Noetinger S.,Museo Argentino de Ciencias Naturales Bernardino Rivadavia
Palaeogeography, Palaeoclimatology, Palaeoecology | Year: 2015
Devonian deposits in northwestern Argentina were historically studied with stratigraphical purposes, since these layers conform the source rocks of the producing basins of the region. A fairly well preserved palynomorph assemblage, from the Tonono Formation, provides an opportunity to perform the first quantitative analysis to study the evolution of diversity in the succession. Two associations are here defined by both, stratigraphic distribution of species and cluster analysis, ranging from the lower Eifelian to the lower Givetian. Rarefaction analysis reveals the existence of a relatively rich miospore population. Species richness increases while there is a drop in diversity and evenness towards the top of the column. The increment of the marine components towards the latter section indicates shifts in the shoreline. The influx of warmer water into higher latitudes, as highlighted by the arrival of the brachiopod Tropidoleptus, could have favored the inception of new spore species in the settled community. These results add to evidence that some groups build up the number of species in disturbed settings, and evenness is reduced with each new species introduced. © 2014 Elsevier B.V.
Cruz L.E.,Museo Argentino de Ciencias Naturales Bernardino Rivadavia
Journal of South American Earth Sciences | Year: 2013
In the last twenty years, several geological and stratigraphical studies have been undertaken in Córdoba Province, and they have provided useful bases for biostratigraphic work in the late Cenozoic. However, paleontological contributions have been limited to preliminary analyses of mammal assemblages, or specific discoveries. The aim of this work is to contribute to biostratigraphic knowledge of Argentina through the study of late Cenozoic mammals from Córdoba Province. Five localities have been analyzed: San Francisco, Miramar, Río Cuarto, Isla Verde, and Valle de Traslasierra. Through biostratigraphic analysis the first records of several taxa were established, and mammal assemblages with the description and correlation of the sedimentary strata were confirmed. Finally, three Assemblage Zones (Biozonas de Asociación) were proposed: 1) Neosclerocalyptus paskoensis-Equus (Amerhippus) assemblage zone with type area and profile based on the San Francisco locality, referred to the Lujanian (late Pleistocene-early Holocene), and comparable to the Equus (Amerhippus) neogeus Biozone of Buenos Aires Province; 2) Neosclerocalyptus ornatus-Catonyx tarijensis assemblage zone with type area and profile based on the San Francisco locality, referred to the Ensenadan (early Pleistocene) and comparable to the Mesotherium cristatum Biozone of Buenos Aires Province, and 3) Nonotherium hennigi-Propanochthus bullifer assemblage zone with type area and profile based on the Los Sauces river, Valle de Traslasierra, referred to the Montehermosan-Chapadmalalan interval (Pliocene), and comparable to the Trigodon gaudryi, Neocavia depressidens and/or Paraglyptodon chapadmalensis Biozones of Buenos Aires Province. © 2012 Elsevier Ltd.
Michalik P.,University of Greifswald |
Ramirez M.J.,Museo Argentino de Ciencias Naturales Bernardino Rivadavia
Arthropod Structure and Development | Year: 2014
The male reproductive system and spermatozoa of spiders are known for their high structural diversity. Spider spermatozoa are flagellate and males transfer them to females in a coiled and encapsulated state using their modified pedipalps. Here, we provide a detailed overview of the present state of knowledge of the primary male reproductive system, sperm morphology and the structural diversity of seminal fluids with a focus on functional and evolutionary implications. Secondly, we conceptualized characters for the male genital system, spermiogenesis and spermatozoa for the first time based on published and new data. In total, we scored 40 characters for 129 species from 56 families representing all main spider clades. We obtained synapomorphies for several taxa including Opisthothelae, Araneomorphae, Dysderoidea, Scytodoidea, Telemidae, Linyphioidea, Mimetidae, Synotaxidae and the Divided Cribellum Clade. Furthermore, we recovered synspermia as a synapomorphy for ecribellate Haplogynae and thus propose Synspermiata as new name for this clade. We hope that these data will not only contribute to future phylogenetic studies but will also stimulate much needed evolutionary studies of reproductive systems in spiders. © 2014 Elsevier Ltd.
Prevosti F.J.,Museo Argentino de Ciencias Naturales Bernardino Rivadavia
Cladistics | Year: 2010
South America currently possesses a high diversity of canids, comprising mainly small to medium-sized omnivorous species, but in the Pleistocene there were large hypercarnivorous taxa that were assigned to Protocyon spp., Theriodictis spp., Canis gezi, Canis nehringi and Canis dirus. These fossils have never been included in phylogenies based on quantitative cladistics, but hand-constructed cladograms published in the 1980s included some of them in the South American canine clade and others in the Canis clade. In this work, the phylogenetic position of the large extinct South American canids was studied using a large sample of living and extinct canids, as well as different sources of characters (e.g. DNA and 133 osteological characters). The phylogenetic analysis corroborates the inclusion of Theriodictis and Protocyon in the " South American clade" , where C. gezi is also included. In addition, the position of C. dirus as a highly derived Canis species is confirmed. The simultaneous analysis supports hypercarnivory having arisen at least three times in Caninae and once in the " South American clade" The combination of the phylogenetic analyses, the fossil record and divergence dates estimated in previous works suggests that at least three or four independent lineages of the " South American clade" invaded South America after the establishment of the Panama bridge around 3 million years ago, plus other events corresponding to the immigration of Urocyon and Canis dirus.© The Willi Hennig Society 2009. © The Willi Hennig Society 2009.
Ezcurra M.D.,Museo Argentino de Ciencias Naturales Bernardino Rivadavia
Journal of Systematic Palaeontology | Year: 2010
It was traditionally thought that the oldest known dinosaur assemblages were not diverse, and that their early diversification and numerical dominance over other tetrapods occurred during the latest Triassic. However, new evidence gathered from the lower levels of the Ischigualasto Fm. of Argentina challenges this view. New dinosaur remains are described from this stratigraphical unit, including the new species Chromogisaurus novasi. This taxon is distinguished from other basal dinosauriforms by the presence of proximal caudals without median notch separating the postzygapophyses, femoral lateral surface with deep and large fossa immediately below the trochanteric shelf, and metatarsal II with strongly dorsoventrally asymmetric distal condyles. A phylogenetic analysis found Chromogisaurus to lie at the base of Sauropodomorpha, as a member of Guaibasauridae, an early branch of basal sauropodomorphs composed of Guaibasaurus, Agnosphitys, Panphagia, Saturnalia and Chromogisaurus. Such an affinity is for the first time suggested for Guaibasaurus, whereas Panphagia is not recovered as the most basal sauropodomorph. Furthermore, Chromogisaurus is consistently located as more closely related to Saturnalia than to any other dinosaur. Thus, the Saturnalia + Chromogisaurus clade is named here as the new subfamily Saturnaliinae. In addition, Eoraptor is found to be the sister-taxon of Neotheropoda, and herrerasaurids to be non-eusaurischian saurischians. The new evidence presented here demonstrates that dinosaurs first appeared in the fossil record as a diverse group, although they were a numerically minor component of faunas in which they occur. Accordingly, the early increase of dinosaur diversity and their numerical dominance over other terrestrial tetrapods were diachronous processes, with the latter preceded by a period of low abundance but high diversity.© 2010 The Natural History Museum.