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Ghosts of the Holobiont: Borings on a Miocene Turtle Carapace from the Pisco Formation (Peru) as Witnesses of Ancient Symbiosis
No full textIn spite of the widespread occurrence of epibiotic turtle barnacles (Coronuloidea: Chelonibiidae and Platylepadidae) on extant marine turtles (Chelonioidea: Cheloniidae and Dermochelyidae), and although the association between these cirripedes and their chelonian hosts has existed for more than 30 million years, only a few studies have investigated the deep past of this iconic symbiotic relationship on palaeontological grounds. We describe probable platylepadid attachment scars in the form of hemispherical/hemiellipsoidal borings on an Upper Miocene (Tortonian) fragmentary turtle carapace, identified herein as belonging to Cheloniidae, from the Pisco Lagerstätte (East Pisco Basin, southern Peru). When coupled with the available molecular data, this and other similar ichnofossils allow for hypothesising that platylepadid symbionts were hosted by sea turtles as early as in early Oligocene times and became relatively widespread during the subsequent Miocene epoch. Chelonian fossils that preserve evidence of colonisation by platylepadid epibionts in the form of pits on the turtle shell should be regarded as fossil holobionts, i.e., palaeontological witnesses of discrete communal ecological units formed by a basibiont and the associated symbionts (including the epibiota). A greater attention to the bone modifications that may be detected on fossil turtle bones is expected to contribute significantly to the emerging field of palaeosymbiology
A puzzling occurrence of the bite mark ichnogenus Linichnus from the Lower Miocene Chilcatay Formation of Peru
No full textAn upper anterior tooth of Cosmopolitodus hastalis (Elasmobranchii: Lamnidae) from
Burdigalian strata of the shallow-marine Chilcatay Formation exposed at Zamaca (East Pisco Basin, Peru) exhibits the remarkable occurrence of a serrated bite mark consistent with Linichnus serratus (Praedichnia: Machichnidae). In marine successions of Cenozoic age, traces belonging to the ichnogenus Linichnus are typically found occurring on the bones of marine mammals and interpreted as due to predation or scavenging by sharks provided with smooth-edged (Linichnus bromleyi) or denticulated (L. serratus) teeth. Only a few fossil shark teeth exist preserving serrated bite marks, all of which have been interpreted as due to self-biting, which may occur when a shark loses a tooth while feeding and accidentally bites into it. Since C. hastalis is a smooth-toothed species, self-biting cannot explain our unusual find of L. serratus, which in turn may either reflect some kind of trophic interaction between large carnivorous sharks (with a late juvenile or young adult C. hastalis being fed upon by another elasmobranch, possibly a large-sized carcharhinid) or testify to accidental biting during multispecies shark scavenging on the carcass of a third organism that did not get preserved alongside the bitten tooth
Vertebrate palaeoecology of the Pisco Formation (Miocene, Peru): Glimpses into the ancient Humboldt Current Ecosystem
Get PDFThe northward-flowing Humboldt Current hosts perpetually high levels of productivity along the western coast of South America. Here, we aim to elucidate the deep-time history of this globally important ecosystem based on a detailed palaeoecological analysis of the exceptionally preserved middle–upper Miocene vertebrate assemblages of the Pisco Formation of the East Pisco Basin, southern Peru. We summarise observations on hundreds of fossil whales, dolphins, seals, seabirds, turtles, crocodiles, sharks, rays, and bony fishes to reconstruct ecological relationships in the wake of the Middle Miocene Climatic Optimum, and the marked cooling that followed it. The lowermost, middle Miocene Pisco sequence (P0) and its vertebrate assemblage testify to a warm, semi-enclosed, near-shore palaeoenvironment. During the first part of the Tortonian (P1), high productivity within a prominent upwelling system supported a diverse assemblage of mesopredators, at least some of which permanently resided in the Pisco embayment and used it as a nursery or breeding/calving area. Younger portions of the Pisco Formation (P2) reveal a more open setting, with wide-ranging species like rorquals increasingly dominating the vertebrate assemblage, but also local differences reflecting distance from the coast. Like today, these ancient precursors of the modern Humboldt Current Ecosystem were based on sardines, but notably differed from their present-day equivalent in being dominated by extremely large-bodied apex predators like Livyatan melvillei and Carcharocles megalodon
On the ecotrophic role of the giant Neogene shark Carcharocles megalodon: some notes from the Pisco Formation of Peru
No full textThe extinct otodontid shark species Carcharocles megalodon is known by giant serrated teeth and large vertebrae from Mio-Pliocene marine deposits worldwide. Reaching a total body length greater than 16 m, C. megalodon is regarded as an apex predator which likely occupied the top of the trophic chains of the Neogene global ocean. Despite C. megalodon being interpreted as a whale-eating predator, and its fossil remains being common in Neogene deposits worldwide, little direct evidence for the trophic ecology of this mega-toothed shark arose from the fossil record to date. We report on long and serrated shark bite marks attributed to C. megalodon affecting fossil mammalian bones collected from late Miocene shallow-marine deposits of the Pisco Formation exposed at Aguada de Lomas (South Peru). These occurrences, the first in their kind from the Southern Hemisphere, significantly expand the record of bite marks of C. megalodon; moreover, for the first time a prey of C. megalodon is identified at the specific level (as Piscobalaena nana, a diminutive member of the extinct mysticete family Cetotheriidae). Due to the fragmentary nature of the studied material, it was not possible to ascertain if the observed bite marks were due to scavenging or to active predation. Nevertheless, based on actualistic observations and size-based considerations, we propose that small-sized mysticetes (e.g., P. nana) could have been one of the target prey of adult C. megalodon. A predatory behavior somewhat similar to that of the great white shark attacking seals may be hypothesized for C. megalodon preying upon small mysticetes. We suggest that C. megalodon was a generalist apex predator whose trophic spectrum was still focussed on small-sized baleen whales. It is therefore interesting to observe that the extinction of C. megalodon (occurring at the end of Pliocene) roughly coincides with the the decline and fall of various lineages of small-sized baleen whales (including most Cetotheriidae). The disappearance of the last mega-toothed shark could thus have been triggered by the collapse of the archaic diminutive mysticetes (mostly inhabiting coastal upwelling-influenced waters of warm to temperate oceans) in favor of modern gigantic baleen whales (seasonally migrating to high latitude cold waters), the latter event being possibly driven by long-term planetary oceanographic and climatic changes
Did the giant fossil shark Carcharocles megalodon eat small prey? Insights from bitten mammalian bones from the late Miocene of Peru.
No full textUnlike bony fish, sharks are K-selected animals whose life history strategies generally include the use of protected nursery areas by young of the year and juveniles. Nursery areas can be primary (i.e., grounds where the sharks are born and spend the very first part of their lives) or secondary (i.e., grounds inhabited by slightly older but not yet adolescent or mature individuals). Criteria utilized to recognize and define these strategic habitats include: high concentration of young sharks, continuous or repeated use on various temporal scales, high food availability, and low predation risk. Since the fossil record of sharks is mainly composed of isolated teeth, identification of paleo-nurseries involves a series of problems due to difficult application of the above reported criteria. In fact, only four putative shark paleo-nurseries have been individuated to date: three of them regard lamniform sharks and were proposed on the basis of a few isolated small-sized teeth, whereas the fourth one comprises hybodontid and xenacanthid taxa and is testified by both selachian eggs and juvenile teeth.
In the upper Miocene (Tortonian) deposits of the Pisco Formation exposed at Cerro Colorado (South Peru), a very rich shark tooth bearing level has recently been discovered. About 80% of the teeth collected from this level belong to the extant copper shark Carcharhinus brachyurus (Chondrichthyes: Carcharhinidae). These teeth are small-sized and compatible with extant individuals ranging from 80 cm to 210 cm in total length (i.e., immature and subadult copper sharks ranging in age between 4 and 16 years); adult teeth of C. brachyurus are in turn completely absent (although they are known from other Neogene deposits of Southeast Pacific, including a single site of the Pisco Formation). By analyzing the paleoenvironment of the Cerro Colorado shark tooth bearing level, we found that it meets the ecological criteria for individuating extant shark nurseries. The absence of very small-sized teeth (i.e., teeth referable to neonates and young of the year) allows us to hypothesize a secondary nursery ground inhabited by preadolescent copper sharks. The teeth size distribution of other chondrichthyan taxa (Lamniformes, Carcharhiniformes, and Myliobatiformes) that occur along with C. brachyurus put in evidence a significantly juvenile composition of the fossil shark assemblage, thus supporting the hypothesis of a communal use of the Cerro Colorado paleo-nursery by various mesopredator shark species.
This study resulted in the identification of the first paleo-nursery for a carcharhiniform taxon, as well as in the first fossil shark nursery investigated with an ecology-based, actualistic approach
A new barnacle (Cirripedia: Neobalanoformes) from the early Miocene of Peru: Palaeoecological and palaeobiogeographical implications
No full textA new megabalanine barnacle, Austromegabalanus carrioli sp. nov., is described from lower Miocene strata of the Chilcatay Formation (East Pisco Basin, southern Peru). An assessment of the value of interlaminate figures in distinguishing species within the tribe Austromegabalanini from thin sections is provided– a useful identificationtool with fossil taxa such as the austromegabalanines, which are commonly found only as fragmented shells. The paper concludes with a reassessment of the palaeobiogeography and distribution patterns of the austromegabalanines, proposing a circumequatorial origin for this tribe
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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