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Aetosaurs are quadrupedal archosaurs that had a worldwide distribution during the Late Triassic. They had small heads relative to their body size and a long tail, and they are characterized by a dorsal and ventral carapace formed by ornamented and articulated osteoderms. Although aetosaurs historically have been considered the only herbivorous among the early pseudosuchian archosaurs, few analyses quantitatively assess their feeding habits, and some authors have proposed omnivorous and/or scavenging habits for the group. Neoaetosauroides engaeus is an aetosaur from the Late Triassic of the Los Colorados Formation, La Rioja, Argentina. N. engaeus is known from three relatively well-preserved skulls, making it an excellent taxon to study the feeding ecology. We applied the Finite Element Method to estimate bite force and to evaluate the structural response of the skull at different positions during food processing. Our results show that the skull of N. engaeus generated a bite force of 3.6 kN, a magnitude comparable with the measurement made in Alligator mississippiensis, and could resist lateral and longitudinal forces during feeding. This indicates that N. engaeus was capable of hunting of small living prey (e.g., cynodonts) with its jaws, and/or dragging carcasses of larger sizes (e.g., dicynodonts). These results bring new evidence that supports possible zoophagy or omnivory for N. engaeus, thus expanding the potential ecological roles of aetosaurs.

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., Hechenleitner et al. describe two new titanosaurians and the finding of numerous accumulations of titanosaurian eggs in La Rioja, Argentina. This study suggests nesting site philopatry among Titanosauria and that this clade was spread throughout southern South America at the end of the Late Cretaceous.

The reproduction of titanosaur dinosaurs is still a complex and debated topic. Their Late Cretaceous nesting sites are distributed worldwide and their eggs display substantial morphological variations according to the parent species. In contrast to the typical 1.3-2.0 mm thick shells common to eggs of most titanosaur species (e.g., those that nested in Auca Mahuevo, Tama, Toteşti or Boseong), the Cretaceous Sanagasta eggs of Argentina display an unusual shell thickness of up to 7.9 mm. Their oviposition was synchronous with a palaeogeothermal process, leading to the hypothesis that their extra thick eggshell was an adaptation to this particular nesting environment. Although this hypothesis has already been supported indirectly through several investigations, the mechanical implications of developing such thick shells and how this might have affected the success of hatching remains untested. Finite element analyses estimate that the breaking point of the thick-shelled Sanagasta eggs is 14-45 times higher than for other smaller and equally sized titanosaur eggs. The considerable energetic disadvantage for piping through these thick eggshells suggests that their dissolution during incubation would have been paramount for a successful hatching. Fil: Hechenleitner, E. Martín. Centro Regional de Investigaciones Cientificas y Transferencia Tecnologica La Rioja (CRILAR) - (Provincia de La Rioja - UNLaR - SEGEMAR - UNCa - CONICET; Argentina Fil: Taborda, Jeremías Ramón Alejandro. Universidad Nacional de Córdoba, Facultad de Ciencias Exactas Físicas y Naturales (FCEFyN), Centro de Investigaciones en Ciencias de la Tierra (CICTERRA-CONICET); Argentina Fil: Fiorelli, Lucas Ernesto. Centro Regional de Investigaciones Cientificas y TRansferencia Tecnológica La Rioja (CRILAR) - Provincia de La Rioja - UNLaR - SEGEMAR - UNCa - CONICET.; Argentina Fil: Grellet-Tinner, Gerald. Centro Regional de Investigaciones Cientificas y TRansferencia Tecnológica La Rioja (CRILAR) - Provincia de La Rioja - UNLaR - SEGEMAR - UNCa - CONICET.; Argentina Fil: Nuñez-Campero, Segundo R.. Centro Regional de Investigaciones Cientificas y TRansferencia Tecnológica La Rioja (CRILAR) - Provincia de La Rioja - UNLaR - SEGEMAR - UNCa - CONICET.; Argentina

Cretaceous titanosaur nesting sites are currently known only from Europe, Asia and South America. In the latter, only the Auca Mahuevo and Sanagasta nesting sites have been confidently assigned to this clade of sauropod dinosaurs. Here we report the discovery of the first eggs and egg clutches found at Tama, a new Upper Cretaceous fossiliferous locality in the Los Llanos Formation, Sierra de Los Llanos (La Rioja, NW Argentina). At least five egg clutches, several partially preserved, isolated eggs and many eggshell fragments were discovered in a single outcrop of a sandstone horizon which represents a cumulative palaeosol profile. Although the mechanical and digital preparation of eggs did not reveal any embryonic remains in ovo, the morphology of the eggs and eggshells closely matches that of titanosaur eggs and eggshells found worldwide. The morphology and spatial grouping of the titanosaur eggs from Tama, along with geological observations support a burrow‐nesting strategy for these dinosaurs. Although the Sanagasta and Tama eggs were found in the same stratigraphical unit and share several morphological characters, they clearly differ in shell thickness and egg size. This, coupled with the interpretation of different sedimentary contexts for these nesting sites, strongly suggests that at least two different titanosaur species nested in La Rioja during the Late Cretaceous, using different nesting strategies. The occurrence of this new titanosaur nesting site in a semiarid palaeoenvironment represents an interesting case study for the reproductive biology of the titanosaur dinosaurs, particularly their labile nesting behaviour. Fil: Hechenleitner, Esteban Martín. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Regional de Investigaciones Científicas y Transferencia Tecnológica de La Rioja. - Universidad Nacional de La Rioja. Centro Regional de Investigaciones Científicas y Transferencia Tecnológica de La Rioja. - Universidad Nacional de Catamarca. Centro Regional de Investigaciones Científicas y Transferencia Tecnológica de La Rioja. - Secretaría de Industria y Minería. Servicio Geológico Minero Argentino. Centro Regional de Investigaciones Científicas y Transferencia Tecnológica de La Rioja. - Provincia de La Rioja. Centro Regional de Investigaciones Científicas y Transferencia Tecnológica de La Rioja; Argentina Fil: Fiorelli, Lucas Ernesto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Regional de Investigaciones Científicas y Transferencia Tecnológica de La Rioja. - Universidad Nacional de La Rioja. Centro Regional de Investigaciones Científicas y Transferencia Tecnológica de La Rioja. - Universidad Nacional de Catamarca. Centro Regional de Investigaciones Científicas y Transferencia Tecnológica de La Rioja. - Secretaría de Industria y Minería. Servicio Geológico Minero Argentino. Centro Regional de Investigaciones Científicas y Transferencia Tecnológica de La Rioja. - Provincia de La Rioja. Centro Regional de Investigaciones Científicas y Transferencia Tecnológica de La Rioja; Argentina Fil: Grellet-tinner, Gerald. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Regional de Investigaciones Científicas y Transferencia Tecnológica de La Rioja. - Universidad Nacional de La Rioja. Centro Regional de Investigaciones Científicas y Transferencia Tecnológica de La Rioja. - Universidad Nacional de Catamarca. Centro Regional de Investigaciones Científicas y Transferencia Tecnológica de La Rioja. - Secretaría de Industria y Minería. Servicio Geológico Minero Argentino. Centro Regional de Investigaciones Científicas y Transferencia Tecnológica de La Rioja. - Provincia de La Rioja. Centro Regional de Investigaciones Científicas y Transferencia Tecnológica de La Rioja; Argentina Fil: Leuzinger, Léa Sylvia. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Regional de Investigaciones Científicas y Transferencia Tecnológica de La Rioja. - Universidad Nacional de La Rioja. Centro Regional de Investigaciones Científicas y Transferencia Tecnológica de La Rioja. - Universidad Nacional de Catamarca. Centro Regional de Investigaciones Científicas y Transferencia Tecnológica de La Rioja. - Secretaría de Industria y Minería. Servicio Geológico Minero Argentino. Centro Regional de Investigaciones Científicas y Transferencia Tecnológica de La Rioja. - Provincia de La Rioja. Centro Regional de Investigaciones Científicas y Transferencia Tecnológica de La Rioja; Argentina Fil: Basilici, Giorgio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Regional de Investigaciones Científicas y Transferencia Tecnológica de La Rioja. - Universidad Nacional de La Rioja. Centro Regional de Investigaciones Científicas y Transferencia Tecnológica de La Rioja. - Universidad Nacional de Catamarca. Centro Regional de Investigaciones Científicas y Transferencia Tecnológica de La Rioja. - Secretaría de Industria y Minería. Servicio Geológico Minero Argentino. Centro Regional de Investigaciones Científicas y Transferencia Tecnológica de La Rioja. - Provincia de La Rioja. Centro Regional de Investigaciones Científicas y Transferencia Tecnológica de La Rioja; Argentina Fil: Taborda, Jeremías Ramón Alejandro. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Museo Argentino de Ciencias Naturales ; Argentina Fil: de la Vega, Sergio Ruben. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Regional de Investigaciones Científicas y Transferencia Tecnológica de La Rioja. - Universidad Nacional de La Rioja. Centro Regional de Investigaciones Científicas y Transferencia Tecnológica de La Rioja. - Universidad Nacional de Catamarca. Centro Regional de Investigaciones Científicas y Transferencia Tecnológica de La Rioja. - Secretaría de Industria y Minería. Servicio Geológico Minero Argentino. Centro Regional de Investigaciones Científicas y Transferencia Tecnológica de La Rioja. - Provincia de La Rioja. Centro Regional de Investigaciones Científicas y Transferencia Tecnológica de La Rioja; Argentina Fil: Bustamante, Carlos Antonio. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Regional de Investigaciones Científicas y Transferencia Tecnológica de La Rioja. - Universidad Nacional de La Rioja. Centro Regional de Investigaciones Científicas y Transferencia Tecnológica de La Rioja. - Universidad Nacional de Catamarca. Centro Regional de Investigaciones Científicas y Transferencia Tecnológica de La Rioja. - Secretaría de Industria y Minería. Servicio Geológico Minero Argentino. Centro Regional de Investigaciones Científicas y Transferencia Tecnológica de La Rioja. - Provincia de La Rioja. Centro Regional de Investigaciones Científicas y Transferencia Tecnológica de La Rioja; Argentina

Los aetosaurios son un grupo de arcosaurios pseudosuquios cuadrúpedos y acorazados del Triásico superior. Se Caracterizan por tener una coraza dorsal, una ventral, y osteodermos apendiculares, todos ornamentados. Los aetosaurios fueron propuestos como fósiles guía con base en características distintivas en algunos osteodermos. Por lo tanto, es importante comprender las variaciones intraespecíficas de estos elementos dentro del clado. En la presente contribución, se describen tres tipos de ornamentación en el área medial de los osteodermos paramediales de la coraza dorsal de Aetosauroides scagliai Casamiquela 1960: un “patrón radial”; un “patrón anastomosado”; y uno “intermedio” o “patrón transicional” entre el radial y el anastomosado. Las corazas articuladas de los especímenes PVL 2059 y PVL 2073 muestran los tres tipos de ornamentación, pero con una variación en la posición dentro de la coraza de los osteodermos con estas ornamentaciones. Recientes estudios paleohistológicos en osteodermos de A. scagliai muestran la ausencia de remodelación en los tejidos de los mismos permitiendo la estimación de edad mediante el conteo de LACs (líneas anuales de crecimiento). El PVL 2073 es ligeramente más corto (∼10% en los centros) pero también más joven ontogenéticamente (5 LACs) que el PVL 2059 (10 LACs; y osteodermos ligeramente más anchos). Combinando esta información y comparándola con los cocodrilos actuales (donde los machos son generalmente más grandes que las hembras para una misma edad), concluimos que la variación intraespecífica observada en A. scagliai es compatible con la hipótesis de un dimorfismo sexual. Estos resultados evidencian la necesidad de estudiar las variaciones intraespecíficas en aetosaurios. Aetosaurs are a group of quadrupedal, armoured pseudosuchian archosaurs from the Upper Triassic. They are characterized by dorsal and ventral carapaces, and appendicular osteoderms, all of them ornamented. Aetosaurs have been proposed as index fossils largely based on the distinctiveness of some osteoderms. Therefore, it is important to understand the intraspecific variation of these elements in the clade. In the present contribution, we describe three types of ornamentation on the medial area of paramedian osteoderms in the dorsal armour of Aetosauroides scagliai Casamiquela: the “radial pattern” the “anastomosing pattern”; and an “intermediate” or “transitional pattern”, that is an intermediate between “radial” and “anastomosing” patterns. The articulated dorsal armour preserved in specimens PVL 2059 and PVL 2073 possesses osteoderms carrying all three patterns of ornamentation, but they differ by the position of each type of osteoderm on the carapace. Recent studies on histological thin-sections of osteoderms of A. scagliai reveal the absence of osteoderm tissue remodeling, allowing the estimation of age by counting LAGs (lines of arrested growth). PVL 2073 is slightly shorter (∼10% longer centra) but also ontogenetically younger (5 LAGs) than PVL 2059 (10 LAGs; slightly wider osteoderms). Combining this information and comparing it with that of living crocodiles (where male specimens typically are relatively larger than females of the same age), we conclude that the intraspecific variation observed in A. scagliai is compatible with the hypothesis of sexual dimorphism. These results suggest the need to explore the sources of intraspecific variation in aetosaurs. Fil: Taborda, Jeremías Ramón Alejandro. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Museo Argentino de Ciencias Naturales "Bernardino Rivadavia"; Argentina Fil: Heckert, Andrew Bittinger. Appalachian State University; Estados Unidos Fil: Desojo, Julia Brenda. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Museo Argentino de Ciencias Naturales "Bernardino Rivadavia"; Argentina

The paleoneuroanatomy of pseudosuchian archosaurs is poorly known, based on direct examination of the internal morphology of braincases and a few artificial endocasts. Among aetosaurs, only one endocast has been described almost a century ago by Case (1921) corresponding to Desmatosuchus spurensis from the Chinle Formation (Norian) of Texas, US, based on a resin cast. Here, we describe the first natural endocast of an aetosaur, Neoaetosauroides engaeus from the Los Colorados Formation (Norian) of NW Argentina, and also developed the first digital endocast of this taxon including the encephalon, cranial nerves, inner ear, and middle ear sinuses. The neuroanatomy of Neoaetosauroides engaeus exhibits several differences from that of Desmatosuchus spurensis despite their phylogenetic proximity, which may be a reflection of their different habits. The information provided by the endocasts of Neoaetosauroides engaeus about its olfactory region and the orientation of its head, based on the inclination of the inner ear, could support the proposal for an animalivorous diet, instead of an herbivorous one as in most aetosaurs. The new information here obtained contributes to the knowledge of the neuroanatomical diversity of archosauriforms and more specifically among pseudosuchians and their paleobiological roles in the Triassic continental communities. Fil: Von Baczko, Belen. Museo de la Plata; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Taborda, Jeremías Ramón Alejandro. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Centro de Investigaciones en Ciencias de la Tierra. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Centro de Investigaciones en Ciencias de la Tierra; Argentina Fil: Desojo, Julia Brenda. Museo de la Plata; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina

Defecation in communal latrines is a common behaviour of extant mammals widely distributed among megaherbivores. This behaviour has key social functions with important biological and ecological implications. Herbivore communal latrines are only documented among mammals and their fossil record is exceptionally restricted to the late Cenozoic. Here we report the discovery of several massive coprolite associations in the Middle-Late Triassic of the Chañares Formation, Argentina, which represent fossil communal latrines based on a high areal density, small areal extension and taphonomic attributes. Several lines of evidence (size, morphology, abundance and coprofabrics) and their association with kannemeyeriiform dicynodonts indicate that these large synapsids produced the communal latrines and had a gregarious behaviour comparable to that of extant megaherbivores. This is the first evidence of megaherbivore communal latrines in non-mammal vertebrates, indicating that this mammal-type behaviour was present in distant relatives of mammals, and predates its previous oldest record by 220 Mya. Fil: Fiorelli, Lucas Ernesto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Regional de Investigaciones Cientificas y Transferencia Tecnológica de Anillaco; Argentina Fil: Ezcurra, Martin Daniel. University of Birmingham. School of Geography; Reino Unido. Ludwig Maximilians Universitat; Alemania Fil: Hechenleitner, Esteban Martín. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Regional de Investigaciones Cientificas y Transferencia Tecnológica de Anillaco; Argentina Fil: Argañaraz, Eloisa. Universidad Nacional de Cordoba. Facultad de Cs.exactas Fisicas y Naturales. Centro de Invest.paleobiologicas; Argentina Fil: Taborda, Jeremías Ramón Alejandro. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Museo Argentino de Ciencias Naturales; Argentina Fil: Trotteyn, Maria Jimena. Universidad Nacional de San Juan. Facultad de Ciencias Exactas, Fisicas y Naturales. Instituto de Geologia "Dr. Emiliano Aparicio"; Argentina Fil: Von Baczko, Belen. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Museo Argentino de Ciencias Naturales; Argentina Fil: Desojo, Julia Brenda. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Museo Argentino de Ciencias Naturales; Argentina

Rhynchosaurs first appear in the Early Triassic fossil record and flourished during the late Carnian as the dominant members of several assemblages worldwide. In Argentina, the rhynchosaur record is currently restricted to the Ischigualasto Formation of late Carnian–earliest Norian age. Recent fieldwork in the new locality of Brazo del Puma, in the lowermost levels of the Chañares Formation, yielded three rhynchosaur tooth-bearing bones, which were collected five metres above the contact with the underlying Tarjados Formation. The most complete specimen is the posterior end of the alveolar region of a left dentary. The dentary possesses densely packed tooth rows on the lingual surface and medial half of the occlusal surface, showing longitudinal Zahnreihen. The teeth of the occlusal surface are worn flat and those of the lingual surface are organized in multiple rows, supporting the referral of the specimen to Rhynchosauridae. In addition, the dentary teeth are conical to mesiodistally compressed, resembling the condition observed in hyperodapedontines. The rhynchosaur remains reported here are the oldest collected in Argentina and among the oldest in South America, together with an unnamed form from Brazil. The new rhynchosaur specimens come from levels in which dicynodonts are numerically dominant, whereas cynodonts are considerably less abundant. Accordingly, the specimens reported here bolster faunal differences within the Chañares Formation and add a new faunal component to this already diverse vertebrate assemblage. Fil: Ezcurra, Martin Daniel. University of Birmingham; Reino Unido. Universität München; Alemania Fil: Trotteyn, Maria Jimena. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Bahía Blanca. Instituto Geológico del Sur; Argentina Fil: Fiorelli, Lucas Ernesto. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Regional de Investigaciones Cientificas y Transferencia Tecnológica de Anillaco; Argentina Fil: Von Baczko, Belen. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Museo Argentino de Ciencias Naturales; Argentina Fil: Taborda, Jeremías Ramón Alejandro. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Museo Argentino de Ciencias Naturales; Argentina Fil: Iberlucea, Maximiliano Javier. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Museo Argentino de Ciencias Naturales; Argentina Fil: Desojo, Julia Brenda. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Museo Argentino de Ciencias Naturales; Argentina

Recent paleohistological studies on paramedian osteoderms of aetosaurs revealed the presence of growth lines (lines of arrested growth or LAG’s) and a minimal or nonexistent secondary remodelling in the bone matrix of these elements. This feature allows estimating the age of individuals through growth line count. In the present contribution we study the growth curve of the South American aetosaur Aetosauroides scagliai. We estimated the age (obtained from LAG’s counting) and body size (body length and body mass were used as proxies) of different aetosaur specimens in order to reconstruct the growth curve of the South American species. The data obtained for Aetosauroides scagliai was compared with that of other aetosaurs, such as Neoaetosauroides engaeus, Aetosaurus ferratus, Aetobarbakinoides brasiliensis, Typothorax coccinarum, and Paratypothorax sp. Our results indicate that, if body length is considered as proxy, all studied aetosaur specimens have a similar or almost identical growth rate. However, important variations arose among aetosaur taxa if body mass is considered as proxy, which would be related with a body morphology ranging from slender (e.g. Aetobarbakinoides brasiliensis) to very wide (Typothorax coccinarum) morphotypes. In comparison with extant pseudosuchians, (i.e. crocodylians), Aetosauroides scagliai possesses a relatively lower growth rate. Fil: Taborda, Jeremías Ramón Alejandro. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Museo Argentino de Ciencias Naturales; Argentina Fil: Cerda, Ignacio A. Universidad Nacional de Rio Negro. Sede Alto Valle. Instituto de Investigaciones En Paleobiologia y Geologia; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Desojo, Julia Brenda. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Museo Argentino de Ciencias Naturales; Argentina