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The southern Central Andes (∼25–40°S) exhibit a complex tectonic history, crucial for understanding orogenic processes in subduction-related orogens, yet debate on the timing and mechanisms of early Cenozoic topographic growth persists. We present double-dated detrital zircon U-Pb and (U-Th)/He thermochronology data from the early Oligocene–Miocene Bermejo Basin at ∼30°S to investigate source unroofing during development of the High Andes. (U-Th)/He results yield dates of ca. 565–16 Ma (n = 73), with distinct detrital modes that indicate a mixing of sediment sources characterized by variable cooling and exhumation histories. We employ a novel approach for modeling detrital thermochronology data that leverages the shared basin subsidence history of multiple detrital modes to resolve provenance and source unroofing histories. Results from the lower Oligocene Vallecito Formation (northwestern Argentina) reveal that detritus was sourced from Permian–Triassic Choiyoi Group rocks that underwent rapid late Eocene cooling, indicated by short lag time (2–5 m.y.) between source cooling and deposition. Our findings are consistent with bedrock studies of Eocene exhumation in the High Andes and establish source-to-basin connectivity during this time. Other detrital modes with pre-Cenozoic cooling histories were derived from Carboniferous Elqui-Colangüil and Choiyoi Group rocks or recycled from Paleozoic basins. We propose that an early Oligocene drainage divide in the High Andes was located west of the Punilla–La Plata fault, an active thrust front at ∼30°S. These findings challenge Paleogene neutral stress-state models for the Andes and underscore the importance of improved knowledge of erosion and deformation histories for refining models of Andean orogenesis. [ABSTRACT FROM AUTHOR]

There are few studies focused on spore and pollen clumps in paleopalynological samples, and these are only reports from the Northern Hemisphere. These aggregates may be of animal or floral origin. The goal of this contribution is to provide the first detailed study of spore and pollen clumps from the Southern Hemisphere, and to discuss their possible origin, botanical affinities, and pollination modes, based on their morphological characteristics, preservation and comparison with putative living representatives. Three fern spore clumps and 18 angiosperm pollen clumps were recognized in Maastrichtian-Danian La Colonia Formation sediments that outcrop at Chubut Province, Patagonia, Argentina. Most clumps are monospecific and composed of undamaged elements but some of them have two types of spore/pollen with corroded and/or fragmented exines. These findings represent the most diverse and abundant record of fern and angiosperm clumps from the Late Cretaceous and early Paleocene so far known from South America and the Southern Hemisphere. These results are indicative of the need for comprehensive large-scale studies on pollination of modern taxa and careful processing of palynological samples to lessen the already large bias in paleopalynological interpretations. The paucity of information on clumps in the fossil record has impaired our comprehension of dispersion/pollination in deep time. [ABSTRACT FROM AUTHOR]

This document provides a concise summary of a text or document that discusses the discovery and description of a dinoflagellate cyst species called Trithyrodinium verrucosum in the North of Patagonia, Argentina. The article explores the species' potential as a biostratigraphical marker for the Danian period and its paleoecological preferences in relation to global warming episodes. It also provides information about the paleogeographic location of the YPF-CH-PV.es-1 borehole and the Roca Formation in the Neuquén Basin. Additionally, the document includes details about the taxonomic analysis of dinoflagellate cysts and provides a list of references related to the study of micropaleontology and sedimentology in various regions and time periods. [Extracted from the article]

On the Fueguian Atlantic coast and in the southern Andean fold and thrust belt, the Paleogene is partially represented by numerous turbiditic deposits. Between Río Bueno and Cabo Leticia in Península Mitre, the Paleocene-Eocene is represented by the Río Claro Group (Cabo Leticia, La Barca, Punta Noguera, and Cerro Ruperto formations) and the Río Bueno Formation; which together constitute a ~1050-m-thick succession. Calcareous nannofossil assemblages recovered from 95 samples were analyzed to determine their relative ages. The Cabo Leticia Formation was barren in nannofossils. The upper LB2 Member of La Barca Formation contained Rhomboaster cuspis and Fasciculithus richardii, frequent in the Paleocene/Eocene boundary (subzones NP9a/NP9b). Nannofossils recovered from Punta Noguera Formation indicate an early Eocene age (biozones NP9b-NP10), with Fasciculithus tympaniformis, Rhomboaster cuspis, and abundant Toweius spp. The Cerro Ruperto Formation provided one productive sample, with specimens of Reticulofenestra spp. and Toweius spp., which indicates an early Eocene age for the formation (biozones NP12-NP13). The Río Bueno Formation yields calcareous nannofossil assemblages characterized by Chiasmolithus eograndis, Chiasmolithus expansus, Toweius spp., and Reticulofenestra spp., which indicate a late early Eocene to middle Eocene age (biozones NP14-NP15). Although the calcareous nannofossil record is discontinuous due to preservational biases in the Río Claro Group, our data allow a better age constraint for the investigated formations and to correlate these units with other surface and subsurface units in the Austral Basin. [ABSTRACT FROM AUTHOR]

The Yacoraite Fm. (Salta rift basin, Argentina) consists of a mixed carbonate–siliciclastic lacustrine succession, interbedded with volcanic ash layers and organised in four third-order stratigraphic sequences. It is one of the few sites in South America that encompass the Cretaceous–Paleogene (K–Pg) transition, the position of which remains debated. Here, samples were collected along a depocentral stratigraphic section that was previously dated by zircon and carbonate U-Pb geochronology. The consistency between zircon and carbonate U-Pb ages, together with an accurate petrographic analysis, allowed the selection of carbonates potentially preserving the original geochemical signature. Accordingly, C-O stable isotopes were analysed from microbialites, oncoids, ooids and lacustrine cements. The available depositional age model from zircon geochronology defined the stratigraphic interval, potentially including the K–Pg transition. Within this interval, carbonates provided negative δ13C values consistent with the negative C anomaly recorded in various K–Pg sites elsewhere. Additionally, spherical particles resembling spherulites related to meteorite impacts were found in two samples. Accordingly, the K–Pg transition could be placed at the top of the second stratigraphic sequence. These findings encourage further investigation of the Yacoraite Fm. to gain insights into the response of South American terrestrial settings to the K–Pg palaeoenvironmental crisis. [ABSTRACT FROM AUTHOR]

We report herein a new genus and species of Pyrotheria, Berracotherium koimeterion, from the Quebrada de Los Colorados Formation (middle Eocene-early Oligocene), Salta Province (Argentina). Up to this contribution, pyrotheres had only been known from northwestern Argentina by a single fragmentary tusk referred to Propyrotherium from the Geste Formation (late Eocene), Catamarca Province. This new taxon is based on a right mandibular fragment with the roots of dp4–m1 and m2 in eruption, and it can be differentiated from other pyrotheres as follows: horizontal mandibular ramus high and robust; mandibular symphysis large that extends posteriorly to reach m1; lower cheek teeth longer than wide; m2 bilophodont; mesial and distal lophids completely separated at the labial and lingual ends; both lophids transverse, parallel, nearly straight, and low; crenulations on lophids; the cristid obliqua that connects mesial and labial lophids is conspicuous, almost perpendicular to both lophids, and it is labially placed; and well-expanded distal cingulum that forms a third lobe. A cladistic analysis was performed that recovers Berracotherium gen. nov. as a member of Pyrotheriidae and includes it within an unresolved clade with Griphodon, Propyrotherium, Baguatherium, and Pyrotherium. Berracotherium koimeterion gen. et sp. nov. increases the known diversity of Pyrotheria at both regional and global scales, as well as its geographic and stratigraphic distribution. [ABSTRACT FROM AUTHOR]

We report a new small podocnemidid, Gestemys powelli gen. et sp. nov., based on one nearly complete skull, lower jaw, two shells, and remains of the appendicular skeleton belonging to two specimens from the Eocene Geste Formation of the San Antonio de la Cobres Basin, Salta Province, north-western Argentina. As in other podocnemidid genera, Gestemys exhibits a fully developed and medially extensive cavum pterygoidei, an incisura columellae auris enclosing the stapes and Eustachian tube, and lacks an exoccipital quadrate contact. Gestemys powelli bears a huge foramen palatinum posterius and a short pterygoid flange that does not reach the basisphenoid suture, exposing the cavum pterygoid. Phylogenetic analyses place Gestemys powelli as a member of Podocnemididae more closely related to Erymnochelyinae than Podocnemidinae. In regards to the palaeoenvironmental settings of the Palaeogene formations (Maíz Gordo and Geste) of north-western Argentina, at least two features differentiate the palaeoenvironment where G. powelli was recovered and those of other podocnemidid turtles from the Maíz Gordo Formation: 1) G. powelli was found in situ with very little re-working; and 2) in contrast to the muddy rocks indicating the marginal lacustrine setting and humid climate of the Maíz Gordo Formation, G. powelli is associated with a coarse-grained floodplain setting and a dry, temperate climate. Such differences highlight the contrasting environmental dynamics in which podocnemidid turtles lived during the Palaeogene. [ABSTRACT FROM AUTHOR]

Volkheimerites labyrinthus gen. et sp. nov., an angiosperm pollen type, is fully described and illustrated. The specimens were retrieved from lower Paleocene strata of the Salamanca Formation (San Jorge Basin) located in Chubut Province, Patagonia, Argentina. Medium to large size (25.5–55 μm) and a characteristic striate sculpture with labyrinthine pattern are distinguishing features of the grains in this new genus. Volkheimerites labyrinthus shares the presence of a coarse tectum supported by columellae with the fossil genera Dichastopollenites, Trisectoris and Periretisyncolpites, and some Winteraceae and Annonaceae species, but differs in having striate-labyrinthine as opposed to reticulate ornamentation. Our material is also distinguishable by the occurrence of solitary grains (monads) instead of the more frequent presence of tetrads in the Winteraceae family or grains separated into two hemispheres as in Dichastopollenites. The large thin area of the exine appears to be morphologically analogous to the proximal thinning of the exine in the monads of tetrads as occurs in some Annonaceae species. The detailed description and illustration of this new angiosperm pollen genus expands our understanding of Paleocene plant diversity in Patagonia. [ABSTRACT FROM AUTHOR]

Glyptodonts (Xenarthra, Cingulata) are one of the most amazing Cenozoic South American mammals, with some terminal forms reaching ca. two tons. The Paleogene record of glyptodonts is still poorly known, although some of their diversification is observable in Patagonian Argentina. Since the early and middle Miocene (ca. 19–13 Ma), two large clades can be recognized in South America. One probably has a northern origin (Glyptodontinae), while the other one, called the "austral clade", is interpreted to have had an austral origin, with the oldest records represented by the "Propalaehoplophorinae" from the late early Miocene of Patagonian Argentina. In this scenario, the extra-Patagonian radiations are still poorly known, despite their importance for understanding the late Miocene and Pliocene diversity. Here, we carry out a comprehensive revision of late Miocene (Chasicoan Stage/Age) glyptodonts of central Argentina (Buenos Aires and San Juan provinces). Our results show that, contrary to what is traditionally assumed, it was a period of very low diversity, with only one species recognized in this region, Kelenkura castroi gen et sp. nov. Our phylogenetic analysis shows that this species represents the sister taxon of the remaining species of the "austral clade", representing the first branch of the extra-Patagonian radiation. Additionally, K. castroi is the first taxon showing a "fully modern" morphology of the caudal tube. [ABSTRACT FROM AUTHOR]

The Madtsoiidae are an extinct lineage of snakes known from the Late Cretaceous to the Late Pleistocene, with a rich fossil record distributed mainly across Gondwanan landmasses. However, only a few taxa are represented by cranial or articulated remains, and most madtsoiids are known only by isolated vertebrae. The unambiguous record of Madtsoiidae from the Cenozoic in South America had been restricted to the genus Madtsoia from Eocene and Oligocene deposits of Patagonia and Brazil. Here, we describe a new madtsoiid taxon, Powellophis andina gen. et sp. nov., based on an articulated postcranial skeleton from the Mealla Formation (middle–late Paleocene) in northwestern Argentina. The new taxon is estimated to be around 3 meters long, with a vertebral morphology sharing similar features with other mid-to-large forms. Its inclusion in a recent analysis of madtsoiid relationships recovers Powellophis as an early member of a clade formed by mostly large bodied and gigantic taxa. Its presence in the Paleocene of northwestern Argentina fills the gap between the diverse Late Cretaceous and Eocene–Oligocene records of madtsoiids in South America, confirms their presence in northern Gondwana by the early Paleogene, and expands the diversity of the group. [ABSTRACT FROM AUTHOR]

T heCretaceous/Paleogene (K/Pg) boundary Classopollis pollen “spike” in Patagonia, Argentina, is viewed as a singular event with no coeval analog anywhere else in the world. Review of global palynological records, however, reveals that similar K/Pg boundary Classopollis spikes involving monotaxial C. classoides (Pflug) Pocock and Jansonius assemblages have previously been reported from the Colorado Basin, Argentina, as well as the Tarim Basin, China, suggesting that this was a global phenomenon. The presence of this morphotaxon in the Danian strata of western North America has previously been interpreted as evidence of reworking from older, pre-Turonian (i.e., Triassic through Early Cretaceous) sediments during the Laramide orogeny. This hypothesis appears supported by the results of contemporary detrital zircon studies coupled with the physical degradation of pollen. However, the interpretation that all Danian examples of this pollen, particularly those from coal deposits, have been reworked from much older sediments is questioned on the basis of this review. Within this context, assorted hypotheses regarding the enigmatic coup de grâce of Classopollis-producing Cheirolepidiaceae are also considered, particularly the hypotheses that the ecologic distribution of Cheirolepidiaceae retracted to include xeric, upland habitats (e.g., the Rocky Mountains) or brackish-water, physiologically dry habitats (e.g., the margin of the Cannonball Sea) during the Late Cretaceous and Danian. [ABSTRACT FROM AUTHOR]

The ghost shrimp Turbiocheir minutospinata has so far been known only from its holotype from the Eocene/Oligocene rocks of Río Turbio, Patagonia in Argentina. Recently, the additional specimen has been found in the Eocene strata of the Boca Lebu Formation of the Arauco Basin, Chile. New material adds information on the morphology of chelipeds and allows evaluation of the degree of heterochely of the studied ghost shrimp. Moreover, comparison of Turbiocheir minutospinata with extant ghost shrimp taxa allows synonymisation of Turbiocheir with Anacalliax. With this act the fossil record of Anacalliax is extended into early Eocene. The occurrence of Anacalliax minutospinata comb. nov. is proposed to represent a reliable calibration point for Anacalliacidae, which was not available until now. [ABSTRACT FROM AUTHOR]

The North Patagonian Massif (NPM) area in Argentina includes a plateau of 1200 m a.s.l. (meters above sea level) average height, which is 500–700 m higher than its surrounding areas. The plateau shows no evidence of internal deformation, while the surrounding basins have been deformed during Cenozoic orogenic events. Previous works suggested that the plateau formation was caused by a lithospheric uplift event during the Paleogene. However, the causative processes responsible for the plateau origin and its current state remain speculative. To address some of these questions, we carried out 3D lithospheric-scale steady-state and transient thermal simulations of the NPM and its surroundings, as based on an existing 3D geological model of the area. Our results are indicative of a thicker and warmer lithosphere below the NPM plateau compared with its surroundings, suggesting that the plateau is still isostatically buoyant and thus explaining its present-day elevation. The transient thermal simulations agree with a heating event in the mantle during the Paleogene as the causative process leading to lithospheric uplift in the region and indicate that the thermo-mechanical effects of such an event would still be influencing the plateau evolution today. Although the elevation related to the heating would not be enough to reach the present plateau topography, we discuss other mechanisms, also connected with the mantle heating, that may have caused the observed relief. Lithosphere cooling in the plateau is ongoing, being delayed by the presence of a thick crust enriched in radiogenic minerals as compared to its sides, resulting in a thermal configuration that has yet to reach thermodynamic equilibrium. [ABSTRACT FROM AUTHOR]

Recently, the basal beds of the lower section of the Lumbrera Formation have been referred to the early Eocene (Ypresian) based on the identification of a succession of hyperthermal events globally dated between 52 and 55 Ma. Nevertheless, this section have also been referred to the middle Eocene (Lutetian) based on the 'evolutionary stage' of its fossil mammals. In this contribution, we present a new 238U-206Pb isochron age (46.2 Ma) obtained from samples taken on various independent points across paleosol and matrix positioned at the top of the lower section of the Lumbrera Formation. The new age is consistent with the hyperthermal scheme and constrains the deposition of the lower section of the Lumbrera Fm. between 55–46.2 Ma. In this new geochronological framework, we present one of the most ancient cingulate assemblages from America, recorded during the early Eocene hyperthermal. The specimens involved were recovered from the lowest levels of the lower section of the Lumbrera Formation at Los Cardones National Park, Calchaquí Valleys, Salta Province, Argentina. This cingulate assemblage is formed by the armadillos Pucatherium parvum, a species widely distributed in the Eocene of northwestern Argentina and a new taxon, Noatherium emilioi, gen. et sp. nov. In this new geochronological framework, the taxonomic composition and morphological variations observed in the two species described here and their probably contemporaneous Riostegotherium yanei from the Itaboraí basin (Brazil) support an early diversification of the Cingulata during the Paleocene, and reinforce an intertropical origin for the group. [ABSTRACT FROM AUTHOR]

This work documents the biostratigraphy of dinoflagellate cysts from the La Barca Formation at the Punta Ainol Locality, Tierra del Fuego Province, Argentina. The succession at Punta Ainol represents a new record for the Paleogene (late Paleocene–middle Eocene) from southern South America, based on current data on nannofossils and dinoflagellate cysts. Some significant events are in agreement with nannofossil data. In ascending stratigraphic order, they include the first occurrences (FOs) of Impagidinium crassimuratum, Apectodinium homomorphum, Pyxidiniopsis waipawaensis, Samlandia septata, Cleistosphaeridium diversispinosum, and Enneadocysta dictyostila, and the latest occurrence (LO) of Palaeocystodinium golzowense. Three Paleocene/Eocene dinoflagellate cyst zones (Palaeocystodinium golzowense, NZDP7 and Apectodinium homomorphum) are recognized here. [ABSTRACT FROM AUTHOR]

Caimaninae is one of the few crocodylian lineages that still has living representatives. Today, most of its six extant species are restricted to South and Central America. However, recent discoveries have revealed a more complex evolutionary history, with a fossil record richer than previously thought and a possible North American origin. Among the oldest caimanines is Eocaiman cavernensis, from the Eocene of Patagonia, Argentina. It was described by George G. Simpson in the 1930s, representing the first caimanine reported for the Palaeogene. Since then, E. cavernensis has been ubiquitous in phylogenetic studies on the group, but a more detailed morphological description and revision of the taxon were lacking. Here, we present a reassessment of E. cavernensis, based on first‐hand examination and micro‐computed tomography of the holotype, and reinterpret different aspects of its morphology. We explore the phylogenetic affinities of E. cavernensis and other caimanines using parsimony and Bayesian inference approaches. Our results provide evidence for a monophyletic Eocaiman genus within Caimaninae, even though some highly incomplete taxa (including the congeneric Eocaiman itaboraiensis) represent significant sources of phylogenetic instability. We also found Culebrasuchus mesoamericanus as sister to all other caimanines and the North American globidontans (i.e. Brachychampsa and closer relatives) outside Caimaninae. A time‐calibrated tree, obtained using a fossilized birth–death model, shows a possible Campanian origin for the group (76.97 ± 6.7 Ma), which is older than the age estimated using molecular data, and suggests that the earliest cladogenetic events of caimanines took place rapidly and across the K–Pg boundary. [ABSTRACT FROM AUTHOR]

A new crocodyliform, Sebecus ayrampu, sp. nov., is described based on the rostral region of the skull, mandibular rami, and a distal portion of the femur collected in Paleocene rocks of northwestern Argentina. The new taxon is diagnosed (among other characters) by the presence of a sharp sagittal torus on the palatal surface of the premaxilla and maxilla, the surface of the alveolar region of the premaxilla descending vertically with respect to the palatal surface of the maxilla and the rest of the premaxilla, deep premaxillary fossa for the hypertrophied mandibular tooth with a ridge along its anterior margin, a differential pattern of ornamentation of the rostrum external surface, and a V-shaped anterior margin of the choana (with the vertex pointing anteriorly). This specimen is recovered as a new member of Sebecidae in a phylogenetic analysis, increasing the taxonomic diversity of the group in the Paleogene of northwestern Argentina. A sensitivity parsimony analysis using equal and implied weights (with different K values) retrieves two distinct lineages within Sebecidae: the Ayllusuchus + Bretesuchus clade and the Sebecus clade (in which the new taxon is included). Sebecidae is also recovered as a sister group to Baurusuchidae, forming together the monophyletic Sebecosuchia within Notosuchia. [ABSTRACT FROM AUTHOR]

The structural and topographic evolution of orogenic plateaus is an important research topic because of its impact on atmospheric circulation patterns, the amount and distribution of rainfall, and resulting changes in surface processes. The Puna region in the north-western Argentina (between 13°S and 27°S) is part of the Andean Plateau, which is the world's second largest orogenic plateau. In order to investigate the deformational events responsible for the initial growth of this part of the Andean plateau, we carried out structural and stratigraphic investigations within the presentday transition zone between the northern Puna and the adjacent Eastern Cordillera to the east. This transition zone is characterized by ubiquitous exposures of continental middle Eocene redbeds of the Casa Grande Formation. Our structural mapping, together with a sedimentological analysis of these units and their relationships with the adjacent mountain ranges, has revealed growth structures and unconformities that are indicative of syntectonic deposition. These findings support the notion that tectonic shortening in this part of the Central Andes was already active during the middle Paleogene, and that early Cenozoic deformation in the region that now constitutes the Puna occurred in a spatially irregular manner. The patterns of Paleogene deformation and uplift along the eastern margin of the present-day plateau correspond to an approximately north-south oriented swath of reactivated basement heterogeneities (i.e. zones of mechanical weakness) stemming from regional Paleozoic mountain building that may have led to local concentration of deformation belts. [ABSTRACT FROM AUTHOR]

Background and Aims Cunoniaceae are woody plants with a distribution that suggests a complex history of Gondwanan vicariance, long-distance dispersal, diversification and extinction. Only four out of ~27 genera in Cunoniaceae are native to South America today, but the discovery of extinct species from Argentine Patagonia is providing new information about the history of this family in South America. Methods We describe fossil flowers collected from early Danian (early Palaeocene, ~64 Mya) deposits of the Salamanca Formation. We compare them with similar flowers from extant and extinct species using published literature and herbarium specimens. We used simultaneous analysis of morphology and available chloroplast DNA sequences (trnL – F , rbcL , matK , trnH – psbA) to determine the probable relationship of these fossils to living Cunoniaceae and the co-occurring fossil species Lacinipetalum spectabilum. Key Results Cunoniantha bicarpellata gen. et sp. nov. is the second species of Cunoniaceae to be recognized among the flowers preserved in the Salamanca Formation. Cunoniantha flowers are pentamerous and complete, the anthers contain in situ pollen, and the gynoecium is bicarpellate and syncarpous with two free styles. Phylogenetic analysis indicates that Cunoniantha belongs to crown-group Cunoniaceae among the core Cunoniaceae clade, although it does not have obvious affinity with any tribe. Lacinipetalum spectabilum , also from the Salamanca Formation, belongs to the Cunoniaceae crown group as well, but close to tribe Schizomerieae. Conclusions Our findings highlight the importance of West Gondwana in the evolution of Cunoniaceae during the early Palaeogene. The co-occurrence of C. bicarpellata and L. spectabilum , belonging to different clades within Cunoniaceae, indicates that the diversification of crown-group Cunoniaceae was under way by 64 Mya. [ABSTRACT FROM AUTHOR]

The fossil record of fishes from the Farola de Monte Hermoso locality (lower Pliocene) in the southern Buenos Aires province, Argentina, shows an unusual composition. The locality at the southern boundary of the Brazilian Ichthyogeographic Realm. However, its fossil record is composed of fossil fishes that are not necessarily related to Brazilian lineages, namely indeterminate siluriforms, trichomycterid catfishes, and percomorphaceans. The aim of the present contribution is to describe and report for the first time isolated specimens belonging to Characidae fishes. In the Pampean region the fossil record of characids is restricted to Oligosarcus Günther, 1864 sp. from the late-middle Pleistocene. The present finding fills a temporal gap between the Paleogene and Quaternary reports and indicates that Brazilian fish lineages were present in the area by early Pliocene times, and may constitute an indirect evidence of the evolution of the basins in the southern Pampean Area. [ABSTRACT FROM AUTHOR]

It is widely recognized that fossil leaves are good proxies for paleoclimate estimates, and leaf physiognomy analysis is a traditional technique used to make climate estimates. There are only a few paleoclimate reconstructions for the southern part of South America based on this technique. Here we report climate parameters using fossil leaves from the Río Turbio (Eocene-Oligocene) and Río Guillermo (Oligocene-early Miocene?) formations in southern South America, Cuenca Austral, Argentina. We used univariate (leaf margin and leaf foliar area analysis) and multivariate methods (CLAMP, DiLP) on two datasets from South America, in the Southern Hemisphere. Lower and upper members of the Río Turbio Formation show a mixed paleoflora represented by paratropical as well as cool-temperate taxa such as Nothofagus, with a similar percentage of untoothed fossil leaves. Climate estimates indicate warm and humid conditions for both Río Turbio Formation members. The Río Guillermo Formation is represented by mostly cool-temperate elements, mainly Nothofagus, and most with toothed margins. The paleoclimate analysis indicates a decrease in temperature and precipitation when comparing the two studied formations. Today, temperate forests in southern Argentina have a plant composition and climate more similar to the estimates made for the Río Guillermo Formation. [ABSTRACT FROM AUTHOR]

In the last few years, the Quebrada de Los Colorados Formation has become an important middle Eocene fossiliferous unit in Northwestern Argentina. In this unit, the South American native ungulates were until now only represented by the order Notoungulata, including one family of Typotheria and three of Toxodontia. In this contribution, we present a new faunistic assemblage of South American native ungulates, collected from outcrops of the Quebrada de Los Colorados Formation at Los Cardones National Park, Calchaquí Valleys, Salta Province (Argentina). This new assemblage is constituted by the following taxa: litoptern Didolodontidae cf. Ernestokokenia sp., Astrapotheria indet., and notoungulate Notostylopidae Homalostylops sp., a Homalostylops sp., typothere "Oldfieldthomasiidae" Colbertia falui sp. nov., Colbertia lumbrerense, and Colbertia sp. and toxodont "Notohippidae" Pampahippus secundus. Colbertia falui sp. nov. differs from the other species of Colbertia by the following features: lower cheek teeth with both more labially angular and oblique trigonid; lower premolars more labio-lingually compressed; with proportionally larger trigonid, and shorter talonid; ectoflexid transversally deeper; lower molars with a more developed paralophid, and more expanded metalophid and entoconid; the latter is located in a more mesial position, being closer to the metaconid; deep and lingually narrower talonid basin; disto-lingual sulcus transversally shallower; more developed cingulids; and m3 with less lingually projected hypoconulid. This new fauna markedly increases the taxonomic richness known for this formation since it includes the first mention of notostylopids, "oldfieldthomasiids", litoptern didolodontids, and astrapotheres. With the current evidence, we postulate an ungulate migration from Patagonia to Northwestern Argentina during the Eocene. We also hypothesize that the observed taxonomic differences among the Quebrada de Los Colorados, Geste, and Lumbrera formations are more probably associated to orogenic factors that have regulated the faunal dynamic in Northwestern Argentina during the Paleogene than to a differential sampling effort or taphonomic biases. [ABSTRACT FROM AUTHOR]

Introduction: Scutelliforms were diverse and widespread in shallow marine environments during Neogene times in South America. Nevertheless, they have almost never been used as biostratigraphic tools. Objective: To provide a refined stratigraphic frame useful for calibrating temporal dimensions of scutelliform diversity from Argentina and Uruguay and its correlation with the molluscan assemblages previously proposed. Methods: A detailed survey of their geographic and stratigraphic provenance was carried out. We revised both the bibliography and collections (institutional and from our own field work). Results: The group is represented by 14 species belonging to six genera, and four assemblages were identified. Numerical dates of the Neogene marine rocks obtained recently allowed their placement in a chronological scheme: "Iheringiella" sp. A is restricted to the late Oligocene, the genera Camachoaster and "Eoscutella" and the species Monophoraster telfordi to the early Miocene, Abertella gualichensis and Abertella miskellyi to the middle Miocene, and Monophoraster duboisi, Amplaster coloniensis and Amplaster ellipticus to the late Miocene. Non-lunulate scutelliforms are not restricted to the late Oligocene as previously supposed. The oldest occurrence of the genus Monophoraster corresponds to the early Miocene, and along with Iheringiella are long-living taxa that embrace the 25.3 Ma-18.1 Ma (Iheringiella patagonensis) and approximately 15 Ma-6.48 Ma (Monophoraster darwini) intervals. The presence of Iheringiella in the early Miocene of northeastern Patagonia is corroborated, reaching there its northernmost distribution. Monophoraster darwini has a temporal range from the late Miocene (where it was previ- ously thought to be restricted) back to the middle Miocene, since this is the species yielded in the well-known and discussed "Monophoraster and Venericor Beds". Conclusions: The Paleogene-Neogene scutelliforms of Argentina and Uruguay range from the late Oligocene to the late Miocene. There is a good correspondence among the numerical ages, molluscan biozones and scutelliform assemblages. [ABSTRACT FROM AUTHOR]

Fungal remains similar to those described as Desmidiospora willoughbyi were found in samples from the Río Foyel section (El Foyel Group of Paleogene age), Ñirihuau Basin, Argentina. A full description and illustrations are presented. The names D. willoughbyi and D. marginiconvoluta as defined are shown to be inadequate. The history of the names and actual affinity of taxa presently assigned to those names are discussed. Arguments against the use of Desmidiospora for fungal remains other than the conidia of an entomopathogenic species are presented. Instead, the lobulate fossil remains should be treated as germlings or immature ascomata from epiphyllous fungi of polyphyletic origin. [ABSTRACT FROM AUTHOR]

The dentition in the only known specimen of Adalatherium hui, a gondwanatherian mammal from the Late Cretaceous of Madagascar, is markedly different from that of any previously known mammaliaform, extinct or extant. The two preserved upper incisors and single lower incisor of Adalatherium are each very large, open-rooted, and bear a restricted band of enamel. A shallow-rooted, rudimentary upper canine is present. The upper postcanine dentition is composed of a small, simple, two-rooted tooth mesially and four large, multiple-rooted (five roots or more) teeth distally. The latter are quadrangular in outline, each with four major cusps and three perimetric ridges bordering a central valley that opens buccally. There are four lower postcanines, also with four major cusps each. The first postcanine has two roots, but the following ones each have (or likely had) at least four. The two distal lower postcanines bear a prominent mesiobuccal basin. The cusps and other topographic features of the postcanines cannot be unambiguously homologized with those of other known mammaliaforms. Diastemata are present in the upper dentition between the incisors and canines and between the canines and postcanines, and in the lower dentition between the incisors and postcanines. Adalatherium, like several gondwanatherians from the Late Cretaceous and Paleogene of Argentina, retains relatively plesiomorphic, 'normal' radial enamel (i.e., single-layered schmelzmuster, non-decussating small prisms, interprismatic matrix anastomosing around prisms). This stands in contrast to the modified radial enamel found in other gondwanatherians from the Late Cretaceous of India and Madagascar, which exhibit prominent interrow sheets of interprismatic matrix. [ABSTRACT FROM AUTHOR]

Xenungulates are a peculiar group of bilophodont ungulates, widespread over South America during the Paleocene and early Eocene. Here we describe, illustrate and analyse a new Xenungulata, Rodcania kakan gen. et sp. nov., the first from the lower latitudes of Argentina. It was recovered from the Río Loro Formation (Tucumán Province), for which a Paleocene age was estimated. The material comprises a fragment of the left dentary with an incomplete m2, eroded over the enamel surface, and an almost complete m3. Both teeth share with Xenungulata strong enamel, vertically oriented Hunter–Schreger bands (HSB), and wear facets sloping distally. Rodcania kakan differs from other xenungulates in the m3 trigonid, simplified and mesiodistally short; absence of a paraconid; more oblique protolophid in relation to the mesiodistal axis and a straight cristid obliqua, pointing to the protoconid position; and has a wider and longer talonid. A phylogenetic analysis of 13 species and 36 craniodental characters recovered R. kakan as a basal member of the Carodniidae, supported by 10 synapomorphies in the four most parsimonious trees. The body mass estimation of the Río Loro Fauna and of the rest of the xenungulate taxa revealed that R. kakan is the largest mammal of the Río Loro assemblage, weighing around 165 kg and with a size comparable to Carodnia feruglioi. The increase in body mass showed no clear relation with evolutionary trends in xenungulates. [ABSTRACT FROM AUTHOR]

Here I describe and illustrate 19 leaf morphospecies from the Paleogene Río Turbio Formation, Santa Cruz Province, Argentina. They were referred to the extant tropical and subtropical families Lauraceae (9 morphospecies), Malpighiaceae (1 morphospecies), Vitaceae (2 morphospecies), Anacardiaceae (2 morphospecies) and Sapindaceae (5 morphospecies). These taxa were recorded throughout the unit, but they are more abundant in the lower member of the Río Turbio Formation. The observed decreasing trend in megathermal taxa throughout the unit indicates the beginning of the flora turnover that characterized Patagonian ecosystems from the Late Eocene onwards and it is in agreement with the marked global cooling trend of the terminal Paleogene. [ABSTRACT FROM AUTHOR]

Notoungulates represent the most taxonomically diverse and temporally and geographically widespread group among South American native ungulates. Here, we analyze anatomical and systematic aspects of proximal tarsal bones recovered from the Lower and Upper Lumbrera formations (middle and late middle Eocene) in northwestern Argentina. We provide detailed descriptions, comparisons, and infer foot stances and range of movements for the taxa implicated. Material studied includes astragali belonging to the oldfieldthomasiid Colbertia lumbrerense (Lower Lumbrera Formation), a set of proximal tarsals referred as Typotheria indet. (Lower Lumbrera Formation), and tarsals (also including navicular and cuboid) of the informal taxon "Campanorco inauguralis" (Upper Lumbrera Formation). The comparison of the tarsals of Colbertia lumbrerense (middle Eocene of Argentina) with Colbertia magellanica (early Eocene of Brazil) reveals several differences including variations on the development and arrangement of articular facets, and the size of the dorsal astragalar foramen in the Argentinean species. The specimen of Typotheria indet. shows morphological affinities with basal interatheriid taxa. However, its larger size contrasting with the overall small body sizes of Eocene interatheriids precludes an indisputable taxonomic assignment. Concerning "Campanorco inauguralis", our observations indicate that there is no morphological evidence for a close phylogenetic relationship with Mesotheriidae. It presents a "reversed alternating tarsus" condition, which is also observed in Leontiniidae, "Notohippidae", Toxodontidae, and some typotherians. However, the spectrum of singularities exhibited by this form precludes the assessment of its relationships in the context of the Paleogene radiation of Typotheria and it is necessary to extend the comparison to Eocene notoungulates. Finally, in a morphofunctional context a plantigrade foot posture is inferred for the specimens here reported. These observations have the potential to provide functional proxies for paleoecological reconstructions to be applied to the study of the early radiation of these notoungulate faunas. [ABSTRACT FROM AUTHOR]

The Magallanes-Austral Foreland Basin preserves an important record of orogenesis and landscape evolution in the Patagonian Andes of Chile and Argentina. This paper evaluates the comparison between the thick Paleogene sequences in the Chilean Peninsula Brunswick (Chorrillo Chico and Agua Fresca formations) and the reduced Paleogene sequence (La Barca Formation) in the Punta Ainol locality, Argentina, by taking account of palynological and geochemical analyses. Warm and humid subtropical conditions (Subtropical Gondwanic Paleoflora) are inferred for the late Paleocene-Eocene interval studied. A new record of Lactoridaceae in the La Barca Formation expanded the known fossil range of this family in Patagonia. During the late Paleocene the Chorrillo Chico and La Barca formations would have been deposited mainly from hyperpycnal flows and this accumulation process continued until the Lutenian in the La Barca Formation. A relative rise in the sea level in the early Eocene would be recognized in both sections. In the middle Eocene a relative fall in the sea level would have occurred with increased terrigenous influx. The rate of sedimentation was similar in both sections during the Thanetian and Ypresian intervals according to the ages assigned by biostratigraphy, suggesting that the sedimentation rate would have been controlled mainly by relative changes in sea level during the Paleocene-Eocene transition. Paleoenvironmental changes during the Paleocene-Eocene transition were characterized at the La Barca Formation of the Punta Ainol section, considering the new geochemical and palynological data provided in this contribution. • A new register of early Paleogene flora of Patagonia. • Paleogeographic changes based on palynological and geochemical data. • New geochemical inferences of the Paleocene-Eocene transition in South America. • A new Paleocene-Eocene record from Southern Hemisphere. [ABSTRACT FROM AUTHOR]

Proborhyaenidae are the largest known sparassodonts, with a fossil record spanning from the early Eocene to the Pliocene. The Eocene record of this group is scarce, occurring only in four geological units: Las Violetas Formation, lower Lumbrera Formation, Sarmiento Formation and Geste Formation, all in Argentina. Herein, a new occurrence of this clade is described from the Guabirotuba Formation (late middle Eocene) of the Curitiba Basin in Brazil. This unit, along with the Itaboraí and Taubaté basins are the only units in Brazil with Paleogene continental mammal records. The specimen MCN.P.1340 is an isolated lower left canine, that displays the main features associated with the lower canines of proborhyaenids, such as, an open root, median sulci, a thin enamel layer and posterior curvature. This new occurrence not only represents the biggest mammalian predator of the Guabirotuba Fauna, an expansion of the known geographical range of the family, but also provides further support for the relative dating of the Guabirotuba Formation and its fauna. • Description of a canine attributed to Proborhyaenidae. • First record of a Proborhyaenidae for the Guabirotuba Formation and second for Brazil. • First occurrence of a Proborhyaenidae outside Argentina on the Eocene. • Phylogenetic analysis recovered it as a member of the clade that includes Proborhyaenidae and Thylacosmilidae. • Expansion of the known geographical range of the family and further support for the dating of the Guabirotuba Formation. [ABSTRACT FROM AUTHOR]

†Mesopassandra keyao gen. et sp. nov., representing the first Mesozoic record of the family Passandridae (Coleoptera: Cucujoidea), is here described from Upper Cretaceous Burmese amber. Based on a phylogenetic analysis of 30 adult characters †Mesopassandra was recovered as the sister group to all remaining Passandridae, having a large labrum, bidentate mandibles and presumably 5-5-4 tarsi in the male. It is here placed in a new subfamily, †Mesopassandrinae subfam. nov. Ancestral area was reconstructed using the phylogeny and an ancient Gondwanan origin was inferred for the whole family. The Eocene species Catogenus punctatus Ramírez, Corsolini & Di Iorio, 2016 from Patagonia, Argentina is here transferred from Passandridae to Cucujidae Latreille, 1802, in the genus Platisus Erichson, 1842 as Platisus punctatus (Ramírez, Corsolini & Di Iorio, 2016) comb. nov. [ABSTRACT FROM AUTHOR]

The aim of the present contribution is to describe a new genus and species of Pipoidea from the Huitrera Formation (Eocene) from Patagonia, Argentina. The new genus shows a unique combination of characters indicating that it is a valid taxon different from other pipimorphs, including the coeval Llankibatrachus truebae. The phylogenetic analysis resulted in the nesting of the new taxon within a previously unrecognized endemic clade of South American aglossans. This new clade turns out to be the sister-group of crown-group Pipidae. This phylogenetic proposal reinforces the hypothesis sustaining the dispersal of pipids between Africa and South America through an island chain or a continental bridge across the Atlantic Ocean by Early Tertiary times. [ABSTRACT FROM AUTHOR]

Premise of research. While Azolla has a rich fossil record based on dispersed megaspore apparatuses and microspore massulae, fossil sporophytes are relatively rare. In this contribution, we describe two fossil Azolla species based on both sporophytes and spores from Chubut Province, Patagonia, Argentina: Azolla coloniensis De Benedetti & Zamaloa, emend. Hermsen et al., and A. keuja Jud et al., sp. nov. Azolla coloniensis and A. keuja are the first fossil species of Azolla to be represented by vegetative structures (i.e., leaves, stems, and roots) from both South America and the Southern Hemisphere. Methodology. We examined sporophyte material of A. coloniensis from the Cañadón del Irupé locality, Upper Cretaceous, La Colonia Formation, and A. keuja from the Palacio de los Loros locality PL-2, Paleocene, Salamanca Formation. Spores of A. keuja were obtained from a sporophyte specimen and its surrounding rock matrix. Material was studied using standard light microscopy, epifluorescence microscopy, and scanning electron microscopy. Fossils are held at the Museo Paleontológico Egidio Feruglio, Trelew, Chubut Province, Argentina. Pivotal results. Azolla coloniensis produced many-floated megaspore apparatuses and microspore massulae with anchor-tipped glochidia, placing it in the fossil Azolla section Florschuetzia. Azolla keuja sporophytes are structurally similar to those produced by the extant African species A. nilotica and the Late Cretaceous–Paleocene North American species A. schopfii in overall size, growth form, leaf structure, and production of fascicled roots; while all three taxa produce similar microspore massulae, the structure of their megaspore apparatuses differ. Azolla keuja cannot be assigned to any section of Azolla. Conclusions. Azolla coloniensis and A. keuja are important because they provide two new organismal concepts for extinct species of Azolla. Our inability to fully classify A. keuja to section, in combination with the great morphological diversity of fossil Azolla , indicates that a comprehensive reevaluation of phylogeny and taxonomy that incorporates both extant and fossil species is needed. [ABSTRACT FROM AUTHOR]

Peligrochelys walshae is a meiolaniform turtle originally described based on four specimens represented by cranial remains found in the classic locality of Punta Peligro (Chubut, Argentina) in outcrops of the Salamanca Formation (Danian). Recent field work in the vicinity of Punta Peligro resulted in the discovery of almost 30 new specimens, represented by cranial and postcranial remains that can be assigned to P. walshae. In this contribution, we provide a detailed anatomical description of the new specimens, provide an emended diagnosis for the species, and explore its phylogenetic relationships based on all anatomical data available for the species. The new specimens bring valuable information about the anatomy of the skull and postcranium of P. walshae as well as for meiolaniforms in general. The 3D preservation of the skull bones allows us to provide a 3D reconstruction using novel techniques. The updated phylogenetic analysis confirms that P. walshae is part of the clade Meiolaniformes, which spans from the Early Cretaceous until the Holocene and contains the giant, horned turtles (Meiolaniidae). This phylogenetic analysis reinforces the previous hypothesis that the clade Meiolaniformes is dominated by Gondwanan taxa, but also includes some Laurasian representatives. Alternate phylogenetic positions of taxa included in Meiolaniformes in this analysis were tested using the Templeton test. The lineage leading to Peligrochelys walshae is the only meiolaniform non-meiolaniid lineage to have survived the K-Pg mass extinction; its study provides valuable information to evaluate the effects of the K-Pg extinction in turtles. [ABSTRACT FROM AUTHOR]

A new specimen of Pucatherium parvum from the lower levels of the Upper Lumbrera Formation of Salta Province is reported. An almost complete dorsal carapace and several postcranial remains were preserved, providing important information about this particular taxon. The specimen is comparable in size to Dasypus novemcinctus, although the osteoderms are very small. The dorsal carapace seems to be completely integrated by movable osteoderms, providing a high degree of mobility in the anteroposterior axis. There is no evidence of pseudoshield, scapular shield, or pelvic shield. The dating of 39.9 ± 0.4 Ma (U-Pb zircon), taken from a tuff close to the top of the Upper Lumbrera Formation, allows us to refer this record of P. parvum to the middle Eocene (Bartonian). This, together with its broad geographic distribution, allows correlating the Upper Lumbrera Formation with the Quebrada de los Colorados Formation in Salta Province and with the Casa Grande Formation in Jujuy Province. On the other hand, the estimated depositional age of 37.3–35.4 Ma for the Geste Formation in Salta Province extends the biocron of P. parvum to the late Eocene. [ABSTRACT FROM AUTHOR]

The Quebrada de Los Colorados Formation (Los Cardones National Park, Salta Province, north-western Argentina), is an Eocene--Oligocene unit well represented in the Calchaquí Valley area. Here we describe a new metatherian association recorded from the base of this formation, inferred as middle Eocene. Represented taxa are: Sparassodonta, family indet.: Patene simpsoni; Polydolopimorphia, Bonapartheriiformes, Argyrolagoidea: family, genus, and species indet.; and Bonapartherioidea, Prepidolopidae: Punadolops alonsoi and Coloradolops cardonensis gen. et sp. nov. Patene simpsoni is also found in the Tonco Valley, near Los Cardones, and at São José de Itaboraí, Rio de Janeiro, Brazil. Punadolops alonsoi was originally described from the Geste Formation in Salta and Catamarca provinces. Hitherto, no other Argyrolagoidea have been found in north-western Argentina in the Palaeogene. Coloradolops cardonensis is unique to the locality and levels here described. The preservation of part of the skull constitutes the best prepidolopid remains known. North-western Argentina is a key region for the study of the evolution of South American mammals, since it has a singular geographical location between the Neotropics and the southernmost part of South America. Due to biogeographical constraints, it may lead to a better comprehension of the continental distribution of metatherian lineages during Cenozoic times. [ABSTRACT FROM AUTHOR]

The Andes offer a distinctive example of the intricate interplay among climate, tectonics, and surface processes. This is exemplified by the mountain range's north-south orientation, which contrasts with the prevailing east-west wind direction. This interplay controls the uplift evolution of the broken foreland and thus the sediment transfer and erosion from mountain ranges to their forelands. The Neuquén Andes is a peculiar segment of the southern Central Andes, registering dramatic North-South variabilities in elevation, climate, and tectonic intensities established during the Neogene and Quaternary. In this study, we aimed to identify the tectono-stratigraphic evidence of the Neogene to Quaternary evolution of paleo-environments and drainage networks in the intramountainous basin of Pampa de Agua Amarga in the broken foreland of the southern Neuquén Andes of Argentina. Starting with a non-depositional and/or erosional phase during the Paleogene, the Pampa de Agua Amarga Basin underwent several phases of syn-orogenic sedimentation in the late Oligocene to early Miocene. The basin gradually shifted from a lacustrine to an alluvial depositional environment, with alluvial deposits becoming dominant in the mid-Miocene and fluvial deposits dominating in the Pliocene. A significant event occurred during the late Pliocene to early Pleistocene when coarse fluvial deposits were deposited, marking the last aggradation phase. In the early Pleistocene, the onset of incision triggered the drainage system to cut through the downstream topographic barrier. The excavation of the basin was abrupt, as evidenced by a mid-Pleistocene stepped fluvial terrace and alluvial fan that filled a large canyon across the southern end of the downstream topographic barrier. The study confirms the regional trend that Miocene basin infill is related to dry climate and high tectonic uplift, which overwhelmed the erosive power of the drainage network. The lowering of tectonic uplift intensity in the southern Neuquén Basin during the Plio-Pleistocene, along with sudden fluctuations in the global colder and wetter climate, ultimately led to the excavation of the intramountainous basin. The Westerlies Wind Belts generate high precipitation rates in the southern Neuquén Andean Cordillera, feeding the Negro River catchment in the retroarc Andean broken foreland. Consequently, the erosive power of the Negro River catchment overcame the declining tectonic uplift, causing significant erosion of the entire broken foreland and Cordillera of the southern Neuquén Andes. Conversely, more intense tectonic uplifts in the northern Neuquén Andes built a more effective orographic barriers that limited precipitation rates of both the Westerlies Wind Belt and South America Summer Monsoon, and preserved the intramountainous basins and mountain interior from erosion. • Tectono-sedimentary analyze of an intramountainous basin in the South Neuquén Andes. • Neogene coarsening-up sequence due to a dry and warm climate and intense shortening. • Pleistocene basin excavation due to lower shortening and colder and wetter climate. • Pleistocene significant erosion and sedimentary transfer in the South Neuquén Andes. • Opposite tectonic, climate and thus basins' evolution in the North Neuquén Andes. [ABSTRACT FROM AUTHOR]

The Paleocene-Eocene Catán Lil Ignimbrite (CLI) is one of the few occurrences within the explosive acid volcanism of this age in the extra-Andean region of the North Patagonian Massif. It represents a small-scale explosive eruption covering an area of 214 km2, with an estimated volume of 1.27 km3 and consisting of three weakly-to densely welded cooling units. The maximum thickness of this sequence is 90 m. Its basal unit is the best preserved, and has allowed a lithofacial analysis that reveals different aspects of the eruption and the emplacement mode of the Catán Lil pyroclastic flows. The CLI ignimbrites are generally massive, poorly sorted, matrix-supported deposits (tuff and lapilli tuff) resulting from dense pyroclastic currents (PDCs). They are composed mainly of juvenile fragments, scarce lithoclasts and crystalloclasts, being a product of a purely magmatic fragmentation occurred at a shallow level. A pyroclastic fountaining eruptive model is interpreted, resulting from the collapse of a low eruptive column, and a rapid and high-temperature emplacement. The CLI PDCs generally respond to slow moving pyroclastic flows with low erosive energy. The morphology and stratigraphy indicate radial emissions with thicknesses decreasing towards the periphery that become evident in Central-South ignimbrites. These PDCs flowed over a planar terrain, giving rise to most of the CLI deposits (South-Central area and North- East). The Northwestern ignimbrites are deposits in the interior (south and middle part) of the Catán Lil creek, forming thick deposits within the latter valley and thin, veneer-like deposits over the flanking Lipetrén granitoids. In the North- East region, the ignimbrites show stratigraphic relationships that suggest that the PDCs would slightly postdate those of the South-Central area. The Catán Lil Ignimbrites represent the most eastern exposures of the Paleocene-Eocene Pilcaniyeu Belt, differing from the latter in that it lacks a conspicuous lava facies, and by the unimodal character and the tectonic signature of the Catán Lil sequence. • Small-volume explosive volcanic event in Extraandean Patagonia. • High-temperature, crystal- and lithic-poor PDCs associated with a pyroclastic fountain-type eruption. • The Catán Lil ignimbrite is the easternmost expression of the Paleocene-Eocene belt in the North Patagonian Massif. [ABSTRACT FROM AUTHOR]

Caimanines are crocodylians currently restricted to South and Central America and the oldest members are from lower Palaeocene localities of the Salamanca Formation (Chubut Province, Argentina). We report here a new caimanine from this same unit represented by a skull roof and partial braincase. Its phylogenetic relationships were explored in a cladistic analysis using standard characters and a morphogeometric two-dimensional configuration of the skull roof. The phylogenetic results were used for an event-based supermodel quantitative palaeobiogeographic analysis. The new species is recovered as the most basal member of the South American caimanines, and the Cretaceous North American lineage 'Brachychampsa and related forms' as the most basal Caimaninae. The biogeographic results estimated north-central North America as the ancestral area of Caimaninae, showing that the Cretaceous and Palaeocene species of the group were more widespread than thought and became regionally extinct in North America around the Cretaceous-Palaeocene boundary. A dispersal event from northcentral North America during the middle Late Cretaceous explains the arrival of the group to South America. The Palaeogene assemblage of Patagonian crocodylians is composed of three lineages of caimanines as a consequence of independent dispersal events that occurred between North and SouthAmerica and within South America around the Cretaceous-Palaeogene boundary. [ABSTRACT FROM AUTHOR]

The response of sedimentary basins to earliest onset of Andean contraction and lithospheric flexure in the southern Central Andes is debated and not well-resolved. The Upper Cretaceous to Oligocene strata of the Cuesta de Huaco anticline in the Argentine Precordillera record sedimentation, regional deformation, and climate patterns prior to the highly studied Oligocene-Miocene foreland basin phase. These deposits have recently been recognized as Cretaceous and Paleogene in age, prompting a re-evaluation of this depocenter as part of the early Andean system, prior to deposition of the aeolian foredeep sediments of the Oligocene Vallecito Formation. This work presents new data from the Argentine Precordillera fold-and-thrust belt at 30°S that sheds light on new reinterpretations of the timing of sedimentation for an important interval in Andean retroarc foreland basin history. We report the first Paleocene detrital radiometric ages from the Cuesta de Huaco ‘red strata’ of the pre-Oligocene Bermejo Basin. Detailed sedimentology and provenance data from the Cenomanian-Turonian Ciénaga del Río Huaco and Danian-Priabonian Puesto La Flecha formations reveal a Cenomanian-Turonian braided stream system that transitioned into a shallow freshwater lacustrine depocenter in Paleocene-Eocene time. During Late Cretaceous time, sediment in the braided river system was derived primarily from northeastern cratonic sources; during the Paleocene-Eocene, uplift and unroofing of the Andean arc and Frontal Cordillera resulted in an influx of western-derived sediment. We therefore suggest a revised timing of sedimentation for the transition to Andean retroarc foreland basin deposition. [ABSTRACT FROM AUTHOR]

The lower Eocene Lumbrera Formation in Salta province, northwestern Argentina, outstands for providing snake remains from a non-Patagonian Paleogene site. The material consists of articulated precloacal vertebrae that represent a new medium-sized macrostomatan snake, namely Amaru scagliai nov. gen., nov. sp. The vertebral characters of Amaru scagliai nov. gen., nov. sp., suggest affinities with advanced clades, which is consistent with the recognition of derived macrostomatans in the early Paleocene of Bolivia and early Eocene of Brazil. The new snake confirms the presence of macrostomatan snakes in South America as early as the Eocene and suggests that the southern continents may have played an unsuspected role in the origin and evolution of advanced macrostomatans during the earliest Cenozoic. [ABSTRACT FROM AUTHOR]

The study of Paleogene mammals of intermediate and low latitudes has increased in the last decades and has been clearly demonstrated their importance in the comprehension of the evolution and faunistic changes outside Patagonia. The study of these faunas permits establishing new comparisons among contemporaneous faunistic associations, completing the distributional patterns, and evaluating evolutionary changes in the lineages in relation to climatic conditions prevailing in each of the different regions. In this work we study the diversity of Dasypodidae recovered from the Geste Formation (Northwestern Argentina). Bearing levels of Geste Formation were referred alternatively to a Barrancan subage of Casamayoran SALMA (middle Eocene, Lutetian-Bartonian) or a Mustersan SALMA (middle-late Eocene, Bartonian- Priabonian) on faunistic comparations with their equivalent in Patagonia, although absolute isotopic data indicates ca. 37-35 Ma (late Eocene, Priabonian). We described the following taxa of Dasypodidae: (i) Dasypodinae Astegotheriini: cf. Astegotherium sp., ?Prostegotherium sp., Parastegosimpsonia cf. P. peruana; (ii) Dasypodinae indet.; (iii) Euphractinae Euphractini: Parutaetus punaensis sp. nov.; (iv) Dasypodidae incertae sedis: Pucatherium parvum, Punatherium catamarcensis gen. et sp. nov. In comparison with other beds bearing Eocene cingulate faunas from Northwestern Argentina, Geste Formation presents the greatest diversity of dasypodids. This association is consistent with a late Eocene age and shows a taxonomic and biogeographic relevant features given by a unique specific composition: (i) it differs from that known for contemporaneous faunas from Southern latitudes and younger associations from more tropical areas; (ii) it includes genera with close affinities to those distant areas; (iii) it presents unique taxa typical from Eocene units exposed at Northwestern Argentina. This highlights the evolutionary and biogeographic meaning of the cingulate of the Geste Formation and supports the idea that the faunistic regionalization probably obeyed to latitudinal than to temporal factors. [ABSTRACT FROM AUTHOR]

The Lumbrera Formation in north-western Argentina is notable for preserving lizard remains from the Palaeogene of South America. In this paper, we offer a re-description and re-evaluation of the material belonging to the holotype of the teiid lizardLumbrerasaurus scagliai(Donadío, 1985) recovered from sediments of the Lumbrera Formation near Pampa Grande, Salta province, Argentina.Lumbrerasaurus scagliaiis considered here as an extinct genus of Tupinambinae. These remains are the earliest record of teiid lizards and confirm the presence of tupinambine teiids in the South American Palaeogene. [ABSTRACT FROM AUTHOR]

The Eocene Las Flores and Koluel-Kaike formations in southern Patagonia (~48° S, Golfo San Jorge Basin, Argentina) are pedogenically modified fluvial and fluvio-eolian successions, respectively, which document early-middle Eocene environments at mid-paleolatitudes in the Southern Hemisphere. In order to reconstruct the paleoenvironment for the Las Flores and Koluel-Kaike formations, we performed a multiproxy and coordinated study of sediments and paleosols of both units, considering abiotic components. Using detailed sedimentology and paleopedology (macro- and micromorphology), bulk paleosol geochemistry and clay mineralogy, and organic carbon concentrations and stable isotope (δ13C org) compositions, we show that the Las Flores and Koluel-Kaike paleosols are overall Ultisol-like paleosols, mineralogically and chemically consistent with a high to high-moderate degree of weathering, and developed on different parent materials (sedimentary with sandy and silty texture vs. silty volcaniclastic). Climate proxies and a comparison with modern Ultisols with similar features suggest that these paleosols formed under a broadly tropical-temperate and humid-subhumid climate with distinct seasonality. Overall, these combined data record long-term environmental conditions during the Paleogene (early-middle Eocene), and preserve a record of Eocene terrestrial climate in the Southern Hemisphere. This research is relevant for understanding latitudinal climatic gradients during warm periods like the Eocene, a key knowledge gap for future predictions, and these sites are particularly important because mid-latitude reconstructions in the Southern Hemisphere are the poorest resolved. • Fluvial and fluvial/eolian sediments in Patagonia preserve Eocene paleosols. • Basin environments record well-preserved, stacked Ultisols and plinthitic Ultisols. • Las Flores paleosols show thermic-hyperthermic, seasonal humid-perhumid climate. • Koluel-Kaike paleosols show thermic, seasonal subhumid-humid climate. • Southern Hemisphere records are relevant for understanding latitudinal Eocene climatic gradients. [ABSTRACT FROM AUTHOR]

We describe a new metatherian mammal,Fieratherium sorexgen. et sp. nov., found in western Argentina (Quebrada Fiera locality, southern Mendoza Province), in Late Oligocene deposits (Agua de la Piedra Formation, Deseadan age). The only known specimen is a juvenile with fragments of both dentaries, the right maxilla and a fragment of the left premaxilla with dentition. The loci and the number teeth preserved suggest a dental formula of I?3/i3, C1/c1, P3/p3, M?3/m?3.Fieratherium sorexhas a convergent shrew-like appearance and a unique combination of features among metatherians and other South American mammals of Palaeogene age, including the well-known faunas of Patagonia. An analysis of its phylogenetic affinities suggests thatFieratheriumis the sister-group of the Paucituberculata. As already described by other authors for several mammalian taxa, the mainly Patagonian South American Palaeogene fossil record offers little information to understanding the evolution of northern lineages.Fieratheriummay represent a taxon belonging to a lineage that had its origin in Neotropical regions, so far unrecorded in the southern region of South America. http://zoobank.org/urn:lsid:zoobank.org:pub:5F6D3A50-6345-4E66-BE3E-7FEF6CC66A9B [ABSTRACT FROM AUTHOR]

A comprehensive overview of all the South American and Antarctic fossil records of Rheiformes and close relatives, accompanied by updated stratigraphic data, is provided here. Fossil rheas are represented by fragmentary remains of hindlimb bones and several footprints that include paleospecies, extinct representatives of the living species as well as putative ratites. To date, the oldest record corresponds to the early Eocene of Argentina, Brazil and maybe Antarctica, thus the Palaeocene antiquity of several fossil sites with rheas is no longer valid. Neogene sediments present records of the exclusively fossil taxon Opisthodactylus as well as ' Pterocnemia'. Most of the Quaternary records come from late Pleistocene-Holocene sediments from Argentina, Chile, Uruguay, Bolivia, and Brazil and are represented by extinct representatives of living species. Finally, Argentina is the country with the highest number of fossil records and taxa. • The oldest record corresponds to the early Eocene of Argentina, Brazil and Antarctica. • Neogene representatives are restricted to Argentina and mainly comprises several paleospecies. • Quaternary records belong mostly to Argentina and are referred to the living representatives. [ABSTRACT FROM AUTHOR]

Eocene early-diverging representatives of South American extinct notungulates are traditionally considered to have been "generalists" and "non-specialized" in terms of the appendicular skeleton and locomotor behavior, as is the case with the notostylopid Notostylops, a middle Eocene iconic taxon from Patagonia (Argentina). However, they are mainly known from dental remains, and associated cranial and postcranial elements are scarce. The discovery of a nearly complete specimen attributed to N. murinus allows us to: (1) increase the knowledge of the anatomy of its appendicular skeleton; (2) identify isolated bones from several collections and suggest different taxonomic interpretations for published specimens; (3) perform a biomechanical and functional study using functional morphological analysis to infer its paleoecological attributes (e.g. posture, locomotor habit, estimated speed, and body mass); and (4) establish morphofunctional comparisons, based on possible functional ranges, with other extinct early-diverging notoungulates from the middle Eocene, such as the Notopithecid Notopithecus. Our evidence suggests that Notostylops was a medium-sized mammal (8.5-20 kg), which could achieve a dynamic digitigrade posture that allowed a scansorial secondary locomotor habit and a speed of up to 50 km/h. However, Notopithecus was a small-sized mammal (0.6-1.4 kg) with a plantigrade posture both in a static and dynamic context, terrestrial habits, and a speed of up to 35 km/h. Therefore, we conclude that these Eocene notoungulates show different locomotor capabilities, which can be associated with early niche diversifications, clearly contrasting with the "all-generalists" paradigmatic view., (© 2022 Wiley Periodicals LLC.)

Abstract: The dominant Cenozoic structural grain in northwestern Argentina trends north–south. However, several oblique folds have been mapped, mainly in the Cordillera Oriental and the Sistema de Santa Bárbara. Two oblique NE–SW-trending anticlines are well exposed in the Luracatao Valley-Salta, along the western border of the Cordillera Oriental. These oblique anticlines are defined by the Palaeogene Santa Bárbara Subgroup and are cut by the reverse faults bounding the Luracatao Valley. We constructed analogue models to simulate the generation of oblique NE–SW anticlines inside the narrow, trough-like Luracatao Valley. Orthogonal compression and basement oblique heterogeneities, oblique compression and basement oblique heterogeneities, and oblique compression configurations were tested in the models. The first two configurations simulate the anticline formation well. In addition, we analyse dextral rotation and the influence of Neoproterozoic basement/Cretaceous rift structures as the cause of the oblique orientation. The analogue models suggest pre-Andean oblique structures controlling the oblique orientation of these Andean folds despite being a second-order planes of weakness. [Copyright &y& Elsevier]

Abstract: In the present paper, the distal end of a humerus referable to a Dendrocygninae anseriform bird is reported. The specimen was collected at the Monte Hermoso Formation (early Pliocene) of the Farola Monte Hermoso locality (Buenos Aires Province, Argentina). This record constitutes one of the oldest for the group in South America and elsewhere. The overview of the anseriform record in South America indicates a similar pattern to that of other localities across the world. Paleogene localities are dominated by non-Anatinae taxa, whereas more recent faunas are dominated by anatines. Following this pattern, in South America the Anatinae appears in the fossil record as recently as in the Pleistocene, probably arriving from North America during the Great American Biotic Interchange. Pleistocene and Recent anseriform avifaunas are dominated by Anatinae taxa, and this dominance is probably due to some “key characters” regarding reproductive biology. In fact, the anatines exhibit a high reproductive success probably due to the capability of having two molts per year, and that the parental care of the downy young is only conducted by the female. The combination of characters may have allowed anatines to dominate most aquatic environments, surpassing in diversity more plesiomorphic taxa. [Copyright &y& Elsevier]

Paleogene dinoflagellate cysts were recorded from the Chorrillo Chico and Agua Fresca formations at Punta Prat, southern Chile. Due to the presence of Palaeoperidinium pyrophorum, the Chorrillo Chico Formation is no younger than Late Selandian. By comparison with other basins, a Late Danian to Late Selandian age is proposed for the Chorrillo Chico Formation at Punta Prat. The Paleocene-Eocene boundary is characterized by Apectodinium-dominated assemblages in the mid and high latitudes,the Atlantic coast of Isla Grande de Tierra del Fuego in Argentina, and Chile. The absence of this event at Punta Prat suggests aregional hiatus across the Paleocene-Eocene boundary. An Early to Middle Eocene age is assigned to the lower part of the Agua Fresca Formation by comparison with dinoflagellate cyst assemblages from elsewhere in the Southern Hemisphere. [ABSTRACT FROM AUTHOR]