Nuevos aportes a la fauna, geocronologia y paleoambientes del neoterciario del sur del uruguay
Boletín de la Sociedad zoológica del Uruguay, 1985
... Signatura: BN-PP BOL soc. Aut. Analit.: Perea Negreira, Daniel; Ubilla Gutiérrez, Martín; Mar... more ... Signatura: BN-PP BOL soc. Aut. Analit.: Perea Negreira, Daniel; Ubilla Gutiérrez, Martín; Martínez Chiappara, Sergio Agustín. Título: Nuevos aportes a la fauna, geocronología y paleoambientes del Neoterciario del sur del Uruguay. Notas: Bibliografía: p. 52-54. ...
Journal of South American Earth Sciences, Nov 1, 2020
This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
A new ctenochasmatid (Pterosauria, Pterodactyloidea) from the late Jurassic of Uruguay
Journal of South American Earth Sciences
Abstract A new ctenochasmatid pterosaur from the Tacuarembo Formation (Late Jurassic of Uruguay),... more Abstract A new ctenochasmatid pterosaur from the Tacuarembo Formation (Late Jurassic of Uruguay), Tacuadactylus luciae gen. et sp. nov. is described, based on a rostrum fragment with spatulated tip and dentary fragments. It closely resembles Gnathosaurus in the orientation of the teeth and the presence of interalveolar concavities. However, a unique combination of synapomorphies distinguishes it from other members of the Ctenochasmatidae. These include the presence of a spoon-shaped spatula not sharply demarcated from the post-spatula rostrum, teeth set in alveoli with raised alveolar borders and deep interalveolar concavities, teeth both anteriorly (i.e. procumbent) and laterally oriented, tooth density of 1.58–2 teeth/cm, tooth separation subequal to tooth size, absence of dorsal concavity, presence of a conspicuous system of vessels and foramina at least in the ventral part of the snout, teeth with veined sub millimetric texture of the enamel and unconspicuous carinae. In a phylogenetic analysis, the new taxon was retrieved as a gnathosaurine closely related to Gnathosaurus. The Tithonian-Berriasian biochron of the latter is coherent with the Late Jurassic age of the Batovi Member, as suggested by conchostracans and theropod teeth. This is one of the few South American Jurassic pterosaur taxa named so far and the oldest ctenochasmatid in this continent. As in Plataleorhynchus and Lonchodraco, Tacuadactylus luciae gen. et sp. nov. shows features that can be correlated with tactile foraging.
This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Durante el Cenozoico, Sudamérica se mantuvo mayormente aislada del resto de las masas continental... more Durante el Cenozoico, Sudamérica se mantuvo mayormente aislada del resto de las masas continentales, lo que motivó el origen y diversificación de grupos particulares endémicos Benton, 2005). Los Litopterna son uno de estos grupos, constituido por ungulados superficialmente semejantes a caballos, jirafas o camellos. Los miembros recuerdan los de los perisodáctilos, con una tendencia a la reducción de dígitos (siendo el dedo III el principal) como adaptación al hábito cursorial . Su dentición es completa, aunque relativamente más sencilla que la de otros ungulados y con diastema breve o ausente. La familia Proterotheriidae Ameghino, 1887 (Paleoceno tardío-Pleistoceno tardío) es la más diversa del orden, con una amplia distribución que incluye Colombia,
The Tacuarembó Formation contains a faunal assemblage with some taxa clearly indicative of a Late... more The Tacuarembó Formation contains a faunal assemblage with some taxa clearly indicative of a Late Jurassic-Early Cretaceous age. In this context, the first remains of Uruguayan pterosaurs are described. These correspond to a dorsoventrally compressed and narrow fragment of a rostrum widening anteriorly, with alveoli and a very fragmentary dentition including a tooth base. The orientation of the alveoli and preserved tooth base allows the assumption that the teeth were projected laterally and forward from the dental borders. The deep interdental concavities make up a wavy contour of the lateral margins of the rostrum. Both morphology and size correspond to that observed in the ctenochasmatid gnathosaurines. The Uruguayan pterosaur remains represent the oldest ctenochasmatid found in South America and suggest an age of the fossiliferous horizon no older than Late Jurassic, which was already established on the basis of other fossils, such as Priohybodus arambourgui d' Erasmo, 1960.
This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
The first record for Uruguay of the dinomyid rodent Tetrastylus Ameghino, an almost complete righ... more The first record for Uruguay of the dinomyid rodent Tetrastylus Ameghino, an almost complete right mandible from the upper Miocene Camacho Formation, is described. According to the p4 and m3 morphology it is inferred a juvenile-subadult ontogenetic stage for this specimen.
The uppermost sandstones of the Asencio Formation of southwestern Uruguay are characterized by a ... more The uppermost sandstones of the Asencio Formation of southwestern Uruguay are characterized by a striking iron-rich geochemical overprint, which has been interpreted as paleopedogenic in origin. Among the notable features of the Asencio is the extension of the overprint into tubes that extend several meters into the underlying Mercedes Formation. Field
RESUMEN La fauna local La Paz (34º44´6º17élevación 31 m) constituye una asociación fosilífera con... more RESUMEN La fauna local La Paz (34º44´6º17élevación 31 m) constituye una asociación fosilífera con abundantes restos de mamíferos típicos del Pleistoceno del sur de Sudamérica. Esta asociación se encuentra conformando un banco osario de características únicas en Uruguay, el cual contiene una gran concentración de restos óseos en su mayoría completamente desarticulados y fragmentados, aunque también otros, que están muy bien conservados. Los principales objetivos de este trabajo son contribuir al entendimiento de los procesos sedimentarios y tafonómicos actuantes y aportar nuevos datos a la cronología del depósito. Los fragmentos óseos estudiados se presentan sin conexión anatómica, en su mayoría sumamente fracturados, y acumulados conformando un banco osario multidominante. El número de elementos identificados (NISP) es de 130. El 50% de las piezas estudiadas no presentó signos de meteorización; el 70 % mostró algún tipo de fractura, en la mayoría de los casos (40%) paralelas al eje ...
Previamente, esta escala cronológica fue basada sobre una sucesión de "Edades Mamífero" pero reci... more Previamente, esta escala cronológica fue basada sobre una sucesión de "Edades Mamífero" pero recientemente se desarrolló una escala bioestratigráfica que da sustento a la cronológica y permite una mayor resolución temporal. Desde el Pleistoceno al Holoceno se han reconocido cuatro unidades bioestratigráficas (Biozonas de Asociación). Las biozonas de Mesotherium cristatum Serres y de Megatherium americanum Cuvier constituyen, respectivamente, la base bioestratigráfica de los Pisos Ensenadense (Pleistoceno temprano a medio) y Bonaerense (Pleistoceno medio); adicionalmente, en la base del Bonaerense se reconoció una biozona basada en micromamíferos, la biozona de Ctenomys kraglievichi (Rusconi). La Biozona de Equus (Amerhippus) neogaeus Lund es la base del Piso Lujanense (Pleistoceno tardío a Holoceno temprano), y la de Lagostomus maximus (Desmarest) representa la base bioestratigráfica del Piso Platense (Holoceno temprano a tardío). Un importante recambio faunístico se produce entre las biozonas de Mesotherium cristatum y de Megatherium americanum, mientras que la biozona de Equus (Amerhippus) neogaeus está definida por un recambio menos significativo. Los sedimentos que representan al Platense se depositaron con posterioridad al proceso de extinción que generó en América del Sur la desaparición del nivel trófico correspondiente a los megamamíferos. Durante el Sanandresense tardío (Plioceno tardío) y comienzos del Ensenadense (ca. 1,8 Ma) se verifica un importante recambio faunístico, consistente en la extinción de clados autóctonos (Microtragulidae, Eumysops Ameghino), la extinción local de mamíferos adaptados a condiciones cálidas y húmedas (Echimyidae, Tayassuidae, Procyonidae) y los primeros registros de mamíferos adaptados a condiciones frías y áridas o semiáridas (Lestodelphys Tate, grandes tardígrados). Estos eventos biogeográficos son coevos con avances glaciales en el sur de la Argentina. En el Ensenadense se verifica un incremento en los primeros registros de especies de clados holárticos, así como de nuevas especies de clados autóctonos. En el Ensenadense superior se registran por última vez en la región pampeana, grandes mamíferos indicadores de condiciones cálidas y húmedas. En niveles coevos al techo del C1r1r (>0,78 Ma) se registran micromamíferos que indican condiciones frías y áridas. Probablemente el Ensenadense se extiende dentro de la zona de polaridad normal (C1n, < 0,78 Ma), que comienza con indicadores litológicos compatibles con condiciones áridas y frías. El Bonaerense, faunísticamente caracterizado por la diversificación de los grupos de origen holártico, comienza con un evento cálido, que tentativamente se correlaciona con el MIS 11 (ca. 0,40 Ma). También con un evento cálido (MIS 5e, 0,126 Ma) comienza el Lujanense que incluye en su parte tardía al Último Máximo Glacial (0,018 Ma) y al último avance glacial (0,013 a 0,118 Ma). Durante el Platense los cambios en las distribuciones de las poblaciones de mamíferos son congruentes con varios eventos climáticos.
Dinosaurios cretácicos del Triángulo Minero (Grupo Baurú, Brasil), el Grupo Paysandú (Uruguay Occidental) y la Cuenca Neuquina (Grupo Neuquén, Argentina)
This work relates the dinosaur faunas from the Triángulo Minero, in center-south Brazil, the Nort... more This work relates the dinosaur faunas from the Triángulo Minero, in center-south Brazil, the Norte Basin in western Uruguay and those from the Neuquina Basin, in the Argentinian Patagonia. The bioestratigraphical and biochronological comparison, considering not only those taxa efectively found but also those absent but frequent in other basins allow discussing the age and distribution relationships among the three basins. It is discussed the assignation of post-Coniacian isolated teeth to Carcharodontosauridae as well as the purported spinosaurs in Argentina. Other materials are evaluated as that of Entre Ríos, an Argentinian part of the Norte Basin of Uruguay, as well as materials from deinonychosaurs, neovenatorids, ankylosaurs, hadrosaurids and sauropods, particularly those assigned to the genus Aeolosaurus. Egg material is included too. Este trabajo relaciona las faunas de dinosaurios del Triángulo Minero, en el centro-sur de Brasil, los de la Cuenca Norte en el oeste de Uruguay y los de la Cuenca Neuquina, en la Patagonia argentina. La comparación bioestratigráfica y biocronológica, teniendo en cuenta no solo los taxones presentes sino también aquellos ausentes que son frecuentes en otras cuencas permiten discutir las relaciones de edad y de distribución entre las tres cuencas. Se discute la asignación de dientes aislados post-Coniacianos a Carcharodontosauridae así como los supuestos espinosaurios de Argentina. Otros materiales son evaluados, como aquellos de Entre Ríos, parte argentina de la Cuenca Norte de Uruguay, así como materiales de deinonicosaurios, neovenatóridos, anquilosaurios, hadrosáuridos y saurópodos, particularmente del género Aeolosaurus. Se incluyen los materiales de huevos.
Fossil bones are often the only materials available for chronological reconstruction of important... more Fossil bones are often the only materials available for chronological reconstruction of important archeological sites. However, since bone is an open system for uranium, it cannot be dated directly and therefore it is necessary to develop models for the U uptake. Hence, a radial diffusion-adsorption (RDA) model is described. Unlike the classic diffusion-adsorption (D-A) model, RDA uses a cylindrical geometry to describe the U uptake in fossil bones. The model was applied across a transverse section of a tibia of an extinct megamammal Macrauchenia patachonica from the La Paz Local Fauna, Montevideo State, Uruguay. Measurements of spatial distribution of Na, K, Ca, and Mg were also performed by neutron activation analysis (NAA). Gamma-ray spectrometric U-series dating was applied to determine the age of the bone sample. From U concentration profile, it was possible to observe the occurrence of a relatively slow and continuous uranium uptake under constant conditions that had not yet r...
Paleoecology and Geochronology of Uruguayan Coastal Marine Pleistocene Deposits
Quaternary Research, 2001
Minimum radiocarbon ages of marine Pleistocene molluscs from Uruguay range from 29,500±600 to 35,... more Minimum radiocarbon ages of marine Pleistocene molluscs from Uruguay range from 29,500±600 to 35,500±1900 14C yr B.P. Because knowledge of the marine Quaternary stratigraphy of Uruguay remains inadequate, no attempt is made to correlate between these deposits and recognized lithostratigraphic units. Analysis of the temperature and salinity ranges of the various molluscs suggests the establishment of a poly-euhaline fauna that inhabited waters warmer than present at the same latitude. This is supported by a northward retreat in the recent distribution of Chrysallida cf. C. gemmulosa, Nioche subrostrata, and probably Anomalocardia brasiliana. These marine Pleistocene deposits can probably be correlated with the last interglaciation (oxygen-isotopic substage 5e). At that time the fluvial-marine front of the Rio de la Plata was displaced much further northwestward than previously supposed. Chrysallida cf. C. gemmulosa and Limaria sp. are recorded in Uruguayan Quaternary deposits for the...
Uruguaysuchus is a small mesoeucrocodylian known from several partial skeletons and skulls from t... more Uruguaysuchus is a small mesoeucrocodylian known from several partial skeletons and skulls from the Guichón Formation (middle Cretaceous, Uruguay). Several authors have pointed out derived similarities of this taxon with different basal notosuchian genera, highlighting its importance for mesoeucrocodylian phylogeny and biogeography. However, the holotype is only partially prepared and has not been available for study for many years. Thus, phylogenetic studies have included this form based on the original description, thereby resulting in a large amount of missing data in the character scorings of this taxon. Here, we describe a new specimen from the type locality consisting of a partial skull, lower jaw and cervical vertebrae which can be referred to U. aznarezi. The new specimen allows for the recognition and scoring of several characters previously unknown for this taxon, thus providing a more extensive diagnosis, as well as new information for understanding its phylogenetic relationships. These characters are congruent with the morphology present in basal notosuchians. The relationships of Uruguaysuchus are tested through a cladistic analysis using a recently published data set including the new information. The phylogenetic results differ from previous analyses, recovering this taxon as the sister group of the Araripesuchus clade. U. terrai is considered a juvenile individual of U. aznarezi.
Nuevos aportes a la fauna, geocronologia y paleoambientes del neoterciario del sur del uruguay
Boletín de la Sociedad zoológica del Uruguay, 1985
... Signatura: BN-PP BOL soc. Aut. Analit.: Perea Negreira, Daniel; Ubilla Gutiérrez, Martín; Mar... more ... Signatura: BN-PP BOL soc. Aut. Analit.: Perea Negreira, Daniel; Ubilla Gutiérrez, Martín; Martínez Chiappara, Sergio Agustín. Título: Nuevos aportes a la fauna, geocronología y paleoambientes del Neoterciario del sur del Uruguay. Notas: Bibliografía: p. 52-54. ...
Journal of South American Earth Sciences, Nov 1, 2020
This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
A new ctenochasmatid (Pterosauria, Pterodactyloidea) from the late Jurassic of Uruguay
Journal of South American Earth Sciences
Abstract A new ctenochasmatid pterosaur from the Tacuarembo Formation (Late Jurassic of Uruguay),... more Abstract A new ctenochasmatid pterosaur from the Tacuarembo Formation (Late Jurassic of Uruguay), Tacuadactylus luciae gen. et sp. nov. is described, based on a rostrum fragment with spatulated tip and dentary fragments. It closely resembles Gnathosaurus in the orientation of the teeth and the presence of interalveolar concavities. However, a unique combination of synapomorphies distinguishes it from other members of the Ctenochasmatidae. These include the presence of a spoon-shaped spatula not sharply demarcated from the post-spatula rostrum, teeth set in alveoli with raised alveolar borders and deep interalveolar concavities, teeth both anteriorly (i.e. procumbent) and laterally oriented, tooth density of 1.58–2 teeth/cm, tooth separation subequal to tooth size, absence of dorsal concavity, presence of a conspicuous system of vessels and foramina at least in the ventral part of the snout, teeth with veined sub millimetric texture of the enamel and unconspicuous carinae. In a phylogenetic analysis, the new taxon was retrieved as a gnathosaurine closely related to Gnathosaurus. The Tithonian-Berriasian biochron of the latter is coherent with the Late Jurassic age of the Batovi Member, as suggested by conchostracans and theropod teeth. This is one of the few South American Jurassic pterosaur taxa named so far and the oldest ctenochasmatid in this continent. As in Plataleorhynchus and Lonchodraco, Tacuadactylus luciae gen. et sp. nov. shows features that can be correlated with tactile foraging.
This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Durante el Cenozoico, Sudamérica se mantuvo mayormente aislada del resto de las masas continental... more Durante el Cenozoico, Sudamérica se mantuvo mayormente aislada del resto de las masas continentales, lo que motivó el origen y diversificación de grupos particulares endémicos Benton, 2005). Los Litopterna son uno de estos grupos, constituido por ungulados superficialmente semejantes a caballos, jirafas o camellos. Los miembros recuerdan los de los perisodáctilos, con una tendencia a la reducción de dígitos (siendo el dedo III el principal) como adaptación al hábito cursorial . Su dentición es completa, aunque relativamente más sencilla que la de otros ungulados y con diastema breve o ausente. La familia Proterotheriidae Ameghino, 1887 (Paleoceno tardío-Pleistoceno tardío) es la más diversa del orden, con una amplia distribución que incluye Colombia,
The Tacuarembó Formation contains a faunal assemblage with some taxa clearly indicative of a Late... more The Tacuarembó Formation contains a faunal assemblage with some taxa clearly indicative of a Late Jurassic-Early Cretaceous age. In this context, the first remains of Uruguayan pterosaurs are described. These correspond to a dorsoventrally compressed and narrow fragment of a rostrum widening anteriorly, with alveoli and a very fragmentary dentition including a tooth base. The orientation of the alveoli and preserved tooth base allows the assumption that the teeth were projected laterally and forward from the dental borders. The deep interdental concavities make up a wavy contour of the lateral margins of the rostrum. Both morphology and size correspond to that observed in the ctenochasmatid gnathosaurines. The Uruguayan pterosaur remains represent the oldest ctenochasmatid found in South America and suggest an age of the fossiliferous horizon no older than Late Jurassic, which was already established on the basis of other fossils, such as Priohybodus arambourgui d' Erasmo, 1960.
This is a PDF file of an article that has undergone enhancements after acceptance, such as the ad... more This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
The first record for Uruguay of the dinomyid rodent Tetrastylus Ameghino, an almost complete righ... more The first record for Uruguay of the dinomyid rodent Tetrastylus Ameghino, an almost complete right mandible from the upper Miocene Camacho Formation, is described. According to the p4 and m3 morphology it is inferred a juvenile-subadult ontogenetic stage for this specimen.
The uppermost sandstones of the Asencio Formation of southwestern Uruguay are characterized by a ... more The uppermost sandstones of the Asencio Formation of southwestern Uruguay are characterized by a striking iron-rich geochemical overprint, which has been interpreted as paleopedogenic in origin. Among the notable features of the Asencio is the extension of the overprint into tubes that extend several meters into the underlying Mercedes Formation. Field
RESUMEN La fauna local La Paz (34º44´6º17élevación 31 m) constituye una asociación fosilífera con... more RESUMEN La fauna local La Paz (34º44´6º17élevación 31 m) constituye una asociación fosilífera con abundantes restos de mamíferos típicos del Pleistoceno del sur de Sudamérica. Esta asociación se encuentra conformando un banco osario de características únicas en Uruguay, el cual contiene una gran concentración de restos óseos en su mayoría completamente desarticulados y fragmentados, aunque también otros, que están muy bien conservados. Los principales objetivos de este trabajo son contribuir al entendimiento de los procesos sedimentarios y tafonómicos actuantes y aportar nuevos datos a la cronología del depósito. Los fragmentos óseos estudiados se presentan sin conexión anatómica, en su mayoría sumamente fracturados, y acumulados conformando un banco osario multidominante. El número de elementos identificados (NISP) es de 130. El 50% de las piezas estudiadas no presentó signos de meteorización; el 70 % mostró algún tipo de fractura, en la mayoría de los casos (40%) paralelas al eje ...
Previamente, esta escala cronológica fue basada sobre una sucesión de "Edades Mamífero" pero reci... more Previamente, esta escala cronológica fue basada sobre una sucesión de "Edades Mamífero" pero recientemente se desarrolló una escala bioestratigráfica que da sustento a la cronológica y permite una mayor resolución temporal. Desde el Pleistoceno al Holoceno se han reconocido cuatro unidades bioestratigráficas (Biozonas de Asociación). Las biozonas de Mesotherium cristatum Serres y de Megatherium americanum Cuvier constituyen, respectivamente, la base bioestratigráfica de los Pisos Ensenadense (Pleistoceno temprano a medio) y Bonaerense (Pleistoceno medio); adicionalmente, en la base del Bonaerense se reconoció una biozona basada en micromamíferos, la biozona de Ctenomys kraglievichi (Rusconi). La Biozona de Equus (Amerhippus) neogaeus Lund es la base del Piso Lujanense (Pleistoceno tardío a Holoceno temprano), y la de Lagostomus maximus (Desmarest) representa la base bioestratigráfica del Piso Platense (Holoceno temprano a tardío). Un importante recambio faunístico se produce entre las biozonas de Mesotherium cristatum y de Megatherium americanum, mientras que la biozona de Equus (Amerhippus) neogaeus está definida por un recambio menos significativo. Los sedimentos que representan al Platense se depositaron con posterioridad al proceso de extinción que generó en América del Sur la desaparición del nivel trófico correspondiente a los megamamíferos. Durante el Sanandresense tardío (Plioceno tardío) y comienzos del Ensenadense (ca. 1,8 Ma) se verifica un importante recambio faunístico, consistente en la extinción de clados autóctonos (Microtragulidae, Eumysops Ameghino), la extinción local de mamíferos adaptados a condiciones cálidas y húmedas (Echimyidae, Tayassuidae, Procyonidae) y los primeros registros de mamíferos adaptados a condiciones frías y áridas o semiáridas (Lestodelphys Tate, grandes tardígrados). Estos eventos biogeográficos son coevos con avances glaciales en el sur de la Argentina. En el Ensenadense se verifica un incremento en los primeros registros de especies de clados holárticos, así como de nuevas especies de clados autóctonos. En el Ensenadense superior se registran por última vez en la región pampeana, grandes mamíferos indicadores de condiciones cálidas y húmedas. En niveles coevos al techo del C1r1r (>0,78 Ma) se registran micromamíferos que indican condiciones frías y áridas. Probablemente el Ensenadense se extiende dentro de la zona de polaridad normal (C1n, < 0,78 Ma), que comienza con indicadores litológicos compatibles con condiciones áridas y frías. El Bonaerense, faunísticamente caracterizado por la diversificación de los grupos de origen holártico, comienza con un evento cálido, que tentativamente se correlaciona con el MIS 11 (ca. 0,40 Ma). También con un evento cálido (MIS 5e, 0,126 Ma) comienza el Lujanense que incluye en su parte tardía al Último Máximo Glacial (0,018 Ma) y al último avance glacial (0,013 a 0,118 Ma). Durante el Platense los cambios en las distribuciones de las poblaciones de mamíferos son congruentes con varios eventos climáticos.
Dinosaurios cretácicos del Triángulo Minero (Grupo Baurú, Brasil), el Grupo Paysandú (Uruguay Occidental) y la Cuenca Neuquina (Grupo Neuquén, Argentina)
This work relates the dinosaur faunas from the Triángulo Minero, in center-south Brazil, the Nort... more This work relates the dinosaur faunas from the Triángulo Minero, in center-south Brazil, the Norte Basin in western Uruguay and those from the Neuquina Basin, in the Argentinian Patagonia. The bioestratigraphical and biochronological comparison, considering not only those taxa efectively found but also those absent but frequent in other basins allow discussing the age and distribution relationships among the three basins. It is discussed the assignation of post-Coniacian isolated teeth to Carcharodontosauridae as well as the purported spinosaurs in Argentina. Other materials are evaluated as that of Entre Ríos, an Argentinian part of the Norte Basin of Uruguay, as well as materials from deinonychosaurs, neovenatorids, ankylosaurs, hadrosaurids and sauropods, particularly those assigned to the genus Aeolosaurus. Egg material is included too. Este trabajo relaciona las faunas de dinosaurios del Triángulo Minero, en el centro-sur de Brasil, los de la Cuenca Norte en el oeste de Uruguay y los de la Cuenca Neuquina, en la Patagonia argentina. La comparación bioestratigráfica y biocronológica, teniendo en cuenta no solo los taxones presentes sino también aquellos ausentes que son frecuentes en otras cuencas permiten discutir las relaciones de edad y de distribución entre las tres cuencas. Se discute la asignación de dientes aislados post-Coniacianos a Carcharodontosauridae así como los supuestos espinosaurios de Argentina. Otros materiales son evaluados, como aquellos de Entre Ríos, parte argentina de la Cuenca Norte de Uruguay, así como materiales de deinonicosaurios, neovenatóridos, anquilosaurios, hadrosáuridos y saurópodos, particularmente del género Aeolosaurus. Se incluyen los materiales de huevos.
Fossil bones are often the only materials available for chronological reconstruction of important... more Fossil bones are often the only materials available for chronological reconstruction of important archeological sites. However, since bone is an open system for uranium, it cannot be dated directly and therefore it is necessary to develop models for the U uptake. Hence, a radial diffusion-adsorption (RDA) model is described. Unlike the classic diffusion-adsorption (D-A) model, RDA uses a cylindrical geometry to describe the U uptake in fossil bones. The model was applied across a transverse section of a tibia of an extinct megamammal Macrauchenia patachonica from the La Paz Local Fauna, Montevideo State, Uruguay. Measurements of spatial distribution of Na, K, Ca, and Mg were also performed by neutron activation analysis (NAA). Gamma-ray spectrometric U-series dating was applied to determine the age of the bone sample. From U concentration profile, it was possible to observe the occurrence of a relatively slow and continuous uranium uptake under constant conditions that had not yet r...
Paleoecology and Geochronology of Uruguayan Coastal Marine Pleistocene Deposits
Quaternary Research, 2001
Minimum radiocarbon ages of marine Pleistocene molluscs from Uruguay range from 29,500±600 to 35,... more Minimum radiocarbon ages of marine Pleistocene molluscs from Uruguay range from 29,500±600 to 35,500±1900 14C yr B.P. Because knowledge of the marine Quaternary stratigraphy of Uruguay remains inadequate, no attempt is made to correlate between these deposits and recognized lithostratigraphic units. Analysis of the temperature and salinity ranges of the various molluscs suggests the establishment of a poly-euhaline fauna that inhabited waters warmer than present at the same latitude. This is supported by a northward retreat in the recent distribution of Chrysallida cf. C. gemmulosa, Nioche subrostrata, and probably Anomalocardia brasiliana. These marine Pleistocene deposits can probably be correlated with the last interglaciation (oxygen-isotopic substage 5e). At that time the fluvial-marine front of the Rio de la Plata was displaced much further northwestward than previously supposed. Chrysallida cf. C. gemmulosa and Limaria sp. are recorded in Uruguayan Quaternary deposits for the...
Uruguaysuchus is a small mesoeucrocodylian known from several partial skeletons and skulls from t... more Uruguaysuchus is a small mesoeucrocodylian known from several partial skeletons and skulls from the Guichón Formation (middle Cretaceous, Uruguay). Several authors have pointed out derived similarities of this taxon with different basal notosuchian genera, highlighting its importance for mesoeucrocodylian phylogeny and biogeography. However, the holotype is only partially prepared and has not been available for study for many years. Thus, phylogenetic studies have included this form based on the original description, thereby resulting in a large amount of missing data in the character scorings of this taxon. Here, we describe a new specimen from the type locality consisting of a partial skull, lower jaw and cervical vertebrae which can be referred to U. aznarezi. The new specimen allows for the recognition and scoring of several characters previously unknown for this taxon, thus providing a more extensive diagnosis, as well as new information for understanding its phylogenetic relationships. These characters are congruent with the morphology present in basal notosuchians. The relationships of Uruguaysuchus are tested through a cladistic analysis using a recently published data set including the new information. The phylogenetic results differ from previous analyses, recovering this taxon as the sister group of the Araripesuchus clade. U. terrai is considered a juvenile individual of U. aznarezi.
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