1,721,072 research outputs found
Huaridelphis raimondii, a new early Miocene Squalodelphinidae (Cetacea, Odontoceti) from the Chilcatay Formation, Peru
No full textThe fossil record of odontocetes (toothed cetaceans) is relatively scarce during the Oligocene and early Miocene compared with later in the Miocene and Pliocene; most of the odontocete families from these epochs are known by a limited number of species and specimens. Among those, Squalodelphinidae is a family of small- to medium-sized platanistoids with single-rooted teeth, which until now has included only four genera based on diagnostic material, from the early Miocene of Europe, Argentina, and North America. Recent field work in the Pisco-Ica desert, southern coast of Peru, has resulted in the discovery of several marine vertebrate-rich localities in various levels of the late Oligocene–early Miocene Chilcatay Formation. Based on three specimens from Ullujaya and Zamaca, including two well-preserved skulls with periotics, we describe a new squalodelphinid genus and species, Huaridelphis raimondii. This new species increases the early Miocene diversity of the family and is also its smallest known member. It further differs from other squalodelphinids by its thin antorbital process of the frontal, abruptly tapering rostrum, and higher tooth count. A more fragmentary skull, from Zamaca, is referred to Squalodelphinidae aff. H. raimondii. This skull provides information on the morphology of the tympanic, malleus, and incus, currently unknown in H. raimondii. Focusing on platanistoids with single-rooted teeth, our phylogenetic analysis suggests that Squalodelphinidae are monophyletic and confirms the sister-group relationship between the latter and Platanistidae. The relationships within Squalodelphinidae are not fully resolved, but H. raimondii might be one of the earliest diverging taxa
A new record of Notocetus vanbenedeni (Squalodelphinidae, Odontoceti, Cetacea) from the Early Miocene of Peru
No full textAn almost complete skull with associated periotics and one cervical vertebra from theEarly Miocene strata of the Chilcatay Formation (Pisco Basin, Peru) is described here andreferred to Notocetus vanbenedeni, a species previously recorded from Argentina, belong-ing to the extinct odontocete family Squalodelphinidae (Platanistoidea). The fossil wascollected in the same locality and approximately the same stratigraphical horizon as Huar-idelphis raimondii, suggesting the sympatric coexistence of two squalodelphinids during theEarly Miocene along the Pacific coast of South America. Considering the new record heredescribed, N. vanbenedeni lived both along the Atlantic and Pacific coasts of South America,two marine areas in wide contact during the Late Oligocene and Early Miocene. Despitethe relative commonness of squalodelphinids in the Chilcatay Fm., the worldwide recordof this family remains globally rather scarce and significant specimens were only found inItaly, France, along the East Coast of USA, Argentina, Peru, and possibly New Zealand
A new inioid (Cetacea, Odontoceti, Delphinida) from the Miocene of Peru and the origin of modern dolphin and porpoise families
No full textIn this paper we describe Brujadelphis ankylorostris gen. nov., sp. nov., a new delphinidan (Cetacea,
Odontoceti, Delphinida), based on a well-preserved skull with ear bones, associated mandibles, most of the teeth
in situ and a fragment of the atlas, from the late middle to early late Miocene (Serravallian to early Tortonian) of
the Pisco Formation, Pisco Basin, Peru. The new taxon differs from all other delphinidans in the following unique
combination of character states: partial ankylosis of the thickened premaxillae above the mesorostral groove;
presence of premaxillary eminences; premaxilla does not contact nasal; inflated nasals with a transversely convex
dorsal surface; presence of an internasal fossa; and a longitudinal crest on the vertex formed by transversely
pinched frontals. Our cladistic analyses of a supermatrix that includes molecular and morphological data
identifies B. ankylorostris as an inioid (Iniidae + Pontoporiidae) that is more closely related to Inia than to
Pontoporia. This result persists even if a molecular scaffold based on published Bayesian analyses is used. The
inclusion of a large sample (12 taxa) of ‘kentriodontids’ allows us to confirm the paraphyly of this group of
archaic Miocene delphinidans but contradicts the prevailing views in placing all of these taxa outside of
Delphinoidea (Delphinidae + Monodontidae + Phocoenidae). In our unconstrained analysis ‘kentriodontids’ are
split into five separate clades that occur along the stem of Inioidea + Delphinoidea. Based on our most
parsimonious trees, we discuss published calibration points for molecular divergence estimates within Odontoceti
and propose one new point: 18 Ma for an unnamed clade including Delphinida + Ziphiidae
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
Evidence of dietary niche partitioning in the Squalodelphinidae (Cetacea, Odontoceti): a new large-sized taxon from the early Miocene of Peru
No full textThe South Asian river dolphin (Platanista gangetica) is the only extant survivor of the superfamily Platanistoidea (Cetacea, Odontoceti), a clade characterized by a diversified fossil record since the late Oligocene. The early Miocene family Squalodelphinidae differs from other members of the Platanistoidea by having a moderately elongated and tapered rostrum, single-rooted posterior teeth retaining ornamentation, and marked skull asymmetry. Similar to the extant common dolphin, the few squalodelphinids described are all relatively small in size, having an estimated body length (based on the bizygomatic width of the skull) between ca 2 m (Huaridelphis raimondii) and ca 2.5 m (Squalodelphis fabianii).
Based on a partial skeleton (MUSM 2545), including a well-preserved skull, collected from the Chilcatay Formation (Peru), we report here a new squalodelphinid genus and species. A volcanic ash layer sampled near MUSM 2545 yielded a 40Ar/39Ar age of 18.80 ± 0.06 Ma (early Burdigalian, early Miocene). In addition to several morphological characters, this new squalodelphinid differs from all the other genera of the family in its markedly larger size: condylobasal length of the skull greater than 770 mm and bizygomatic width equal to 370 mm. Based on this last measurement, the body length of MUSM 2545 can be estimated to ca 3.5 m. Combined with some cranial features, such as the robust rostrum less tapered than in other squalodelphinids, the large temporal fossa, and the prominent nuchal and temporal crests, this large body size suggests that the new taxon consumed larger prey than other members of its family. Together with Huaridelphis raimondii and Notocetus vanbenedeni, both of them also found in the Chilcatay Formation, this new archaic platanistoid increases further the peculiar local diversity of squalodelphinids along the southeastern Pacific coast, a diversity possibly related to their partition in different, size-related dietary niches
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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