Lucas Ernesto Fiorelli

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 Chañares 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 Chañares Formation.

During the Late Triassic epoch (237–201 million years ago), the terrestrial ecosystems of Pangaea underwent drastic changes^1,2 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 Unión^6,7 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 counterparts^9,10, 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.

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.

Tarjadia ruthae is a quadrupedal terrestrial pseudosuchian from the Middle‐early Upper Triassic of the Chañares Formation, La Rioja Province, Argentina. Originally, this species was identified as an indeterminate archosaur and later as a doswelliid archosauriform based on very fragmentary specimens characterized by the ornamentation of the skull roof and osteoderms. Additional specimens (including skulls and postcrania) recovered in the last decade show that Tarjadia is an erpetosuchid, an enigmatic pseudosuchian group composed of six species registered in Middle‐Upper Triassic continental units of Tanzania, Germany, Scotland, North America, Brazil, and Argentina. Tarjadia ruthae from Argentina and Parringtonia gracilis from Tanzania are the best preserved and more abundant species. Although the monophyly of Erpetosuchidae is well supported, alternative high‐level positions within Archosauria have been suggested, such as sister taxon to Crocodylomorpha, Aetosauria, or Ornithosuchidae. In order to improve the knowledge about the erpetosuchids, we performed a detailed description and paleoneurological reconstruction of the skull of Tarjadia ruthae, based on two articulated partial skulls (CRILAR‐Pv 478 and CRILAR‐Pv 495) and other fragmentary specimens. We analyzed the stratigraphic and geographic occurrence of historical and new specimens of Tarjadia and provided a new emended diagnosis (the same for the genus as for the species, due to monotypy) along with a comparative description of the cranial endocast. The skull of Tarjadia is robust, with a thick and strongly ornamented skull roof, triangular in dorsal view, with concave lateral margins at mid‐length that form an abrupt widened posterior region. The external nares are the smallest openings of the skull. The antorbital fossa is deeply excavated and has a small heart‐shaped fenestra with both lobes pointing anteriorly. The supratemporal fenestrae are as large and rounded as the orbits, and the infratemporal fenestrae are L‐shaped with an extensive excavation along the jugal, quadratojugal and quadrate. The hemimandibles are low, slightly concave on the dentigerous region and strongly convex on the posterior region, conferring them a S‐shaped profile in dorsal view. The external mandibular fenestra is small and elliptic, being twice longer than high. The maxillary dentition is restricted to the anterior to mid region of the rostrum. Since the braincase of both specimens is partially damaged, the dorsal surface of the brain could not be entirely reconstructed. As a result, the endocast is anteroposteriorly elongated and seemingly flat, and the cephalic flexure seems to be lower than expected for a suchian. The labyrinth is twice wider than high, the semicircular canals are remarkably straight, and the anterior canal is longer than the posterior one.

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.

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.