Embryonic osteology of titanosaur sauropods from Neuquén (Argentina): ontogenetic and evolutionary considerations. Titanosaur embryonic remains are described from megaloolithid eggs collected in the Anacleto Formation (Late Cretaceous) at Auca Mahuevo in Neuquén province (Argentina). These remains include complete articulate and disarticulate skulls, and numerous cranial and appendicular isolated elements. The embryonic skull is short, high, and presents numerous fenestrae, most of which are known in adult titanosaurs. However, the morphology of the maxilla and jugal is very different from that of adult titanosaurs. These elements show a series of processes that arise from their central body, which seem to have become reduced and transformed during ontogeny. The dental formula (Pm4 M7-8 /D10?) is similar to that of known adult titanosaurs. Detailed osteological study of these remains shows features of taxonomic, phylogenetic, and evolutionary significance. Several of the characters, including the snout with “stepped” anterior margin and the infratemporal fenestra extending ventrally to the orbit support the identification of the embryos as eusauropods. Other characters, such as the absence of crown denticles and the presence of a preantorbital fenestra are considered to be synapomorphies of Neosauropoda. Finally, the posteriorly wide skull and a maxillary notch at the ventral margin of the skull are regarded as synapomorphies of Titanosauria. Characters such as relatively large orbit, short rostral portion of the skull, long alveolar rows, “egg tooth”, tooth crowns lacking wear facets, frontal occupying practically the entire dorsal margin of the orbit, and nonossified postcranial axial skeleton are typical characters of sauropod embryonic and juvenile stages.

The La Laja Formation lies exposed almost continuously along the western margin of two hill ranges, i.e., the Sierra Chica de Zonda and Sierra de Villicum. This limestone unit bears a remarkable fauna of Cambrian trilobites. In this work we analyse the Delamaran trilobite fauna from the upper part of the El Estero Member and the lower third of the Soldano Member of the La Laja Formation. Taxa described are Glossopleura walcotti Poulsen, Glossopleura lodensis (Clark), Fieldaspis sp., and Prozacanthoides zondaensis n. sp. The Poliella denticulata, Mexicella mexicana?, and Glossopleura walcotti Zones are documented; these had been previously included in a hiatus. Trilobites-based correlations are established between the La Laja Formation and olistoliths of the Western Precordillera. Additional correlations are also suggested between the Precordillera and different localities in Laurentia. Finally, we discuss the biogeographic implications of the described material. Delamaran taxa reported from the La Laja Formation are characteristic and so far restricted to Laurentia. Analysis of the trilobite fauna from this unit supports the allochtonous origin of the Precordillera.

Plesiosaurs are recorded for the first time from the lower section of Mata Amarilla Formation, Santa Cruz Province, Patagonia, Argentina. The stratigraphic succession consists of mudstones and siltstones interbedded with medium to fine-grained sandstone, deposited in a littoral environment during the Cenomanian-Santonian; therefore the material is the oldest record of plesiosaurs from the lower Late Cretaceous rocks of Argentina. The remains include teeth, some vertebrae, and one propodium assigned to Elasmosauridae indet. and Plesiosauria indet. The status of Polyptychodon patagonicus Ameghino, 1893, as well as its stratigraphic position are discussed, leading to the conclusion that the material described by Ameghino is probably from the Mata Amarilla Formation and can only be referred to Plesiosauria indet. Analysis of sedimentologic features suggests that the material described here was deposited in an estuarine environment, strongly influenced by tides. The characters of the inferred environment are consistent with the type of preservation of the materials.

Paleogene distribution of Enneadocysta (Dinoflagellata) in the Southwestern Atlantic Ocean: paleoceanographic implications. The study of Middle to Late Eocene dinoflagellate cyst assemblages from subtropical Southwest Atlantic basins shows the presence of species of Enneadocysta, including E. dictyostila (Menéndez) Stover and Williams emend. Fensome et al., E. brevistila Fensome et al. and E. multicornuta (Eaton) Stover and Williams. The species Enneadocysta dictyostila has been widely recorded in middle Paleogene sections from Southern Hemisphere high latitudes. High representativity of Enneadocysta spp., along with other components of the Southern Ocean endemic dinoflagellate flora, have been observed in samples from Colorado Basin (∼38°S), Argentina and Punta del Este Basin (∼36°S), Uruguay. Previous research in the Tasman area has related the presence of these endemic taxa at mid-latitudes to the formation of a strong clockwise subpolar gyre (“cold trap”) favoured by the continental blockage of the Tasman Gateway. In this paper we propose that the observed dinoflagellate cyst distribution in the Southwest Atlantic basins can be explained by a similar dynamical mechanism operating close to the present Weddell Gyre. The blockage of the Tasman Gateway and a partially open Drake Passage both contributed to the formation of a strong western-intensified clockwise gyre that may have transported the endemic flora components, mainly represented by Enneadocysta spp., from the Antarctic continent northward along the Southwest Atlantic Shelf during the Middle - Late Eocene.

The Oxfordian-Kimmeridgian deposits of the Lotena Formation: new perspectives on the Late Jurassic stratigraphy of the Neuquén Basin, Argentina. New micropaleontological and stratigraphical data of the Lotena Formation at Barda Norte locality suggest that the Picún Leufú sub-basin was connected to open marine conditions at least until latest Oxfordian- early Kimmeridgian. These data reinforce the hypothesis of a temporary physical disconnection between the Picún Leufú sub-basin and the Neuquén Basin. The transitional characteristics of the palynological assemblages containing taxa recognized in Argentina since the Late Jurassic and the presence of sporomorphs belonging to the Stereisporites pandoi Zone (late Oxfordian) suggest a latest Oxfordian - early Kimmeridgian age for the analyzed deposits. According to the micropaleontological and stratigraphical analysis, the age of the Lotena Formation in the Picún Leufú sub-basin could span from the middle Callovian to the late Oxfordian-early Kimmeridgian. The microfossils (palynomorphs and foraminifers) suggest a moderate energy marginal-marine environment, located close to the terrigenous source area, and in which salinity varied with changes in freshwater influx.

Climatic trends for the Pampa grasslands during the late Pleistocene-Holocene: quantitative estimations based on fossil pollen sequences. Pollen-climate calibration models for mean annual temperature (T_an), annual precipitation (P_an) and precipitation efficiency (EP) are presented for the Pampa grasslands region (33°–41°S and 56°–67°W). The P_an and EP models were optimal (r²_boots =0,669 and 0,717; RMSEP;_boots= 16%) to apply Modern Analog Technique and to obtain late Pleistocene-Holocene quantitative climatic estimations based on fossil pollen from two alluvial sequences. In the central Pampa grasslands, P_an and EP values were 100 to 200 mm lower than present ones during the late Pleistocene (16000-12000 yr cal BP). During the Pleistocene-Holocene transition, early Holocene and late Holocene the values were similar to modem ones. In the southwest, P_an and EP values were c. 200 mm higher than present ones during the mid-Holocene (5500-3000 yr cal BP), and decreased during the late Holocene reaching similar modern values during the last 500 years cal. The climatic inferences agree with previous paleoclimatic interpretations that state dry to semiarid conditions during the late Pleistocene, and subhumid humid conditions during the Pleistocene-Holocene transition and early Holocene. However, there are discrepancies as from 5000 yr cal BP, probably related to the different sensitivity of the climate proxy data. The NE-SW precipitation gradient during the last c. 5500 yr cal may have been steeper than at present. These estimations are the first quantitative climatic reconstructions for the Pampa grasslands region, and should be taken as trends until new reconstructions confirm them.

Sandbian (Late Ordovician) conodonts at Quebrada La Pola, Sierra de Villicum, San Juan Precordillera (Argentina). In this contribution we better define the age and discuss the stratigraphic significance of a Late Ordovician brownish siliciclastic unit at the top of the La Cantera Formation at Quebrada La Pola (Sierra de Villicum), in the light of new biostratigraphic evidences here provided. The La Pola Formation includes siltstones and interbedded sandstones with brachiopod shells deposited in a proximal to intermediate shelf environment. A conodont association contained in this unit allows defining the Amorphognathus tvaerensis Zone, in the lower Late Ordovician. Within this zone, the unit can be assigned to the Baltoniodus variabilis Subzone, defining quite accurately the time of deposition. The conodont association suggests some paleobiogeographical affinities with the Midcontinent Province but some North Atlantic Province influence is also possible.