Palaeolatitudinal gradients along the southeastern Palaeopacific margin and the distribution of Early Jurassic bivalves

Presence-absence bivalve species data for each Early Jurassic stage along southeastern South America between 20 and 46°S present-day latitude were processed by a set of analytical methods to analyse the palaeolatitudinal patterns of diversity and distribution. The expected decrease in species diversity towards higher latitudes is punctuated by a consistent local diversity increase between 34 and 42°, especially evident during Pliensbachian and Toarcian times, which may be due to an abrupt change in palaeogeography at that latitude, coinciding with the Curicó direct connection to the open ocean and the establishment of an increased variety of habitats within the extensive Neuquén Basin. The proportions of systematic groups show relative increases towards both higher latitudes (Crassatelloidea, Nuculanoidea, Pectinoidea, Monotoidea, Inoceramoidea) and lower latitudes (Trigonioidea, Pholadomyoidea, Limoidea, Lucinoidea). Epifaunal bivalves were dominant during the Hettangian but by Pliensbachian-Toarcian times they were less common than infaunal ones, while semi-infaunal species had low diversities during the whole Early Jurassic. This study suggests that (a) large scale geographical conditions should be taken into account for the analysis of latitudinal diversity trends among benthonic faunas; and (b) latitudinal trends of some living bivalve lineages may have a longer and more complex history than previously thought.Fil: Damborenea, Susana Ester. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Departamento de Paleontología Invertebrados; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata; ArgentinaFil: Echevarría, Javier. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. División Paleozoología Invertebrados; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata; Argentin

América del Sur y Nueva Zelanda: una vieja relación

Hoy en día Nueva Zelanda y el sur de América del Sur están separadas por más de 10.000 km de distancia, por el Océano Pacífico y casi 180° de longitud geográfica. Sin embargo, durante muchos millones de años, hasta el Jurásico, ambas regiones compartieron la costa sur del continente de Gondwana, y tuvieron entonces una historia en común, que ha quedado documentada por sus fósiles marinos.Fundación Museo de La Plat

A review of jurassic marine worlwide biochoremas based on the distribution of bivalve mollusks

Numerosos trabajos regionales o locales han propuesto el reconocimiento de unidades biogeográficas de distintos rangos (biocoremas) basadas sobre la distribución de los moluscos bivalvos para el Jurásico, pero no existía una síntesis a nivel mundial. Este trabajo es una revisión de las más significativas de esas propuestas, en un intento de lograr una síntesis de los patrones biogeográficos globales desde el Jurásico Temprano al Tardío, mientras se producían cambios sustanciales en la paleogeografía de la Tierra y los patrones de circulación oceánica como resultado de la disgregación de Pangea. Se hace también un breve análisis de la evolución en el tiempo y el espacio de cada una de las principales unidades reconocidas y de sus relaciones. Estos biocoremas pueden agruparse en tres unidades de primer orden que han tenido continuidad en el tiempo: Boreal, Tethys y Austral. Las unidades revisadas aquí han sido reconocidas y caracterizadas de forma muy heterogénea por los distintos autores, pero los criterios básicos más utilizados incluyen desde el grado de endemismo y la diversidad relativa, hasta las afinidades paleobiogeográficas de los taxones a nivel genérico. Los patrones de distribución de los bivalvos jurásicos no solamente son claves para entender cuestiones puramente biogeográficas, sino que han sido utilizados como argumento y evidencia en discusiones de índole paleogeográfica (como el establecimiento de corredores oceánicos, o patrones de circulación marina superficial), e incluso son pruebas de peso para la discusión de tópicos paleotectónicos, como la localización de terrenos desplazados y la deriva continental.Local and regional papers analyzing the distribution of Jurassic bivalves and proposing new palaeobiogeographic units of various ranks are numerous, but a worldwide synthesis was lacking. This paper is a review of those proposals with the aim to obtain a coherent synthesis of the global biogeographic patterns from Early to Late Jurassic times, when significant changes in the Earth palaeogeography and oceanic circulation took place as the result of the breakup of Pangea. A brief account of the evolution in time and space of the recognized units and their relationships is also made. The biochoremas can be grouped into three first order units which had temporal continuity: Boreal, Tethys and Austral Realms. The units analysed here were recognized and characterized in very different grounds by their authors; the most commonly used criteria are degree of endemism, relative diversity and palaeobiogeographic affinities of bivalve genera. The patterns of Jurassic bivalve distribution are key to understand general biogeographic issues, but they were also used as evidence in palaeogeographic discussions (such as the establishment of seaways and changing patterns of superficial water circulation); they are even arguments in some palaeotectonic issues, such as the localization and history of displaced terranes, and continental drift.Facultad de Ciencias Naturales y Muse

A review of jurassic marine worlwide biochoremas based on the distribution of bivalve mollusks

Numerosos trabajos regionales o locales han propuesto el reconocimiento de unidades biogeográficas de distintos rangos (biocoremas) basadas sobre la distribución de los moluscos bivalvos para el Jurásico, pero no existía una síntesis a nivel mundial. Este trabajo es una revisión de las más significativas de esas propuestas, en un intento de lograr una síntesis de los patrones biogeográficos globales desde el Jurásico Temprano al Tardío, mientras se producían cambios sustanciales en la paleogeografía de la Tierra y los patrones de circulación oceánica como resultado de la disgregación de Pangea. Se hace también un breve análisis de la evolución en el tiempo y el espacio de cada una de las principales unidades reconocidas y de sus relaciones. Estos biocoremas pueden agruparse en tres unidades de primer orden que han tenido continuidad en el tiempo: Boreal, Tethys y Austral. Las unidades revisadas aquí han sido reconocidas y caracterizadas de forma muy heterogénea por los distintos autores, pero los criterios básicos más utilizados incluyen desde el grado de endemismo y la diversidad relativa, hasta las afinidades paleobiogeográficas de los taxones a nivel genérico. Los patrones de distribución de los bivalvos jurásicos no solamente son claves para entender cuestiones puramente biogeográficas, sino que han sido utilizados como argumento y evidencia en discusiones de índole paleogeográfica (como el establecimiento de corredores oceánicos, o patrones de circulación marina superficial), e incluso son pruebas de peso para la discusión de tópicos paleotectónicos, como la localización de terrenos desplazados y la deriva continental.Local and regional papers analyzing the distribution of Jurassic bivalves and proposing new palaeobiogeographic units of various ranks are numerous, but a worldwide synthesis was lacking. This paper is a review of those proposals with the aim to obtain a coherent synthesis of the global biogeographic patterns from Early to Late Jurassic times, when significant changes in the Earth palaeogeography and oceanic circulation took place as the result of the breakup of Pangea. A brief account of the evolution in time and space of the recognized units and their relationships is also made. The biochoremas can be grouped into three first order units which had temporal continuity: Boreal, Tethys and Austral Realms. The units analysed here were recognized and characterized in very different grounds by their authors; the most commonly used criteria are degree of endemism, relative diversity and palaeobiogeographic affinities of bivalve genera. The patterns of Jurassic bivalve distribution are key to understand general biogeographic issues, but they were also used as evidence in palaeogeographic discussions (such as the establishment of seaways and changing patterns of superficial water circulation); they are even arguments in some palaeotectonic issues, such as the localization and history of displaced terranes, and continental drift.Facultad de Ciencias Naturales y Muse

Robin Whatley (1936-2016)

Robin Charles Ignatius Whatley was born in England (Hawkhurst) on December 2nd 1936 and, being 79 years old, died in Wales on June 4th 2016. He attended the Sir Norton Knatchbull Grammar School in Ashford, Kent, and then took various jobs in farming, fishing and the National Service in the fifties. He received his higher education at the University of Hull, where he graduated with a First-class honours degree in both Geology and Zoology (1962). There, he subsequently earned a Ph.D. with an excellent Thesis on the Callovian and Oxfordian Ostracoda of England and Scotland (1965).Facultad de Ciencias Naturales y Muse

Constructional morphology of the shell/ligament system in opisthogyrate rostrate bivalves

The bivalve ligament provides the thrust for shell opening, acting as the resistance in a lever system against which adductor muscle effort is applied. Usually, its outer lamellar layer is subjected to tensile stress, while the inner fibrous layer is compressed, with the pivotal axis located between them. However, opisthogyrate rostrate bivalves display a concave dorsal margin, and both the umbo and the postero-dorsal angle of the shell project dorsally to the ligament, which then fails to act as pivotal axis. Three opisthogyrate rostrate genera of unrelated lineages show somewhat different solutions to this morpho-functional challenge. In Cuspidaria (Anomalodesmata), the ligament is internal, subjected only to compression and ventral to the pivotal axis, a thickened periostracum develops, forcing the dorsal margins of the valves to act as pivotal axis, and the posterior parts of the shell’s dorsal margins gape dorsally. In Nuculana (Palaeotaxodonta), the inner layer of the ligament is internal, the outer layer is external but reduced, and some species develop a dorsal ridge parallel to the commissural plane, on a level with the rostrum and acting as pivotal axis. In Pterotrigonia (Palaeoheterodonta) and other rostrate trigoniides, the ligament is external opisthodetic, but is allometrically reduced. Trigoniides may also develop a dorsal ridge.Facultad de Ciencias Naturales y Muse

Palaeolatitudinal gradients along the southeastern Palaeo-Pacific margin and the distribution of Early Jurassic bivalves

Presence-absence bivalve species data for each Early Jurassic stage along southeastern South America between 20 and 46°S present-day latitude were processed by a set of analytical methods to analyse the palaeolatitudinal patterns of diversity and distribution. The expected decrease in species diversity towards higher latitudes is punctuated by a consistent local diversity increase between 34 and 42°, especially evident during Pliensbachian and Toarcian times, which may be due to an abrupt change in palaeogeography at that latitude, coinciding with the Curicó direct connection to the open ocean and the establishment of an increased variety of habitats within the extensive Neuquén Basin. The proportions of systematic groups show relative increases towards both higher latitudes (Crassatelloidea, Nuculanoidea, Pectinoidea, Monotoidea, Inoceramoidea) and lower latitudes (Trigonioidea, Pholadomyoidea, Limoidea, Lucinoidea). Epifaunal bivalves were dominant during the Hettangian but by Pliensbachian–Toarcian times they were less common than infaunal ones, while semi-infaunal species had low diversities during the whole Early Jurassic. This study suggests that (a) large scale geographical conditions should be taken into account for the analysis of latitudinal diversity trends among benthonic faunas; and (b) latitudinal trends of some living bivalve lineages may have a longer and more complex history than previously thought.Facultad de Ciencias Naturales y Muse

Analisis paleodemecológico de signos de actividad de bivalvos infaunales de la Formación Mulichinco, Cretácico Inferior, Cuenca Neuquina, Argentina

El estudio de rasgos paleodemecológicos requiere de ciertas condiciones tafonómicas particulares. En la Formación Mulichinco (Valanginiano) se cumplen dichas condiciones, siendo frecuentes los signos de actividad de bivalvos excavadores que aparecen en sección transversal sobre las superficies de estratificación. Dos grupos de tales superficies fueron analizados, midiendo densidad poblacional, disposición espacial, distribución de tamaños y orientación en planta de las excavaciones. El paleoambiente se determinó por medio de un análisis sedimentológico detallado, y se registró la fauna de bivalvos presente con la intención de identificar a los potenciales productores. Se encontraron altas densidades poblacionales para ambos grupos, lo que indica condiciones físicas favorables y buen suministro de alimento, en tanto que la disposición espacial y la distribución de tamaños difiere entre dichos grupos; no se advirtió orientación preferencial en la mayoría de las superficies. El primer grupo (grupo A) muestra un patrón uniforme de disposición espacial y trazas de mayor tamaño; llama la atención la ausencia de pequeños tamaños. En el segundo grupo (grupo B), el patrón de disposición es indistinguible de uno al azar (salvo en un caso donde parece haber un patrón agregado). Se interpreta al grupo A como un conjunto de rastros de escape realizados por excavadores profundos en respuesta a depósitos de tormenta, en tanto que el grupo B es considerado como un conjunto de rastros de reposo/escape hechos por excavadores superficiales en ambientes dominados por mareas. Estudios paleodemecológicos de este tipo representan herramientas potencialmente útiles para los análisis sedimentológicos y de cuencas.The study of palaeodemecological features requires some particular taphonomic conditions. These conditions were met in the Mulichinco Formation (Valanginian), where burrowing bivalve trace fossils are widespread and often appear in cross section on bedding surfaces. Two groups of such beds were analyzed, measuring population density, spatial distribution, size distribution and horizontal orientation of the burrows. The palaeoenvironment was established by means of a detailed sedimentological analysis, and the bivalve fauna present was checked, in order to attempt identifying their potential producers. High population densities were found for both groups, indicating favourable physical conditions and good food supply, while differences in both spatial and size distributions were noticed between them; on most surfaces there was no preferred orientation. The first group (group A) showed a uniform pattern of spatial distribution and larger traces, with a remarkable absence of small sizes. In the second group (group B), the spatial distribution pattern is indistinguishable from a random distribution (except one case in which the pattern appears to be aggregated). Group A is interpreted as a set of escape traces made by deep burrowers in response to storm deposition, while group B is considered as resting/escape traces made by shallow burrowers in tide-dominated environments. Palaeodemecological studies of this kind are potentially useful tools for sedimentary and basin analyses.Fil: Echevarría, Javier. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata; Argentina. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. División Paleozoología Invertebrados; ArgentinaFil: Damborenea, Susana Ester. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata; Argentina. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. División Paleozoología Invertebrados; ArgentinaFil: Manceñido, Miguel Oscar. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata; Argentina. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. División Paleozoología Invertebrados; Argentin

The Triassic-Jurassic boundary in the Andes of Argentina

The Arroyo Malo Formation at Alumbre Creek, on the northern bank of the Atuel River, west central Argentina, comprises a c. 300 m thick continuous marine succession across the Triassic-Jurassic System boundary, consisting of massive and laminated pelites indicative of a slope depositional environment. Late Triassic invertebrates, including ammonoids, nautiloids, bivalves, gastropods, brachiopods and corals are restricted to the lower 150 m. Beds between 125-135 m from the bottom yield Choristoceras cf. marshi Hauer, a species found in the Marshi/Crickmayi Zone of Europe and North America, together with loose fragments of Psiloceras cf. pressum Hillebrandt, coeval with the lower to middle part of the Hettangian Planorbis Zone. About 80 m higher are beds yielding Psiloceras cf. rectocostatum Hillebrandt, a species that gives name to an Andean biozone partially coeval with the Johnstoni and Plicatulum Subzones, upper Planorbis Zone. Other fossils recorded in the Rhaetian strata of this section are foraminifers, ostracods and plant remains identified as Zuberia cf. zuberi (Szaj.) Freng. and Clathropteris sp. The section was also sampled for conodonts and radiolarians, thus far with negative results. A palaeomagnetic study is underway.La Formazione Arroyo Malo ad Alumbre creek, sulla sponda settentrionale del fiume Atuel, Argentina centro-occidentale, comprende una successione marina continua spessa circa 300 m attraverso i! limite Triassico-Giurassico, ed e costituita da peliti massive e laminate indicative di un ambiente deposizionale di scarpata. Gli inverttfjrati del Ttiassico superiore, che includono ammonoidi, nautiloidi, bivalvi, gasteropodi, brachiopodi e coralli sono limitati ai primi 150 m. Gli strati fra i 125-135 m dalla base hanno dato Choristoceras cf. marshi Hauer, una specie trovata nella Zona a Marshi/Crickmayi di Europa e Nord America, insieme con frammenti sparsi di Psiloceras cf. pressum Hillebrandt, coeva con la parte mediana della Zona a Planorbis dell'Hettangiano. Circa. 80 m piu in alto ci sono strati contenenti Psiloceras cf. rectocostatum Hlllebrandt, una specie che da i! no me ad una biozona andina parzialmente coeva con le Sottózone a Johnstoni e Plicatulum, Zona a Planorbis superiore. Altri fossili documentati negli strati del Retico di questa sezione sono foraminiferi, ostracodi e resti di piante identificati come Zuberia cf. zuberi (Szaj.) Freng. e Clathropteris sp. La sezione e stata anche campionata per quanto riguarda conodonti e radiolari, finora con risultati negativi. Uno studio paleomagnetico e in corso.Fil: Riccardi, Alberto Carlos. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata; Argentina. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Departamento de Paleontología Invertebrados; ArgentinaFil: Damborenea, Susana Ester. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata; Argentina. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Departamento de Paleontología Invertebrados; ArgentinaFil: Manceñido, Miguel Oscar. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata; Argentina. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. Departamento de Paleontología Invertebrados; ArgentinaFil: Iglesia Llanos, Maria Paula. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Geología. Instituto de Geofísica "Daniel Valencio"; Argentin

Taxa dedicated to Alberto C. Riccardi

Dr. Alberto Riccardi has greatly impacted in the advance of palaeontological and geological knowledge in several areas of the world, particularly in LatinAmerica. As a token of appreciation to his outstanding career, contributions, and positive influence, he has been recognized in several instances with the dedication of taxa bearing his name. His former mentor, several of his former students, and colleagues are among the people that have dedicated scientific names to him. This brief contribution summarizes the taxa and the circumstances related to each genus and species dedicated to Dr. Riccardi of which the authors are aware.Fil: Macellari, Carlos E.. Repsol Exploración; EspañaFil: Damborenea, Susana Ester. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. División Paleozoología Invertebrados; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Manceñido, Miguel Oscar. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo. División Paleozoología Invertebrados; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentin