Showing papers by "National University of Comahue published in 1997"

Evolution of titanosaurid sauropods. 1:phylogenetic analysis based on the postcranial evidence

Abstract: "The phylogenetic relationships of titanosaurid sauropods are examined by means of a clodistic parsimony analysis based on postcranel features. Eusauropoda tBarapasaurus tagorei + Neosauropoda) have, at least, two synapomorphies. The Camarasauromorpha (Camarasauridae + Titanosauriformes) have five synapomorphies. The Titanosauriformes [Brachiosaurus brancai + tChubunsaurus insignis + Titanosauria)] share six derived characters (e.g., presence of medial prespinallamina in posterior trunk vertebrae, neural arches positioned anteriorly in mid and posterior caudal centra, c1aw on manual digit 1reduced or absent). Chubutisaurus insignis Del Corro shares with Titanosauria one apomorphy. Titanosauria is rediagnosed based on five synapomorphies (e.g., eye-shape pleurocoels in trunk vertebrae, anterior caudals procoelous, pubis considerably longer than ischium). Titanosauridae comprises titanosaurids with: absence of hyposphene-hypantrum articulation in posterior trunk vertebrae, six sacral vertebrae, anterior caudals strongly procoelous having ""ball and socket"" articular faces, mid and posterior caudals strongly procoelous, semilunar sternal plates, claw on manual digit I absent, manual phalanges absent and preacetabular lobe of ilium nearly horizontal, outwardly projected. Titanosaurids more derived than Epachthosaurus sciuttoi Powell and Malawisaurus dixeyi Haughton have medial prespinal lamina formed down to the base of neural spine in posterior trunk vertebrae and quadrangular coracoids. Argentinosaurus huinculensis Bonaparte and Coria, Opisthocoelicaudia skarzynskii Borsuk-Bialynicka and Titanosauridae indet*(DGM ""Serie B"") form a monophyletic group characterized by presence of accesory spino-diapophyseallaminae in trunk vertebrae. Aeolosaurus Powell shares with Alamosaurus sanjuanensis Gilmore and the Saltasaurinae biconvex first caudal and presence of dorsal prominence on inner face of scapula. Alamosaurus sanjuanensis is the sister-taxon of the Saltasaurinae."

Evolution of titanosaurid sauropods. ii: the cranial evidence

Abstract: "The titanosaurid skull is interpreted as Camarasaurus-Iike, but with ""peg-like"" teeth restricted to the extremity of the jaws, which exhibit wear facets sharply inclined with respect to the labio-lingual axis. The last character is shared with Brachiosaurus Riggs and Pleurocoelus Marsh, and it is considered a probable synapomorphy of Titanosauriformes. Several cranial characters are considered synapomorphies of Titanosauria or a less inclusive group (long recurved paraoccipital processes, becoming slender downwards; reduced, narrow supratemporal fenestra), or synapomorphies within Titanosauridae (""peg-Iike"" teeth; teeth restricted ro the anterior region of the snout and mandibular symphysis perpendicular to the long axis of the lower jaw). Several characters, such as ""peg-like"" teeth restricted to the anterior region of the snout, wear facets sharply inclined with respect to the labiolingual tooth axis, and mandibular symphysis perpendicular to the long axis of the lower jaw, suggest that Nemegtosaurus mongoliensis Nowinski and Quaesitosaurus orientalis Kurzanov and Banikov are related to the Titanosauridae. ""Pleurocoelus"" sp., from the Lower Cretaceous of Texas and Utah, is considered a basal titanosaur by having procoelous anterior caudals, teeth with an intermediate morphology between Brachiosaurus and titanosaurids, and dorsal verterbrae with centro-parapophyseallamina and ventrally widened, sligthly forked infradiapophyseal Iarnina. Basal titanosaurs and other titanosaur-related sauropods had a wide distribution during the Early Cretaceous. The hypothesis that Alamosaurus sanjuanensis Gilmore is a Late Cretaceous inmigrant from South America is consistent with its phylogenetic position. The Saltasaurinae, in turn, represent an endemic group of South America. "

School yards and nature trails: ecology education outside the university

Abstract: Ecologists, conservation biologists and other natural historians increasingly recognize the need to become involved in public education. An ecologically literate public may be the 'last best hope' for a sustainable biosphere. Partnerships between ecologists and educators may be the best hope, though not the last, for moving towards an ecologically literate public. What are some practical schemes for such partnerships? We present a model for ecology education that has shown promise in several South American settings and describe its application in two quite different contexts in southern Argentina. We hope that our colleagues will ponder, criticize, modify, improve and apply the model in settings other than those we present here.

Influence of local floral density and sex ratio on pollen receipt and seed output: empirical and experimental results in dichogamous Alstroemeria aurea (Alstroemeriaceae).

Abstract: Local density and sexual composition are two aspects of floral neighborhoods thought to influence pollination and seed output of recipient plants. I characterized the floral neighborhood of 436 flowering ramets of Alstroemeria aurea, a southern Andean perennial, distributed among three sites. On each ramet, I measured total pollen receipt and seed output. The long-lived, bumblebee-pollinated flowers of A. aurea are synchronously protandrous with a given ramet being either all male or all female and thus incapable of self or geitonogamous pollination at the ramet level. Even though each ramet changes sex over time, A. aurea forms floral neighborhoods that remain stable with respect to density and sex ratio during the span of a focal ramet female phase. Contrary to expectation, under field conditions neither local density nor sexual identity explained significant amounts of variation in pollen receipt. Density of neighboring flowering ramets marginally affected pollen receipt in two of the three populations but in opposite directions. Despite the absence of strong effects of neighborhood sexual composition on pollen receipt, the sexual identity of neighbors affected seed output which suggests effects on the quality of pollination due to changes in patterns of pollen flow. I also compared pollen loads on the stigmas of artificially isolated ramets (6 m) with those on experimental focal ramets surrounded by six close neighbors (20 cm) that were either all male or all female. Here, pollen receipt by focal ramets in all-male neighborhoods was 1.3 times greater than in isolated ramets, and 3.8 times greater than in ramets in all-female neighborhoods. In these artificial neighborhoods, stigmatic pollen deposition increased significantly over time. In nature, rates of bumblebee visits were higher in female-biased (early-flowering) than in male-biased (late-flowering) co-occurring floral patches. Thus, spatio-temporal shifts in visitation frequencies associated with the sexual composition of floral neighborhoods might compensate for spatial variability in pollen availability within populations and explain the discrepancies between empirical and experimental results.

The generalized Ornstein-Uhlenbeck process

Abstract: Langevin-like equations have been studied in the presence of arbitrary noise. The characteristic functional of the generalized Langevin process has been built up. Exact results for all cumulants are given. Particular stress has been put on the Campbell, dichotomous and radioactive decay noises. Transient relaxation, susceptibility and diffusion constants for different (noisy) media have been sketched in order to exemplify the theory. The generalized Ornstein - Uhlenbeck and Wiener processes have been completely characterized. The generalized Kubo oscillator has been worked out and all its 1-time moments have been calculated for different noise structures.

New materials of Gasparinisaura cincosaltensis (Ornithischia, Ornithopoda) from the Upper Cretaceous of Argentina

Abstract: New material of Gasparinisaura cincosaltensis from the Rio Colorado Formation (Upper Cretaceous) of northwestern Patagonia (Rio Negro Province, Argentina) provides seven new characters that are interpreted as autapomorphies of the species: 1) four true sacrals; 2) first sacral rib not coalescent with second sacral rib; 3) long pubic peduncle of ilium; 4) absence of anterior intercondylar groove on femur; 5) both malleoli of the tibia approximately at the same level; 6) metatarsal II posteriorly compressed laterally; and 7) low ascendant process of the astragalus. A phylogenetic analysis of selected ornithopods indicates that Gasparinisaura cincosaltensis is the most plesiomorphic Euiguanodontia. A complete absence of hatchlings indicates that Cinco Saltos was not a nest site.

Long‐term exposure of Boeckellagibbosa (Copepoda, Calanoida) to in situ levels of solar UVB radiation

Abstract: 1. The freshwater calanoid copepod Boeckella gibbosa is typical of high elevation lakes and ponds in Patagonia (Argentina). Previous studies have shown that this species is highly tolerant to short-term exposure to natural and artificial UVB radiation, and that its tolerance is due to photoreactivation by longer wavelength radiation. In this study, we investigate the potential sublethal effects of solar radiation after prolonged exposure. 2. We incubated B. gibbosa at 1 m depth in oligotrophic Lake Toncek for 24 days. The incubation chambers were 1.2 l acrylic cylinders covered with appropriate filters in order to obtain three radiation treatments: visible radiation only, visible radiation + UVA and visible radiation + UVA + UVB. 3. The three treatments did not differ significantly in variables considered as indicators of survival (number of individuals), reproduction (proportion of ovigerous females, clutch size) and development (instar composition). Although resistance to solar UVB radiation is certainly a requisite to live in transparent high elevation habitats, the fact of being effectively exposed to natural levels of UVB radiation does not seem to have measurable consequences on an already adapted species, such as B. gibbosa

Lethal temperatures of a Neotropical fish relic in Patagonia, the scale-less characinid Gymnocharacinus bergi

Abstract: Southern South America has a rather low fish species diversity. Gymnocharacinus bergi, the southernmost characid fish of the world, is the only member of Characoidei in the Argentine Patagonia. The isolation of this species in an endorheic stream has been linked to the thermal conditions of its habitat, the head-waters of the Valcheta Stream, which is the only site where this species occurs. We provide information on the distribution and thermal habitat of this species and other fishes in the Valcheta Stream. The responses of G. bergi to high and low temperatures were assessed in the laboratory under different temperatures and heating and cooling rates. Our results suggest that G. bergi is unable to extend its distribution to the colder waters nearby, as well as to waters with greater temperature fluctuations. We discuss the implications of our experimental data, the habitat of G. bergi, and the known responses of a few other paranensean fishes to temperature, within the framework of the thermal ecology of freshwater fishes.

Analytical and statistical analysis of elemental composition of lichens

Abstract: The elemental composition of lichens from remote southern South America regions has been studied with analytical and statistical techniques to determine if the values obtained reflect species, growth forms or habitat characteristics. The enrichment factors are calculated discriminated by species and collection site and compared with data available in the literature. The elemental concentrations are standardized and compared for different species. The information was statistically processed, a cluster analysis was performed using the three first principal axes of the PCA; the three groups formed are presented. Their relationship with the species, collection sites and the lichen growth forms are interpreted.

Redescription of Acanthocephalus tumescens (von Linstow, 1896) (Palaeacanthocephala: Echinorhynchidae) in Galaxias maculatus (Pisces: Galaxiidae) in Patagonia (Argentina)

Abstract: A redescription of Acanthocephalus tumescens is made using specimens taken from the digestive tube of Galaxias maculatus (Pisces, Galaxiidae) from Lake Gutierrez (Patagonia, Argentina). Information is presented concerning the characteristics of the praesoma, genital system and eggs which is additional to previous descriptions (von Linstow, 1896; Hartwich, 1955). Detailed descriptions and measurements of the hooks are also included.

Human diphyllobothriasis in Patagonia, Argentina

Abstract: OBJECTIVE: In view of the amateur fishing practices and the importance of salmonids in the region the study sets out to detect human hosts in the Andean-Patagonian zone. MATERIAL AND METHOD: Information campaigns were carried out by Clinical Analysis Laboratories of Andean Patagonia between 1986 and 1995 to detect diphyllobothriasis more efficiently by means of coproparasitological analysis. RESULTS: Further, forms were prepared for the collection of information about infection, treatment and the characteristics of the human host. During this period 13 new cases were registered either through direct identification of the parasite or through the presence of eggs in the faeces. The characteristics of infection are similar to those described for the genus Diphyllobothrium. CONCLUSIONS: The favourite game fish in Andean Patagonia are salmonids. This fish, often infected with plerocercoids, when eaten insufficiently cooked or cold smoked, constitutes the main source of human infection.

Helminth parasites of Larus dominicanus in Argentinian Patagonia

Abstract: The presence of 9 endohelminths was quoted for Larus dominicanus of which 6 were new citations in Patagonia (Argentina) for this host: Stephanoprora, Cryptocotyle, Anomotaenia, Polymorphus, Contracaecum and Capillaria. For the first time Cryptocotile is being cited in Argentina.

Influence of altered irradiance on fruits and leaves of mature pear trees

Abstract: The response of pear fruit and leaf parameters to shade imposed during development was studied. Whole branches of mature trees of Pyrus communis L. cv. Bartlett growing in the High Valley area of Argentina were covered with a shade cloth (80 % reduction in irradiance) from 6 to 18 weeks after full bloom (WAFB) during the 1995-96 growing season. Fruit diameter was measured at two-weekly intervals; flesh firmness, soluble solids concentration, and leaf area were determined 18 WAFB. Prolonged shading significantly reduced fruiting spur specific leaf mass and consequently resulted in 20.79 % less final fruit fresh mass. However, flesh firmness was 8.07 % lower under full irradiance.

Alsodes Australis, A New Species of Leptodactylid Frog from the Temperate Nothofagus Forest of Southern Chile and Argentina

Abstract: A new species of frog, Alsodes australis, is described from the temperate Nothofagus forest of southern Chile and Argentina, based on adults and tadpoles. Up to now, no sympatric occurrence of another congeneric species is known from the type locality. The genus comprises three species groups. From a karyological point of view this species is included in the monticola group, whose species have 26 chromosomes.

Relaciones suelo-paisaje en la evaluación de la potencialidad forestal de la región central andino-patagónica, Argentina

Abstract: The western region of the Argentinian Patagonia lies between parallels 36 and 46 and is characterised by a Mediterranean climate with a decreasing rainfall gradient of 100 mm/km in a west-cast direction starting from an annual rainfall of 3.5 to 4 m in the Argentina-Chile border. The area is mountainous with absolute height variations between 800 and 1000 m covered with a thick basic holocenic Piroclastic layer. The marked variation in the climate gives way to rapid changes in the magnitude of the pedogenetic processes, on the volcanic ash. The magnitude of the andosolization process gives way to different soil characteristic with significant impact on the vegetation that is linked to how the water retention is taken advantage of at the end of the dry season. The hydric balance (latitude/altitude/exposure and gradient) linked to the landscape characteristics, become important when the soil maps are drawn and their interpretation is done in order to evaluate forest productivity. In conclusion, at the time of defining forest potential, the selection of adequate soil characteristic (Soil Landscape relationship) becomes an important aspect.

Aportes a la descripción morfológica de Tylodelphys barilochensis y Tylodelphis crubensis (Trematoda, Diplostomidae) parásitos del encéfalo de Galaxias maculatus (Teleostei, Galaxiidae)

Abstract: Taxonomic characteristics, for species identification, of metacercarie of T. barilochensis and T. crubensis found in the encephalon of the fish Galaxias maculatus, not included in the original descriptions, particularly those concerning to the excretory system, are described.

Some physical and biological factors affecting a spring‐summer phytoplankton dynamics in a shallow, temperate lake of South Andes (Argentina)

Abstract: The phytoplankton dynamics of Laguna Ezquerra (Rio Negro, Argentina) was analysed on the basis of high frequency sampling, each 3-4 days during a spring-summer period, in relation to physical factors and to the zooplankton community structure. The phytoplankton biomass presented a marked seasonality, accompanied by similar seasonal patterns in temperature and zooplankton dynamics. Community variations were reflected in the diversity, dominance and equitability values. The greatest change was associated during a short flooding period produced in late spring. The wind exposure was irregular during the whole study period, and was assumed to be a factor of stress for the phytoplankton growth. During spring and early summer, the phytoplankton community was dominated by nanoplanktonic forms like Rhodomonas lacustris, and the large sized Asterionella formosa presented an exponential increment at late summer. This Asterionella growth permitted to affirm that the community evolved towards plagioclimatic stages, attending the highly disturbed conditions of the shallow and wind exposed environment.

Reduction of vibrations in complex structures with viscoelastic neutralizers: a generalized approach and a physical realization

Abstract: A general procedure for the optimization of the parameters of dynamic neutralizers is reviewed. It can be applied to the minimization of the vibration response and sound radiation of linear structures subjected to excitations in a specified frequency range. Modal theory and generalized equivalent quantity concept for the neutralizers, introduced by Espindola and Silva (1992), as applied to a non-linear optimization scheme, are also reviewed for clarity. That proposed procedure can be applied to relaxed and time invariant structures. It is not dependent on the structure complexity and the degree of discretization adopted. In such conditions, a significant reduction in computing work is achieved, if compared with the more traditional methods. Experimental results are compared with numerical ones.

[Contribution to the morphological description of Tylodelphys barilochensis and Tylodelphys crubensis (Trematoda, Diplostomidae) encephalon parasites of Galaxias maculatus (Teleostei, Galaxiidae)].

Abstract: Taxonomic characteristics, for species identification, of metacercarie of T. barilochensis and T. crubensis found in the encephalon of the fish Galaxias maculatus, not included in the original descriptions, particularly those concerning to the excretory system, are described.

Noé Jitrik. Historai e imaginación literaria. Las posibilidades de un género, Buenos Aires, Biblios, 1995.

Abstract: En lo que va de la presente decada son pocos los trabajos de relevancia que han puesto su atencion a la novela historica. Recientemente, el libro de Seymour Menton que se titula La nueva novela historica de America Latina (1993) se propone ofrecer una presentacion del estado de la cuestion atendiendo a la emergencia de la produccion narrativa latinoamericana de los ultimos treinta anos. De modo que “nueva” aqui supne un corte y este lo representa un texto. El reino de este mundo, de A Carpentier. A partir de este punto de insercion, intenta precisar los rasgos que distinguen la “nueva novela historica” de su canon decimononico. El tan desafortunado intento proviene de la adhesion a una definicion que el autor a tribuye a Anderson Imbert, que dice: “llamamos novelas historicas a las qu cuentan un version ocurrida en una epoca anteror a la del novelista” (sic). Estimo que pocos comentarios merece una publicacion que promete mas de lo que ofrece sobre un genero el novelsco, ya en si mismo controvertido, y al que se suma el atributo de historico.