The orthocerid Dawsonoceras? (Nautiloidea) from the Lipeón Formation (Silurian, Northwestern Argentina)

Turic et al. (1982) erected the name "Rectogloma" zaplensis for a problematic fossil found at Las Capillas River, 20 km northeast of San Salvador de Jujuy city (figure 1). The fossil was collected from beds belonging to the Lipeón Formation (Turner,1960), on the western flank of the Zapla range (Subandean Ranges). Based on the work of Antelo (1978), the Lipeón Formation was assigned to the Llandovery-Wenlock interval. The fossil was assigned to the problematic genus Rectogloma, described by Tuyl and Berckhemer (1914) for R. problematica but based on a more complete ornamentation and the presence of sinuous striations, which denotes its better preservation state, they defined a new species: "Rectogloma" zaplensis (Turic et al., 1982). A restudy of the specimen indicates that the fossil is a nautiloid cephalopod that can be assigned with reservation to the genus Dawsonoceras Hyatt, 1884.Fil: Cichowolski, Marcela. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Estudios Andinos "Don Pablo Groeber". Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Estudios Andinos "Don Pablo Groeber"; Argentin

A review of the endocerid cephalopod Protocyptendoceras from the Floian (Lower Ordovician) of the Eastern Cordillera, Argentina

Ordovician cephalopods from Western Gondwana are still poorly known and published data is in need of systematic and stratigraphical revision. In this work, the endocerid proterocameroceratid Protocyptendoceras from the Floian of the Eastern Cordillera of Argentina is revised using new material from La Ciénaga, 5 km upstream from Purmamarca. The species P. corvalani and P. teicherti are considered to be junior synonyms of P. fuenzalidae, which is redescribed in detail and reillustrated. Specimens preserve adapical parts of isolated siphuncles, related here to the presence of endocones in a posterior portion. Evidently P. fuenzalidae had a nektobenthic mode of life in a shallow water environment, oriented horizontally. Its palaeobiogeographical affinities are mainly with Floian proterocameroceratids from Eastern Gondwana, such as Anthoceras decorum and the related genera Lobendoceras, Ventroloboceras, and Notocycloceras.Fil: Cichowolski, Marcela. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Estudios Andinos "Don Pablo Groeber". Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Estudios Andinos "Don Pablo Groeber"; Argentin

Lamellorthoceratid cephalopods in the cold waters of Southwestern Gondwana: Evidences from the Lower Devonian of Argentina

Based on three specimens assigned to Arthrophyllum sp., the family Lamellorthoceratidae is reported from the Lower Devonian Talacasto Formation in the Precordillera Basin, central western Argentina. These Devonian cephalopods have been known only from low to mid palaeolatitudes and its presence in the cold water settings of southwestern Gondwana is notable. A nektonic mode of life, not strictly demersal but eventually pelagic, with a horizontal orientation of the conch is proposed for adults lamellorthoceratids, whereas a planktonic habit is suggested for juvenile individuals. These features would had allow their arrival to this southern basin, explaining their unusual presence in the Malvinokaffric Realm, and reinforcing the need of re-evaluate the distribution pattern of several groups of cephalopods.Fil: Cichowolski, Marcela. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Estudios Andinos "Don Pablo Groeber". Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Estudios Andinos "Don Pablo Groeber"; ArgentinaFil: Rustán, Juan José. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Centro de Investigaciones en Ciencias de la Tierra. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Centro de Investigaciones en Ciencias de la Tierra; Argentina. Universidad Nacional de La Rioja; Argentin

Estudio preliminar de la diversidad de los cefalópodos ordovícicos del noroeste argentino

Los cefalópodos ordovícicos del noroeste argentino provienen principalmente de la Cordillera Oriental y las Sierras Subandinas. Los mismos han sido poco estudiados, siendo principalmente importantes los trabajos de Cecioni en los años 1950 y 1960, quien describe numerosas especies del Llanvirniano de Sierras Subandinas y otras del Tremadociano temprano de la Cordillera Oriental. Estos trabajos deben ser revisados tanto taxonómica como estratigráficamente. En base a la revisión de parte de la colección original de Cecioni, junto a material adicional colectado en esos tiempos pero que no se publicó, y a material recientemente colectado, se presenta una visión preliminar de la diversidad de los cefalópodos a través del Ordovícico de la cuenca del NOA. Las especies descriptas por Cecioni para el Tremadociano inferior, hoy se sabe que son más jóvenes (en general Floiano). Por lo que la especie más antigua registrada en la cuenca es un eothinocerátido del Tremadociano medio. Luego se encuentra Purmamarcoceras kobayashii Cecioni del Tremadociano tardío. El Floiano se encuentra muy bien representado en la Cordillera Oriental, donde se han colectado recientemente numerosos especímenes. La gran radiación ordovícica de los cefalópodos se halla representada en el Floiano de esta región por las familias Proterocameroceratidae, Eothinoceratidae, Protocycloceratidae y, probablemente, Ellesmeroceratidae y Cyclostomiceratidae. En las Sierras Subandinas, los estratos fosilíferos con cefalópodos son principalmente del Sandbiano temprano. Cecioni asignó sus especímenes a las familias Protocycloceratidae, Cyclostomiceratidae y Baltoceratidae. Si la presencia de los protocyclocerátidos se confirma, entonces serían los registros más jóvenes de la misma. Otros especímenes colectados en la época de Cecioni pero sin publicar corresponden a endocerátidos de gran tamaño y cuellos septales macrocoaníticos.Simposio I: 2º Simposio de bioestratigrafía y eventos del Paleozoico inferiorFacultad de Ciencias Naturales y Muse

Geometric morphometrics in ammonoids based on virtual modelling

Linear morphometrics is the most widely applied technique to study the variationof the conch morphology in ammonoids and other ectocochleate cephalopods. However,because this method frequently relies upon a few linear measurements, it lacksthe explanatory power to accurately characterize the shape of the whorl cross-section,which is instead discussed solely in descriptive terms, e.g., elliptical, triangular, or subquadrate.Here, we introduce a landmark-based geometric morphometric approach tostudy ammonoid whorl cross-sections, derived from the regularly used morphometricparameters in cephalopods. This new technique uses virtual modelling to generatesemi-landmark configurations and virtual models of whorl cross-sections. We applied itto study 50 ammonoid specimens belonging to 48 genera exhibiting a wide range ofmorphologies and ages. Results indicate that this new method is appropriate todescribe the shape of ammonoid whorl cross-sections, allowing us to construct a morphospaceshowing several biological patterns (e.g., clustering and homeomorphy), andcomplex morphological transformations that, in some cases, correlate with evolutionarytendencies described by previous authors. Further, this technique can be used togenerate the basic segment required for the elaboration of the virtual models employedin hydrostatic and hydrodynamic studies.Fil: Moron Alfonso, Daniel Andres. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Estudios Andinos "Don Pablo Groeber". Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Estudios Andinos "Don Pablo Groeber"; ArgentinaFil: Hoffmann, René. Ruhr Universität Bochum; AlemaniaFil: Cichowolski, Marcela. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Estudios Andinos "Don Pablo Groeber". Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Estudios Andinos "Don Pablo Groeber"; Argentin

The oldest record of cephalopods (ellesmeroceratida) from the Central Andean Basin

This study reports the oldest record of cephalopods from the Central Andean Basin. Numerous small ellesmeroceratids were collected from the Alfarcito Member of the Santa Rosita Formation in the Quebrada de Arenal/Trancas, Jujuy, Argentina. The cephalopods were found associated with the trilobite Kainella meridionalis, indicating an early Tremadocian (Tr1) age. They are not exceeding 20 mm in length and have slightly curved apices and very short chambers. The siphuncle is marginal and rather big, with straight and ortho- to hemichoanitic septal necks. Based on these features, an assignment to the Family Ellesmeroceratidae is suggested.The oldest record of cephalopods worldwide is from the Jiangshanian Stage (Furongian Series) of North China. In the early Stage 10, the cephalopod diversity and abundance increased. They are also known from Laurentia and other isolated or dubious localities (e.g., Siberia, Kazakhstan). By the end of the Cambrian, cephalopods underwent an important crisis, leading to the extinction of 95% of the existing genera. Only two of the forty known genera from the Furongian survived this event.Cephalopods from the early Tremadocian (Tr1) are not abundant or widespread but are dominated by ellesmeroceratids. So far, they were unknown from mid to high paleolatitude basins. This is the first record from a temperate water region and the oldest from the Central Andean Basin. Contrary to coetaneous cephalopod assemblages from Laurentia, this association seems to be of very low diversity. One particular trait makes it outstanding: the very small size of the specimens, which reminds those known from the late Cambrian.Fil: Cichowolski, Marcela. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Estudios Andinos "Don Pablo Groeber". Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Estudios Andinos "Don Pablo Groeber"; ArgentinaFil: Vaccari, Norberto Emilio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Centro de Investigaciones en Ciencias de la Tierra. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Centro de Investigaciones en Ciencias de la Tierra; ArgentinaFil: Vaucher, R.. University Fraser Simon; CanadáFil: Waisfeld, Beatriz Graciela. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Centro de Investigaciones en Ciencias de la Tierra. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Centro de Investigaciones en Ciencias de la Tierra; ArgentinaReunión de Comunicaciones de la Asociación Paleontológica ArgentinaLa PlataArgentinaAsociación Paleontológica ArgentinaUniversidad Nacional de La Plata. Facultad de Ciencias Naturales y Muse

An exceptional storm accumulation of nautilids in the Lower Cretaceous of the Neuquén Basin, Argentina

Fil: Cichowolski, Marcela. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. IDEAN. Buenos Aires, Argentina.Fil: Pazos, Pablo J. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. IDEAN. Buenos Aires, Argentina.Fil: Tunik, Maisa A. Universidad Nacional de Río Negro. Instituto de Investigaciones en Paleobiología y Geología. Río Negro, Argentina.Fil: Aguirre Urreta, Beatriz. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Ciencias Geológicas. Instituto de Estudios Andinos “Don Pablo Groeber". Buenos Aires, Argentina.An exceptional accumulation of nautilid shells of the species Cymatoceras perstriatum (Steuer) is reported and described in the Lower Cretaceous Agrio Formation of the Neuque´n Basin (west-central Argentina). The bed represents a storm deposit in a shallowwater environment within the mid-ramp. The evidences of a storm-related origin of the bed come from the petrographic analysis and taphonomic features of the shells, specially the sedimentary infill pattern. The shells are dispersed in patches within the stratum, without any orientation relative to the bedding plane. It is proposed that the shells were floating after the death of the animals, although most of them have an almost complete living chamber. The presence of some heavily encrusted shells suggests that there is a mixing of specimens with different drift times. A variety of factors related to the origin of such high number of nautilid shells are discussed, including a transgressive stand system tract, the possible existence of a gregarious behaviour, changes in salinity and wind directions. h Lower Cretaceous, Nautilids, Neuque´n Basin, shell accumulation, storm deposit

Ascocerid cephalopods from the Hirnantian?-Llandovery stages of the southern Paraná Basin (Paraguay, South America): First record from high paleolatitudes

Ascocerid cephalopods are described for the first time from high paleolatitudes of Gondwana. Studied material was collected from the Hirnantian?-Llandovery strata of the Eusebio Ayala and Vargas Peña formations, Paraná Basin, southeastern Paraguay. The specimens are poorly preserved and were questionably assigned to the subfamily Probillingsitinae Flower, 1941, being undetermined at genus and species rank because diagnostic characters are not visible. A particular feature seen in our material is the presence of both parts of the ascocerid conch (the juvenile or cyrtocone and the mature or brevicone) joined together, which is a very rare condition in the known paleontological record. The specimens are interpreted as at a subadult stage of development because fully grown ascocerids would have lost the juvenile shell. A planktonic vertical migrant mode of life with a subvertical attitude is proposed for the juvenile, and a horizontal demersal nektonic mode for the adult form, as has been previously suggested. A subvertical orientation near the bottom is proposed for the subadult stage. We suggest that the immigration of ascocerids to southwestern Gondwana was possible through ocean currents that would carry the planktonic juveniles from low to high latitudes during the end-Ordovician postglacial transgression that flooded the intracratonic basins of the region.Fil: Cichowolski, Marcela. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Estudios Andinos "Don Pablo Groeber". Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Estudios Andinos "Don Pablo Groeber"; ArgentinaFil: Uriz, Norberto Javier. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Alfaro, Marta Beatriz. Universidad Nacional de La Plata. Facultad de Ciencias Naturales y Museo; ArgentinaFil: Galeano Inchausti, Julio C.. Ministerio de Obras Públicas y Comunicaciones ; Paragua

Early Tremadocian cephalopods from Santa Rosita Formation in NW Argentina: the oldest record for South America

We describe early Tremadocian (Kainella meridionalis Biozone) cephalopods from the Cordillera Oriental, Jujuy, NW Argentina. They consist of numerous small specimens collected at the Quebrada de Arenal, Trancas section, near the town of Tilcara, in the Alfarcito Member of the Santa Rosita Formation. All but three specimens were assigned to a new species of Ellesmeroceras (Family Ellesmeroceratidae), E. humahuacaensis sp. nov., based on its slightly endogastric curvature, the characteristics of the siphuncle and chambers dimensions. Micro CT scanning of one specimen aided in the description of the apex and facilitated the construction of a 3D model of the species. A single, similar specimen was assigned to Ellesmeroceras sp. pending the availability of additional material. Two specimens differ from the rest, being exogastric with a lower angle of expansion. They are tentatively assigned to Bassleroceras sp. This material indicates that Cambrian and early Tremadocian cephalopods are not as different as previously thought. “Diversification” and “extinction” events during the late Cambrian may be attributed to taxonomic “over-splitting” and taphonomic and/or sampling biases, respectively. These specimens are currently the oldest recorded in the Central Andean Basin and of West Gondwana, and probably represent the first migration of cephalopods into the region, when the water column was still poorly colonized. During the middle Tremadocian, subsequent immigrations and originations of several cephalopod orders accounted for a rise in diversity and expansion into new niches during this interval. Some of these taxa persisted into the middle Floian, at which time, a second increase in diversity is recorded. Ellesmeroceras humahuacaensis sp. nov. is interpreted as a sub-vertical nektobenthic organism.Fil: Cichowolski, Marcela. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Estudios Andinos "Don Pablo Groeber". Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Estudios Andinos "Don Pablo Groeber"; ArgentinaFil: Vaccari, Norberto Emilio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Centro de Investigaciones en Ciencias de la Tierra. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Centro de Investigaciones en Ciencias de la Tierra; ArgentinaFil: Pohle, Alexander. Ruhr Universität Bochum; AlemaniaFil: Moron Alfonso, Daniel Andres. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Estudios Andinos "Don Pablo Groeber". Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Estudios Andinos "Don Pablo Groeber"; ArgentinaFil: Vaucher, Romain. Universidad de Ginebra; Suiza. Universite de Lausanne; SuizaFil: Waisfeld, Beatriz Graciela. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Centro de Investigaciones en Ciencias de la Tierra. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Centro de Investigaciones en Ciencias de la Tierra; Argentin

Ascocerid cephalopods from the Hirnantian?-Llandovery stages of the southern Paraná Basin (Paraguay, South America): First record from high paleolatitudes

Ascocerid cephalopods are described for the first time from high paleolatitudes of Gondwana. Studied material was collected from the Hirnantian?-Llandovery strata of the Eusebio Ayala and Vargas Pena formations, Parana Basin, southeastern Paraguay. The specimens are poorly preserved and were questionably assigned to the subfamily Probillingsitinae Flower, 1941, being undetermined at genus and species rank because diagnostic characters are not visible. A particular feature seen in our material is the presence of both parts of the ascocerid conch (the juvenile or cyrtocone and the mature or brevicone) joined together, which is a very rare condition in the known paleontological record. The specimens are interpreted as at a subadult stage of development because fully grown ascocerids would have lost the juvenile shell. A planktonic vertical migrant mode of life with a subvertical attitude is proposed for the juvenile, and a horizontal demersal nektonic mode for the adult form, as has been previously suggested. A subvertical orientation near the bottom is proposed for the subadult stage. We suggest that the immigration of ascocerids to southwestern Gondwana was possible through ocean currents that would carry the planktonic juveniles from low to high latitudes during the end-Ordovician postglacial transgression that flooded the intracratonic basins of the region.Facultad de Ciencias Naturales y Muse