PALYNOLOGICAL STUDY OF THE PUNTA DEL BARCO FORMATION (APTIAN), SANTA CRUZ PROVINCE, ARGENTINA: GYMNOSPERM POLLEN GRAINS AND CHARACTERIZATION OF THE FLORA. This contribution completes the palynological investigation of the Punta del Barco Formation (Baqueró Group) with gymnosperm pollen analysis, including a new species-Microcachryidites cesariae-, and provides a comprehensive analysis of the flora. This taphocenosis is an interesting example of the biota disturbances by volcanic events prevailing in Patagonia during the Aptian. Through the integration of megafloristic, lithological and palynological data an open forest is interpreted, which gradually lost its tree layer after successive episodes of volcanic ash fall, with the consequent progressive decrease in taxonomic diversity. The palynological assemblage allows recognizing the fern family Gleicheniaceae as a dominant component of this Aptian flora, being highly resistant to strong environmental stress. Primitive angiosperms and lycophytes also developed successfully in this context, being linked to freshwater bodies. In contrast, gymnosperms were the most vulnerable group to environmental stress caused by volcanic eruptions. Among them, the Araucariaceae and Podocarpaceae families are the most resistant and the only conifers -with Cupressaceae- inhabiting Andean-Patagonian forests today. In contrast, Cheirolepidiaceae, Pteridospermales and Bennettitales were most affected, and although restored from Albian, they became extinct later.

PALYNOLOGY AND PALEOENVIRONMENTAL CONDITIONS DURING THE LAST 12,600 CAL. YEARS BP AT SALINAS DEL BEBEDERO (SAN LUIS, ARGENTINA). The availability of late Quaternary paleoenvironmental information in central-western Argentina is still scarce because of the paucity of archives recording past environmental changes. This work reports palynological and sedimentological analyses of a sedimentary sequence from a core taken in the Salinas del Bebedero playa-lake basin (33°20′S-66°45′W), with the main objective of contributing towards the knowledge on vegetation and paleoenvironmental history in central western Argentina during the last c. 12,600 cal. yrs BP. Sedimentological results suggest a maximum lake high-stand c. 12,600 after which lake levels decreased until c. 3600 cal. yrs BP when modern lake levels were reached. Pollen analysis suggests a regional vegetation with Monte-Espinal affinity similar to the present-day vegetation, which essentially remained unchanged during the Holocene. Prior to that time, the predominance of halophytic communities around c. 12,600 cal. yrs BP suggests more arid conditions due to lower precipitation (and/or higher temperatures) compared with the present day conditions.

MICROBIOTHERIIDAE (MAMMALIA, MARSUPIALIA) FROM THE PINTURAS FORMATION (EARLY MIOCENE, ARGENTINA). The Pinturas Formation (early Miocene, northwestern Santa Cruz Province, Argentina) is a continental succession that can be divided into three sequences based on its major intraformational erosive surfaces and lithological changes. Previous studies concluded that the lower and middle sequences have an absolute age of more than 16.5 Ma and they bear a mammal assemblage (“Astrapothericulan fauna”) different from and older than that typifying the Santacrucian Land Mammal Age. Recently, the first microbiotheriid marsupial species, Pachybiotherium illuminatum Goin, Tejedor, Abello, and Martin, was described from the middle sequence of this unit. In this contribution, new microbiotheriid specimens from the same sequence, represented by dental elements, are described from three localities of Santa Cruz Province: Cerro de los Monos, Portezuelo Sumich Norte, and Portezuelo Sumich Sur. These specimens are referred to Microbiotherium tehuelchum Ameghino, Microbiotherium divisum Ameghino, and Microbiotherium cf. M. gallegosense Sinclair. Similarly to what was observed for other mammals from these levels of the Pinturas Formation, the microbiotheriid association includes a combination of taxa previously known from the Santacrucian SALMA, others known from the Colhuehuapian SALMA, and a taxon recorded exclusively in these levels (Pachybiotherium illuminatum). This combination of taxa reinforces the idea of the “Pinturan assemblage” as distinct and intermediate in age between the Colhuehuapian and the Santacrucian. The four microbiotheriids represent the most diverse community so far known for this marsupial group as they positively occur in a single locality and stratigraphic level (i.e., Portezuelo Sumich Sur).

The sedimentary section at the Quitéria outcrop (Pantano Grande, central portion of Rio Grande do Sul State, Brazil) carries diverse and abundant fossil associations of plants and palynomorphs. This section includes coal deposits of the Early Permian Rio Bonito Formation in the Paraná Basin. This contribution presents a taxonomic re-evaluation on paleobotanical records based on an in-depth revision of available data as well as direct analysis from materials deposited in collections (published and unpublished). A taxonomic list is presented, based on the anlysis of all published data. A stratigraphic framework is offered, showing previous and new records in order to better understand the biostratigraphy of the rocks involved. Accordingt to this re-evaluation, the Quitéria Outcrop carries 14 morphospecies of plant macrofossils —including leaves and seeds of Glossopteridales— constituting a typical coal-forming flora. New palynological data derived from six samples taken in this section reveal diversified and abundant associations, including 29 species of spores, 36 of pollen grains and four taxa related to algae and fungi. Quantitative analysis shows that most samples are closely correlated with the previously known “Lundbladispora-Punctatisporites-Portalites Association”, derived from a hygrophilous environment. The associations are compatible with the Glossopteris-Rhodeopteridium Zone and with the Protohaploxypinus goraiensis Subzone (base of the Vittatina costabilis Zone), related to the Cisuralian (Early Permian). Stratigraphical considerations are based on comparision with neighboring sections and on the regional erosional surface recognized in this outcrop.

PALYNOLOGY OF THE GRAN BAJO MEMBER, SAN JULIÁN FORMATION (LATE OLIGOCENE) IN ITS TYPE LOCALITY, SANTA CRUZ, ARGENTINA: PALEOENVIRONMENTAL CONSIDERATIONS. The aim of this paper is to present the palynological results from the Gran Bajo Member of the San Julián Formation in its type area (Gran Bajo de San Julián). The studied section crops out in the eastern Santa Cruz Province and has been assigned to the late Oligocène based on ⁸⁷Sr/⁸⁶Sr data. The sedimentological analysis suggests a shallow marine environment close to the coast barely influenced by ocean waters at the lower part of the section, which evolved toward a foreshore-shoreface environment at the middle part of the section and to a shoreface-offshore towards the upper part of the section. The palynological assemblages from Gran Bajo section are primarily conformed by terrestrial elements with high preservation stage. A detailed palynological study allowed reconstructing the structure and composition of the forest in relation to depositional environments. Changes in the depositional environments correlate with the pollen zones determined by cluster analysis. Among the arboreal elements, the Podocarpaceae dominated the middle part of the section and Nothofagaceae (mainly Nothofagidites brassii type) dominates in the upper part, associated with Araucariaceae and Proteaceae in lower proportions. Myrtaceae, Arecaceae, Sapindaceae and Anacardiaceae were scarcely represented. The understory was composed by different species of monilophytes, mainly Cyatheaceae and Dicksoniaceae that decrease towards the top of the analyzed interval.

We report on a new dryolestoid (Mammalia, Dryolestoidea, Meridiolestida) from the Los Bastos Formation (Coniacian), Neuquén Province, Patagonia, Argentina, consisting of an edentulous left dentary (MCF-PVPH 412). The alveoli preserved suggest the presence of three incisors, one double-rooted canine, and six double-rooted postcanines (probably three premolars and three molars). Based on comparisons with previously known dentaries and isolated teeth, MCF-PVPH 412 would have been about the same size as Reigitheriurn Bonaparte. Among Dryolestoidea, MCF-PVPH 412 is assigned to Meridiolestida because there were probably three molars, the roots of the posterior molars are anteroposteriorly compressed, and there is no Meckelian groove. In addition, the penultimate lower premolar would be the largest in the tooth series, which is also true in other meridiolestidans. The position of the mandibular foramen, the probable presence of three premolars, and the outline of the posteroventral part of the jaw suggest affinities with the Mesungulatoidea (e.g., Coloniatherium Rougier, Forasiepi, Hill and Novaceck; Peligrotherium Bonaparte, Van Valen and Kramarz; and Reigitheriurn). The Coniacian specimen represents the oldest Mesungulatoidea and fills the gap in the record between the oldest South American dryolestoid (i.e., Cenomanian) and the better known Campanian—Maastrichtian taxa. The discovery of MCF-PVPH 412 in the Coniacian of Patagonia is consistent with the dryolestoid diversification during the Late Cretaceous that makes them the most abundant mammals during that period in South America.

This study includes a thorough systematic analysis of the ichnological record in the uppermost section of the Agua de la Mula Member of the Agrio Formation (Mendoza Group) in the Neuquén Basin (Argentina). The Bajada del Agrio section represents an environment evolving from marine to marginal-marine. Five main facies were defined: (1) an oolitic-skeletal bar; (2) transgressive pelites and coquinas (bioclastic conglomerates); (3) progradational coarsening-upward sandstones; (4) heterolithic deposits; and (5) heterolithic and carbonatic deposits. Fluctuating salinity and/or hypersalinity is inferred in the open tidal-flat deposits (facies 4). Sixteen ichnotaxa were identified and three types of trace fossils were described using open nomenclature because of the poor preservation of the material. Three ichnoassemblages are described. The section yielded trace fossils of callianasid decapods, palaeotaxodont bivalves, annelids and small tetrapods. Paleoenvironmental information drawn from trace fossils is coincident with sedimentologic evidence. It also highlights the current lack of accurate ichnological models for marginal marine hypersaline or fluctuating-saline environments, and suggests that sharp salinity changes in the environment not necessarily implie a decrease in ichnodiversity.

GYMNOSPERM FLORA FROM THE ÑIRIHUAU FORMATION (LATE OLIGOCENE-EARLY MIOCENE), RÍO NEGRO PROVINCE, ARGENTINA. The Cenozoic paleofloras in the area of San Carlos de Bariloche, Argentina are located mainly along the Ñirihuau and Pichileufú rivers, and belong to several stratigraphic units. Of these, the flora of Pico Quemado is situated in the most basal part of the Ñirihuau Formation and is probably late Oligocene-early Miocene in age. It is described herein, gymnospermous foliar impressions and compressions of Araucaria nathorstii Dusén (section Araucaria) and an ovuliferous scale of Araucariaceae; the latter constitutes the first evidence of reproductive structures belonging to section Araucaria for the Cenozoic of South America. Foliar impressions and compressions of Podocarpaceae are also present. Among them, the presence of podocarps with bilateral leaves related to Dacrycarpus de Laubenfels, previously known from Eocene outcrops of Chile, Argentina and Antarctica, allows extending their record up to the late Oligocene-early Miocene of Patagonia and relating them with the fossil and extant floras from the Australasian region. The morphology of the studied leaves, as well as their affinities with extant forms, together with the sedimentology, palynology, angiospermous megaflora and presence of freshwater bivalvia, allow suggesting a fluvial-shallow lacustrine depositional setting, developed under temperate to warm-temperate and humid climate.

A NEW HADROSAURID (DINOSAURIA, ORNITHOPODA) FROM ALLEN FORMATION, LA PAMPA PROVINCE, ARGENTINA. New studies of a Hadrosauridae specimen collected in the Allen Formation, Late Campanian/Early Maastrichthian from La Pampa Province, Argentina, allow recognizing a new taxon, Lapampasaurus cholinoi gen. et sp. nov., which is diagnosed by the following combination of characters: anterior cervical vertebrae with lateral foramina on the dorsal side of the diapophyses, scapula with laterally sharp deltoid crest and convex dorsal surface, pedal ungual phalanx longer than wide with superficial grooves and foramina, and shallow, longitudinal ventral ridge. The identification of Lapampasaurus as a member of Hadrosauridae is confirmed by the recognition of several synapomorphies, such as cervical neural arches with zygapophysial peduncles that elevate above the neural canal, long and dorsally arched postzygapophyses, coracoid relatively small when compared with the scapula, with concave anterior margin and well developed bicipital knob, and hoof-shaped pedal ungual phalanx. The record of Lapampasaurus in the Late Cretaceous of Patagonia suggests the presence of a more diverse hadrosaurid fauna than previously recorded.

PALM TRUNK IN THE CAMPANIAN OF NEUQUÉN GROUP, NEUQUÉN PROVINCE, ARGENTINA. In this paper a new species of fossil palm is described from the Auca Mahuevo locality, where the Anacleto Formation (Campanian) crops out, in the Neuquén province, Argentina. The described fossils correspond to palm trunks, referred to the genus Palmoxylon Schenk. These stems were compared with other species of this genus and with extant representatives of the family Arecaceae, and such comparisons allowed to assign it to a new species, Palmoxylon garridoi sp. nov. Martínez. The fossil record of palms in the Anacleto Formation suggests warm climate conditions in the Campanian of the Neuquén Group, and also extends the biochron of this genus in Argentina.

Fossil sirenians are well known from the Western Atlantic and Caribbean (WAC) region. Neogene records from the Atlantic coast of South America, although scarce, seem to reflect a similar taxonomic composition to its northern contemporaries. Fossil sirenians from Argentina are known from the late Miocene Paraná and Ituzaingó formations in Entre Ríos Province. An upper third molar housed in the Museo de Paleontología de la Universidad Nacional de Córdoba (CORD-PZ 4301), from the Paraná Formation, was originally described and assigned to the dugongid genus Metaxytherium Christol. Subsequent workers suggested it could instead belong to the dugongid genus Dioplotherium Cope, a designation that we confirm upon examination of the material. Additionally, we describe new sirenian remains from the Paraná Formation, consisting of two incomplete maxillae with teeth, belonging to one individual, deposited at the Museo de Ciencias Naturales de Paraná (MASP 373). This specimen shows similarities with species of Metaxytherium from the northern WAC. The Paraná Formation sirenians represent the southernmost occurrences of these two genera, and the geologically youngest occurrence of dugongids in the southern WAC. Dioplotherium and Metaxytherium also occur in the early Miocene of northern Brazil. The presence of these taxa as far south as Entre Ríos latitude suggests two possible dispersal routes: (1) across a marginal connection between a southern arm of the Amazonian Sea and the “Paranense Sea”; (2) along the Brazilian coast. Lastly, the occurrence of dugongids, which feed mainly on seagrasses, indicates that these marine angiosperms were present in the region as well.

TAPHONOMIC ANALYSIS OF MOLLUSKS BELOW THE SEDIMENT-WATER INTERFACE IN NAHUEL RUCÁ LAKE (BUENOS AIRES PROVINCE, ARGENTINA). The preservation of mollusk remains below the sediment-water interface in Nahuel Rucá lake (37°37′S–57°25′W) was analyzed in order to determine the degree of taphonomic alteration and to estimate the vertical extension of the taphonomically active zone (TAZ). To achieve that, the preservation patterns observed in five cores sampled from the littoral zone were described, and the effect of depth and presence of periostracum on shell dissolution was assessed by means of a field experiment. In all cores the recovered remains were dominated by fragments. Seven species were found: Biomphalaria peregrina (d'orbigny, 1835), Drepanotrema kermatoides (d'Orbigny, 1835), Heleobia australis (d'Orbigny, 1835), H. parchappii (d'Orbigny, 1835), Pomacea canaliculata (Lamarck, 1801), Uncancylus concentricus (d'Orbigny, 1835) and Musculium argentinum (d'Orbigny, 1835). We concluded that the TAZ extends from the surface to a depth of approximately 25 cm. The highest destruction takes place in the first 10 cm and decreases gradually with depth. In a similar way, specific richness and abundance decrease downward through the TAZ, and only H. parchappii and unidentified fragments are found near the bottom. Dissolution was higher in shells without periostracum. No differences in dissolution were observed with depth.

FOSSIL WOOD FROM EL PALMAR FORMATION (LATE PLEISTOCENE) IN THE EL PALMAR NATIONAL PARK, ENTRE RÍOS, ARGENTINA. This paper analyzes new fossil wood from El Palmar Formation (late Pleistocene) recovered from the El Palmar National Park, central-eastern Entre Ríos province, Argentina. Two new morphospecies of Beilschmiedioxylon Dupéron-Laudoueneix and Dupéron 2005 (Lauraceae) and other of Terminalioxylon Schönfeld 1947 (Combretaceae) are described, as well as Piptadenioxylon chimeloi Suguio and Mussa 1978 (Fabaceae-Mimosoideae) is cited for the first time in Pleistocene deposits of Argentina. This species was described from the ancient alluvial Tietê River “Porto de areia of Itaquaquecetuba”, São Paulo, Brazil. Wood anatomical characters suggest an affinity with the taxa Beilschmiedia taubertiana (Schw. and Mez) Kosterm., Terminalia australis Cambess, and Parapiptadenia Brenan respectively. The relationships and comparisons with the nearest living relatives were used to infer paleogeographic, paleoclimatic and paleoecological requirements. This fossil record suggests warm and humid climatic conditions for central-eastern of Entre Ríos, and during the period comprising the development of this geological formation. The fossil wood would correspond to components of riparian mixed forests (Lauraceae and Combretaceae) and semi-arid mixed forests (Fabaceae).

EQUIDS AND GOMPHOTHERES FROM THE LATE PLEISTOCENE OF SOUTHEASTERN OF BUENOS AIRES PROVINCE. The fossil mammal localities of El Conglomerado, Cascada Paleolama, and Rocas Chicas (Buenos Aires Province, Argentina) are poorly known. This paper describes the best-preserved specimens of equids (Perissodactyla) and gomphotheres (Proboscidea) stored at the Municipal Museum of Natural Sciences of Monte Hermoso city. The comparative study with other horses and gomphotheres, mainly from different localities of South America, mostly Argentina and Brazil, allowed to identify them as Hippidion principale (Lund), Hippidion devillei (Gervais), Equus (Amerhippus) neogeus Lund, and Stegomastodon platensis (Ameghino). A sample of S. platensis enamel of M2 from El Conglomerado was dated by AMS ¹⁴C 17,600 ± 135 years AP, while a sample of E. (A.) neogeus enamel of M1 from Cascada Paleolama gave an age of 14,020 ± 60 years AP. The data presented here are consistent with a lapse of time dominated by fauna adapted to arid and cold conditions.

FAUNAL ASSEMBLAGES FROM THE QUATERNARY OF SAN FRANCISCO, CÓRDOBA PROVINCE, ARGENTINA. BIOSTRATIGRAPHIC AND TAXONOMIC IMPLICATIONS. The chronological scale and continental biostratigraphy of South America was established on the base of fossil mammals from the Pampean Region. This scheme consists of Stages/Ages based on Biozones, with the late Miocene—early Holocene type localities in the Buenos Aires province. In the Córdoba province, several geological and stratigraphical studies have been undertaken since the 1990s and have provided a regionally useful scheme for biostratigraphic studies of the Quaternary. The aim of this work is to perform a biostratigraphic study of the San Francisco locality, in the east central region of the Cordoba province through the analysis of its mammal assemblages and to analyze the correlation with the scale proposed for the Pampean Region. We describe two faunal assemblages from two stratigraphical levels: (1) the faunal assemblage from the stratigraphic level 2 consisting of Lomaphorus sp., Neosclerocalyptus ornatus Owen, Catonyx tarijensis (Gervais and Ameghino), Scelidotheriinae indet., Macrauchenia patachonica Owen, Hemiauchenia paradoxa Gervais and Ameghino, Smilodon populator Lund and Panthera onca (Linnaeus) and assigned to the Ensenadan (early—middle Pleistocene) of the Pampean region; and (2) the faunal assemblage from the stratigraphic level 3 consisting of Neosclerocalyptus paskoensis (Zurita), Equus (Amerhippus) sp., Toxodon sp., Arctotherium sp., and cf. Lagostomus Brokes and assigned to the Lujanian (late Pleistocene—early Holocene) of the Pampean region. New records for Córdoba Province include Neosclerocalyptus ornatus, Panthera onca, and Arctotherium sp.; in addition, the latter represents the first record of the Ursidae family.