Gerardo Cladera

Bio: Gerardo Cladera is an academic researcher. The author has contributed to research in topics: Aptian & Riparian zone. The author has an hindex of 10, co-authored 11 publications receiving 300 citations.

Historical biogeography of the Andean region: evidence from Listroderina (Coleoptera: Curculionidae: Rhytirrhinini) in the context of the South American geobiotic scenario

Abstract: The weevil subtribe Listroderina belongs in the tribe Rhytirrhinini (subfamily Cyclominae), and has 25 genera and 300 species in the Americas. The distributional history of this subtribe was reconstructed applying dispersal-vicariance analysis (DIVA) using its genera as terminals. The results suggest that Listroderina originated within an area presently represented by the Central Chile, Paramo, Puna, Patagonia and Subantarctic subregions of the Andean region. Posteriorly, the subtribe was affected by extinctions and was confined to Central Chile, Paramo and Subantarctic subregions. Later, extinctions and dispersals took place and the subtribe was restricted to the Paramo and Puna subregions. From there, a dispersal event to the Subantarctic subregion occurred, enlarging again the geographical range of the subtribe. Subsequently, a vicariant event separated the Puna and Paramo subregions from the Subantarctic one. While the Macrostyphlus generic group was confined to the Paramo and Puna subregions and from there dispersed to other areas, the Antarctobius, Falklandius, Listronotus, and Listroderes generic groups diversified in the Subantarctic subregion. The results obtained by DIVA may be linked to major geological events of South America. Thus, the geobiotic scenarios recorded in this subcontinent since the late Cretaceous could be used to interpret the biogeographical events which drove Listroderina evolution. © 2003 The Linnean Society of London, Biological Journal of the Linnean Society, 2003, 80, 339–352.

Estratigrafía del Grupo Baqueró, Patagonia (provincia de Santa Cruz, Argentina)

Abstract: The stratigraphy of early Cretaceous strata in the central area of Santa Cruz Province has been a matter of study since the time when E.W. Berry published his first paleobotanical descriptions in 1924. Detailed sedimentological a nd petrographica 1investiga tions performed d uring recent years in the area of Meseta Baquero, Bajo Tigre and Anfiteatro de Tico localities have been added to the available paleontological information. It is now possible to present a new strabgraphic interpretabon of the sequence that has been previously referred to the Baquero Forrnation. This unit is now considered at a higher rank, Baquero Croup, that includes, from bottom to top the fol1owing forrnations: Anfiteatro de Tico, Bajo Tigre and Punta del Barco. The stratotypes for each unit are located and the main lithofacies are described and interpreted. Fossil plant assemblages are placed in this new stratigraphic context and related to paleoenvironments that were strongly influenced by recurrent volcanic ash fal\. A model of paleoenvironmental development and changing geographic sceneries is also discussed. On the basis of paleobotanical and palynological data, a Barremian to Aptian age was previously suggested for the Baquero Group. Recent isotopic datings confirm an Aptian age.

Early Cretaceous riparian vegetation in Patagonia, Argentina

Abstract: Early Cretaceous riparian vegetation in Patagonia, Argentina. An autochthonous plant as-semblage found at the Bajo Grande locality, Anfiteatro de Tico Formation, Baquero Group, Early Aptian of Santa Cruz province, Argentina, is described. Sedimentological data show an alternation of sandstone and lime-stone, with recurrent fossil levels associated to a fluvial system. The frequent flood in areas close to the levee had an influence on the vegetation growing along the banks of the channels. A plant assemblage composed of Ricciopsis grandensis nov. sp. (bryophyte), Adiantopteris tripinnata nov. sp., Schizaeaceae pinnules (ferns), and the gnetalean fructification Ephedra verticillata nov. sp. was found in this paleoenvironment. The taphonomical studies suggest that the plant assemblage was autochthonous, and it grew and was buried in an area near a levee. This result is congruent with environmental data provided by living representative of the fossil taxa analyzed.

Tafonomía de la Gran Hondonada (Formación Sarmiento, Edad-mamífero Mustersense, Eoceno Medio) Chubut, Argentina

Abstract: Resumen. Los restos de mamiferos del yacimiento fosil de la Gran Hondonada (Formacion Sarmiento, “Edad-mamifero” Mustersense), fueron hallados en depositos de canal fluvial, desarticulados, con escasas evidencias de transporte y distribuidos en forma caotica. El estudio tafonomico fue realizado sobre 1.539 piezas, de las cuales se identifico taxonomicamente el 65%. La mayoria de los restos corresponden a Notoungulata Isotemnidae (Periphragnis y Rhyphodon) y Archaeohyracidae (Pseudhyrax). El numero minimo de individuos (NMI) total calculado fue de 256, en su mayoria adultos juveniles y adultos. Los restos oseos no presentan evidencias de exposicion aerea prolongada, lo cual favorecio una excelente preservacion. Las carcasas habrian permanecido en descomposicion en zonas cercanas al canal fluvial hasta su desarticulacion, incorporandose posteriormente al canal. El analisis geometrico de los restos indica una seleccion hacia las formas cilindricas y esfericas, sin marcas de abrasion. Sobre la base de los datos tafonomicos puede concluirse que existirian relaciones de coexistencia entre las asociaciones faunisticas, formandose un yacimiento autoctono con transporte desde areas cercanas sin que los restos salieran del area de produccion. Asimismo, existen fuertes evidencias (i.e., mortalidad no selectiva, alto NMI y alta tasa de sedimentacion) que permiten concluir que la concentracion de restos obedecio a un evento catastrofico, ocurrido en un corto intervalo temporal. Abstract. TAPHONOMY OF THE “GRAN HONDONADA” (SARMIENTO FORMATION, MUSTERSAN “LAND-MAMMAL AGE”, MIDDLE EOCENE), CHUBUT, ARGENTINA.The fossil remains of the mammal deposit known as the “Gran Hondonada” (Sarmiento Fm., Mustersan “land-mammal age”) were found in sediments of fluvial channels, disjointed, without transport evidence, and chaotically deposited. The taphonomic study was made on 1539 remains, 65% of which were determined. Most of the fossil remains correspond to Isotemnidae (Periphragnis and Ryphodon) and Archaeohyracidae (Pseudhyrax) Notoungulata. The calculated total minimum number of individuals (MNI) was 256, most of them assigned to young adults and adults. The fossil remains do not present evidences of long aerial exposition during the first biostratinomic stage. This fact allowed excellent preservation conditions. Before the incorporation of the skeletons to the fluvial channel, they would have remained in areas closer to the channel until their disarticulation. The geometric study of the bones shows a selection toward cylindrical and spherical forms, but without abrasion marks. On the basis of the taphonomic data, we can conclude that there was a relation of coexistence among fossil associations. This relation yields an autochthonous fossil deposit with transport from closer areas, and without the bones leaving their production area. Also, there exist strong evidences (i.e., non selective mortality; a high MNI; and a high sedimentation rate) to conclude that this fossil accumulation was due to a catastrophic event, occurred during a short time interval.

Arecaceae Fossil Fruits from the Paleocene of Patagonia, Argentina

Abstract: We describe fossil fruits collected from outcrops of the Salamanca Fm. (Paleocene, Danian, 63.3–61.9 Ma) at the Estancia Las Violetas locality, Chubut, Argentina that show affinities with members of the Subtribe Attaleinae, Tribe Cocoseae, Subfamily Arecoideae within the Arecaceae. The fossils are preserved as permineralizations, and were examined by longitudinal, tangential and cross-sections, as well as by the application of Computed Tomography Scanning technology (CT Scan). The fruits are ovoid drupes with 3 longitudinal grooves delimiting three valves; displaying apical stigmatic remains and a single apical germination pore. The exocarp and mesocarp are fused and anatomically indistinguishable one from another; they contain longitudinal fibrous bands with brachysclereids. A centrally placed seed occupies the single locule entirely; the seeds are deltoid with a basal hilum and acuminate tip while the endosperm is ruminate. The taxonomic position of the fossils was explored using phylogenetic analyses of molecular sequences combined with morphological data. Along with the suite of morphological characters that points to an affinity with the Subtribe Attaleinae, Tribe Cocoseae, subfamily Arecoideae, the results of the combined phylogenetic analyses confirm the taxonomic placement. This report constitutes the first confirmed record for the Subtribe Attaleinae worldwide and the first record of fossil palm fruits from Argentina.

Taphonomic and Ecologic Information Form Bone Weathering

Abstract: Bones of recent mammals in the Amboseli Basin, southern Kenya, exhibit distinctive weathering characteristics that can be related to the time since death and to the local conditions of temperature, humidity and soil chemistry. A categorization of weathering characteristics into six stages, recognizable on descriptive criteria, provides a basis for investigation of weathering rates and processes. The time necessary to achieve each successive weathering stage has been calibrated using known-age carcasses. Most bones decompose beyond recognition in 10 to 15 yr. Bones of animals under 100 kg and juveniles appear to weather more rapidly than bones of large animals or adults. Small-scale rather than widespread environmental factors seem to have greatest influence on weathering characteristics and rates. Bone weathering is potentially valuable as evidence for the period of time represented in recent or fossil bone assemblages, in- cluding those on archeological sites, and may also be an important tool in censusing populations of animals in modern ecosystems.

Historical biogeography of South American freshwater fishes

Abstract: Aim To investigate biogeographical patterns of the obligate freshwater fish order Characiformes. Location South America. Methods Parsimony analysis of endemicity, likelihood analysis of congruent geographical distribution, and partition Bremer support were used. Results Areas of endemism are deduced from parsimony analysis of endemicity, and putative dispersal routes from a separate analysis of discordant patterns of distribution. Main conclusions Our results demonstrate the occurrence of 11 major areas of endemism and support a preferential eastern–western differentiation of the characiforms in the Amazonian region, contrasting with the southern–northern differentiation of terrestrial organisms. The areas of endemism identified seem to be deeply influenced by the distribution of the emerged land during the 100-m marine highstand that occurred during the late Miocene and allow us to hypothesize the existence of eight aquatic freshwater refuges at that time. The raw distribution of non-endemic species supports nine patterns of species distribution across the 11 areas of endemism, two of which support a southern–northern differentiation in the eastern part of the Amazon. This result shows that the main channel of the Amazon limited dispersal between tributaries from each bank of the river. The levels of endemism further demonstrate that the aquatic freshwater refuges promoted allopatric speciation and later allowed the colonization of the lowlands. By contrast, the biogeographical pattern found in the western part of the Amazon is identified as a result of the Miocene Andean foreland dynamic and the uplift of the palaeoarches that promoted allopatric divergence across several sedimentary basins by the establishment of disconnected floodplains. The assessment of conflicting species distributions also shows the presence of seven putative dispersal routes between the Amazon, Orinoco and Parana rivers. Our findings suggest that, rather than there being a single predominant process, the establishment of the modern South American freshwater fish biotas is the result of an interaction between marine incursions, uplift of the palaeoarches, and historical connections allowing cross-drainage dispersal.