We report a new Fossil-Lagerstätte at the Cretaceous hydrothermal field of Sanagasta, La Rioja, northwestern Argentina, which opens a window into the paleobiology of an exceptionally preserved fossil ecosystem. Active geothermal systems harbor a diverse microbial life that thrive in high temperature, unique mineral composition and fluctuating pH. These environments are dominated by a meso- and hyperthermophilic community, including bacteria and archaea, that proliferate around the hot springs and geysers. In these environments, fossilization occurred rapidly by abiotic factors and through biomineralization—chiefly biosilicification. This process is mediated by thermophilic microorganisms, mainly cyanobacteria, allowing for the exceptional preservation of the biota. Here, we describe an ~80 million-year-old fossil extremophile biocoenosis encrusted within microbialites from the Sanagasta paleohydrothermal field. The core of the microbialites was explored using petrography, Scanning Electron Microscopy (SEM) and Energy-Dispersive Spectroscopy (EDS) analyses in SEM. These microbialites exhibit remarkable three-dimensional preservation of microorganisms through extensive biosilicification, directly mediated by the extremophile communities. The taxonomic range of the sinterized assemblage encompasses the three domains: a noteworthy array of thermophilic ‘prokaryotes’ (chiefly bacteria and archaea), along with a rich diversity of eukaryotic ‘protists’ microorganisms (i.e., amoebozoans, myxomicetes, red algae, diatoms, and alveolates), green algae, plant remains, fungi and a variety of arthropod remains, all preserved in notable microanatomical details. The Sanagasta GeoPark contains one of the most diverse and exquisitely preserved records of microfossils known to date, illuminating a complex inland ecosystem within the first documented Cretaceous terrestrial hydrothermal environment.

We describe a new large-sized paracrocodylomorph pseudosuchian, Shakajlura riojanensis gen. et sp. nov., from the Tarjadia Assemblage Zone (AZ) levels (upper Ladinian to lower Carnian) of the Cha & ntilde;ares Formation, La Rioja Province, northwestern Argentina. The specimen consists of several disarticulated cranial, and a few postcranial, bones and was collected from stratigraphic levels seemingly coeval with those where Luperosuchus fractus, a loricatan of similar size, was found. The general morphology and stratigraphic occurrence of Shakajlura riojanensis suggests the possibility of close affinities with Luperosuchus fractus, but considerable differences in key features between the two holotypes (e.g. Shakajlura riojanensis lacks the following: ornamentation on the lateral side of the maxilla, a prominent curvature of the dorsal portion of the nasals, and a knob-like structure on the postorbital) and a unique combination of character states among pseudosuchians enabled us to erect a new genus and species. Shakajlura riojanensis can be distinguished by the presence of a prominent shelf on the medial surface of the jugal, an incision on the ventral portion of the ascending process of the quadrate, and an enlarged prearticular compared with the preserved jaw elements. Shakajlura riojanensis is recovered as an early-diverging paracrocodylomorph, but the possibility that it represents an early-diverging member of Loricata cannot be discarded. This new species expands the current knowledge of the paracrocodylomorphs of the Tarjadia AZ and introduces a new component to the top predators of the Cha & ntilde;ares Formation.

Life on Earth nearly came to an end during the end-Permian mass extinction (EPME; c. 252 Ma). In its aftermath, the Triassic witnessed the adaptation of survivors to a postapocalyptic world and the establishment of modern ecosystems. Inland, these changes included an outstanding turnover between amniote groups triggered by the diversification of plants and arthropods. A super-radiation of morphologically modern insects occurred in the Triassic, including some of their most successful and ecologically relevant groups, such as Diptera (flies and mosquitoes) and Lepidoptera (moths and butterflies). Here, we describe the oldest evidence of hexapod scales, preserved within a megaherbivorous kannemeyeriiform dicynodont coprolite. This specimen comes from a communal latrine in the lower Carnian deposits (similar to 236 Ma) of the Chanares Formation, La Rioja Province, northwestern Argentina. The tiny fossil scales are hollow and ornamented, which is a synapomorphy of Lepidoptera and suggests that they could belong to this group. If this is the case, the Chanares scales would partially fill the temporal mismatch between phylogenomic date and the fossil evidence of butterflies and moths because they preceded the previously oldest lepidopteran record by c. 35 million years. Moreover, the scales have a combination of features present in early diverging glossatan lepidopterans. The inclusion of the temporal data provided by the Chanares scales into an updated temporal calibration of lepidopteran phylogeny shows that the proboscis, a key evolutionary novelty for the group (Glossata), evolved between c. 260-244 Ma. Thus, the proboscis-bearing lepidopterans would be part of the repertory of new plants and animals that diversified during the aftermath of the EPME.

Abelisauridae is a group of ceratosaurian theropods that thrived mainly in Gondwana during the Cretaceous. Their fossil record is currently represented by more than 25 species, and their most complete and abundant records are from the Argentinean Patagonia. Outside Patagonia, the record of named Argentinean ceratosaurians has been limited to the Cretaceous of the Salta Province, with the noasaurid Noasaurus-represented by a fragmentary skeleton-and the brachyrostran abelisaurid Guemesia-represented by a nearly complete braincase and partial skull roof-. Here, we report a new abelisaurid theropod specimen (CRILAR-Pv 506) from the Late Cretaceous of La Rioja Province, northwestern Argentina. It was found at the Tama locality, in outcrops of the Campanian Los Llanos Formation, and associated with titanosaurian sauropod remains. The new abelisaurid specimen is represented by a first dorsal centrum, a second dorsal vertebra, a partial sacrum, left ilium, pubis and ischium, and other indeterminate elements. A unique combination of character states led us to propose the new genus and species Vitosaura colozacani. Phylogenetic analyses found Vitosaura either as a non-brachyrostran abelisaurid, closely related to Indo-Malagasy species in some trees, or a non-carnotaurinin furileusaurian. However, the interrelationships among abelisaurids are poorly supported. Our comparisons confirm the presence of abelisaurids in the Los Llanos Formation and this is the first named theropod taxon in the Cretaceous of La Rioja Province.

During the Late Triassic epoch (237-201 million years ago), the terrestrial ecosystems of Pangaea underwent drastic changes1,2 that led to the rise and diversification of mammaliaforms3, crocodylomorphs4 and dinosaurs5. Although the Carnian sedimentary rocks of South America provided much of the available evidence for understanding the early evolution of these clades, key discoveries have remained restricted to the Ischigualasto-Villa Unión6,7 and Paraná basins8 in Argentina and Brazil, respectively. Here we report a Carnian tetrapod assemblage from the previously unrecognized Northern Precordillera Basin in northwestern Argentina. Discoveries at this basin, in the Quebrada Santo Domingo site, include a nearly complete skeleton of the early sauropodomorph Huayracursor jaguensis gen. et sp. nov., and typical components of Late Carnian faunas, such as hyperodapedontine rhynchosaurs, gomphodontosuchine traversodontid cynodonts, and aetosaurs. Compared to its generally small and short-necked Carnian counterparts9,10, Huayracursor is larger and exhibits an incipient elongation of its cervical vertebrae, representing an intermediate condition for size and cervical elongation between known Carnian and Norian sauropodomorphs11. This discovery provides one of the oldest pieces of evidence of increased body mass and neck elongation in early Sauropodomorpha.

Palaeosols are common in sedimentary successions of continental origin, and notably they comprise the majority of the thickness of some accumulated successions of fluvial origin. Yet, detailed investigation of palaeosols and evaluation of their palaeoenvironmental significance are not routinely undertaken in detail in many sedimentological studies. A careful analysis of palaeosols may, however, reveal that sedimentary units, which appear similar if based solely on the facies analysis, indeed show strongly distinct palaeoenvironmental and depositional characteristics. This is the case of the upper portion of the Bauru Group, a 100-190 m-thick Maastrichtian red sandstone unit of fluvial origin, present over an area of c. 180,000 km2 in south-eastern Brazil. In this study, the palaeosols of this unit, which constitute 25-92 % of the succession by thickness, are used to decipher palaeoenvironmental climate conditions, sediment source areas, and relationships between pedogenic and depositional processes. Through the combined study of macroscopic, micromorphological, and geochemical aspects of the palaeosols and of facies analysis of the deposits, the upper portion of the Bauru Group succession is separated into three sectors: north -western, north-eastern, and south-eastern. Although these three areas are all characterised by similar lithology types and lithofacies, indicative of deposition in alluvial systems, the palaeosol analysis highlights that they were each characterised by different climate, different clastic source areas and different dynamics and interaction of the pedogenic and sedimentary processes. This research reveals the critical significance of the palaeosols for discriminating otherwise apparently similar depositional units. (c) 2024 Elsevier B.V. All rights reserved.

The Lower Member of the Ituzaingo Formation (LMIF), fluvial in origin and assigned to the Upper Miocene, contains a conglomerate level known as "Mesopotamiense" or "Conglomerado osifero" that has yielded a rich fauna of vertebrates. The aim of this contribution is to describe a titanosaurian dinosaur eggshell fragment recovered from the LMIF at the locality of Toma Vieja (western Entre Rios Province), discussing its paleogeographic history and implications. Fragments of eggshells referred to Titanosauria are frequent from litostratigraphic units of the Upper Cretaceous of western Uruguay (e.g., Guichon, Mercedes, and Queguay Formations). Besides, a fragment of eggshell recovered from the Puerto Yerua Formation (Upper Cretaceous) at eastern Entre Rios Province was described. Geophysical data from the Entre Rios Province allow to propose the presence of a Lower Cretaceous field of extensional tectonic stresses that generated structural lineaments with a E-W and ENEWSW trend. This ancient penetrative Cretaceous tectonic framework would have exerted control on the shape of the basin and sediment flow patterns and subsequent sedimentation, by promoting the generation of accommodation space over the late Paleogene and the Neogene. The phenomenon would have conditioned the deposition of the Fray Bentos Formation, the subsequent marine Parana Formation, and the sedimentation of the LMIF, with source materials coming from the east. Thus, it is hypothesized that the fragment of eggshell of Titanosauria would come from the eastern area of the basin (western Uruguay) as a consequence of the existence of a paleohydric system with predominantly E-W and ENE-WSW directions. This late Neogene system would have been controlled by inherited Cretaceous structural lineaments with orientations similar to those that also govern the current fluvial systems of western Uruguay, developed on the Mesozoic substrate.

The Chañares Formation (Ischigualasto-Villa Unión Basin) is worldwide known by its exquisitely preserved fossil record of latest Middle-to-early Late Triassic tetrapods, including erpetosuchids, “rauisuchians,” proterochampsids, gracilisuchids, dinosauromorphs, pterosauromorphs, kannemeyeriiform dicynodonts, and traversodontid, chiniquodontid and probainognathid cynodonts, coming from the Tarjadia (bottom) and Massetognathus - Chanaresuchus (top) Assemblage Zones of its lower member. Regarding cynodonts, most of its profuse knowledge comes from the traditional layers discovered by Alfred Romer and his team in the 1960s that are now enclosed in the Massetognathus - Chanaresuchus Assemblage Zone (AZ). In this contribution we focus our study on the probainognathian cynodonts discovered in levels of the Tarjadia Assemblage Zone. We describe a new chiniquodontid cynodont with transversely broad postcanine teeth ( Riojanodon nenoi gen. et sp. nov.) which is related to the genus Aleodon . In addition, the specimen CRILAR-Pv 567 previously referred to cf. Aleodon is here described, compared, and included in a phylogenetic analysis. It is considered as an indeterminate Aleodontinae nov., a clade here proposed to included chiniquodontids with transversely broad upper and lower postcanines, by having a cuspidated sectorial labial margin and a lingual platform that is twice broader than a lingual cingulum. Cromptodon mamiferoides , from the Cerro de Las Cabras Formation (Cuyo Basin), was also included in the phylogenetic analysis and recovered as an Aleodontinae. The new cynodont and the record of Aleodontinae indet. reinforce the faunal differentiation between the Tarjadia and Massetognathus - Chanaresuchus Assemblage Zones, in the lower member of the Chañares Formation, and inform on the diverse chiniquodontid clade with both sectorial and transversely broad postcanine teeth.

Two lineages of Kannemeyeriiformes (Synapsida, Dicynodontia) are currently known in the Ladinian-Carnian Chanares Formation (Ischigualasto-Villa Union Basin, Argentina): stahleckeriine stahleckeriids, based upon postcrania, and a single non-stahleckeriine species, Dinodontosaurus brevirostris, known mostly by cranial material. Available data on the mandible of Dinodontosaurus brevirostris is mainly based on specimen PULR-V 03, holotype of D. "platygnathus". Here we present a comprehensive and comparative osteological study of the lower jaw of D. brevirostris, based on PULR-V 03 and the new specimens CRILAR-Pv 94 and PULR-V 144, and revise its phylogenetic relationships with the inclusion of the mandibular data. Our results resemble previous analyses, with a monophyletic Dinodontosaurus as the sister group of the Angonisaurus + Stahleckeriidae clade. Dinodontosaurus brevirostris is reinterpreted has having an angular contribution to the mandibular symphysis, rounded and hypertrophied reflected lamina of the angular, wide angular gap, and well-developed and anteriorly curving retroarticular process. Previous hypotheses of stahleckeriine affinities are rejected based on the markedly convex symphysial chin, wide angular gap, median symphysial ridge, and moderately sloping articular surface, but the shape and size of the reflected lamina is consistent with the position of Dinodontosaurus as a close relative of Stahleckeriidae. Traits potentially relevant for the distinction from D. tener and other kannemeyeriiforms (tall medial ridge on the dentary table, anterolateral trough in the angular, angular contribution to symphysis, extreme narrowness of the symphysial ridge, wide and deep median dentary groove) need further research in other dicynodont groups in order to robustly interpret their evolutionary history.

Extra-Patagonian records of Cretaceous theropod dinosaurs in Argentina are limited. When it comes to the Northwest of Argentina, most of the records come from the Cretaceous rocks of Salta Province, which yielded ceratosaurian abelisauroids like Noasaurus and Guemesia. Preliminary studies of the Los Llanos Formation at Eastern La Rioja Province recognized bone remains of Upper Cretaceous undetermined Abelisauridae and Coelurosauria. Recent surveys in the Northwest of the same province, in the outcrops of the Upper Cretaceous Ciénaga del Río Huaco Formation, at Quebrada Santo Domingo (Precordillera), resulted in the discovery of six isolated shed tooth crowns of putative abelisaurid theropods and crocodyliforms. They were found in association with partial skeletons of titanosaurid sauropod dinosaurs from two quarry sites, in the lower and upper sections of the same unit. Here we corroborate the taxonomic assignment of these specimens and their phylogenetic relationships. Five out of six teeth were assigned to Abelisauridae, whereas the remaining is considered to belong to a peirosaurid crocodyliform. Thus, the first occurrence of abelisaurid theropods and peirosaurid crocodyliforms in the Upper Cretaceous of the Precordillera of La Rioja is confirmed. Even though the teeth cannot be assigned to a less inclusive taxon, the difference in their stratigraphic position might indicate the presence of more than a single abelisaurid species in this region. The new results offer an optimistic perspective for future expeditions in this area, which intend to recover more skeletal elements.

Eggshell morphology is a valuable indicator of the local conditions within the nests of modern crocodilians and birds. In contrast to these latter, the anatomical structure of the eggshells of most crocodilian species is practically unknown. Here, we provide the first characterization of crocodilian eggshells, using x-ray micro-CT scans. We studied eggshells of Caiman latirostris and Caiman yacare from various developmental stages that coincide with the beginning of embryonic ossification. The new 3D renderings revealed complex ornamentation, unique among crocodilians, and amphora-shaped pore canals, some of which converge in single pore openings. We also documented a high density of pore canals with a gas diffusion capacity 45 times higher than the average predicted for modern avian eggshells. The external ornamentation and the thickness of the compact layer of the eggshells (i.e. excluding ornamentation) showed ontogenetic and interspecific differences that could be related to nesting materials and nesting areas selected by each species. The shell features described here evidence a greater structural complexity than previously recognized in phylogenetically close, sympatric crocodilian species. Further comprehensive morphological analyses on other modern and fossil crocodilian eggshells using micro-CT technology will shed new light on the evolution of reproductive strategies in this intriguing archosaur clade.

Titanosaurs were successful herbivorous dinosaurs widely distributed in all continents during the Cretaceous, with the major diversity in South America. The success of titanosaurs was probably due to several physiological and ecological factors, in addition to a series of morphological traits they achieved during their evolutionary history. However, the generalist nesting behaviour using different palaeoenvironments and strategies was key to accomplish that success. Titanosaur nesting sites have been found extensively around the world, with notable records in Spain, France, Romania, India, and, especially, Argentina. Here, we describe the first titanosaur nesting site from the Late Cretaceous of Brazil that represents the most boreal nesting site for South America. Several egg-clutches, partially preserved, isolated eggs and many eggshell fragments were discovered in an Inceptisol palaeosol profile of the mining Lafarge Quarry, at the Ponte Alta District (Uberaba Municipality, Minas Gerais State), corresponding to the Serra da Galga Formation (Bauru Group, Bauru Basin). Although classical mechanical preparation and CT scans have not revealed embryonic remains in ovo, the eggs and eggshell features match those eggs containing titanosaurian embryos found worldwide. The morphology of the egg-clutches and observations of the sedimentary characteristics bolster the hypothesis that these sauropods were burrow-nester dinosaurs, as was already suggested for the group based on other nesting sites. The egg-clutches distributed in two levels along the Lafarge outcrops, together with the geopalaeontological data collected, provide clear evidence for the first colonial nesting and breeding area of titanosaur dinosaurs in Brazil.

The geological-paleontological heritage of a region represents a component on which tourist activ-ity can be based. The objective of this study is to show how the policies created at all levels of government directly or indirectly affect the sustainable development of tourist activity in natural protected areas (ANP) with paleontological heritage. The area under analysis in this case is the Dinosaur Park contained within the Geological Park Sanagasta (PGS), La Rioja, Argentina, ANP with tourism based on paleontological findings. By way of method, we used analytical, critical review of policies devoted to conservation, protection, and subsequent tourism development around these sites. Some of the main results are: norms lacking regulation for stakeholder participation to be operational for tourism in conservation units. It is believed necessary to achieve shared management (public-private community-State) in pursuit of adequate tourism management.

The geological‑paleontological heritage of a region represents a component on which tourist activ‑ ity can be based. The objective of this study is to show how the policies created at all levels of government directly or indirectly affect the sustainable development of tourist activity in natural protected areas (ANP) with paleontological heritage. The area under analysis in this case is the Dinosaur Park contained within the Geological Park Sanagasta (PGS), La Rioja, Argentina, ANP with tourism based on paleontological findings. By way of method, we used analytical, critical review of policies devoted to conservation, protection, and subsequent tourism development around these sites. Some of the main results are: norms lacking regulation for stakeholder participation to be operational for tourism in conservation units. It is believed necessary to achieve shared management (public‑private community‑State) in pursuit of adequate tourism management.

Desde la creación del CRILAR (Centro Regional de Investigaciones Científicas y Transferencia Tecnológica) hace más de 20 años en la provincia de La Rioja, la paleoherpetología estuvo presente en su historia de investigación y transferencia. En el presente trabajo se narran los detalles de su creación, sus objetivos iniciales y los difíciles primeros años. Se describe cómo y cuándo comenzaron los estudios paleoherpetológicos del instituto, el hallazgo del sitio de nidificación de Sanagasta, el redescubrimiento del Cretácico de Los Llanos, los trabajos paleontológicos en Quebrada Santo Domingo y las investigaciones en el Triásico de la Cuenca Ischigualasto-Villa Unión. Además de las diferentes líneas de investigación, se mencionan diferentes colegas que colaboran con el CRILAR y las redes inter-institucionales que se generaron durante su historia. El CRILAR es el único centro de investigación del CONICET en la provincia de La Rioja, pero también es una institución de trasferencia científica, aspectos que serán abordados en detalle a lo largo del trabajo.

The kannemeyeriiforms of the latest Ladinian-?early Carnian Chañares Formation (Ischigualasto-Villa Unión Basin) exemplify the historical taxonomic controversies of several South American dicynodonts. Three taxa were originally recognized based on skull anatomy: “Chanaria” platyceps and two species of Dinodontosaurus (genus otherwise known in the Pinheiros-Chiniquá Sequence, Brazil), but in a recent taxonomic revision they were all synonymized in a single valid species (i.e., Dinodontosaurus brevirostris). The only postcranial record includes some undescribed specimens referred to D. brevirostris, an indeterminate shoulder girdle (MCZ 3459), and an ulna recently referred to Stahleckeria sp. Here we describe a new, large dicynodont specimen (CRILAR-Pv 82) from the Tarjadia Assemblage Zone (AZ) of the lowermost levels of the Chañares Formation, consisting of a right scapula, left ilium, sternum, and a few indeterminate fragments. The tall, dorsally expanded scapular blade with anteroventrally inclined dorsal margin and the anterolaterally directed acromion process broadly match the stahleckeriid morphotype. CRILAR-Pv 82 shares with Stahleckeria potens a sharp, vertical scapular spine on the anteroventral margin of the scapular blade, markedly convex in anterior view. The “hook-shaped” curvature of the preacetabular iliac process also resembles Stahleckeria potens and Eubrachiosaurus browni. These features differ at least with the Brazilian specimens of Dinodontosaurus (D. tener). The available data shows that MCZ 3459 also fits the stahleckeriid morphology, becoming the first historical record of the clade for the unit. A rigorous comparison with D. brevirostris will await the examination of more complete specimens. The dicynodont postcrania described so far from the Chañares Formation represent the oldest record of Stahleckeriinae in the Ischigualasto-Villa Unión Basin, expanding back its Argentinian record very likely beyond the Ladinian-Carnian boundary.

Proterochampsids were a group of stem archosaurs from the Middle–Late Triassic of South America. Using for the first time in proterochampsids quantitative microanatomical and morphological data and an inference model, we analyze the microstructure of postcranial bones of proterochampsids to infer life-history traits dealing with growth dynamics, ontogenetic changes, dermal armor histogenesis and lifestyle. We studied proterochampsid individuals from the Middle–Late Triassic Chañares Formation: three specimens of Chanaresuchus bonapartei: PVL 4575 (osteoderms and femur), CRILAR-Pv 80 (osteoderm) and CRILAR-Pv 81 (humerus), and a femur of a non-identified Rhadinosuchinae specimen (CRILAR-Pv 488). The osteoderms show a compact-uniform composition of parallel-fibered bone and lines of arrested growth (LAGs). The long bones are composed mainly of highly vascularized, parallel-fibered bone and isolated areas of woven-fibered bone in the innermost portion of cortex (only in C. bonapartei PVL 4575). The absence of an external fundamental system (EFS) indicates that all of the sampled individuals were somatically immature at time of death. The absence of mineralized bundles of collagenous fibers supports intramembranous ossification as the developmental origin for the osteoderms. With an inference model used for the first time in proterochampsids, the lifestyle inferred for C. bonapartei is terrestrial. Histological evidence indicates that sexual maturity is reached before both somatic and skeletal maturity. The growth patterns among proterochampsids exhibit some degree of variation even within a single species. Such variation can be due to different causes, including possibly phenotypic plasticity.

Eggshells represent an important part of the fossil record of Titanosauria (Dinosauria - Neosaumpoda) and their stable isotope compositions are valuable palaeoenvimnmental proxies. A new set of conventional (delta O-18 and delta C-13) and clumped (Delta(47)) stable isotope compositions of titanosaurian eggshells is presented, together with that of a bone and a single associated tooth, sampled in three Late Cretaceous nesting sites from La Rioja Province, NW Argentina. The preservation state of the fossils was first evaluated using optical and analytical techniques, such as transmitted light and optical cathodoluminescence (CL) microscopy, energy dispersive X-ray spectroscopy (EDX), and laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS). The isotopic compositions of the fossils were then compared to those of associated carbonate rocks and nodules, hydrothermal calcite and quartz, and those reported for eggshells from other nesting sites worldwide. This large, combined sample set allows us to define an isotopic hallmark (delta C-13(VPDB )= -15 to -11 parts per thousand; delta O-18(VSMOV) = 27 to 33 parts per thousand) typical for well-preserved mid-palaeolatitude titanosaurian eggshells. This hallmark is intended to identify the oological specimens best suited for palaeoenvimnmental reconstructions, for instance in museum collection samples that may lack associated abiogenic materials such as host rocks. In addition, our isotopic data support that titanosaurians were animals with an elevated body temperature, mainly feeding on C3 plants, and reproducing under conditions more arid than the long-term average. The data are in excellent agreement with the isotopic data reported from other mid-palaeolatitude nesting sites around the world, indicating that titanosaurians needed similar environmental conditions to reproduce, regardless of the palaeogeographic location of their habitat. Finally, we raise the question whether titanosaurians experienced reproduction-related fasting, as noted for several extant vertebrates, and discuss the complexity of interpreting Delta(47)-derived temperatures, despite very consistent bulk isotopic data.

South American titanosaurians have been central to the study of the evolution of Cretaceous sauropod dinosaurs. Despite their remarkable diversity, the fragmentary condition of several taxa and the scarcity of records outside Patagonia and southwestern Brazil have hindered the study of continental-scale paleobiogeographic relationships. We describe two new Late Cretaceous titanosaurians from Quebrada de Santo Domingo (La Rioja, Argentina), which help to fill a gap between these main areas of the continent. Our phylogenetic analysis recovers both new species, and several Brazilian taxa, within Rinconsauria. The data suggest that, towards the end of the Cretaceous, this clade spread throughout southern South America. At the same locality, we discovered numerous accumulations of titanosaurian eggs, likely related to the new taxa. With eggs distributed in three levels along three kilometres, the new site is one of the largest ever found and provides further evidence of nesting site philopatry among Titanosauria.

Present knowledge of Late Triassic tetrapod evolution, including the rise of dinosaurs, relies heavily on the fossil-rich continental deposits of South America, their precise depositional histories and correlations. We report on an extended succession of the Ischigualasto Formation exposed in the Hoyada del Cerro Las Lajas (La Rioja, Argentina), where more than 100 tetrapod fossils were newly collected, augmented by historical finds such as the ornithosuchid Venaticosuchus rusconii and the putative ornithischian Pisanosaurus mertii. Detailed lithostratigraphy combined with high-precision U–Pb geochronology from three intercalated tuffs are used to construct a robust Bayesian age model for the formation, constraining its deposition between 230.2 ± 1.9 Ma and 221.4 ± 1.2 Ma, and its fossil-bearing interval to 229.20 + 0.11/− 0.15–226.85 + 1.45/− 2.01 Ma. The latter is divided into a lower Hyperodapedon and an upper Teyumbaita biozones, based on the ranges of the eponymous rhynchosaurs, allowing biostratigraphic correlations to elsewhere in the Ischigualasto-Villa Unión Basin, as well as to the Paraná Basin in Brazil. The temporally calibrated Ischigualasto biostratigraphy suggests the persistence of rhynchosaur-dominated faunas into the earliest Norian. Our ca. 229 Ma age assignment to Pi. mertii partially fills the ghost lineage between younger ornithischian records and the oldest known saurischians at ca. 233 Ma.