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

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

Origen y diversificación de la Fauna Evolutiva de Trilobites Ibex-II (Furongiano tardío-Ordovícico Temprano) en el noroeste argentino

Faunas Evolutivas de Trilobites (FET) fueron propuestas como grupos de familias de trilobites que tienen trayectorias de diversidad en común. En particular la FET whiterockiana, objeto de intensos estudios, se habría originado en ambientes intermedios de plataforma carbonática y sólo más tarde accedería a ambientes litorales y marino profundos. Analizamos aquí en detalle la trayectoria de diversidad y abundancia de la etapa de desarrollo inicial, y posterior expansión de la FET Ibex-II durante el Furongiano tardío-Ordovícico Temprano. La fauna estudiada se desarrolló en una cuenca de foreland con altas tasas de sedimentación silicoclástica (Grupo Santa Victoria, Cordillera Oriental, noroeste argentino). En este contexto, la FET Ibex-II tiene su origen como elementos raros en ambientes intermedios de la plataforma durante el Furongiano tardío. Más tarde (Tremadociano medio), los miembros de la FET Ibex-II son poco diversas pero abundantes (no dominantes) en ambientes litorales si bien están aún ausentes en los ambientes más profundos. Los miembros de la FET Ibex-II dominan las comunidades a lo largo de todo el perfil batimétrico a partir del Tremadociano tardío. En el Floiano la FET Ibex-II es diversa y dominante, tanto a través del gradiente onshore-offshore como del óxico-disóxico, y muestra una dinámica de diversificación variada con un fuerte control ambiental dada por la radiación de formas endémicas y en menor medida inmigración. Estudios paleoecológicos de detalle muestran que la FET Ibex-II se relaciona en su origen con comunidades desarrolladas en ambientes con disturbio intermedio y sus componentes son formas en mayor medida cosmopolitas. Su trayectoria de diversidad y abundancia subsecuente sugiere que las distintas familias de trilobites que componen la FET Ibex-II exhiben historias y patrones de diversificación dispares tanto a escala regional como global. Estudios de mayor detalle permitirán esclarecer si la FET Ibex-II es una entidad biológica o un epifenómeno macroevolutivo.Sesiones libresFacultad de Ciencias Naturales y Muse

Trilobita

Los trilobites fueron artrópodos marinos paleozoicos, provistos de una cutícula dorsal mineralizada (exoesqueleto) y fosilizable, la que permitió que tengan gran representación en el registro fósil. Desde que aparecen en el Cámbrico Temprano, su diversidad alcanzó valores elevados en el Cámbrico Tardío-Ordovícico, para decrecer durante el Silúrico-Devónico y reducirse aún más en el Paleozoico Tardío, antes de extinguirse a fines del Pérmico. Durante los 300 m.a. de su historia evolutiva, estos organismos desarrollaron una amplia gama de modificaciones en el exoesqueleto, adquiriendo distintos hábitos de vida y notable capacidad de adaptación a los diversos ambientes marinos, desde sublitorales hasta profundos. Aunque la mayoría posee tamaños que oscilan entre 30 y 100 mm, muchos alcanzan dimensiones desde 2 mm hasta más de 70 cm. Se describieron alrededor de 5000 géneros y gran cantidad de especies, muchas de ellas valiosas en la resolución de problemas estratigráficos, paleobiogeográficos y paleoecológicos.Facultad de Ciencias Naturales y Muse

Trilobite expansion into estuarine environments during the Ordovician radiation

Trilobites have traditionally been considered fully marine. Through the integration of ichnological, palaeobiological and sedimentological datasets within a sequence-stratigraphic and strati­graphic palaeobiology framework, we challenge this assumption. This analysis is based on the study of incised fluvio-estuarine valley deposits from the Furongian Tilcara Member (TM) and the latest Furongian Pico de Halcón Member (PHM) of the Santa Rosita Formation, the early late Tremadocian Cardonal Formation (CF), and the DapingianâDarriwilian Alto del Cóndor Formation (ACF), from Cordillera Oriental of northwest Argentina. These valleys were incised into wave-dominated shallow-marine strata and filled with transgressive deposits that accumulated in tide-dominated estuaries. Whereas the TM lacks any body or trace fossil evidence of the presence of trilobites in estuarine settings, the other three units reveal that trilobites were able to inhabit these settings. The PHM and CF are host to trilobite trace fossils in outer estuarine facies, both containing various ichnospecies of Cruziana (e.g., C. omanica and C. semiplicata in the TM) and Rusophycus (e.g., R. latus in both units). In addition, the PHM also contains body fossils of the olenid trilobite Neoparabolina frequens argentina in the same deposits in which the trace fossils are preserved, as well as from middle estuarine facies. The ACF displays trilobite trace fossils of the C. rugosa group in inner, middle, and outer estuarine deposits, illustrating further landward incursions. This unit also contains body fossils of the asaphid trilobite Ogyginus sp. Accordingly, our data indicate two attempts of landward exploration via brackish water: phase 1 in which the outer to middle portion of estuaries were colonized by olenids (Furongianâearly late Tremadocian) and phase 2 involving exploration of the inner, middle, and outer estuarine zones by asaphids (DapingianâDarriwilian). Our study indicates that these trilobites were tolerant to salinity stress and able to make use of the ecological advantages offered by marginal-marine environments migrating up-estuary, following salt wedges either reflecting amphidromy or as euryhaline marine wanderers. It is suggested that tolerance to salinity stress arose independently among different trilobite groups as a result of the broad array of behaviors and adaptations of trilobites during the Ordovician radiation. We speculate that the assumption that all trilobites were stenohaline may have resulted in the misinterpretation of some tide-dominated estuarine deposits as fully marine

The strophomenide brachiopod Ahtiella Öpik in the Ordovician of Gondwana and the early history of the plectambonitoids

The Precordilleran species Ahtiella Argentina Benedetto and Herrera, 1986 is redescribed and illustrated and Monorthis coloradoensis Benedetto, 1998b from northwestern Argentina is reassigned to the genus Ahtiella Öpik, 1932. Ahtiella famatiniana new species from volcaniclastic rocks of the Famatina range (western Argentina) and Ahtiella tunaensis new species from the Precordillera basin (Cuyania terrane) are proposed. Paleogeographic and stratigraphic evidence strongly suggests that Ahtiella originated in the Andean region of Gondwana to further migrate to Avalonia, Baltica, and Cuyania. Contrary to previous assumptions, the fossil record from the Famatina volcaniclastic succession suggests that the plectambonitoid Ahtiella famatiniana n. sp. evolved from the hesperonomiid orthoid Monorthis transversa Benedetto, 2003 that always occurs in the underlying strata. Phylogenetic analysis of Ahtiella species shows that A. famatiniana n. sp. and the Peruvian A. zarelae Villas in Gutiérrez-Marco and Villas, 2007 are not only the earliest species of the genus but also are morphologically intermediate between Monorthis Bates, 1968 and the later and more derived species of Ahtiella from Baltica and Cuyania. If, as empirical evidence presented here shows, Ahtiella originated from Monorthis through a series of minor transformations, then the impressive morphological gap between orthides and strophomenides was bridged through short-time cladogenesis events, suggesting that it might not have a definite discontinuity between the species level evolution and the origin of higher taxa (macroevolution).Fil: Benedetto, Juan Luis Arnaldo. 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

First Appearance Datums (FADs) of selected acritarch taxa and correlation between Lower and Middle Ordovician stages

First Appearance Datums (FADs) of selected, easily recognizable acritarch morphotypes are assessed to determine their potential contribution to correlation between Lower and Middle Ordovician stages and substage divisions along the Gondwanan margin (Perigondwana) and between Perigondwana and other palaeocontinents. The FADs for 19 genera, species and species groups are recorded throughout their biogeographical ranges. The taxa investigated fall into three groups. Some have FADs at about the same level throughout their biogeographical ranges and are useful for long‐distance and intercontinental correlation. Among these are Coryphidium, Dactylofusa velifera, Peteinosphaeridium and Rhopaliophora in the upper Tremadocian Stage; Arbusculidium filamentosum, Aureotesta clathrata simplex and Coryphidium bohemicum in the lower–middle Floian Stage; Dicrodiacrodium in the upper Floian Stage; Frankea in the Dapingian–lower Darriwilian stages; and Orthosphaeridium spp., with FADs in the Dapingian–lower Darriwilian stages of Perigondwanan regions and at about the same level in Baltica. Other taxa, however, have diachronous (or apparently diachronous) FADs, and this needs to be taken into account when using them for correlation. A second group of genera and species, comprising Striatotheca, the Veryhachium lairdii group and the V. trispinosum group, have a recurring pattern of FADs in the Tremadocian Stage on Avalonia and in South Gondwana and West Gondwana, but in the Floian Stage of South China and East Gondwana. The third group, consisting of Arkonia, Ampullula, Barakella, Dasydorus, Liliosphaeridium and Sacculidium, have FADs that are markedly diachronous throughout their biogeographical ranges, although the global FADs of Arkonia, Ampullula, Liliosphaeridium and Sacculidium are apparently in South China and/or East Gondwana. It is possible that diachronous FADs are only apparent and an artefact of sampling. Nevertheless, an alternative interpretation, suggested by recurring patterns, is that some as yet undetermined factor controlled a slower biogeographical spread over time, resulting in diachroneity

Temps et mode dans le remplacement des faunes évolutives de trilobites du bassin oriental de la Cordillère (Nord-Ouest de l’Argentine)

Les transitions écologiques majeures au sein des faunes évolutives font l’objet d’un débat continu. Le présent travail analyse le rythme et le mode de remplacement des faunes évolutives de trilobites (TEF) Ibex I et II au cours des successions de l’Ordovicien basal dans le Nord-Ouest de l’Argentine. Les olénidés et les asaphidés y sont particulièrement étudiés, car ils correspondent, respectivement, aux groupes principaux des faunes Ibex I et II. La richesse faunistique est caractérisée en utilisant la méthode de raréfaction des échantillons et leur répartition grâce à une base de données présence/absence. Le Trémadocien terminal (Tr2) représente une inflexion dans la diversité et la distribution des asaphidés et olénidés. Alors que le nombre de genres des olénidés diminue au cours du temps, les asaphidés deviennent la famille la plus diversifiée à partir du Tr3, ce qui précède la tendance globale reconnue pour l’expansion de la faune Ibex II. Les asaphidés gagnent en diversité, contrairement aux autres trilobites ; de plus, ils voient leur diversification ralentie après la colonisation de nouvelles zones géographiques, ce qui suggère un déplacement comme mode probable de remplacement des faunes Ibex I et II. Apparemment, ces processus de remplacement varient suivant les régions, ce qui correspond à une mosaïque globale et complexe de patrons régionaux.Major ecological transitions among evolutionary faunas are matters of continual debate. Our study analyses the timing and mode of replacement of Ibex I and II Trilobite Evolutionary Faunas (TEF) in Lower Ordovician successions of northwestern Argentina, with special emphasis on olenids and asaphids as key groups of the Ibex I and Ibex II faunas, respectively. We explore richness by using the sample rarefaction method, and occupancy based on a presence–absence dataset. The late Tremadocian 2 (Tr2) represents an inflexion point in richness and occupancy trajectories of asaphids and olenids. While olenids diminish their generic richness through time, asaphids became the richest family since the Tr3 predating the global trend recognized for the expansion of the Ibex II Fauna. Asaphids gained diversity at the expense of other trilobites as well, their rise in diversity lags behind the increase in occupancy suggesting a displacement scenario as the probable mode of replacement between the Ibex I and II TEFs. Apparently, the processes of replacement variate among regions across the globe, configuring a complex global mosaic of regional patterns.</p

Furongian dataset

Abundance dataset. Samples were collected from restricted 10-20 cm shale intervals. Localities and depositional environments are indicated. Individuals were counted using the MNI protocol. The dataset was taxonomically standardized by the authors. Part of this dataset has been published by Balseiro et al. 2011 Palaio

Tremadocian 1 dataset

Abundance dataset. Samples were collected from restricted 10-20 cm shale intervals. Localities and depositional environments are indicated. Individuals were counted using the MNI protocol. The dataset was taxonomically standardized by the authors