Pliosaurus patagonicus sp. nov., from the middle Tithonian, Vaca Muerta Formation, Neuquén Province, Argentina, is described on an autapomorphic trait —i.e., the distance between the posterior functional alveolus and coronoid eminence (300 mm) equivalent to the last fourteen alveoli— and a unique combination of characters: short and robust mandibular symphysis with six pairs of functional alveoli; in lateral view the dorsoventral height is almost constant along the symphysis; low coronoid eminence and mandibular rami almost straight. As in other species of Pliosaurus genus the new taxon has trihedral teeth but the typical lateral expansion of the mandibular symphysis is missing. This new record reinforces the hypothesis of a trend toward the shortening of the mandibular symphysis observed in late Kimmeridgian—Tithonian species from the northern hemisphere. The presence of the macropredator Pliosaurus patagonicus sp. nov. in a protected marine environment close to the coast may be interpreted as the result of predatory and/or reproductive behaviors.

The genus Reigechimys (Rodentia, Echimyidae) was originally described on the basis of two mandibular fragments recovered from Huayquerian (late Miocene) outcrops of the Cerro Azul Formation in La Pampa Province (Argentina). The included species (R. plesiodon Verzi et al. and R. octodontiformis Verzi et al.) represent a peculiar lineage characterized by its molar morphology with occlusal simplification that is extreme for the family. New materials recently found at the Cerro Azul Formation allow for a more detailed knowledge of the variation of Reigechimys and recognition of a new species, Reigechimys simplex sp. nov. characterized by the absence of mesoflexid/fossettid in the m1–2. The morphological changes of Reigechimys are described in the context of the turnover exhibited by octodontoid rodents in the Huayquerian of the Cerro Azul Formation. The polarity of changes described for Reigechimys is consistent with those of the other lineages. This evolutionary pattern enhances the biochronological interpretation of the Huayquerian in this formation.

Late Furongian (late Cambrian) trilobites are described from the black, deep water limestones of the El Relincho Formation in Cerro Pelado, Precordillera of Mendoza, western Argentina. In addition, selected type specimens of the Carlos Rusconi collections at the Museo de Ciencias Naturales y Antropológicas J.C. Moyano, (Mendoza) are revised. The assemblages are largely dominated by the agnostoid Lotagnostus peladensis (Rusconi), which proved to be a species with variably effaced dorsal furrows. Polymeroids include Mendoparabolina pirquinensis Rusconi, Hungaia peladensis Rusconi, and Loganellus cf. macropleurus Rasetti, as well as some fragmentary remains of uncertain affinities. Generic occurrences strongly support connections with Laurentia. Although the species identified are endemic to the southern Precordillera, they mostly resemble faunas from the lower Saukia Zone of western North America, and the Onchonotus richardsoni and Keithia subclavata faunas of eastern Canada and USA.

REVISION OF THE SUBFAMILY CRASSATELLINAE (BIVALVIA: CRASSATELLIDAE) IN THE PALEOGENE—NEOGENE OF ARGENTINA. A revision of the Subfamily Crassatellinae Férussac, from the Paleogene—Neogene of Argentina is carried out. It is there represented by the genera Crassatella Lamarck, Bathytormus Stewart, Spissatella Finlay and Talabrica Iredale. Eight species are described and the new Talabrica elotroyoae sp. nov. and Spissatella susanae sp. nov. are introduced. It is demonstrated that the genus Bathytormus is present in Patagonia and the record of Talabrica becomes the oldest known for the taxon, and the first beyond the Indo-Pacific area, where it was thought to be restricted to the Pliocene—Actual interval. Its occurrence in the Miocene of Patagonian indicates the presence of a Cenozoic disperser taxon, that having originated in the Patagonian latitudes during Miocene times, would have migrated through the Antarctic Circumpolar Current (CCA) towards New Zealand and Australia. In turn, Spissatella Finlay, would have moved through the CCA from New Zealand to Patagonia during Miocene times.

The purple clam Amiantis purpurata (Lamarck) is a warm-temperate species inhabiting shallow water along the coast from Espiritu Santo (Brazil) to northern Patagonia. It is one of the few survivors of the middle—late Miocene faunal turnover which was characterized by the appearance of new taxa, most of them living now along the Argentinean coast. In order to study the biogeographic history of A. purpurata, a detailed review of its records was carried out. The oldest record of this species is from late Miocene rocks in Uruguay, and it appears that A. purpurata survived because its wide thermal tolerance range allowed larvae to migrate southwards from Uruguay, settling on the southern coast of Buenos Aires Province and San Matías Gulf. The characteristics of this gulf would have favored the development and settlement of the larvae, thus giving rise to the most abundant southern population during the Pleistocene. At the end of the Pleistocene, A. purpurata also survived the Last Glacial Maximum. During the Holocene, the population of A. purpurata in San Matías Gulf became isolated, but also represented the most abundant southern population of this species. During its brief Neogene history, Amiantis purpurata followed main global, regional and local events; thus it can be considered as an environmental indicator for this period.

MULTIPROXY RECORDS OF MID-HOLOCENE ENVIRONMENTAL CHANGES IN NORTHEAST PATAGONIA (BAJO DE LA QUINTA), ARGENTINA. Paleoecology is a useful tool in the exploration of changes occurring in the environment over time. Particularly, multi-proxy studies provide a more comprehensive picture of climatic conditions in the past. This work is a new contribution to the currently available paleoenvironmental information on the northern Patagonian Atlantic coast. It aims to reconstruct the paleoenvironmental history of Bajo de la Quinta (northeastern Patagonia) using pollen, diatoms, organic matter, carbonates and geomorphological studies. The section suggests changes in climate and vegetation occurring since the middle Holocene, revealing an important change from arid to semiarid conditions during the late Holocene —at 3000 years cal. BP. This may be related to more frequent contributions of moisture from the Atlantic and a weakening of the western winds. These environmental conditions favored the development of the shrub communities known as Monte. Such a development was synchronous with geomorphological changes of the coast, where connection to the sea was interrupted to originate a lagoon. The diatom content suggests the deposit represents a shallow fresh-brackish environment possibly exposed to periodic desiccation. This multi-proxy study improves and complements the current paleoenvironmental offsetting accepted for the northern coast of Río Negro Province.