved tomographic data are considerable. Cephalopods are an ideal group to study ontogeny using tomography as the entire life history is preserved within a conch. Although an increasing number of studies apply tomography to cephalopod conchs, the number of conch measurements needed to adequately characterize ontogeny remains unknown. Therefore, the effect of different ontogenetic sampling densities on the accuracy of the resultant growth trajectories needs to be investigated. Here, we reconstruct ontogenetic trajectories of a single conch of Nautilus pompilius using different numbers of ontogenetic points to assess the resulting accuracies. To this end, conch parameters were measured every 10°, 30°, 45°, 90°, and 180°. Results reveal that the overall patterns of reconstructed growth trajectories are nearly identical. Relatively large errors appear to occur where growth changes occur, such as the points of hatching and the onset of morphogenetic countdown before the attainment of maturity. In addition, a previously undocumented growth change before hatching was detected when measurements were taken every 10°, 30°, and 45°, though this growth change was obscured when fewer measurements were used (90° and 180°). The lower number of measurements also masks the subtle fluctuating patterns of conch parameters in middle ontogeny. We conclude that the measurements of a conch every 30° and 45° permit a reasonably precise description of conch ontogeny in nautilids. Since ammonoids were likely more responsive to external stimuli than to nautilids, a much denser sampling may be required for ammonoids.
Subjects Developmental Biology, Marine Biology, Paleontology, Taxonomy, Zoology
Keywords Cephalopods, Nautiloidea, Morphometrics, Ontogeny, Conch, Tomograph
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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