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The origin of the air sac system present in birds has been an enigma for decades. Skeletal pneumaticity related to an air sac system is present in both derived non-avian dinosaurs and pterosaurs. But the question remained open whether this was a shared trait present in the common avemetatarsalian ancestor. We analyzed three taxa from the Late Triassic of South Brazil, which are some of the oldest representatives of this clade (233.23 ± 0.73 Ma), including two sauropodomorphs and one herrerasaurid. All three taxa present shallow lateral fossae in the centra of their presacral vertebrae. Foramina are present in many of the fossae but at diminutive sizes consistent with neurovascular rather than pneumatic origin. Micro-tomography reveals a chaotic architecture of dense apneumatic bone tissue in all three taxa. The early sauropodomorphs showed more complex vascularity, which possibly served as the framework for the future camerate and camellate pneumatic structures of more derived saurischians. Finally, the evidence of the absence of postcranial skeletal pneumaticity in the oldest dinosaurs contradicts the homology hypothesis for an invasive diverticula system and suggests that this trait evolved independently at least 3 times in pterosaurs, theropods, and sauropodomorphs. [ABSTRACT FROM AUTHOR]

Our knowledge on the anatomy of the first dinosaurs (Late Triassic, 235–205 Ma) has drastically increased in the last years, mainly due to several new findings of exceptionally well‐preserved specimens. Nevertheless, some structures such as the neurocranium and its associated structures (brain, labyrinth, cranial nerves, and vasculature) remain poorly known, especially due to the lack of specimens preserving a complete and articulated neurocranium. This study helps to fill this gap by investigating the endocranial cavity of one of the earliest sauropodomorphs, Buriolestes schultzi, from the Upper Triassic (Carnian—c. 233 Ma) of Brazil. The endocranial anatomy of this animal sheds light on the ancestral condition of the brain of sauropodomorphs, revealing an elongated olfactory tract combined to a relatively small pituitary gland and well‐developed flocculus of the cerebellum. These traits change drastically across the evolutionary history of sauropodomorphs, reaching the opposite morphology in Jurassic times. Furthermore, we present here the first calculations of the Reptile Encephalization Quotient (REQ) for a Triassic dinosaur. The REQ of B. schultzi is lower than that of Jurassic theropods, but higher than that of later sauropodomorphs. The combination of cerebral, dental, and postcranial data suggest that B. schultzi was an active small predator, able to track moving prey. [ABSTRACT FROM AUTHOR]

The fusion of the sacrum occurs in the major dinosaur lineages, i.e. ornithischians, theropods, and sauropodomorphs, but it is unclear if this trait is a common ancestral condition, or if it evolved independently in each lineage, or even how or if it is related to ontogeny. In addition, the order in which the different structures of the sacrum are fused, as well as the causes that lead to this co‐ossification, are poorly understood. Herein, we described the oldest record of fused sacral vertebrae within dinosaurs, based on two primordial sacral vertebrae from the Late Triassic of Candelária Sequence, southern Brazil. We used computed microtomography (micro‐CT) to analyze the extent of vertebral fusion, which revealed that it occurred only between the centra. We also assessed the occurrence of sacral fusion in Dinosauria and close relatives. The degree of fusion observed in representatives of the major dinosaur lineages suggested that there may be a sequential pattern of fusion of the elements of the sacrum, more clearly observed in Sauropodomorpha. Our analyses suggest that primordial sacral vertebrae fuse earlier in the lineage (as seen in Norian sauropodomorphs). Intervertebral fusion is observed to encompass progressively more vertebral units as sauropodomorphs evolve, reaching up to five or more fully fused sacrals in Neosauropoda. Furthermore, the new specimen described here indicates that the fusion of sacral elements occurred early in the evolution of dinosaurs. Factors such as ontogeny and the increase in body size, combined with the incorporation of vertebrae to the sacrum may have a significant role in the process and in the variation of sacral fusion observed. [ABSTRACT FROM AUTHOR]

Upper Triassic (Carnian) strata from the Candelária Sequence of southern Brazil bear the oldest records of dinosaurs worldwide. In consequence, investigation of the specimens yielded by these fossiliferous units is crucial for a more comprehensive knowledge regarding the origin, early diversification and radiation of dinosaurs. Herein we reassess a dinosaur specimen from Brazil, informally known as the 'Big Saturnalia', a supposed large-sized sauropodomorph unearthed at the 'Cerro da Alemoa' locality in Santa Maria municipality, Rio Grande do Sul State. However, our phylogenetic analyses and comparisons of the known elements of this specimen resulted in herrerasaurid affinities instead. In fact, it is the largest specimen so far of a herrerasaurid from the Candelária Sequence. It preserves cranial and postcranial elements, with the former being unprecedented for dinosaurs from the Alemoa local fauna. The morphology of the specimen allows new insights into the anatomy, evolution and distribution of some character states among Herrerasauridae, including but not limited to the typical craniocaudally short caudal dorsal vertebrae. Moreover, the specimen adds to the dinosauromorph diversity in the Carnian units of southern Brazil and its large size provides further support for herrerasaurids as top-tier predators during the dawn of dinosaurs in south-western Pangaea. [ABSTRACT FROM AUTHOR]

Predatory dinosaurs were an important ecological component of terrestrial Mesozoic ecosystems. Though theropod dinosaurs carried this role during the Jurassic and Cretaceous Periods (and probably the post-Carnian portion of the Triassic), it is difficult to depict the Carnian scenario, due to the scarcity of fossils. Until now, knowledge on the earliest predatory dinosaurs mostly relies on herrerasaurids recorded in Carnian strata of South America. Phylogenetic investigations recovered the clade in different positions within Dinosauria, whereas fewer studies challenged its monophyly. Although herrerasaurid fossils are much better recorded in present-day Argentina than in Brazil, Argentinean strata so far yielded no fairly complete skeleton representing a single individual. Here, we describe Gnathovorax cabreirai, a new herrerasaurid based on an exquisite specimen found as part of a multitaxic association form southern Brazil. The type specimen comprises a complete and well-preserved articulated skeleton, preserved in close association (side by side) with rhynchosaur and cynodont remains. Given its superb state of preservation and completeness, the new specimen sheds light into poorly understood aspects of the herrerasaurid anatomy, including endocranial soft tissues. The specimen also reinforces the monophyletic status of the group, and provides clues on the ecomorphology of the early carnivorous dinosaurs. Indeed, an ecomorphological analysis employing dental traits indicates that herrerasaurids occupy a particular area in the morphospace of faunivorous dinosaurs, which partially overlaps the area occupied by post-Carnian theropods. This indicates that herrerasaurid dinosaurs preceded the ecological role that later would be occupied by large to medium-sized theropods. [ABSTRACT FROM AUTHOR]

A new sauropodomorph dinosaur from the Late Triassic Candelária Sequence (Santa Maria Formation), south Brazil, Bagualosaurus agudoensis gen. et sp. nov. helps to fill a morphological gap between the previously known Carnian members of the group and younger sauropodomorphs. In some aspects, the skull, lower jaw, and dental anatomy of the new taxon approaches that seen in Norian forms like Pantydraco caducus, Efraasia minor, and Plateosaurus engelhardti. On the contrary, the post-cranial skeleton is broadly reminiscent of coeval, early dinosaurs. Although not reaching the size of most Norian and younger sauropodomorphs, B. agudoensis is significantly larger than coeval forms. The new data thus suggest that modifications in skull anatomy, possibly related to more efficient herbivorous habits, appeared early in sauropodomorph evolution, along with a moderate increase in size, followed in post-Carnian times by further increase in size, accompanied by more radical changes in post-cranial anatomy. [ABSTRACT FROM AUTHOR]

The axial skeleton is proportionally underrepresented in the fossil record of early dinosaurs, when compared to other skeletal parts (e.g., pelvic girdle and hindlimb). For instance, the axis is poorly known in early dinosaurs, which precludes a better understanding of this important anatomical structure. Therefore, the present contribution fills an important gap with a description of the axis of a new early dinosaur (CAPPA/UFSM 0179). The specimen was collected at the Buriol outcrop, a Triassic fossiliferous locality from southern Brazil (Candelária Sequence, Santa Maria Supersequence) biostratigraphically correlated to Carnian units, placing this specimen among the oldest dinosaurs worldwide. Notable features include the combination of a neural spine that bears an almost straight dorsal margin along its length and presence of an epipophysis. This axis arrangement is unique among Carnian dinosaurs, representing a new morphotype, though a similar morphology is observed in some early theropods. Indeed, a phylogenetic analysis nested the specimen within Theropoda. However, this outcome is probably biased by the large amount of missing data in CAPPA/UFSM 0179 and also due to the limited sampling of the axis in early dinosaurs, particularly among sauropodomorphs. As the specimen comes from the site that includes Buriolestes schultzi (an early sauropodomorph), it is quite plausible that CAPPA/UFSM 0179 might be referable to that taxon. If so, the specimen improves the anatomical knowledge of Buriolestes schultzi, given its axis is yet unknown. An alternative possibility to be considered is that the specimen would belong to a dinosaur not yet known in the Candelária Sequence, which would increase its dinosaur diversity for the outcrop, improving the Triassic dinosaurian record from Southern Brazil. [ABSTRACT FROM AUTHOR]

The Vila Botucaraí site is located west of the municipality of Candelária, Rio Grande do Sul State, southern Brazil, and is particularly important because it represents the type locality of the species Exaeretodon riograndensis (Cynodontia, Traversodontidae), Charruodon tetracuspidatus (Cynodontia, Probainognathia) and Proterochampsa nodosa (Archosauriformes, Proterochampsidae). The site is correlated to the Hyperodapedon Assemblage Zone whose fossiliferous content allows to correlate it to the lower half of the Ischigualasto Formation (Ischigualasto-Villa Unión Basin), of late Carnian age, in Argentina. The aim of this study is to record the first remains of dinosaurs from this locality, found in 2001 during the Pró-Guaiba Project and stored in the Scientific Collection of the Paleontology Section of the Museu de Ciências Naturais, Secretaria Estadual do Meio Ambiente e Infraestrutura, Porto Alegre, RS. In addition to the taxa mentioned at the Vila Botucaraí site, the archosauromorph Hyperodapedon sp. was also preliminarily recorded. The Dinosauria specimen includes four dorsal vertebrae (MCN-PV 10347a, b, c, d). The general characteristics observed are: (i) absence of a ventral keel in the vertebral centra, shared with Guaibasaurus , Bagualosaurus , Pampadromaeus ; (ii) amphicoelic centra with concave ventral surface, shared with Bagualosaurus , Guaibasaurus , and most non-sauropod sauropodomorphs (exceptions are, for example, Riojasaurus ; also, this character does not appear in herrerasaurids); (iii) vertebral laminae connected to the diapophysis, and their arrangement results in different fossae, as in Bagualosaurus , Buriolestes , Guaibasaurus , and herrerasaurids; (iv) neural spine anteroposteriorly elongated and transversely narrow, as in Bagualosaurus , Pampadromaeus , Buriolestes , Macrocollum , differing from herrerasaurids and theropods. This set of characters is similar to that observed in basal sauropodomorphs, quite different from the neural spine with a spine table, such as the observed in herrerasaurids. Specimen MCN-PV 10347 is here considered a member of the Sauropodomorpha clade and tentatively identified as cf. Bagualosauria. The features of this specimen are shared among Carnian (e.g., Buriolestes schultzi , Bagualosaurus agudoensis) and Norian (e.g., Unaysaurus tolentinoi , Guaibasaurus candelariensis) sauropodomorphs. In addition to this, the new material expands the knowledge regarding the number of outcrops with the occurrence of sauropodomorphs for the Triassic in Brazil, as well as about the paleofauna of the Vila Botucaraí site, allowing us to infer its biostratigraphic correlation with one of the sub-divisions already proposed for the Hyperodapedon AZ, the Exaeretodon Subzone, interpreted as the top of this AZ. Despite the abundance of sauropodomorphs in Rio Grande do Sul, this record confirms the occurrence of this clade at the Hyperodapedon AZ in the Candelária region. • Taxonomic analysis of the dorsal vertebrae of a non-sauropod sauropodomorph. • The correlations of coeval extracts within the of Hyperodapedon AZ. • First record of a dinosaur cf. Bagualosauria outside the locality -type of Bagualosaurus agudoensis. [ABSTRACT FROM AUTHOR]