The proterochampsids are crocodile-like, small- to medium-sized, quadrupedal and predatory stem-archosaurs. The rhadinosuchines are a clade of deeply nested proterochampsids that are the most abundant diapsids of the Massetognathus-Chanaresuchus Assemblage Zone of the Chañares Formation (lower Carnian) of north-western Argentina. Here, we describe two new rhadinosuchine proterochampsid specimens recently collected from the Massetognathus-Chanaresuchus Assemblage Zone of the Chañares Formation. These specimens are represented by an articulated partial skeleton and disarticulated cranial and postcranial bones, respectively. One of them is less complete, but its well-preserved disarticulated bones considerably expand the anatomical knowledge of certain regions of the rhadinosuchine skeleton. The combination of character-states present in both specimens and shared with other known rhadinosuchine species (e.g., Chanaresuchus bonapartei, Gualosuchus reigi, Rhadinosuchus gracilis) results in an unexpected increase of the morphological diversity of the group (e.g., antorbital fossa on the horizontal process of maxilla, well-exposed antorbital fossa on lacrimal, X-shaped osteoderms). We conclude that the taxonomy of the currently known rhadinosuchine specimens should be revisited, including a careful reappraisal of the intraspecific variation and the post-mortem deformation that affected the specimens in different ways.

In this contribution, we present the first pterosaur post-cranial bone from the Lohan Cura Formation (Albian) of the Cerro de los Leones locality (Picún Leufú, Neuquén Province). The material is an incomplete left ulna, preserved in three dimensions, and composed of the proximal epiphysis and part of the diaphysis. The element shares several affinities with derived pterodactyloid pterosaurs, such as a diaphysis with a sub-oval cross-section, thin bone walls, pneumatic foramina in the dorsal surface of the proximal epiphysis and between the cotyles, and wingspan reconstruction indicating a medium-size specimen. An analysis of the microstructure allowed us to evaluate the ontogenetic stage of the specimen. The thin-section from the mid-shaft shows a wide and sub-circular medullary cavity, encircled by a thin cortical bone ring. In the innermost cortex, secondary lamellar bone forms a distinct and avascular endosteal layer, while the cortical layer is dominated by a well-vascularized primary bone with coarse parallel fibers, as in other pterodactyloids. The presence of an avascular endosteal lamellar layer, an unremodeled cortical layer dominated by parallel-fibered bone, and a well ossified proximal epiphysis suggest that the specimen was an advanced juvenile or sub-adult with active-growth at the time of death. Considering the limited pterosaurian fossil record of Argentina, the new pterosaur specimen not only contributes to the reconstruction of the paleoecosystem of the Lohan Cura Formation in the central Neuquén Basin, but also improves our knowledge on the pterosaur taxonomic diversity during the Early Cretaceous of Patagonia.

Histological and diagenetic features of sauropod and theropod bones from the late Cretaceous Loncoche Formation of southern Mendoza, Argentina were analyzed to elucidate the degree and type of taphonomic alteration in relation to their depositional environment. The histological thin sections reveal a predominance of fibrolamellar bone tissue in the sauropod suggesting an overall fast bone growth, contrary to the presence of parallel-fibered bone tissue that suggests a slow-down growth in the theropod. However, the existence of lines of arrested growth indicates periodic interruptions of growth, andit is likely the expression of their ability to respond to rapid environmental changes. The fossil bones show post-mortem modifications such as weathering, fragmentation, abrasion and hydraulic sorting during transport. Diagenetic processes include substitution, fracturing, plastic deformation due to lithostatic compression, and permineralization events. Petrographic and SEM-EDS analyses show the substitution of hydroxyapatite by fluorapatite in the bone microstructure. Permineralization stages include infilling of vascular canals, trabeculae and fractures with iron oxides and carbonate minerals during the burial history. This work provides an integral approach to the study of dinosaurs from the Loncoche Formation for assessing the diagenetic changes in the bone microstructure and its link with burial environments.

We described a fossil small mammal assemblage from La Mesada (2250 m), Tafí valley, Tucumán, Argentina, recovered from levels referred to late Pleistocene – early Holocene. Gastric corrosion in bones and teeth indicates that the assemblage was generated by the trophic activities of owls. The assemblage is composed by 14 species of rodents: 12 living (Abrothrix illutea, Akodon spegazzinii, Oxymycterus sp., Andinomys edax, Oligoryzomys brendae, Oligoryzomys cf. O. occidentalis, Calomys cf. C. musculinus, Phyllotis sp., Reithrodon auritus, Cavia cf. C. tschudii, Galea leucoblephara, and Ctenomys sp.), one extinct (†Tafimys powelli), and one indeterminate (Sigmodontinae indet.). The sample is characterized by the remarkable dominance of R. auritus (53%) in contrast to its low frequency in other fossil and present-day samples in the area, the presence of †T. powelli, and the absence of one species currently present in the valley (Necromys lactens). The fossil sample shares general similarities with other late Pleistocene – early Holocene assemblages in northwestern Argentina, but there are relevant qualitative and quantitative differences. Although all living species of the fossil sample occur in sympatry in the same area, its quantitative representation (dominance of R. auritus and a higher proportion of herbivore species) is coherent with paleoenvironments with a clear predominance of highland grasslands, involving both the descent and contraction of the vegetation belts on mountain slopes. However, it cannot be discarded that the current scarcity of R. auritus is more related to the anthropic impact than to the prevailing climate in the valley.

A new genus and two new fossil species of continental gastropods from the upper part of the Irene Formation—which is probably Huayquerian–Montehermosian (early Pliocene) and is exposed in the Quequén Salado River (Buenos Aires Province, Argentina)—are described: the new genus and species of freshwater gastropod Argentisioliella pardignasi (Cochliopidae) and a new species of landsnail of the family Bulimulidae (Bocourtia (Kuschelenia?) bonariensis). Argentisioliella pardignasi is morphologically related to those described for the Pebas Formation of Pliocene age. The specimens have bulloid morphology, long and narrow aperture, with a channeled peristome and two folds in the columellar wall. This is the first description of similar snails of the Pebas and Irene formations. Bocourtia (Kuschelenia?) bonariensis is the most ancient record for the genus, being recorded far away from the area of its current distribution (northwest Argentina). The specimen is an internal cast, with more than three convex whorls and a large aperture. Its distribution would coincide with the final phase of the Mio–Pliocene climatic change, when numerous terrestrial gastropods of Patagonian and Pampean provenance disappeared. A well-conserved specimen of the terrestrial snail Austroborus (Strophocheilidae Pilsbry), showing an almost complete shell, with more than 4.5 convex whorls, last whorl and large aperture, was also recorded. In the study area, this genus was present during the Pleistocene and Holocene, living in restricted areas of Argentina and Uruguay, with a disjunctive and relictual distribution.