New Spruce (Picea spp.) Macrofossils from Yukon Territory: Implications for Late Pleistocene Refugia in Eastern Beringia

New radiocarbon-dated plant macrofossils provide evidence for black spruce (Picea mariana) and white spruce (Picea glauca) within the unglaciated Yukon Territory at the onset of glacial conditions during the Marine Isotope Stage 3/2 transition, between about 26 000 and 24500 14C yr BP. These data indicate that spruce trees were able to reproduce sexually and grow to maturity within a glacial environment characterized by widespread steppe-tundra vegetation, loess aggradation, and icewedge formation. These trees may have been restricted to rare valley-bottom habitats that provided adequate shelter and moisture similar to those at the present latitudinal tree line. Previously published hypotheses suggest that low Picea frequencies in regional Beringian pollen data point to the local persistence of spruce trees through the last glaciation. Although our data provide evidence for local spruce trees at the onset of the last glaciation, the available macrofossil record is inconclusive regarding the survival of spruce through the Last Glacial Maximum in Eastern Beringia. These new plant macrofossil data require palynologists to reexamine the relationship between Picea pollen frequency and local trees and highlight the importance of integrated pollen- and macrofossil-based paleoecological reconstructions.De nouveaux macrofossiles de plantes datés au C14 attestent de la présence d’épinette noire (Picea mariana) et d’épinette blanche (Picea glauca) dans le territoire non glaciaire du Yukon au début des conditions glaciaires, pendant la transition Marine Isotope Stage 3/2, et s’étendant entre environ 26 000 et 24 500 années avant le présent, daté au C14. Selon ces données, les épinettes étaient capables de se reproduire par voie sexuée et de croître jusqu’à maturité dans un milieu glaciaire caractérisé par une végétation à forte densité de steppe et de toundra, par l’aggradation de loess et par une formation de glace fossile. Il se peut que ces arbres se limitaient à de rares habitats au fond de vallées, habitats qui leur procuraient un abri adéquat et un degré d’humidité similaires à ceux qui existent dans la limite actuelle transversale de végétation des arbres. D’après des hypothèses déjà publiées, la faible fréquence de Picea dans les données régionales de pollen bérégien laissent supposer la persistance locale des épinettes pendant la dernière glaciation. Bien que nos données fournissent la preuve de l’existence d’épinettes locales au début de la dernière glaciation, les données macrofossiles disponibles ne sont pas concluantes en ce qui a trait à la survie de l’épinette pendant le dernier maximum glaciaire dans la Béringie de l’Est. Ces nouvelles données macrofossiles de plantes impliquent que les palynologues doivent réexaminer la relation entre la fréquence du pollen de Picea et les arbres locaux, et font ressortir l’importance des reconstructions paléoécologiques intégrées du pollen et des macrofossiles

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

Stable Carbon isotope compositions of Eastern Beringian grasses and sedges: investigating their potential as paleoenvironmental indicators

The nature of vegetation cover present in Beringia during the last glaciation remains unclear. Uncertainty rests partly with the limitations of conventional paleoecological methods. A lack of sufficient taxonomic resolution most notably associated with the grasses and sedges restricts the paleoecological inferences that can be made. Stable isotope measurements of subfossil plants are frequently used to enhance paleoenvironmental reconstructions. We present an investigation of the stable carbon isotope composition (d13C) of modern and subfossil grasses and sedges (graminoids) from Eastern Beringia. Modern grasses from wet habitats had a mean d13C of 229.1% (standard deviation [SD] 5 2.1%, n 5 75), while those from dry habitats had a mean of 226.9% (SD 5 1.19, n 5 27). Sedges (n 5 ,50) from dry, wet, marsh, and sand dune habitats had specific habitat ranges. Four modern C4 grasses had d13C values typical of C4 plants. Analyses were also conducted using subfossil graminoid remains from several sedimentary paleoecological contexts (e.g.,arctic ground squirrel nests, loess, permafrost, and paleosols) in Eastern Beringia. Results from these subfossil samples, ranging in age from .40,000 to ca. 11,000 cal. yr BP, illustrate that the d13C of graminoid remains has altered during the past. The range of variation in the subfossil samples is within the range from modern graminoid specimens from dry and wet habitats. The results indicate that stable isotopes could contribute to a comprehensive and multiproxy reconstruction of Beringian paleoenvironments

A multidisciplinary study of a late Pleistocene arctic ground squirrel (Urocitellus parryii) midden from Yukon, Canada

Plant science

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. Copyright © 2019 Massachusetts Medical Society