María José Salas

The earliest ostracods: the geological evidence

The oldest assumed ostracods appear in the fossil record from the TremadocianPaltodus deltifer conodont Biozone. Although geographically widespread these early ostracods have no obvious Cambrian antecedents. Their first appearance at ca. 485 Ma contrasts with molecular evidence that suggests a much earlier (latest Proterozoic or Cambrian) origin for ostracods. Some Cambrian bivalved arthropods such asAltajanella andVojbokalina, conventionally referred to the Bradoriida, have carapace morphologies that resemble Ordovician palaeocopid ostracods, though such a relationship is unproven without soft part anatomy. Evidence from preserved soft anatomy demonstrates that Bradoriida, such asKunmingella, and Phosphatocopida, essentially the Cambrian ‘ostracod’ record of traditional usage, belong outside the Eucrustacea. Early Ordovician ostracods appeared first in shallow marine, oxygenated environments on shelf margins, in a similar setting to other elements of the ‘Paleozoic fauna’. Their biodiversity was low (3 named genera and ca. 12 species), though some taxa such asNanopsis andEopilla achieved widespread dispersal between major Ordovician palaeocontinents. As bradoriids were largely extinct by the Late Cambrian, ostracods do not appear to have directly competed with them for shallow marine environments. The rapid colonisation of these settings by ostracods may have been facilitated by the available ecospace vacated by Bradoriida.

Patterns of ostracod migration for the ‘North Atlantic’ region during the Ordovician

Abstract A review of Ordovician neritic ostracods from the ‘North Atlantic’ region including Europe and North America identifies over 100 genera (including 44 palaeocopes and 31 binodicopes) which show a complex pattern of migration between two or more of the palaeocontinents Gondwana, Ibero-Armorica, Perunica, Avalonia, Baltica and Laurentia. Many dispersals were relatively slow, and the migration of a genus between palaeocontinents often took the duration of one or more graptolite biozones. Over 70 migrations appear to have occurred more rapidly, including those of Pseudulrichia, a genus which dispersed to five palaeocontinents within the duration of three graptolite biozones. Longevity clearly facilitated the chances of migration, as the most widespread genera such as Vannieria, Platybolbina, Medianella and Euprimites, are often the most long-ranging. Low migration rates prior to the Llanvirn are, at least in part, related to low ostracod taxonomic diversity. Greatly increased diversity from the late Llanvirn coincided with a much higher rate of migration. Coupled with the spread of carbonate–mudstone shelf marine facies in Laurentia during the early and mid Caradoc, this resulted in the migration of up to 18 Baltic-origin genera to Laurentia. Relative to overall ostracod diversity, migration rates were generally higher during periods of lower global sea level, suggesting that ostracod dispersal may have been aided by mid-ocean islands or outer-shelf carbonate platforms, which provided more extensive island-hopping routes during periods of low sea level. The palaeogeographical convergence of Avalonia, Perunica and Baltica, and subsequently of Avalonia and Baltica with Laurentia, in low latitudes and warm surface waters, is suggested by increasing ostracod migration between these palaeocontinents from the late Llanvirn onwards. This culminated, during the Ashgill, in numerous species–level links. Baltica may have been the source area for more than 40 migrant genera, reflecting its high-diversity faunas and its intermediate palaeogeographical position between Laurentia and Avalonia. Several ostracod genera used Baltica as a staging-post in migrations between Avalonia and Laurentia. Migrations continued during the late Ashgill Hirnantian Stage (24 migrations), especially between Laurentia, Baltica and Avalonia (up to 19 migrations of genera), suggesting close geographical proximity for these palaeocontinents. Some ostracods, particularly the binodicopes Pseudulrichia, Klimphores, Kinnekullea, Aechmina and Spinigerites, could occupy outer-shelf and cooler-water benthic palaeoenvironments. They were part of a widespread deep-shelf fauna from the mid Caradoc onwards, for which distances or climatic barriers were less of an obstacle for trans-oceanic migration. None of these ostracods were bathyal.

EARLY ORDOVICIAN OSTRACODS FROM ARGENTINA: THEIR BEARING ON THE ORIGIN OF BINODICOPE AND PALAEOCOPE CLADES

Abstract New species of ostracods are described from the Tremadoc of the Cordillera Oriental (Argentina). These are among the earliest well-documented records of Ostracoda sensu stricto. The ostracod assemblages are sourced from shallow marine clastics and are dominated by palaeocopes (Eopilla waisfeldae n. sp., Nanopsis coquena n. sp.), and the binodicope Kimsella luciae n. gen. and sp. Eopilla and Kimsella show affinities with species from paleocontinental Gondwana (e.g., Ibero-Armorica, Turkey, Australia, Carnic Alps), but Nanopsis is previously known only from paleocontinental Baltica. This study confirms that two of the major clades of Ordovician ostracods, namely the Binodicopa and the Palaeocopa, were already geographically widespread during the late Tremadoc, suggesting a still earlier origin for these groups, possibly from within the Cambrian to Early Ordovician Bradoriida. Evidence from soft-part anatomy indicates that phosphatocopids, the other group hypothesized to be ancestral ostracods, have apomorphies that preclude them as direct ancestors. The origin of ostracods is more likely to be found within the Bradoriida, a probable polyphyletic group that resembles Early Ordovician ostracods in the external sculpture of their bivalved carapace. Evidence from carapace morphology suggests that the ancestors of true ostracods might lie within the bradoriid groups Beyrichonidae and Hipponicharionidae, a hypothesis that can only truly be tested when more evidence from fossilized soft tissues becomes available.

Chapter 21 Biogeographical patterns of Ordovician ostracods

Abstract The biogeography of marine shelf ostracod genera is analysed for two Ordovician time slabs, the earliest Late Ordovician and the terminal Ordovician, that have been considered to reflect comparatively warmer and cooler global climate states, respectively. The earlier time slab is equivalent to the Nemagraptus gracilis graptolite interval (centred about 460 Ma), and defined as the total range of the eponymous species. The Hirnantian time slab comprises the Normalograptus extraordinarius and Normalograptus persculptus graptolite biozones (445.6–443.7 Ma). The ostracod dataset consists of 160 taxa from 24 early Late Ordovician localities and 86 taxa from 10 Hirnantian localities. Ordination and variation partitioning analyses show that patterns in ostracod distribution in the gracilis time slab are largely related to palaeocontinental affinity of the samples and to a lesser degree to palaeolatitude. Some decrease of provincialism can be suggested for the Hirnantian, although the ostracod dataset is limited for this interval.

First Middle Devonian Bivalves from Argentina, New Records from the Punta Negra Formation and Insights on Middle Paleozoic Faunas from the Precordillera Basin

Abstract. Middle Devonian bivalves from Argentina are reported for the first time, based on records of the Precordilleran Punta Negra Formation (Emsian—Frasnian?), San Juan Province. This finding is the youngest Devonian record of bivalves from southernmost South America. The impoverished bivalve association in the Punta Negra Formation includes five shallow infaunal deposit feeders, i.e. Nuculites argentinum Sánchez, Anthracoleda (Pseudoleda) minuta Sánchez, Praenucula sp., Deceptrix sp. and Praectenodonta sp. The distribution of the Silurian—Devonian bivalves from Precordillera shows a decreasing diversity trend during this interval, due to potential biases in sampling and paleoecology and thus suggesting that this trend might be apparent. Early and Middle Devonian bivalves from Precordillera show a strong cosmopolitan paleobiogeographic signature, in contrast with other geographically related basins showing endemic (Malvinokaffric Realm) signals during the Devonian. Contrarily, an endemic composition is recorded in the Precordillera Basin when based on coeval Malvinokaffric groups such as ostracods and trilobites. Although more information is needed, the cosmopolitan character of Devonian bivalve assemblages from the Argentine Precordillera Basin might be interpreted under the light of a unique history driving biogeographic processes affecting different taxonomic groups in different ways.

ASSESSING THE BIODIVERSITY OF ORDOVICIAN OSTRACODS FROM THE ARGENTINE PRECORDILLERA

Abstract Ostracod faunas from the Lower to Middle Ordovician rocks of the Argentine Precordillera Basin (Gualcamayo and Las Aguaditas Formations) are studied. A new family, Garcianidae, is erected. One new genus, Jeanvannieria, and six species are recognized, two of which are new (Jachalipisthia bicornata and Jeanvannieria bulbosa). The diversity and composition of the Precordilleran ostracods is evaluated on the basis of previous taxonomic analysis and the fauna studied here. The diversity is moderate, with a peak of 50 species during the early Caradoc. The composition of the fauna is characterized by the dominance of podocopes with a high percentage of binodicopes and a lack of palaeocopes, which is in agreement with a deep shelf environment. The carbonate slope setting of the Las Aguaditas Formation is the deepest environment yet found with Ordovician ostracods and records a relatively diverse fauna. The presence of Ectoprimitioides suggests biogeographic affinities between the Precordillera and Laurentia. The rest of the fauna contains a high percentage of endemic genera and a mixture of genera with several affinities, Baltic, peri-Gondwanan, and Australian.

NEW INSIGHTS ON EARLIEST DEVONIAN (LOCHKOVIAN) OSTRACODS FROM THE ARGENTINE PRECORDILLERA

Abstract. Ostracods from the Lower Devonian (Lochkovian) of the Argentine Precordillera Basin (upper levels of the Los Espejos Formation and lowermost ones of the Talacasto Formation) were studied. These units represent one of the best Lochkovian stratigraphic records in the Malvinokaffric basins. According to this revision, records of Devonian ostracod faunas in southwestern Gondwana can be extended to older stratigraphic levels. One new genus Suinella and ten species, including five new records (Suinella huarpesi gen. and sp. nov., Amphizona? argentinensis sp. nov., Bollia talacastensis sp. nov., Petrisigmoopsis? rotundum sp. nov. and Pircawayra antiqua sp. nov.) and one reassignment (Thilpsurella aff. T. putea Coryell and Cuskley) were hereby defined. The studied taxonomic assemblage differs from younger Devonian Malvinokaffric ostracod associations by being relatively diverse and composed mainly of drepanelloideans together with metacopids. The association is characterised by species with thin and spiny carapaces, a fact suggesting a relatively deep and low-energy environment below storm wave base. The mixed palaeobiogeographic affinities of the Lochkovian ostracod fauna contrasts with the clear Malvinokaffric signature of the upper Lower—Middle Devonian associations previously recognised in Argentina.

Teresa María Sánchez (1945–2011)

Teresa nació el 25 de enero de 1945 en Pehuajó (Provincia de Buenos Aires). En 1969 se graduó como Licenciada en Zoología de la Facultad de Ciencias Naturales y Museo, Universidad Nacional de La Plata y en 1984 recibió el título de Doctora en Paleontología de la Facultad de Ciencias, Universidad de Bretaña Occidental (Brest, Francia). Era Investigadora Principal del CONICET y Profesora Titular en la carrera de Ciencias Biológicas, de la Facultad de Ciencias Exactas, Físicas y Naturales, Universidad Nacional de Córdoba, a cargo de las cátedras de Paleontología e Introducción a la Biología. Inició sus investigaciones en Paleontología con el estudio de vertebrados cretácicos de Argentina. Las circunstancias políticas de la década del 70 impulsaron su exilio a Venezuela. Allí, llevo a cabo un cambio radical en su tema de investigación, comenzando a desarrollar su doctorado acerca de la paleoecología de las comunidades marinas y faunas de moluscos bivalvos del Paleozoico Superior de la Sierra de Perijá (Venezuela). Desde su regreso al país en 1983 y junto a su esposo, el Dr. Juan Luis Benedetto, gestó un equipo de trabajo dedicado a la investigación de los más diversos aspectos de la biota marina del Paleozoico Inferior. En este marco Teresa realizó una importante contribución a la formación de recursos humanos, dirigiendo numerosas tesis doctorales y becas del CONICET, CONICOR y SECyT-UNC. Sus investigaciones estuvieron centradas en el estudio taxonómico y paleoecológico de los bivalvos del Paleozoico Inferior de Argentina. Fue una verdadera pionera en la investigación de la radiación temprana del grupo en nuestro país y de las relaciones de estas formas con representantes más jóvenes. Paralelamente, fue precursora de otra línea de investigación vinculada a la reconstrucción de los ecosistemas del Paleozoico Inferior argentino y a eventos bióticos de gran escala. Sus contribuciones en ambas temáticas, publicadas en las más prestigiosas revistas científicas, han merecido un importante reconocimiento internacional, constituyendo referencias obligadas para los especialistas. En los últimos meses estuvo abocada a la redacción de tres capítulos para el nuevo volumen Bivalvia y Rostroconchia del Treatise on Invertebrate Paleontology. La docencia también fue su vocación y su pasión. Se desempeñó como docente en la Facultad de Ciencias Naturales de la Universidad Nacional de Salta, en la Facultad de Ciencias Puras y Naturales de la Universidad Mayor de San Andrés (La Paz, Bolivia), en la Escuela de Geología, Minas y Geofísica, Facultad de Ingeniería de la Universidad Central de Caracas (Venezuela), en la Facultad de Ciencias Exactas, FísicoQuímicas y Naturales de la Universidad Nacional de Río Cuarto, y en la Facultad de Ciencias Exactas, Físicas y Naturales de la Universidad Nacional de Córdoba. Es importante destacar también la publicación de una importante obra de difusión: “La historia de la vida en pocas palabras” un libro ameno y atractivo para el público general que, además, se ha tornado en libro de consulta para estudiantes de grado. Asimismo, desempeñó una labor activa en la gestión científico-tecnológica, tanto en el ámbito universitario como en organismos científicos provinciales y nacionales. Teresa ha sido la gestora del Centro de Investigaciones Paleobiológicas (CIPAL) dependiente de la Facultad de Ciencias Exactas, Físicas y Naturales de la Universidad Nacional de Córdoba que alberga numerosos investigadores y becarios. Como directora del mencionado Centro siempre propició un ámbito de trabajo, de respeto y de libertad. En todos sus roles, como investigadora, docente, paleontóloga, divulgadora, colega, compañera y amiga, Teresa ha dejado huellas. Tenía una personalidad abierta, leal y afectuosa, era espontánea. Tenía la virtud de saber escuchar y ponerse rápidamente en el lugar del otro, con una palabra adecuada y especial para cada uno siempre a mano, poniendo el afecto y la comprensión por encima de todas las diferencias. Quienes firmamos esta nota, discípulos, compañeros, colegas y amigos, tuvimos el placer de compartir con ella el trabajo cotidiano. Hoy tenemos la satisfacción y la responsabilidad de haber recibido un enorme legado: su entusiasmo genuino por el conocimiento, la dedicación y el compromiso con el trabajo científico, el valor y la fortaleza para enfrentar las adversidades de la vida, la honestidad para apreciar los logros ajenos, la defensa de las convicciones, la pasión por la Paleontología.