MORPHOLOGY AND HISTOLOGY OF OSTEODERMS FROM A PEIROSAURID FROM THE NEUQUEN BASIN. Osteoderms of a new crocodyliform specimen recovered from the Puesto Hernández locality are described here, found in sediments of the Plottier Formation (late Coniacian), near Rincón de los Sauces city, Neuquén Province. The studied osteoderms, that are part of the associated material, include: dorso-sacral region, appendicular osteoderms associated to the right femur, proximoventral region of articulated caudal osteoderms, and isolated osteoderms. The histology of the osteoderms allowed determining they have a compact cortex that surrounds a more cancellous internal region. It was possible to recognize growth marks (annuli) in the entire compact tissue, indicating a minimum age of 18 years for the studied specimen. The osteoderms have characters that allow preliminarily assigning the specimen MAU-Pv-PH-437 to Mesoeucrocodylia closely related to Peirosauridae.

The record of Bennettitales from west-central Argentina and southern Brazil in South America is among the oldest known. In contrast to the better known near-coastal assemblages from the Northern Hemisphere, these Gondwanic elements are restricted to continental areas and isolated rift basins, similar to those in South Africa. Williamsonia potyporanae sp. nov. is preserved by impressions that expose distinct longitudinal sections of the ovulate structure, allowing the reconstruction of its tridimensional aspect, and is accompanied by probable Pterophyllum leaves. It consists of an ovate-shaped flower covered by two layers of delicate and connected ribbon-shaped and hairy bracts, and an obconic receptacle supporting a great number of megasporophylls, with uniformly aligned and apical fusiform ovules or seeds. The bennettite remains are part of an autochtonous-parautochtonous floral assemblage dominated by conifers and restricted to a thin mudstone interval in a mainly fluvial deposition comprisig the Caturrita Formation. The mud interval suggests a shallow lake supplied by periodic, intense rainfall that affected the vegetation growing along the river banks and/or on a floodplain deposits. An initially proposed Norian age, based on diversified vertebrate remains found in lower levels (Ictidosaur or Mammaliamorpha Cenozone), was recently extended to the Rhaetian. The advanced morphology of ovulate structure described here suggest an even younger Jurassic age, supported by comparisons with other fossil assemblages, mainly those from Argentine basins.

SAUROPOD EGGS FROM THE APTIAN-ALBIAN CERRO BARCINO FORMATION, CHUBUT (PATAGONIA, ARGENTINA): A PALEOENVIRONMENTAL AND PALEOBIOLOGICAL ENIGMA. Here are described the first eggs and eggshell fragments from the Lower Cretaceous Chubut province. The two eggs and eggshell materials come from the Huaniman locality at the north-central region of Chubut. In this paper, we provide a paleontological description of the materials to infer their paleoenvironmental setting and we offer a morphological comparison with other South American dinosaur eggs. The egg materials were found in fine tuffaceous sandstone from a proximal floodplain deposits associated to sinuous and multi-episodic river channels, belonging to the Cerro Castaño Member (Aptian-Albian; Cerro Barcino Formation). The eggshell morphology is similar to that of megaloolithid eggs (a paraphyletic group in egg parataxonomy) known from Patagonia such as Auca Mahuevo, Neuquen, positively identified as sauropod titanosaurs on the basis of in ovo embryos, and Salitral Moreno, Rio Negro. However, the new specimens from Chubut exhibit structural features of the eggshell not previously reported such as a horizontal network of pore canals clearly visible near and beneath the outer nodular eggshell surface, similar in morphology but differently placed than in the Auca Mahuevo eggs —where it overlays the membrana testacea. This morphological feature and the 1.5 mm thick eggshell may illustrate a novel adaptation to this specific nesting environment. Although only two isolated eggs were found in Huaniman, this discovery suggests the potential for the existence of a more substantial nesting site in the area.

SOUTH AMERICAN METATHERIANS FROM THE BEGINING OF THE NEOGENE (EARLY MIOCENE, COLHUEHUAPIAN LAND-MAMMAL AGE). MICROBIOTHERIA AND POLYDOLOPIMORPHIA. We review the taxonomy of two South American orders of Metatheria (Mammalia) of Colhuehuapian age (early Miocene): Microbiotheria and Polydolopimorphia. First, we comment and discuss on the cusp homologies of the upper and lower molars of the Argyrolagoidea (Polydolopimorphia). Second, we offer results of a phylogenetic analysis of the Microbiotheriidae (Microbiotheria). Third, we analyze all Colhuehuapian Microbiotheria and Polydolopimorphia known up to date: Order Microbiotheria, Family Microbiotheriidae: Pachybiotherium acclinum Ameghino, Pachybiotherium sp., Clenia minuscula Ameghino, Oligobiotherium divisum Ameghino, Eomicrobiotherium mykerum sp. nov., Microbiotherium sp., and Microbiotheriidae indet.; Order Polydolopimorphia, Suborder Bonapartheriiformes, Superfamily Argyrolagoidea, Family Argyrolagidae: Proargyrolagus argentinus sp. nov. and Anargyrolagus primus Carlini, Pascual and Goin; Family Patagoniidae: Patagonia peregrina Pascual and Carlini; Argyrolagoidea indet. Finally, we add knowledge on the Colhuehuapian Didelphoidea, describing an indeterminate species referable to this superfamily, and comment on the identity of “ Micro biotherium” gutierrezi Simpson, recognizing the new combination Coona gutierrezi.

ANALYSIS OF DINOSAUR EGGSSHELLS OF ALLEN FORMATION, UPPER CRETACEOUS OF THE RIO NEGRO PROVINCE (CAMPANIAN-MAASTRICHTIAN) : USEFULNESS OF MACRO CHARACTERS OF PARATAXONOMIC INTEREST. The present study is a further contribution to the parataxonomy knowledge of dinosaur eggshells from Salitral de Santa Rosa and Salitral Ojo de Agua, Río Negro province, Argentina. We studied 4469 fragments of dinosaur eggshells Allen Formation, Upper Cretaceous (Campanian-Maastrichtian). Twelve of these shells were subject to a principal component analysis (PCA) to classify and establish the relationships between characters commonly used in parataxonomic classifications. We studied under binocular scope 4264 eggshells (BL), 57 eggshells under transmitted light microscope (TLM) and polarized light microscope (PLM), 14 eggshells under scanning electron microscope (SEM). We identified two main groups, type 1 eggshells related to the oofamily Megaloolithidae with five subtypes and type 2 eggshells, with no subtypes assigned. Relevant traits found with the ACP study were: shell thickness, the width of the shell units, the diameter of the nodules, and the diameter of the mamila. Different types of eggshells found were compared with various ootaxa from South America and other regions of the world.

Mariliasuchus amarali is a notosuchian crocodylomorph found in the Bauru Basin, Sao Paulo State, Brazil (Adamantina Formation, Turonian—Santonian). The main trait of M. amarali is its robust construction, featuring short, laterally expanded bones. The centra of the vertebrae are amphicoelous. In the ilium, the postacetabular process is ventrally inclined and exceeds the limits of the roof of the acetabulum. M. amarali has postcranial morphological characteristics that are very similar to those of Notosuchus terrestris, though it also displays traits resembling those of eusuchian crocodyliforms (Crocodyliformes, Eusuchia). The similarity of the appendicular skeleton of M. amarali with the recent forms of Eusuchia, leads us to infer that M. amarali did not have an erect or semi-erect posture, as proposed for the notosuchian mesoeucrocodylians, but a sprawling type posture and, possibly, had amphibian habits (sharing this characteristic with the extant Eusuchia).

Foraminiferal assemblages recovered from Cape Lamb sediments on Vega Island are examined and illustrated herein. The foraminifera were discovered in Cenozoic debris and palagonitic breccia lithofacies that crop out at the southwestern tip of Cape Lamb. Among all the Cenozoic diamictite deposits recognized in this island, the studied sediments are the youngest and the most fossiliferous. Pectinids, brachiopods, and microfaunas are exceptionally well preserved and indicate little or no transport. The foraminiferal assemblage is dominated by infaunal species, with the most abundant including Globocassidulina biora, Cribroelphidiutn sp. aff. E. excavatum, and Cassidulinoides parkerianus, and the epifaunal Cibicides refulgens. These foraminifera suggest a normal inner shelf marine environment. Microfossils and macrofauna, stratigraphical evidence observed in the field and published isotopic ages from the nearby Cape Lamb suggest a Pleistocene age for this deposit.