Quetecsaurus rusconii gen. et sp. nov. is a new titanosaur (Dinosauria, Sauropoda) from the Neuquén Basin of Mendoza Province, Argentina. The specimen comes from red mudstones of the Cerro Lisandro Formation (middle-late Turonian, Upper Cretaceous), and is the first sauropod with well-preserved remains to be discovered in this formation. The holotype includes a postorbital, teeth, the atlas, a posterior cervical vertebra, an incomplete dorsal vertebra, a posterior caudal centrum, dorsal ribs, a coracoid, fragments of a humerus, radius and ulna, and five metacarpals. It is characterized by the following combination of autapomorphies: (1) intercentrum of atlas with a prominent anteroventral border and expanded posteroventral processes; (2) posterior cervical neural spines with incipient lateral expansions; and (3) humerus with strongly sigmoid proximal border, rounded proximomedial border, and angular proximolateral corner. A preliminary cladistic analysis placed Quetecsaurus as a sister taxon of Lognkosauria (Mendozasaurus Futalognkosaurus). Quetecsaurus shares with the lognkosaurs the presence of cervical neural spines with ‘lateral laminae’, but relatively reduced in comparison with those taxa. This discovery provides new information on the diagnosis of Lognkosauria within South American titanosaurs.

The three recognized species of Caiman —C. latirostris, C. yacare and C. crocodilus— currently live in northern and central South America. Except for the fragmentary dentary of a putative Caiman from Oligocene rocks in Brazil, the genus has been reliably recorded in rocks of ages spanning the Neogene, when species of Caiman were a constant component of the South American crocodyliofauna. The major taxonomical diversification of Caiman occurred during the late Miocene, which is well documented in the area of Paraná (northeastern Argentina). Fossil crocodylians in Paraná are represented by one gavialid and caimanines, with at least five species of Caiman (including C. latirostris). This assemblage represents the southernmost record of Crocodylia living in “Amazonia” during the Miocene. In this work we confirm the record of Miocene caimans outside the Paraná and we prove the presence of Caiman cf. latirostris in present-day northwestern Argentina during the late Miocene. The taxonomic identification is based on a fragment of a left mandible with the same ornamentation, outline and dentition as Caiman, and with a symphyseal morphology similar to that of Caiman latirostris. The material comes from the upper part of the Palo Pintado Formation in the southern region of Valle Calchaquí (Salta Province). This unit was deposited in a sand-gravel fluvial system with associated ponds between 10.29 ±0.11 Ma (K/Ar) and 5.27 ±0.28 Ma (²⁰⁶Pb/²³⁸U).

The fossil record of foxes in South America is very rich, with almost all extant South American species recorded. Currently, three fossil species are known in the Plio-Pleistocene of South America: “Dusicyon” cultridens, Dusicyon avus and “Canis” ensenadensis. In the present work we reviewed the systematics of “Canis” ensenadensis from the Pleistocene of Buenos Aires province using both qualitative and quantitative approaches. We also described a new fossil specimen (MCA 2082) from Buenos Aires Province (Argentina) that shares some similarities with “Canis” ensenadensis. We compared the fossil specimens with a large sample of specimens that includes the living species Lycalopex gymnocercus, L. culpaeus, Cerdocyon thous, L. fulvipes, L. vetulus, L. sechurae and Atelocynus microtis. We performed a Principal Component Analysis using mandibular and dental measurements, and then a geometric morphometric analysis using photographs of the lateral view of the mandible. Our results indicate that “Canis” ensenadensis is a valid species and it should be included in the genus Lycalopex. We also conclude that MCA 2082 is a member of the genus Lycalopex, probably belonging to the species L. ensenadensis. These results suggest that the biochron of L. ensenadensis reaches the Lujanian Age. Even if our assignation of MCA 2082 is incorrect, this specimen represents a different taxon from those already described for the Lujanian, thus the diversity of foxes during the Lujanian is greater than previously known.

La morfometría aplicada a graptolitos constituye una herramienta poco desarrollada en la actualidad. Este tipo de análisis se realiza por primera vez en Argentina, con el objetivo de brindar un soporte adicional para la clasificación sistemática a nivel de especie, de ejemplares problemáticos del género Baltograptus. El material proviene de la Cordillera Oriental, asignado previamente a las especies B. turgidus (Lee) y B. kunmingensis (Ni), e incluido sucesivamente en grupos informales. Estas especies fueron definidas originalmente en China, junto a muchas otras difícilmente diferenciables, que se caracterizan por presentar tubarios robustos de carácter deflexo, con rápido ensanchamiento de sus estipes. Material adicional de características similares, que fuera asignado anteriormente a Baltograptus bolivianus (Finney y Branisa), se incluye también en este análisis. A partir de la cuantificación de las variables morfométricas se llevó a cabo un análisis de tipo exploratorio (análisis de componentes principales), seguido del análisis de agrupamiento y del posterior análisis discriminante. Como resultado, el material se separa en tres agrupamientos diferentes, que corresponden claramente a las tres especies en discusión. Si bien las variables correspondientes al extremo proximal del tubario influyen en la discriminación de los grupos resultantes, aquellas correspondientes al resto de la colonia ejercen mayor preponderancia en la separación a nivel de especie. El análisis de los parámetros morfométricos seleccionados constituye una base necesaria de comparación con trabajos similares que se encuentran en desarrollo actualmente en China, donde estas y otras especies semejantes fueron originalmente descriptas.

MORPHOMETRIC ANALYSIS OF EARLY ORDOVICIAN BALTOGRAPTUS SPECIES FROM THE CORDILLERA ORIENTAL, ARGENTINA. The application of morphometric techniques to graptolites is still under development. This kind of analysis is carried out for the first time in Argentina to give additional support to the systematic classification at species level for problematic specimens of the genus Baltograptus. The material comes from the Cordillera Oriental, and was previously assigned to B. turgidus (Lee) and B. kunmingensis (Ni) and subsequently included in informal groups. These species were originally described in China, along with many other species of difficult differentiation, which are characterized by a robust and deflexed tubarium with a rapid widening of the stipes. Additional similar material previously assigned to Baltograptus bolivianus (Finney and Branisa), is included in the analysis. An exploratory analysis (principal component analysis) was carried out, based on the quantification of the morphometric variables. It was followed by a cluster analysis with a subsequent discriminant analysis. The results showed that the specimens are separated into three groups, clearly corresponding to the discussed species. The variables of the distal part of the tubarium appear to have more influence in the separation of species. However, some variables corresponding to the proximal end also influence the resulting group discrimination. The analysis of the selected morphometric variables constitutes a foundation for comparison with similar studies, currently in progress in China, where the analyzed species as well as other related species, were originally described.

REVISION OF GENUS RETROTAPES DEL RÍO (BIVALVIA: VENERIDAE) IN THE EOCENE OF ANTARCTICA. The validity of the genus Retrotapes del Río is discussed and Retrotapes newtoni (Wilckens), R. antarcticus (Sharman and Newton) and R. robustus (Stilwell and Zinsmeister), from the Eocene strata of the Antarctic Peninsula (La Meseta Formation), are described and illustrated. The stratigraphic range of R. robustus is extended from the Acantilados allomember to the Cucullaea I allomember. The morphogeometric analysis performed, allows the recognition of ontogenetic variations of R. antarcticus and R. robustus, as well as to shed light on their taxonomic status. The present is the oldest record of Retrotapes, a taxon that would have originated in the Antarctic region, from where it would have dispersed northwards to lower latitudes during Miocene times when it was widely represented in the Patagonian seas.