National University of Río Negro

About: National University of Río Negro is a education organization based out in Viedma, Argentina. It is known for research contribution in the topics: Population & Cretaceous. The organization has 606 authors who have published 1181 publications receiving 15230 citations. The organization is also known as: UNRN.

Los documentos como campo. Reflexiones teórico-metodológicas sobre un enfoque etnográfico de archivos y documentos estatales

Abstract: Resumen es: En este articulo reflexionamos sobre las aproximaciones utilizadas en nuestras respectivas investigaciones, sobre las logicas de funcionamiento de instit...

Coarse-grained sediment waves in hyperpycnal clinoform systems, Miocene of the Austral foreland basin, Argentina

Abstract: In this paper we present an outcrop example of coarse-grained sediment waves generated by hyperpycnal discharges at the toe of Miocene clinoform systems exposed in the northeast Atlantic coast of Tierra del Fuego, Argentina. An individual set of these sediment waves is formed during the waxing and waning phases of the hyperpycnal discharge. During the waxing phase, accumulation of coarse-grained sediments with generation and migration of dune bedforms occurs at the base of the clinoforms. These deposits show transitions of tractive sedimentary structures with evidence of bedload transport, and a continuous reworking by the overpassing hyperpycnal flow. The continued erosion and reworking during the waxing phase affect mainly the top and the stoss side of the dunes, resulting in isolated lenses having upcurrent aggradation structures. During the waning phase, these isolated lenses are covered by fine-grained heterolithic strata that are thicker on the stoss side than on the lee side, constituting a differential draping. The pulsating and sustained character of the hyperpyc­nal flows and the steep depositional slope clinoforms controlled the stacking­ pattern of the coarse-grained sediment waves during successive hyperpycnal events. In this way, small-scale, coarse-grained sediment waves, with wavelengths of 10–40 m and up to 5 m amplitude, and a stacking pattern showing an up-current growth, are generated by high-density hyperpycnal flows on slopes having steep gradients.

Stingless bees further improve apple pollination and production

Abstract: The use of Africanised honeybee ( Apis mellifera scutellata Lepeletier) hives to increase pollination success in apple orchards is a widespread practice. However, this study is the first to investigate the number of honeybee hives ha -1 required to increase the production of fruits and seeds as well as the potential contribution of the stingless bee Mandacaia ( Melipona quadrifasciata anthidioides Lepeletier). We performed tests in a 43-ha apple orchard located in the municipality of Ibicoara (13o24’50.7’’S and 41o17’7.4’’W) in Chapada Diamantina, State of Bahia, Brazil. In 2011, fruits from the Eva variety set six seeds on average, and neither a greater number of hives (from 7 to 11 hives ha -1 ) nor a greater number of pollen collectors at the honeybee hives displayed general effects on the seed number. Without wild pollinators, seven Africanised honeybee hives ha -1 with pollen collectors is currently the best option for apple producers because no further increase in the seed number was observed with higher hive densities. In 2012, supplementation with both stingless bees (12 hives ha -1 ) and Africanised honeybees (7 hives ha -1 ) provided higher seed and fruit production than supplementation with honeybees (7 hives ha -1 ) alone. Therefore, the stingless bee can improve the performance of honeybee as a pollinator of apple flowers, since the presence of both of these bees results in increases in apple fruit and seed number.

A large accumulation of avian eggs from the late cretaceous of patagonia (Argentina) reveals a novel nesting strategy in mesozoic birds.

Abstract: We report the first evidence for a nesting colony of Mesozoic birds on Gondwana: a fossil accumulation in Late Cretaceous rocks mapped and collected from within the campus of the National University of Comahue, Neuquen City, Patagonia (Argentina). Here, Cretaceous ornithothoracine birds, almost certainly Enanthiornithes, nested in an arid, shallow basinal environment among sand dunes close to an ephemeral water-course. We mapped and collected 65 complete, near-complete, and broken eggs across an area of more than 55 m2. These eggs were laid either singly, or occasionally in pairs, onto a sandy substrate. All eggs were found apparently in, or close to, their original nest site; they all occur within the same bedding plane and may represent the product of a single nesting season or a short series of nesting attempts. Although there is no evidence for nesting structures, all but one of the Comahue eggs were half-buried upright in the sand with their pointed end downwards, a position that would have exposed the pole containing the air cell and precluded egg turning. This egg position is not seen in living birds, with the exception of the basal galliform megapodes who place their eggs within mounds of vegetation or burrows. This accumulation reveals a novel nesting behaviour in Mesozoic Aves that was perhaps shared with the non-avian and phylogenetically more basal troodontid theropods.