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The type specimens of Eothinoceras americanum Ulrich et al., 1944, type species of the genus Eothinoceras Ulrich et al., 1944, are revised based on new photographic material. The resulting interpretation of the conch shape of Eothinoceras shows that the type species is an endogastric cyrtocone, necessitating the restriction of Eothinoceras to the type species and requiring the revision of the family Eothinoceratidae and the order Cyrtocerinida. A new scheme for classifying the genera of the order Cyrtocerinida into its three families is proposed: (1) Eothinoceratidae Ulrich et al., 1944, containing the genera Eothinoceras; Protothinoceras Chen and Teichert, 1987; Mesothinoceras Chen and Teichert, 1987; and Conothinoceras Chen and Teichert, 1987; (2) Cyrtocerinidae Flower, 1946, including Cyrtocerina Billings, 1865; Tangshanoceras Chen, 1976; and Centrocyrtocerina Stait, 1983; (3) Bathmoceratidae Gill, 1871, containing Bathmoceras Barrande, 1865; Saloceras Evans, 2005; Sacerdosoceras Evans, 2005; Margaritoceras Cecioni and Flower, 1985; and Mutveiceras Cichowolski et al., 2014.

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"; Argentina Fil: Hoffmann, René. Ruhr Universität Bochum; Alemania 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"; Argentina

Computed tomography has provided a wealth of biological data that now stands beside a vast, more traditional, morphometric database. By exploiting these two resources, we present a novel methodology to construct intricate, virtual cephalopod shells. As a case of study, we applied this method to Maorites seymourianus using data obtained from a previous work. For this purpose, evaluation of the conch geometry, and the definition of new parameters such as the segment width expansion rate (SWER), segment height expansion rate (SHER), the segment thickness expansion rate (STER), and three indices related, were introduced. The conch geometry of M. seymourianus follows a spiral that can be defined by a polynomial function. While similar to a logarithmic function, a polynomial fit is preferred because it reveals higher values of whorl expansion at the early ontogenetic phase and lower values reaching the adult body chamber. Results on the hydrostatic properties of the virtual models indicate that M. seymourianus would have a near neutral buoyancy, ranging from slightly positive to slightly negative, depending upon parameters that influence organismal mass. Positions of the center of mass and the center of buoyancy indicate that the studied species would have a relatively low hydrostatic stability, estimating a shell orientation of approximately 74–76° with respect to the vertical, with the aperture slightly inclined downwards relative to the horizontal plain. 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"; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Ciencias Geológicas; Argentina Fil: Peterman, David J.. Wright State University; Estados Unidos 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"; Argentina. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Departamento de Ciencias Geológicas; Argentina Fil: Hoffmann, René. Ruhr Universität Bochum; Alemania Fil: Lemanis, Robert E.. Technische Universität Dresden.; Alemania

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"; Argentina Fil: 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; Argentina

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 Museo

Devonian bactritids are described for the first time from South America. They come from siliciclastic rocks of the Talacasto Formation in the Precordillera Basin, west-central Argentina. The host strata span the Lochkovian–Emsian and contain other non-ammonoid cephalopods as well, thus refuting the alleged virtual absence of cephalopods in circumpolar Devonian basins from southwestern Gondwana (the Malvinokaffric Realm). We reportBactrites gracilisandDevonobactrites? sp., whose wide distribution contrasts with the endemic paleobiogeographic signature of some other taxonomic groups in these basins. Furthermore, new Lochkovian and Pragian records ofBactritessp. provide new insights into the earliest bactritid records worldwide.

Fil: Cichowolski, Marcela. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Oficina de Coordinacion Administrativa Ciudad Universitaria. Instituto de Estudios Andinos ; Argentina

Shell morphology affects multiple aspects of the biology of ectocochleate cephalopods (e.g., floatability, life habit, post mortem behavior of the shell, etc.), so it should impact the establishment and development of sclerobiont faunas as well. In this study, the sclerobiont faunas of Weavericeras vacaense (a spherocone) and Holcoptychites agrioensis (a discocone), two early Hauterivian ammonites from the Agrio Formation (Neuquén Basin, Argentina) were compared. The coeval nautilid Cymatoceras perstriatum (studied previously), was contrasted with both ammonites. Results show that the three sclerobiont faunas had similar abundance, taxonomic composition and distribution of individuals across the shells, but H. agrioensis showed a markedly reduced richness, with a fauna almost entirely composed by the oyster Amphidonte (Ceratostreon) sp. The more evolute and compressed H. agrioensis sank more quickly than W. vacaense and C. perstriatum, which may have undergone longer periods of flotation and exposure on the sea bottom. This agrees with the lower taxonomic richness of the sclerobiont fauna and a better overall preservation of H. agrioensis specimens. Differences in the sclerobiont faunas are greater across variations in shell inflation and coiling degree than across nautilids and ammonites; therefore, the latter are important parameters for the sclerobiont fauna as well since they impact how long shells will float and be exposed on the seafloor, and therefore on their time of exposure. The presence of an almost monospecific fauna in H. agrioensis, despite its rapid sinking and burial, indicates that Amphidonte (Ceratostreon) sp. was the earliest settler, and could abundantly colonize hard substrates in a short time. Fil: Luci, Leticia. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Estudios Andinos ; Argentina Fil: Cichowolski, Marcela. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Estudios Andinos ; Argentina Fil: Aguirre-Urreta, Maria Beatriz. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Estudios Andinos ; Argentina

Cichowolski, M., Pazos, P.J., Tunik, M.A. & Aguirre-Urreta, M.B. 2011: An exceptional storm accumulation of nautilids in the Lower Cretaceous of the Neuquen Basin, Argentina. Lethaia, Vol. 45, pp. 121–138. An exceptional accumulation of nautilid shells of the species Cymatoceras perstriatum (Steuer) is reported and described in the Lower Cretaceous Agrio Formation of the Neuquen Basin (west-central Argentina). The bed represents a storm deposit in a shallow-water 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. □Lower Cretaceous, Nautilids, Neuquen Basin, shell accumulation, storm deposit.

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 Cienaga, 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.

Jurassic marine reptiles are best known from the study of European Jurassic collections. The record of these reptiles encompasses most of the period, but that of Aalenian–Bathonian rocks is quite incomplete (Andrews, 1913; Brown, 1981; Buffetaut, 1982; Godefroit, 1994; Bardet, 1995; O'Keefe, 2001; McGowan and Motani, 2003). South American marine reptiles of the early Middle Jurassic are especially significant because they contribute to fill this gap of taxonomic and paleogeographic information (Fernandez, 1994, 1999, 2003; Spalletti et al., 1994; Gasparini, 1997; Gasparini et al., 2000). The largest amount and diversity of Jurassic marine reptiles of the Southern Hemisphere was found in northwestern Patagonia, in the Neuquen Basin (Yrigoyen, 1991; Fig. 1). These reptiles dominate in Tithonian rocks cropping out at numerous sites of the basin (Gasparini and Fernandez, 1996; Spalletti et al., 1999). On the contrary, Middle Jurassic marine reptiles are restricted to Chacaico Sur area, southeast of the Neuquen Province (Fig. 1). There, until present, ichthyosaurs, plesiosaurs, and a crocodile vertebra were found in the upper part of Los Molles Formation, Cuyo Group (Lower Bajocian), and pliosaurs and plesiosauroids were found in the lower part of Lajas Formation, Lower Callovian (Gasparini and Spalletti, 1993; Fernandez, 1994, 1999; Spalletti et al., 1994; Gasparini, 1997). Figure 1 —The Neuquen Basin in west-central Argentina, showing the location of Chacay Melehue section. The crocodile remains proceed from Los Molles Formation. Base map from Digregorio et al. (1984) Recently, during field work performed by the biostratigraphy students of the Geological Sciences Department (University of Buenos Aires) in the area of Chacay Melehue, Neuquen Province (Fig. 1), two of the authors (MC and DL) took part in the finding and extraction of the skull and postcranium …

The lithofacies and macrofossil guilds of the Agrio Formation (Upper Valanginian—Lower Barremian) have been analysed using evidence from sedimentological, taphonomic and palaeoecological studies. The study area is Agua de la Mula and adjacent regions in central Neuquen. Seven lithofacies have been recognized in the field, which indicate that the Agrio Formation was deposited in an open-marine, ramp depositional system under storm influence. Lithofacies indicate conditions that range from low-energy basin to high-energy inner ramp. Outer and mid-ramp deposits are the most abundant. Macrofossils have been grouped into 16 guilds based on tiering, life habit and feeding category. The guilds indicate normal benthic oxygen level, normal salinity, and soft—firm muddy and sandy bottoms. Suspension-feeders are more common than deposit-feeders suggesting the predominance of suspended food particles over deposited food resources. A low input of siliciclastics and, possibly, other palaeoceanographic conditions allowed the development of oolitic facies in the inner ramp and coral patch reefs in the upper mid-ramp for a limited period of time.

Until now, Cretaceous nautiloids from Argentina have been studied only briefly. Here Cymatoceras is described in detail, based on specimens found in the Neuquen and Austral basins, located in west-central and southern Argentina, respectively. Those from the Neuquen Basin are of Valanginian–Barremian age and belong to a single species, Cymatoceras perstriatum (Steuer). Those from the Austral Basin range in age from Hauterivian to Campanian and represent the first record of Cymatoceras from this region. It is represented by a new species, Cymatoceras patagonicum from the Turonian, and by isolated specimens, which are assigned to this genus in open nomenclature, owing to their poor preservation state; their ages range from Early Hauterivian to Early Campanian.

Despite many advances in the study of the paleoecology of nautiloids and amonoids, there is still much ground to cover. Study of their encrusters provides information on their paleoecology and taphonomy. In this work the encrusting fauna of abundant material of the nautilid Cymatoceras perstriatum (Steuer) is statistically and taxonomically analyzed in order to infer paleoecological and taphonomic features of the fossil organism. The available material of C. perstriatum consists mainly of phragmocone fragments, with rare cases in which the body chamber was preserved. Nine encrusting taxa, evenly distributed across the nautilid shell (cementing bivalves, serpulids, sabellids, cyclostome bryozoans, and agglutinated foraminifers), were observed in and on C. perstriatum. Of these taxa, oysters are dominant. Encrusters are abundant, with a mean of 12 encrusters per shell. Internal encrustation is common, especially inside the body chamber. The orientation of encrusters is variable. Intensity of encrustation varies, with some shells heavily colonized while others remained clean. The encrusting fauna is interpreted as mainly postmortem. Encrusters are distributed across the shell in a uniform way, lack particular orientation, and are common on the inside of the body chamber, suggesting that encrustation occurred both during necroplanktonic drift and as the shell rested on the sea bottom. A few encrusters were trapped between shell whorls, indicating that less extensive in vivo encrustation took place. Some differences in encrustation parameters were found among localities, corresponding to minor paleoenvironmental differences. Variable encrustation intensity suggests moderate to prolonged duration of exposure of the shells. However, those collected from an exceptional concentration at the El Salado locality were probably buried shortly after death. Fil: Luci, Leticia. 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 ; Argentina 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 ; Argentina

Middle Tremadocian cephalopods from the Sierra de Mojotoro, Cordillera Oriental, NW Argentina, are assigned to Saloceras cf. sericeum (Salter) based on the siphuncle morphology and general shape of the conch. Saloceras sericeum (Salter) is known from the Upper Tremadocian and Floian of England and Wales, a region that formed part of eastern Avalonia during the Early Ordovician, located at a high southern latitude to the north of the Gondwanan margin. This is the oldest record of this genus and of the family Eothinoceratidae, and extends the geographical range of Saloceras, being the first positive record of its presence in Argentina and the Central Andean Basin. These remains are amongst the oldest cephalopods described from NW Argentina. They represent the third mid Tremadocian record of nautiloids at relatively high palaeolatitudes and away from the low latitude carbonate platform palaeoenvironments where the bulk of the earliest cephalopods resided. 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"; Argentina Fil: 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; Argentina

To date, Cretaceous nautilids from the Antarctic Peninsula have received little attention and only a single species had been reported, Eutrephoceras simile Spath, from Seymour, Snow Hill, and James Ross islands. Currently, it is considered a synonym of Eutrephoceras subplicatum (Steinmann), which has also been described from the Upper Cretaceous of central Chile, southern Argentina and Angola. Here, we report and describe E. subplicatum in detail, based on specimens from the Lower Campanian–Maastrichtian of Vega, Seymour and James Ross islands, presenting, for the first time, embryonic conch features related to the palaeoecology of these organisms. The nauta of this species had a diameter of approximately 30 mm with 5–6 septa. In addition, we describe a new species, Eutrephoceras antarcticum, and one specimen assigned to the same genus in open nomenclature, both recovered from the Lower Campanian beds of James Ross Island. Fil: Cichowolski, Marcela. Universidad de Buenos Aires; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Ambrosio, Alfredo. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Museo Argentino de Ciencias Naturales “Bernardino Rivadavia”; Argentina. Universidad de Buenos Aires; Argentina Fil: Concheyro, Graciela. Ministerio de Relaciones Exteriores, Comercio Interno y Culto. Dirección Nacional del Antártico. Instituto Antártico Argentino; Argentina. Universidad de Buenos Aires; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina

Se describen restos fragmentarios de nautílidos del género Cymatoceras Hyatt, provenientes de estratos barremianos de la Cuenca de Atacama, norte de Chile. Los especímenes corresponden a dos taxones: Cymatoceras sp. del Barremiano tardío alto, cuya preservación es deficiente, aunque su tipo de ornamentación, con costillas gruesas y un seno ventral muy marcado, es sólo conocida, hasta el momento, en este taxón y Cymatoceras cf. perstriatum (Steuer), del Barremiano tardío. El material chileno es comparado, principalmente, con taxones de Cymatoceras presentes en las cuencas Neuquina y Austral, en Argentina. Fragmentary remains of nautilids assigned to the genus Cymatoceras Hyatt, found in Barremian strata at the Atacama Basin, northern Chile, are described. The specimens can be divided into two taxa: Cymatoceras sp., from the late Upper Barremian, that has a poor preservation, but at the moment its ornamentation type, with coarse ribs with a marked ventral sinus, is only known from this taxon, and Cymatoceras cf. perstriatum (Steuer), from the Upper Barremian. The Chilean material is mainly compared with Cymatoceras taxa present at the Neuquén and Austral basins, in Argentina.