New rhadinosuchine proterochampsids from the late Middle-early Late Triassic of southern Brazil enhance the diversity of archosauriforms.

Proterochampsidae is a clade of non-archosaurian archosauriforms restricted to the Middle to the Late Triassic of the Ischigualasto-Villa Unión Basin of Argentina and the Santa Maria Supersequence of Brazil. A reappraisal of proterochampsid specimens from the Brazilian Dinodontosaurus Assemblage Zone (AZ) of the Pinheiros-Chiniquá Sequence (late Ladinian-early Carnian) is presented here. One of the specimens was preliminary assigned to Chanaresuchus sp., whose type species comes from the Massetognathus-Chanaresuchus AZ of the Chañares Formation of Argentina. However, our revision indicates that it differs from Chanaresuchus, being more closely related to the middle-late Carnian Rhadinosuchus gracilis. We therefore propose the new taxon, Pinheirochampsa rodriguesi, to reallocate this specimen. Additionally, we present a revision of other putative Chanaresuchus occurrences in Brazil, including the only known specimen described for the Santacruzodon AZ (Santa Cruz do Sul Sequence; early Carnian), also proposing it as a new taxon: Kuruxuchampsa dornellesi. Both new species are characterized, among other features, by transverse expansion of the anterior end of the rostrum, similar to the condition present in Rhadinosuchus, but absent in Chanaresuchus, Gualosuchus, Pseudochampsa, and non-rhadinosuchine proterochampsids. These two new species expand the growing knowledge of the non-archosaurian archosauriform diversity during the Middle-Late Triassic in South America and enhance faunal and chronological comparisons between approximately coeval geological units between Argentina and Brazil.

Osteology of the sauropodomorph dinosaur Jaklapallisaurus asymmetricus from the Late Triassic of central India.

The Gondwana formations exposed in the Pranhita-Godavari Valley of central India include Middle Triassic to Lower Jurassic continental deposits that provide essential information about the tetrapod assemblages of that time, documenting some of the oldest known dinosaurs and the first faunas numerically dominated by this group. The Upper Maleri Formation of the Pranhita-Godavari Basin preserves an early-middle Norian dinosaur assemblage that provides information about the early evolutionary history of this group in central-south Gondwana. This assemblage comprises sauropodomorph dinosaurs and an herrerasaurian, including two nominal species. Here, we describe in detail the anatomy of one of those early dinosaurs, the bagualosaurian sauropodomorph Jaklapallisaurus asymmetricus. The new anatomical information is used to investigate the position of the species in an updated quantitative phylogenetic analysis focused on early sauropodomorphs. The analysis recovered Jaklapallisaurus asymmetricus as a member of Unaysauridae, at the base of Plateosauria, together with Macrocollum itaquii and Unaysaurus tolentinoi from the early Norian of southern Brazil. This phylogenetic result indicates that the dispersal of early plateosaurian sauropodomorphs between the Southern Hemisphere and what nowadays is Europe would have occurred shortly after Ischigualastian times because of the extension of their ghost lineage. Thus, the presence of early plateosaurians in the early Norian of South America and India reduces a previously inferred diachrony between the biogeographic dispersals of theropods and sauropodomorphs during post-Ischigualastian times.

Old fossil findings in the Upper Triassic rocks of southern Brazil improve diversity of traversodontid cynodonts (Therapsida, Cynodontia).

In this contribution we describe a new genus and species of gomphodontosuchine cynodont from the Late Triassic Hyperodapedon Assemblage Zone (AZ) of the Santa Maria Supersequence of southern Brazil, based on material collected 20 years ago. The new taxon, Santagnathus mariensis gen. et sp. nov., is based on numerous cranial and postcranial remains, which altogether provide data on several parts of the skeleton. Santagnathus mariensis is closely related to Siriusgnathus niemeyerorum and Exaeretodon spp. and expands the knowledge about gomphodontosuchine cynodonts. Morphologically, the new species has a skull bauplan particularly similar to S. niemeyerorum and E. riograndensis, differing from them by a unique combination of traits such as three upper incisors, the absence of a descending process in the jugal, a more posterior position of the postorbital bar and a preorbital region larger than the temporal one. The new traversodontid was found associated with the rhynchosaur Hyperodapedon sp., corroborating the assignment of the cynodont fossils to the Hyperodapedon AZ. We also provide comments on the status of the Argentine traversodontid cynodont Proexaeretodon vincei, typically considered a junior synonym of Exaeretodon argentinus, and here accepted as a valid taxon.

Diphyodont tooth replacement of Brasilodon-A Late Triassic eucynodont that challenges the time of origin of mammals.

Two sets of teeth (diphyodonty) characterise extant mammals but not reptiles, as they generate many replacement sets (polyphyodonty). The transition in long-extinct species from many sets to only two has to date only been reported in Jurassic eucynodonts. Specimens of the Late Triassic brasilodontid eucynodont Brasilodon have provided anatomical and histological data from three lower jaws of different growth stages. These reveal ordered and timed replacement of deciduous by adult teeth. Therefore, this diphyodont dentition, as contemporary of the oldest known dinosaurs, shows that Brasilodon falls within a range of wide variations of typically mammalian, diphyodont dental patterns. Importantly, these three lower jaws represent distinct ontogenetic stages that reveal classic features for timed control of replacement, by the generation of only one replacement set of teeth. This data shows that the primary premolars reveal a temporal replacement pattern, importantly from directly below each tooth, by controlled regulation of tooth resorption and regeneration. The complexity of the adult prismatic enamel structure with a conspicuous intra-structural Schmelzmuster array suggests that, as in the case of extant mammals, this extinct species would have probably sustained higher metabolic rates than reptiles. Furthermore, in modern mammals, diphyodonty and prismatic enamel are inextricably linked, anatomically and physiologically, to a set of other traits including placentation, endothermy, fur, lactation and even parental care. Our analysis of the osteodental anatomy of Brasilodon pushes back the origin of diphyodonty and consequently, its related biological traits to the Norian (225.42 ± 0.37 myr), and around 25 myr after the End-Permian mass extinction event.

New specimens provide insights into the anatomy of the dinosauriform Lewisuchus admixtus Romer, 1972 from the upper Triassic levels of the Chañares Formation, NW Argentina.

Lewisuchus admixtus is an early dinosauriform described by Alfred Romer in 1972 on the basis of a single, incomplete skeleton, collected in lower Upper Triassic rocks of the renowned Chañares Formation, at the Los Chañares type-locality, La Rioja Province, north-western Argentina. Recent field explorations to the type-locality resulted in the discovery of two partial articulated skeletons, which provide significant novel information. The cranial bones, presacral series, femur, tibia, and proximal tarsals of the new specimens match the preserved overlapping anatomy of the holotype and previously referred specimens of L. admixtus, including the presence of unique combination of character states among dinosauriforms (anterior presacral column with additional ossification on the top of neural spines, dorsal neural spines fan-shaped, anterior surface of the astragalus with a dorsally curved groove, and an inflated area on the anterior portion of the medial surface of this bone). This new information improves our understanding of the anatomy and taxonomy of early dinosauriforms and reinforces the role of Argentinean beds on the study of the origin of dinosaurs.

New Specimen Sheds Light on the Anatomy and Taxonomy of the Early Late Triassic Dinosauriforms from the Chañares Formation, NW Argentina.

The lower Carnian levels of the Chañares Formation (Ischigualasto-Villa Unión Basin, La Rioja Province) have yielded some of the most informative dinosaur precursor species known so far. However, these species are based on partial skeletons that in several cases hamper the comparison between them because of the absence of overlapping bones. This has generated a contentious debate during the last 20 years about the synonymy between two of these species, Lewisuchus admixtus and Pseudolagosuchus major. Here, we describe a new dinosauriform partial skeleton (CRILAR-Pv 552) recently collected in the Chañares Formation that preserves previously unknown anatomical regions for the dinosaur precursors of this unit (e.g., premaxilla, inner ear, anterior zeugopodium) and allows comparisons with other dinosauriform specimens. CRILAR-Pv 552 is referred to Lewisuchus admixtus because it possesses a proportionally large skull, a laterally projected, shelf-like ridge on the jugal, and recurved, finely serrated middle-posterior maxillary and dentary teeth ankylosed to the bone, and the absence of a coracoid foramen. The new specimen preserves a dorsally bowed dentary with a lateroventral shelf that is identical to a dentary associated with the holotype of Lewisuchus admixtus. Additionally, the morphology of the new specimen is completely congruent with that of specimens of Pseudolagosuchus major, bolstering the hypothesis that the latter species is a subjective junior synonym of Lewisuchus admixtus. A preliminary phylogenetic analysis with updated scorings for Lewisuchus admixtus found this species at the base of Silesauridae. Anat Rec, 303:1393-1438, 2020. © 2019 American Association for Anatomy.

Skull anatomy and phylogenetic assessment of a large specimen of Ecteniniidae (Eucynodontia: Probainognathia) from the Upper Triassic of southern Brazil.

Ecteniniidae comprises an endemic radiation of carnivore probainognathian cynodonts from the Late Triassic of South America. Three taxa have been included in this clade: Ecteninion lunensis Martínez et al., 1996 and Diegocanis elegans Martínez et al., 2013 from Argentina, and Trucidocynodon riograndensis Oliveira et al., 2010 from Brazil. Herein, a new specimen (skull and mandible) assigned to T. riograndensis from the Carnian of the Candelária Sequence (Southern Brazil) is described. A phylogenetic analysis recovered the new specimen as the sister taxon of the holotype of T. riograndensis, and both in a trichotomy with E. lunensis and D. elegans, all supporting the monophyly of Ecteniniidae. The new specimen of T. riograndensis is almost 20% larger than its holotype. Therefore, it represents one of the largest specimens of a carnivorous probainognathian from the Late Triassic known to date and contributes to knowledge of size variation in ecteniniids.

Ingroup relationships of Lagerpetidae (Avemetatarsalia: Dinosauromorpha): a further phylogenetic investigation on the understanding of dinosaur relatives.

Despite representing a key-taxon in dinosauromorph phylogeny, Lagerpertidae is one of the most obscure and enigmatic branches from the stem that leads to the dinosaurs. Recent new findings have greatly increased our knowledge about lagerpetids, but no phylogenetic analysis has so far included all known members of this group. Here, we present the most inclusive phylogenetic study so far conducted for Lagerpetidae. Phylogenetic analyses were performed based on three independent data matrixes. In two of them, Lagerpeton chanarensis Romer, 1971 is the sister taxon to all other known Lagerpetidae, whereas Ixalerpeton polesinensis Cabreira et al., 2016 is in a sister group relationship with a clade that includes PVSJ 883 and Dromomeron. Conversely, the other analysis supports an alternative topology, where I. polesinensis is the sister taxon to either L. chanarensis or all other Lagerpetidae. Although coeval and geographically close, I. polesinensis and PVSJ 883 do not form a clade exclusive of other lagerpetids. As previously suggested D. gigas Martínez, Apaldetti, Correa Abelín, 2016 is the sister taxon of D. romeri Irmis et al., 2007. The phylogenetic analyses also indicate that the earliest lagerpetids are restricted to southwestern Pangea, whereas later forms spread across the entire western portion of the supercontinent. Finally, quantification of the codified characters of our analysis reveals that Lagerpetidae is one of the poorest known among the Triassic dinosauromorph groups in terms of their anatomy, so that new discoveries of more complete specimens are awaited to establish a more robust phylogeny.

New information on Riograndia guaibensis Bonaparte, Ferigolo & Ribeiro, 2001 (Eucynodontia, Tritheledontidae) from the Late Triassic of southern Brazil: anatomical and biostratigraphic implications

The tritheledontid Riograndia guaibensis was the first cynodont described for the "Caturrita Formation" fauna from the Late Triassic of southern Brazil (Santa Maria 2 Sequence). The type materials did not preserve anatomical information regarding braincase, occiput, basicranium, zygomatic arch, postdentary bones and craniomandibular joint. Here new materials are described and supply the missing information. Riograndia shows a suite of important anatomical features quite derived among the non-mammaliaform eucynodonts, such as the partial closure of the medial orbital wall and braincase, extensive secondary osseous palate, wide primary palate, basicranium with jugular foramen separated from the periphery of fenestra rotunda, narrow zygomatic arch and much reduced postdentary bones. Many of these features constitute synapomorphies shared only with the other members of mammaliamorpha. Thus, the almost complete cranial, mandibular and dental information from the new fossils of Riograndia can bring a significant improve in the understanding of the anatomy and phylogenetic relationships of the tritheledontids and help to elucidate the transformational steps involved in the cynodont-mammal transition. Additionally, Riograndia is a key taxon in refining the "Caturrita Formation" biostratigraphy, enabling the connection of several fossiliferous outcrops that have a rich tetrapod fauna that can be correlated with other Triassic faunas from Gondwana and Laurasia.

O triteledontídeo Riograndia guiabensis foi o primeiro cinodonte descrito para a fauna da "Formação Caturrita" do Triássico Superior do sul do Brasil (Sequência Santa Maria 2). Os materiais da série-tipo não forneceram informações anatômicas relativas à caixa craniana, ociput, basicrânio, arco zigomático, ossos pós-dentários e articulação crânio-mandibular. Neste artigo são descritos novos materiais que suprem as informações anatômicas não contempladas anteriormente. Riograndia apresenta um conjunto de importantes aspectos anatômicos derivados dentre os eucinodontes não-mammaliaformes, tais como fechamento parcial da parede orbital medial e da caixa craniana, extenso palato ósseo secundário, palato primário alargado, basicrânio com separação do forame jugular e da fenestra rotunda, arco zigomático estreito e ossos pós-dentários extremamente reduzidos. Muitas destas feições constituem sinapomorfias compartilhadas somente com os demais membros do clado Mammaliamorpha. Assim, as praticamente completas informações crânio-mandibulares e dentárias de Riograndia trazem uma significante contribuição ao conhecimento da anatomia dos triteledontídeos e suas relações filogenéticas e auxiliam na elucidação sobre os passos transformacionais envolvidos na transição cinodonte-mamífero. Adicionalmente, Riograndia figura como um táxon-chave no refinamento bioestratigráfico da "Formação Caturrita", através da integração de vários afloramentos fossilíferos os quais apresentam uma rica fauna de tetrápodes que pode ser correlacionada com outras faunas triássicas do Gondwana e da Laurásia.