The Quebrada del Barro Formation (QBF) is part of the continental Marayes-El Carrizal Basin, in NW Argentina. Here we report a diverse faunal assemblage recently discovered in the Quebrada del Barro Formation, along with a preliminary discussion of the taxonomic status and affinities of numerous vertebrate specimens found at two localities where this unit is exposed. The new vertebrate association includes remains of at least 12 different new species related to six major vertebrate groups: Cynodontia, Testudinata, Sphenodontia, Pseudosuchia, Pterosauria, and Dinosauromorpha. The most abundant specimens in this faunal assemblage are opisthodontian sphenodonts, tritheledontid cynodonts and basal sauropodomorph dinosaurs, but the assemblage also includes diagnostic remains of lagerpetid dinosauromorphs, theropods, pterosaurs, basal crocodylomorphs, and stem testudinatans. Several of these groups have also been reported for the Los Colorados Formation (LCF), although the two units differ in their taxonomic content at the species level and in the relative abundance of different taxonomic groups. A comparison of these two faunal assemblage suggest the fauna of QBF is younger than that of LCF and we tentatively assess a late Norian-Rhaetian age for the QBF. Some of the specimens reported here are known from well-preserved specimens and yield important new information for understanding the evolution of these groups, which underscores the relevance of the QBF fauna for assessing the dynamics of the major groups of vertebrates that dominated the terrestrial ecosystems during the early Mesozoic in Pangea.

The proterochampsids are small to medium-sized, quadrupedal and probable semi-aquatic reptiles that were part of the evolutionary radiation of Archosauromorpha during the Triassic. The group is restricted to the Middle and Late Triassic of South America with eight nominal species. Rhadinosuchus gracilis Huene was the first described proterochampsid and comes from the late Carnian—earliest Norian of southern Brazil. This genus and species is currently the most enigmatic and poorly known member of the group. For this reason we redescribe here its anatomy and discuss its phylogenetic relationships. We found that this species can be distinguished from other proterochampsids and we dismiss the proposed synonymy with Cerritosaurus binsfeldi Price. Our quantitative phylogenetic analysis found Rhadinosuchus gracilis more closely related to Gualosuchus reigi Romer and Chanaresuchus bonapartei Romer than to other proterochampsids, together forming the subfamily Rhadinosuchinae. Characters supporting this assignment include a maxilla with a distinct longitudinal change in slope between lateral and dorsal surfaces, and dorsal surface of nasal and frontal ornamented by ridges showing a radial pattern. In addition, Rhadinosuchus gracilis was recognized as the sister taxon of Chanaresuchus bonapartei based on a lacrimal with an antorbital fossa that occupies almost half or more of the anteroposterior length of the ventral process. The topology of the phylogenetic analysis shows that the Brazilian species do not form a monophyletic clade and favours multiple dispersal events between the Ischigualasto-Villa Unión (northwestern Argentina) and the Paraná (southern Brazil) basins.

A description is provided of the first sauropod remains (i.e., isolated vertebrae and appendicular bones) from the Late Jurassic of Aysén, in Chilean Patagonia (Toqui Formation, late Tithonian). Although the bones found are fragmentary, they still allow the recognition of an unsuspected sauropod diversity for this period in South America. The materials suggest the presence of at least three different sauropod lineages: an indeterminate group of sauropods, possible Titanosauriformes, and Diplodocoidea. A phylogenetic analysis of this last clade supports the placement of the remains within Diplodocinae and also provides the first unequivocal record of this clade in Late Jurassic rocks of South America. These records provide important information about the poorly known evolutionary history of sauropods in South America before the Cretaceous.

Cretaceous outcrops in southern South America preserve a rich and evolutionarily important record of sauropod dinosaurs. Among Sauropoda, South American titanosaurs have garnered particular interest due to their abundance and taxonomic diversity. Nevertheless, the fossil record of rebbachisaurids has also improved significantly in recent years, and consequently so has knowledge of the group. However, many aspects of the anatomy and phylogenetic relationships of Rebbachisauridae remain unresolved, due in large part to the fragmentary nature of many members of the clade. Within this context, we describe new fossils of Katepensaurus goicoecheai Ibiricu, Casal, Martínez, Lamanna, Luna, and Salgado, a recently-named rebbachisaurid from the Upper Cretaceous (Cenomanian/Turonian) Bajo Barreal Formation of central Patagonia (Argentina). Based on these additional materials, we propose two new autapomorphies of this taxon: (1) ventral portion of posterior articular surface of anterior dorsal vertebral centrum wider than dorsal portion, conferring a ‘teardrop-shaped’ contour; and (2) ovoid fossa on dorsal aspect of anterior to middle dorsal vertebral transverse processes. These features enhance our understanding of morphological diversity within Rebbachisauridae and augment the diagnosis of Katepensaurus. Furthermore, phylogenetic analysis confirms the assignment of this taxon to the rebbachisaurid subclade Limaysaurinae. Katepensaurus is the southernmost record of a rebbachisaurid that is identifiable to the generic level.

Two species of coniferous silicified wood are described from the El Freno Formation (Lower Jurassic) at Cerro La Brea, on the southern margin of the Atuel River, southern Mendoza Province, Argentina. Agathoxylon liguaensis Torres and Philippe (Araucariaceae) and the new species Podocarpoxylon atuelensis sp. nov. (Podocarpaceae) were described based on a detailed description of the secondary xylem. Wood specimens are well preserved, although some sections display variably decaying cell-walls typical of white-rotting by extant fungi. Vegetative and sexual structures in the degraded areas are identifiable as basidiomycetes. This is consistent with fungal saprotrophism and supports the role of fungi in the recycling of the organic matter in Mesozoic terrestrial ecosystems. Considering the available geochronologic and biostratigraphic data and the current lithostratigraphic settings proposed for the unit, the age of the El Freno Formation at the studied locality can be constrained to the Hettangian-Sinemurian.