New Radiocarbon-Dated Vertebrate Fossils from Herschel Island: Implications for the Palaeoenvironments and Glacial Chronology of the Beaufort Sea Coastlands

Palaeontological research on Herschel Island, Yukon, has yielded a diverse collection of Quaternary marine and terrestrial vertebrate fossils. The terrestrial faunal remains, which have largely been collected as allochthonous beach debris at Pauline Cove, are dominated by Yukon horse (Equus sp.), with fewer specimens of steppe bison (Bison priscus), proboscideans (Mammuthus primigenius and a single Mammut americanum specimen), and other large and medium-sized mammals. This pattern of a horse-dominated Late Pleistocene fauna is consistent with those from the North Slope of Alaska and further demonstrates that conditions in northernmost Beringia were more arid than those in interior areas such as Fairbanks or the Klondike. This paper presents new AMS radiocarbon dates on terrestrial vertebrate fossils and peat from the island that span the range from greater than 53 000 to modern 14C yr BP. When considered with other data from the region, our new radiocarbon-dated fauna cannot adequately resolve whether the Herschel Island ice-thrust ridge was formed during the Early Wisconsinan or the Late Wisconsinan advance of the Laurentide Ice Sheet over the Yukon Coastal Plain.Des fouilles paléontologiques réalisées sur l’île Herschel, au Yukon, ont permis de prélever une collection variée de fossiles marins et de fossiles vertébrés terrestres du quaternaire. Les restes de faune terrestre, qui ont surtout été ramassés sous la forme de débris de plage allochtones à Pauline Cove, prennent la forme de restes de chevaux du Yukon en prédominance (Equus sp.), parsemés de quelques spécimens de bisons priscus (Bison priscus), de proboscidiens (Mammuthus primigenius et d’un seul spécimen de Mammut americanum), ainsi que d’autres mammifères de taille moyenne et de grande taille. La prédominance de faune du type cheval du Pléistocène tardif correspond à celle enregistrée sur le versant nord de l’Alaska et montre encore une fois que les conditions qui régnaient dans la partie la plus au nord de la Béringie étaient plus arides que les conditions qui prévalaient dans les régions de l’intérieur, comme à Fairbanks ou au Klondike. Dans ce document, nous présentons de nouvelles dates établies par le radiocarbone SMAquant aux fossiles de vertébrés terrestres et à la tourbe de l’île, dates allant de plus de 53 000 14C années BP à l’ère moderne. Lorsque ces données sont considérées à la lumière d’autres données de la région, la nouvelle faune datée par le radiocarbone ne nous permet pas de déterminer adéquatement si la dorsale découlant de la poussée des glaces de l’île Herschel a été formée pendant la progression du Wisconsinien précoce ou du Wisconsinien tardif de la nappe glaciaire laurentienne sur la plaine côtière du Yukon

Evidence for Selective Caching by Arctic Ground Squirrels Living in Alpine Meadows in the Yukon

Male arctic ground squirrels (Spermophilus parryii) rely on food they cached the previous year for the energy they need to compete for mates each spring. We collected cheek-pouch contents of arctic ground squirrels trapped during three summers (2000–02) as an indication of what squirrels cached. Among adults, both males and females carried material in their cheek pouches, but males did so more frequently than females (4.4% vs. 0.6% of captures). Males carried material later in the summer than females, and also carried different material (seeds and rhizomes as opposed to nesting material). These differences probably reflect different purposes of cheek-pouch contents—females carried material for immediate use, whereas males carried food for caching. Only 24 of over 100 species of vascular plants growing at our alpine study site were carried, and presumably cached, by male arctic ground squirrels. The seeds or rhizomes of one species, Polygonum viviparum, were found in over 90% of cheek-pouch contents examined, even though that species grew at relatively low density and was no more common than another species in the same genus (Polygonum bistorta) that was never found in cheek-pouch contents. Collectively, this evidence indicates that males are highly selective in what species they cache. Many of the species carried by arctic ground squirrels in this study have also been found in Pleistocene fossil caches from central Yukon, indicating that food preferences of this species may have remained stable over time.Les spermophiles arctiques mâles (Spermophilus parryii) dépendent de la nourriture qu’ils ont cachée l’année précédente pour obtenir l’énergie dont ils ont besoin pour se trouver une compagne d’accouplement au printemps. On a recueilli le contenu des abajoues de spermophiles arctiques capturés pendant trois étés (de 2000 à 2002) pour obtenir un aperçu de ce qu’ils emmagasinaient. Les spermophiles adultes, tant mâles que femelles, transportaient des matériaux dans leurs abajoues, mais c’était plus souvent le cas chez les mâles que chez les femelles (4,4 % par rapport à 0,6 % des spermophiles capturés). Les mâles transportaient des matériaux plus tard pendant l’été que les femelles, sans compter que ces matériaux étaient différents (des graines et des rhizomes par opposition à des matériaux destinés à la nidification). Ces différences sont probablement le reflet de la raison d’être différente du contenu des abajoues — les femelles transportaient des matériaux dont elles allaient se servir immédiatement, tandis que les mâles transportaient des aliments qu’ils allaient mettre en réserve. Sur la centaine d’espèces de plantes vasculaires poussant au site alpin que nous avons étudié, seulement 24 d’entre elles étaient présentes. Ces plantes avaient probablement été mises en réserve par les spermophiles arctiques mâles. Les graines ou les rhizomes d’une espèce, soit le Polygonum viviparum, ont été trouvés dans plus de 90 % du contenu des abajoues examiné, même si ces espèces poussaient selon des densités relativement faibles et qu’elles n’étaient pas plus courantes qu’une autre espèce du même genre (Polygonum bistorta) qui ne se retrouvait jamais dans le contenu des abajoues. Dans l’ensemble, cela indique que les mâles font preuve d’une grande sélectivité quant aux espèces qu’ils mettent en réserve. Grand nombre des espèces transportées par les spermophiles arctiques visés par cette étude ont également été retrouvées dans les caches fossiles du Pléistocène du centre du Yukon, ce qui laisse croire que les préférences alimentaires de cette espèce n’ont guère changé au fil du temps

Taxonomy, location of origin, and health status of proboscideans from Western Canada investigated using stable isotope analysis

We investigated the application of stable isotope analysis of proboscidean remains (collagen in bone/dentin/cementum and structural carbonate in enamel bioapatite) for genus-level identification of isolated specimens, assessment of geographic origins, and testing for nutritional stress. Mammoths (Mammuthus sp.) tended to have higher δ15Ncol and lower δ13Ccol than mastodons (Mammut americanum), but differences were not significant in every location. Determining the genus of isolated specimens may be possible for locations and time periods with good isotopic baselines, but environmental changes can confound interpretations. For example, an Alberta proboscidean with a δ15Ncol of +1.4‰ (characteristic of mastodons) ultimately proved to be a mammoth. Its surprisingly low nitrogen isotope composition is attributable to the recently deglaciated environment it inhabited. We provided a baseline for isotopic assessment of geographic origins of isolated proboscideans in Western Canada. Bioapatite δ13Csc and δ18Osc can be used to distinguish specimens from Alberta, Klondike, Old Crow, Herschel Island, and further south (e.g., Arizona, Great Lakes). Finally, we found that an Alberta mammoth with morphological evidence of nutritional stress experienced a change in diet, environment, or physiology prior to death, but its isotopic compositions did not suggest a link to hypothesized starvation (catabolism of proteins or reliance on lipids)

First records of a plesiosaurian (Reptilia: Sauropterygia) and an ichthyosaur (Reptilia: Ichthyosauria) from Yukon, Canada

An isolated centrum collected ex situ from marine shales of the Lower Cretaceous (Albian) Arctic Red Formation along the Road River represents the first documented occurrence of a plesiosaurian from Yukon. This centrum represents the northernmost occurrence of plesiosaurians in the Western Interior Sea of North America prior to the establishment of the first continuous seaway (Western Interior Seaway) connecting the Boreal and Tethyan seas. Additionally, this centrum is potentially the secondoldest elasmosaurid specimen known from North America. A second centrum, collected along the Beaver River, is likely derived from the Lower Cretaceous (Lower Albian) Garbutt Formation exposed farther upstream. It represents the first report of an ichthyosaur from Yukon. Additionally, six associated ribs collected from the Arctic Re

Updated Three-Stage Model for the Peopling of the Americas

Background: We re-assess support for our three stage model for the peopling of the Americas in light of a recent report that identified nine non-Native American mitochondrial genome sequences that should not have been included in our initial analysis. Removal of these sequences results in the elimination of an early (i.e.,40,000 years ago) expansion signal we had proposed for the proto-Amerind population. Methodology/Findings: Bayesian skyline plot analysis of a new dataset of Native American mitochondrial coding genomes confirms the absence of an early expansion signal for the proto-Amerind population and allows us to reduce the variation around our estimate of the New World founder population size. In addition, genetic variants that define New World founder haplogroups are used to estimate the amount of time required between divergence of proto-Amerinds from the Asian gene pool and expansion into the New World. Conclusions/Significance: The period of population isolation required for the generation of New World mitochondrial founder haplogroup-defining genetic variants makes the existence of three stages of colonization a logical conclusion. Thus, our three stage model remains an important and useful working hypothesis for researchers interested in the peopling of th

Evolutionary history of saber-toothed cats based on ancient mitogenomics

Saber-toothed cats (Machairodontinae) are among the most widely recognized representatives of the now largely extinct Pleistocene megafauna. However, many aspects of their ecology, evolution, and extinction remain uncertain. Although ancient-DNA studies have led to huge advances in our knowledge of these aspects of many other megafauna species (e.g., mammoths and cave bears), relatively few ancient-DNA studies have focused on saber-toothed cats, and they have been restricted to short fragments of mitochondrial DNA. Here we investigate the evolutionary history of two lineages of saber-toothed cats (Smilodon and Homotherium) in relation to living carnivores and find that the Machairodontinae form a well-supported clade that is distinct from all living felids. We present partial mitochondrial genomes from one S. populator sample and three Homotherium sp. samples, including the only Late Pleistocene Homotherium sample from Eurasia. We confirm the identification of the unique Late Pleistocene European fossil through ancient-DNA analyses, thus strengthening the evidence that Homotherium occurred in Europe over 200,000 years later than previously believed. This in turn forces a re-evaluation of its demography and extinction dynamics. Within the Machairodontinae, we find a deep divergence between Smilodon and Homotherium ( 18 million years) but limited diversity between the American and European Homotherium specimens. The genetic data support the hypothesis that all Late Pleistocene (or post-Villafrancian) Homotherium should be considered a single species, H. latidens, which was previously proposed based on morphological data

A controlled trial of rivaroxaban after transcatheter aortic-valve replacement

Background: whether the direct factor Xa inhibitor rivaroxaban can prevent thromboembolic events after transcatheter aortic-valve replacement (TAVR) is unclear. Methods: we randomly assigned 1644 patients without an established indication for oral anticoagulation after successful TAVR to receive rivaroxaban at a dose of 10 mg daily (with aspirin at a dose of 75 to 100 mg daily for the first 3 months) (rivaroxaban group) or aspirin at a dose of 75 to 100 mg daily (with clopidogrel at a dose of 75 mg daily for the first 3 months) (antiplatelet group). The primary efficacy outcome was the composite of death or thromboembolic events. The primary safety outcome was major, disabling, or life-threatening bleeding. The trial was terminated prematurely by the data and safety monitoring board because of safety concerns. Results: after a median of 17 months, death or a first thromboembolic event (intention-to-treat analysis) had occurred in 105 patients in the rivaroxaban group and in 78 patients in the antiplatelet group (incidence rates, 9.8 and 7.2 per 100 person-years, respectively; hazard ratio with rivaroxaban, 1.35; 95% confidence interval [CI], 1.01 to 1.81; P = 0.04). Major, disabling, or life-threatening bleeding (intention-to-treat analysis) had occurred in 46 and 31 patients, respectively (4.3 and 2.8 per 100 person-years; hazard ratio, 1.50; 95% CI, 0.95 to 2.37; P = 0.08). A total of 64 deaths occurred in the rivaroxaban group and 38 in the antiplatelet group (5.8 and 3.4 per 100 person-years, respectively; hazard ratio, 1.69; 95% CI, 1.13 to 2.53). Conclusions: in patients without an established indication for oral anticoagulation after successful TAVR, a treatment strategy including rivaroxaban at a dose of 10 mg daily was associated with a higher risk of death or thromboembolic complications and a higher risk of bleeding than an antiplatelet-based strategy. (Funded by Bayer and Janssen Pharmaceuticals; GALILEO ClinicalTrials.gov number, NCT02556203.)

The Prognostic Significance of Whole Blood Global and Specific DNA Methylation Levels in Gastric Adenocarcinoma

Epigenetics, particularly DNA methylation, has recently been elucidated as important in gastric cancer (GC) initiation and progression. We investigated the clinical and prognostic importance of whole blood global and site-specific DNA methylation in GC. tests. Survival analyses were carried out using the Kaplan-Meier method and log rank test. A backward conditional Cox proportional hazards regression model was used to identify independent predictors of survival. = 0.02) respectively.Analysis of global and site-specific DNA methylation in peripheral blood by pyrosequencing provides quantitative DNA methylation values that may serve as important prognostic indicators