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New specimen of the rare requiem shark Eogaleus bolcensis from the Bolca Lagerstätte, Italy
No full textA rare carcharhinid specimen (slab and counter-slab, MSNPV 24625-24626) from the world-renowned Eocene Bolca
locality was recently rediscovered during a restoration project started in 1989 by the Museo di Storia Naturale di Pavia.
The individual, the largest Eogaleus bolcensis known from Bolca, is disarticulated and lies in a massive limestone matrix,
suggesting its provenience from the Monte Postale site. While assessing its taxonomic status, multiple morphological
affinities and ontogenetic trends within the Bolca Carcharhiniformes assemblage where documented. Eogaleus bolcensis
is here distinguished from the school shark Galeorhinus cuvieri exclusively according to dermal denticle morphology,
suggesting partial overlap of ecologic and trophic niches between the two species. Further, measurements and meristic
counts taken on different traits of E. bolcensis (two individuals) and G. cuvieri (five individuals) specimens show high
degree of similarities. The ratios “trunk length/total length” and “sum of vertebral centra (head region)/total length” of
four complete individuals of the fossil assemblage were averaged and employed to estimates the total length of MSNPV
24625-24626. Here, the total length of MSNPV 24625-24626 is estimated in about 172.1±0.1 cm. The same approach is
applied to MCSNV T.311 (E. bolcensis, holotype) and MNHN F.Bol.516 (G. cuvieri, holotype), two partially-preserved
fossil individuals from Bolca locality. To support the ontogenetic variability among the Bolca shark assemblage, the
age of the fossil individuals was estimated following the Von Bertalanffy Growth Function, using the modern chondrichthyans
growth parameters as a reference. Data presented here suggest that all G. cuvieri specimens are juvenile
individuals, whereas the E. bolcensis specimens were young-adult
Reassessment of a large lamniform shark from the Upper Cretaceous (Santonian) of Italy
No full textTo date, only a few partially articulated chondrichthyan specimens are known from the Upper Cretaceous
marine fossil record of northern Italy. Here, we re-evaluate the taxonomic status and geological age of
selachian remains originally discovered during the 19th century from the Castellavazzo locality. The
described specimen is largely embedded in matrix with minute exposure of joined and moderately
deformed sequentially stacked vertebral centra. Computed tomography (CT) image-data obtained of the
specimen enabled the identification of potential cranial-cartilage elements located in close proximity to
teeth and are here interpreted as remnants of the jaws. Based on tooth and vertebral morphology the
specimen is in all likelihood an adult lamniform shark with a measured 3.5 m length. Using ordinary
least-squares regression analysis (OLS) and proportion-based calculations, we estimated a total-length
(TL) of 596.27 and 632.5e672.64 cm respectively. We prefer the size estimation derived through OLS
bivariate regression; however, in the present analysis, reliance on a small sample size (n 1⁄4 11) and evidence
for differential scaling between taxa impose limitations on the precision of our size prediction.
Planktonic foraminifera examined from the surrounding matrix of the slab preserving shark vertebral
centra and teeth indicate a Santonian age (Dicarinella asymetrica zone). Although, the specimen could not
confidently be assigned beyond the ordinal-level, the sheer centrum size, gross dental morphology, and
depositional environment, are indicative of a pelagic apex-predator comparable to coeval lamniforms,
with a specific resemblance towards cretoxyrhinids, reported from elsewhere along the peri-Tethyan
shelf of Europe and Western Interior Seaway of North America. Finally, the re-emergence of this historical
specimen, here re-described using cutting-edge techniques, is of great importance as it contributes
to the otherwise poor record of extinct lamniform shark skeletons
A new specimen of shark from the Monte Postale locality (Eocene, Bolca) and the rise of the Triakids in ancient ecosystems
Get PDFThis thesis focuses on the description of a fossil shark found in the Museo di Storia Naturale di Pavia during a complex restoration project started in 1989. The specimen represents one of the rarest shark taxa from the world–renown Eocene Bolca locality. Unlike the Ypresian taxa Galeorhinus cuvieri and Eogaleus bolcensis, the specimen partly disarticulated and lies in a limestone matrix, suggesting its provenience from the Monte Postale site. The dataset of measurements for body parameters, vertebral centra, teeth and placoid scales was compared to both fossil and extant taxa in order to discuss the overall systematic assessments of the Bolca sharks at higher taxonomic levels. Overall body measurements collected from all Bolca specimens were combine in order to estimate the size of the examined specimen. Statistical approach performed on body measurements and preserved vertebrae support a largely sharing of these characters among the extant taxa of the order Carcharhiniformes. SEM analysis on dermal denticle support that the Pavia specimen is an individual of Eogaleus bolcensis. A comprehensive dataset of teeth was used to compare dental morphologies of the living species Galeorhinus galeus and Galeocerdo cuvier, considered here as standards. The general clustering is primarily based on qualitative characters and ratios between selected measurements. The comparison between fossil and extant taxa based on newly defined tooth morphotypes increase our knowledge on taxonomic identifications of Bolca’s sharks. The morphometrical measurements for each fossil specimen indicates three distinct ontogenetic classes, further supported by estimated ages following standard Von Bertalanffy growth curves. As the present–day Galeocerdo, Eogaleus was most likely a mesopelagic, top predator. The combination of biological and abiotic proxies suggests the Bolca setting as a possible nursery area for the juvenile–schooling individuals of G. cuvieri
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Ancient Predators in a Changing World: How Eocene Climate Shifts Shaped Shark Ecology in Antarctica
Get PDFSharks and their relatives have been successful predators for over 400 million years, playing critical ecological roles in marine environments. Their recent, dramatic population decline—largely due to climate change—poses a serious threat to ecosystem stability. Their fossil record provides a valuable system to document how sharks have coped, survived, or declined in response to major climatic changes over geological time. Insights from these records are vital to inform current conservation practices. This dissertation investigates how major climatic events influenced the temperature, salinity, and dietary preferences of sharks that lived during the Eocene Epoch (54–33.9 Ma) in Antarctica, a region that underwent significant environmental shifts as the global climate cooled at the Epoch's end. The study develops a new protocol to isolate silver phosphate for geochemical analysis, enabling temperature and salinity estimations from bones and teeth, including various shark tooth sizes. Temperature and salinity preferences were inferred for both pelagic and benthic shark taxa (n = 16) across the Eocene. The study also examines geochemical and morphological metrics of Eocene sand tiger sharks and compares them with the critically endangered modern species Carcharias taurus. By addressing a longstanding analytical variability enigma affecting temperature and salinity estimates derived from shark teeth, we found that pelagic and benthic Eocene sharks generally preferred similar conditions, with only cooler-adapted species continuing in the fossil record likely surviving climate change. Additionally, our results suggest that fossil sand tiger sharks serve as valuable analogs for the extant C. taurus in terms of habitat and dietary preferences. Altogether, this study underscores the significant impact of climate on sharks and highlights how their fossil record can illuminate aspects of modern shark ecology
Ancient Predators in a Changing World: How Eocene Climate Shifts Shaped Shark Ecology in Antarctica
No full textAncient Predators in a Changing World: How Eocene Climate Shifts Shaped Shark Ecology in Antarctica
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Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Get PDF“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
Get PDFWe 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
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