1. Control geológico y climático del sistema Andino-Amazónico y de su biodiversidad

Los excepcionales recursos naturales de la Amazonia son el fruto de una larga historia geológica y climática en la que los Andes juegan un papel determinante. Desde su creación hasta la actualidad, el Impacto de esta cadena montañosa sobre el ambiente de la reglón ha dado forma a las faunas y floras sucesivas y sus distribuciones. Regulador de las precipitaciones y de la fantástica biodiversidad animal y vegetal de la región, el sistema geoclimático andino-amazónico debe ser considerado como un elemento fundamental a la hora de estudiar el impacto del cambio climático en la región.Les ressources naturelles exceptionnelles de l’Amazonie sont le fruit d’une longue histoire géologique et climatique où les Andes jouent un rôle déterminant. Depuis son apparition jusqu’á nos jours, l’impact de cette chaîne de montagne sur l’environnement de la région a donné forme aux faunes et flores successives et leurs distributions. Régulateur des précipitations et de la fantastique biodiversité de la région, le système géo-climatique andino-amazonien doit être considéré comme un élément fondamental si l’on souhaite étudier l’impact du changement climatique dans la région.The extraordinary natural resources of the Amazon region are the result of a long geological and climatic history, where the Andes play a decisive role. This mountain range has impacted on the environment of the region, arraying Flora and Fauna, and its successive distribution since its origin to the present. As a regulator of rainfalls and of the fantastic animal and vegetal biodiversity of the region, the Andean-Amazon geo-climate system must be considered as an essential element to study the Climate Change impact in the region

Synergistic roles of climate warming and human occupation in Patagonian megafaunal extinctions during the Last Deglaciation.

The causes of Late Pleistocene megafaunal extinctions (60,000 to 11,650 years ago, hereafter 60 to 11.65 ka) remain contentious, with major phases coinciding with both human arrival and climate change around the world. The Americas provide a unique opportunity to disentangle these factors as human colonization took place over a narrow time frame (~15 to 14.6 ka) but during contrasting temperature trends across each continent. Unfortunately, limited data sets in South America have so far precluded detailed comparison. We analyze genetic and radiocarbon data from 89 and 71 Patagonian megafaunal bones, respectively, more than doubling the high-quality Pleistocene megafaunal radiocarbon data sets from the region. We identify a narrow megafaunal extinction phase 12,280 ± 110 years ago, some 1 to 3 thousand years after initial human presence in the area. Although humans arrived immediately prior to a cold phase, the Antarctic Cold Reversal stadial, megafaunal extinctions did not occur until the stadial finished and the subsequent warming phase commenced some 1 to 3 thousand years later. The increased resolution provided by the Patagonian material reveals that the sequence of climate and extinction events in North and South America were temporally inverted, but in both cases, megafaunal extinctions did not occur until human presence and climate warming coincided. Overall, metapopulation processes involving subpopulation connectivity on a continental scale appear to have been critical for megafaunal species survival of both climate change and human impacts

Synergistic roles of climate warming and human occupation in Patagonian megafaunal extinctions during the Last Deglaciation

The causes of Late Pleistocene megafaunal extinctions (60,000 to 11,650 years ago, hereafter 60 to 11.65 ka) remain contentious, with major phases coinciding with both human arrival and climate change around the world. The Americas provide a unique opportunity to disentangle these factors as human colonization took place over a narrow time frame (~15 to 14.6 ka) but during contrasting temperature trends across each continent. Unfortunately, limited data sets in South America have so far precluded detailed comparison. We analyze genetic and radiocarbon data from 89 and 71 Patagonian megafaunal bones, respectively, more than doubling the high-quality Pleistocene megafaunal radiocarbon data sets from the region. We identify a narrow megafaunal extinction phase 12,280 ± 110 years ago, some 1 to 3 thousand years after initial human presence in the area. Although humans arrived immediately prior to a cold phase, the Antarctic Cold Reversal stadial, megafaunal extinctions did not occur until the stadial finished and the subsequent warming phase commenced some 1 to 3 thousand years later. The increased resolution provided by the Patagonian material reveals that the sequence of climate and extinction events in North and South America were temporally inverted, but in both cases, megafaunal extinctions did not occur until human presence and climate warming coincided. Overall, metapopulation processes involving subpopulation connectivity on a continental scale appear to have been critical for megafaunal species survival of both climate change and human impacts.Jessica L. Metcalf, Chris Turney, Ross Barnett, Fabiana Martin, Sarah C. Bray, Julia T. Vilstrup, Ludovic Orlando, Rodolfo Salas-Gismondi, Daniel Loponte, Matías Medina, Mariana De Nigris, Teresa Civalero, Pablo Marcelo Fernández, Alejandra Gasco, Victor Duran, Kevin L. Seymour, Clara Otaola, Adolfo Gil, Rafael Paunero, Francisco J. Prevosti, Corey J. A. Bradshaw, Jane C. Wheeler, Luis Borrero, Jeremy J. Austin, Alan Coope

A 6,000+ year-old specimen of a spectacled bear from an Andean cave in Peru

STUCCHI, Marcelo. [et al.]. A 6,000+ year-old specimen of a spectacled bear from an Andean cave in Peru. Ursus. [en línea]. 2009, 20, 1, p. 63–68. ISSN 1537-6176.We report the discovery of a partial skeleton of the oldest spectacled bear (Tremarctos ornatus) known to date. It was found at 2,950 m elevation in the Chaquil cave, in the Departamento de Amazonas, north central Peru. Its age, as determined by accelerated mass spectrometry conventional radiocarbon dating, was, within 50 years, 5,980 years before present (YBP). After a standard correction for Holocene irregularities of atmospheric 14 C (carbon 14) levels, this conventional radiocarbon age translates into a calendar age of about 6,790 years before present. Anatomical features of the skull shows no significant differences from extant spectacled bears. Comparative analysis of Chaquil remains with those of modern specimens revealed some intraspecific variation at the sagittal crest, mandibular ramus and symphysis, masseteric crest, and coronoid process. We suggest that the extremely worn teeth, with the pulpar cavity exposed in the sub-fossil, are related to a primarily carnivorous diet

Sobre el origen de la biodiversidad amazónica

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Implication of the presence of Megathericulus (Xenarthra : Tardigrada : Megatheriidae) in the Laventan of Peruvian Amazonia

Middle Miocene remains of giant megatheriine ground sloths (Tardigrada: Megatherioidea) are scarce and generally located in southern South America. The discovery of a well-preserved edentulous dentary of Megathericulus sp. from the Middle Miocene (Laventan South American Land Mammal Age - SALMA; 13.5–11.8 Ma) of the Amazonian Peru increases our knowledge of this genus, which had previously been recognized in Argentina. A preliminary revision of the earliest Megatheriinae allowed clustering the four middle Miocene species within the genus Megathericulus Ameghino: M. patagonicus Ameghino, M. primaevus Cabrera, M. andinum (Kraglievich), and M. cabrerai (Kraglievich). This small-sized genus is mainly characterized by a lateral depression that borders m1, a posterior external opening of the mandibular canal anterior to the base of the ascending ramus that opens anteriorly or anterodorsally, the base of the symphysis located anteriorly to the m1, important anteroposterior compression of the teeth, elongation of the region of the maxilla anterior to the M1, humerus elongated and gracile, patellar trochlea of femur contiguous with medial and lateral articular facets for tibia, strongly developed odontoid tuberosity, and astragalus with prominent odontoid process. The genus Eomegatherium Kraglievich is therefore restricted to the Huayquerian SALMA of Argentina and represented by a single species, E. nanum Burmeister. Megatheriinae constitute the first clade of Tardigrada in which the caniniform tooth has been secondarily modified into a molariform tooth. Three molariform patterns can be observed during megatheriine evolution in relation to tooth compression and loph or lophid orientation. Middle Miocene Megatheriinae occur only in the westernmost part of South America. These giant ground sloths might have dispersed latitudinally from Colombia/Patagonian Argentina before colonizing eastern areas of Andean South America (Bolivia, Venezuela, north, and east of Argentina) during the late Miocene and early Pliocene.Fil: Pujos, François Roger Francis. Consejo Nacional de Investigaciones Científicas y Técnicas. Científico Tecnológico Mendoza. Instituto Argentino de Nivología, Glaciología y Ciencias Ambientales; Argentina. Institut Français d’ Etudes Andines; PerúFil: Salas Gismondi, Rodolfo. Universidad Nacional Mayor de San Marcos. Museo de Historia Natural. Departamento de Paleontología de Vertebrados; PerúFil: Baby, Guillaume. Université de Toulouse; FranciaFil: Baby, Patrice. Université de Toulouse; Francia. Centre National de la Recherche Scientifique. Laboratoire de Mécanismes de Transfert en Géologie; FranciaFil: Goillot, Cyrille. Université de Toulouse; Francia. Centre national de la recherche scientifique. Laboratoire de Mécanismes de Transfert en Géologie; FranciaFil: Tejada, Julia. Universidad Nacional Mayor de San Marcos. Museo de Historia Natural. Departamento de Paleontología de Vertebrados; PerúFil: Antoine, Pierre Olivier. Université Montpellier. Institut des Sciences de l’Evolution; Franci

New Miocene Caribbean gavialoids and patterns of longirostry in crocodylians

Gavialoidea is a clade of slender- and long-snouted crocodylomorphs with a single living species, the Indian gharial Gavialis gangeticus. Because elongated snouts (longirostry) have evolved independently in several crocodylomorph clades, this head shape has been interpreted as an ecological adaptation. How this condition affected patterns of diversification and how longirostrineassociated cranial features changed through adaptive radiations remain poorly understood. Two new small gryposuchine gavialoids, Dadagavialis gunai gen. et sp. nov. (early Miocene, Panama) and Aktiogavialis caribesi sp. nov. (late Miocene, Venezuela), evidence remarkable Miocene diversification of longirostrine forms in the Neotropics and support transmarine biogeographical relations between northern South America, the Caribbean, and southernmost North America before the Isthmus of Panama was fully established. By integrating phylogenetics and geometric morphometrics, we focus on this gavialoid diversity to investigate patterns of longirostry across the crown group of crocodylomorphs (Crocodylia). Analyses revealed that the snout shape of gavialoids has occupied a small, distinct and almost invariable morphospace since the Cretaceous, in contrast with the morphologically labile snout shape of other crocodylians (crocodyloids and alligatoroids). Our results suggest iterative environmental shift occupations throughout gavialoid evolution without major changes in snout proportions, but involving conspicuous rearrangements of the circumorbital bones. The longirostrine gavialoid morphotype is a distinct adaptation for seizing small prey and typically includes short and wide premaxillae and enlarged ‘caniniform’ teeth only at the tip of the snout. In longirostrine crocodyloids (Tomistoma, Crocodylus intermedius), the conservation of powerful bites and ‘caniniforms’ closer to the jaw joints allowed them to exploit a wider range of prey sizes, which could explain their snout shape plasticity. Therefore, the Mio–Pliocene extirpation of gryposuchine gavialoids from the Caribbean by the arrival of Crocodylus is quite unlikely. The last gryposuchine survived throughout the Pliocene in the south-eastern Pacific, where Crocodylus has never been documented

A Miocene relative of the Ganges River dolphin (Odontoceti, Platanistidae) from the Amazonian Basin

A new fossil platanistine (Cetacea, Platanistidae) specimen is described: a periotic from the middle Miocene of Peruvian Amazonia. This highly diagnostic ear bone provides insights on the shifts to freshwater environments by various odontocete clades, a phenomenon probably underestimated due to the lack of fossils from the freshwater sedimentary record, and probably not just limited to extant clades of freshwater odontocete