Cesar Leandro Schultz

The Petrified Forest of the Mata Sequence (topmost of Santa Maria Supersequence) in the southernmost Paraná Basin in Brazil is an important paleobotanical site in South America and part of Brazilian scientific and cultural heritage. The new taxon, Prototaxoxylon sanpedrense, is characterized by steep and wide tertiary helical thickenings in tracheid walls, uniseriate to partially biseriate, and rarely biseriate, alternate, araucarian-type intertracheid radial pitting, two cupressoid pits showing exclusively horizontal rows in crossfields, and smooth ray parenchyma cell walls. This anatomical combination expands the record of gymnosperms near the Triassic-Jurassic boundary at southernmost Brazilian Gondwana, which has thus far been represented by Araucariaceae and Ginkgoales in different outcrops, as well as by some genera whose botanical affinities remain enigmatic. The wood growth pattern identified in Prototaxoxylon sanpedrense sp. nov., characterized by irregular growth cycles and frequent false rings, is consistent with irregular, short-term climatic disturbances, which are mainly attributed to temporary water restrictions during the development of the Norian-Rhaetian Coniferous Flora. This point to an arid/subtropial climate and contrasts with the warm/humid interval delineated for the Carnian Pluvial Episode (CPE), which is characterized by the occurrence of a Dicroidum Flora in the southernmost Paraná Basin.

The tooth enamel is the most mineralized tissue of vertebrates. This is one of the factors that make teeth very common in the fossil record. Most of the carnivorous archosaurs throughout the Mesozoic Era possessed ziphodont teeth, whose denticles are round bumps that are always located on carine, and with a symmetrical or convex-asymmetric border. In some taxa, they are strongly recurved apically. This study presents a paleometric approach to isolated archosaur teeth, integrating macro, micro and scanning electron microscopy (SEM) measurements of denticles from seven ziphodont teeth of archosaurs collected from the Santa Maria Supersequence (SMS) Triassic, Paraná Basin, Brazil. The quantitative data obtained allowed the identification of similarities and differences among the studied specimens, which were compared with published datasets, likely reflecting taxonomic diversity within the assemblage. Despite their superficial similarity, certain dental features suggest a greater diversity of diets and feeding strategies among the SMS archosauriforms. Moreover, this paper provides the first enamel thickness measurements from ziphodont teeth of the SMS, opening new perspectives for the understanding of enamel microstructure and its implications for archosaur taxonomy and functional morphology. Keywords: biomechanic, denticles, Gondwana, SEM, Paraná Basin.

Introdução. Dinocephalia é um clado amplamente distribuído na Pangeia, com ocorrência restrita ao Guadalupiano. O grupo compreende formas de médio a grande porte e é dividido em Tapinocephalia, contendo quatro famílias, e Anteosauria, possuindo apenas a família Anteosauridae. No Brasil, Dinocephalia apresenta um registro escasso, diferente do visto na África do Sul e Rússia. Materiais fragmentários são mais comuns, evidenciando uma diversidade ainda a ser descoberta. Objetivo e Metodologia. Revisar a diversidade taxonômica de Dinocephalia no Brasil, abordando a paleobiologia do grupo baseado na literatura publicada. Resultados. Tapinocephalia carece de uma revisão taxonômica, com os trabalhos mais recentes focando em aspectos paleobiológicos. Anteosauria passou por uma ampla revisão taxonômica na última década, com os trabalhos mais recentes focando também em questões paleobiológicas. Conclusão. Syodontinae é excluído de abordagens paleobiológicas diretas, restringindo-se a comparações com Anteosaurinae, enquanto o conhecimento paleobiológico acerca de Tapinocephalia está em crescimento.

Prestosuchus chiniquensis is an iconic non‐crocodylomorph loricatan from the Brazilian Triassic beds and the best‐known taxon, represented by several specimens. The completeness and preservation of its skeleton make it a valuable taxon for paleobiological studies. We explore the microstructure of bone tissues of appendicular elements and ribs of three specimens of Prestosuchus to access a variety of aspects of its paleobiology, such as histovariability, ontogeny, and growth patterns. Integrating our data and other osteohistologically studied P. chiniquensis specimens, we proposed for the first time an ontogenetic model for non‐crocodylomorph loricatans. The model encompasses six distinct age classes (I–VI) that allow us to infer the growth patterns of P. chiniquensis and possibly expand to other phylogenetically close taxa. During early ontogeny (age classes I–II), sustained fast growth was maintained by a fibrolamellar complex. In mid ontogeny (age classes III–IV), highly vascularized parallel‐fibered bone predominates, suggesting intermediary growth rates. A change for a poorly vascularized parallel‐fibered/lamellar bone would mark the attainment of sexual (age classes IV–V) and skeletal maturity, comprising the age class VI. An external fundamental system (EFS) present in the outermost cortex is the main histological feature that characterize the age class VI. Major histovariability features are present between appendicular bones and ribs of skeletally immature individuals. The most prominent of them is the presence of fibrolamellar complex and highly vascularized parallel‐fibered bone in appendicular bones and poorly vascularized parallel‐fibered bone in ribs. In advanced ontogenetic stages, the histovariability between appendicular bones and ribs tends to be minor. Our data also support previous hypothesis of the presence of one new taxon among the specimens assigned to P. chiniquensis, increasing the diversity of non‐crocodylomorph loricatans. The new taxon, represented by the specimen UFRGS‐PV‐0152‐T, awaits a formal anatomical description. Our study advances the preliminary understand of the ontogeny and growth patterns of non‐crocodylomorphs loricatans and Pseudosuchia as a whole.

Osteohistological evidence is widely used to infer paleobiological traits of fossil vertebrates, such as ontogeny and growth rates. Mesosaurs, an enigmatic group of aquatic reptiles from the early Permian, are the most well‐known Paleozoic amniotes from Africa and South America. Their fossils are abundant in South America, ranging from the central‐west region of Brazil to the southernmost areas, as well as parts of Paraguay and Uruguay. In this contribution, we examined the bone microstructure of Mesosaurus tenuidens by analyzing thin sections of axial and appendicular elements of several specimens collected from various Brazilian sites. The microstructure of the bones showed minimal histological variability among elements, predominantly composed of parallel‐fibered tissues, indicating slow growth rhythm, along with increased bone density attributed to pachyosteosclerosis. The cortical area consists of poorly vascularized parallel‐fibered bone tissue, which was interrupted by multiple cyclical growth marks, some of them being supernumerary, suggesting a strong influence of seasonality. Moreover, the organization of growth marks suggests distinct life history trajectories among individuals collected from different outcrops, reflecting environmental heterogeneity throughout the basin. Internally, the endosteal domain exhibits greater vascularization compared to the cortices and frequently contained calcified cartilage. In the ontogenetic series, there was a progressive filling of the medullary region from small to large individuals. The presence of the External Fundamental System (a proxy indicating somatic maturity) was observed in femora and ribs, suggesting that determinate growth was already occurring in Permian mesosaurs and may not be an exclusive specialization of crown amniotes.

Rhynchosauria is a group of extinct, exclusively Triassic, terrestrial, and herbivorous archosauromorphs, characterized by a peculiar maxillary‐mandibular apparatus. They reached global distribution during the Carnian, with the Hyperodapedontinae clade. The rhynchosaurian record from South America is included in the Ladinian‐?earliest Carnian Dinodontosaurus Assemblage Zone (Pinheiros‐Chiniquá Sequence, Brazil) and Tarjadia Assemblage Zone (Chañares Formation, Argentina), and for strictly Carnian Hyperodapedon Assemblage Zone (Lower Candelária Sequence, Brazil) and Ischigualasto Formation (Argentina). Here, we present the first record of Hyperodapedontinae from the Brazilian Early Carnian Santacruzodon Assemblage Zone (Santa Cruz Sequence). The most diagnostic elements belong to a nearly complete left pes, which presents a combination of hyperodapedontine traits. The presence of a second individual of cf. Hyperodapedontinae is based on a fragmentary, isolated left metatarsal IV. An isolated fragment of premaxilla could belong to the second specimen (based on preservation mode) or to a third individual. This new report fills a gap within the South American rhynchosaurian distribution, strengthening biostratigraphic correlation with other regions from Gondwana (i.e., Madagascar), where similar and coeval faunas are known. The inclusion of these specimens in a phylogenetic dataset resulted in low resolution results, due to missing data because postcranial characters for rhynchosaurs are still poorly explored.

The Linha São Luiz Geosite is one of the most remarkable outcrops from the central region of Rio Grande do Sul state, southern Brazil. With more than 20 meters of vertical exposure, the locality preserves records of distinct sedimentary episodes, and one of the richest fossil assemblages known in southern Brazil. After a quarter of a century from the first expeditions to the site, the Linha São Luiz still yields new discoveries, registering exquisitely preserved fossils from micro and macrovertebrates, invertebrates, and plants, as well as trace fossils generated by these groups. In this contribution, we assembled representatives from distinct fields of paleontological study to provide a summary of the fossil assemblage from this site. We also briefly discuss the history of research and report geoconservation strategies, which are being implemented at the locality, in order to preserve this important window to the Brazilian Mesozoic.

The acquisition of the load-bearing dentary–squamosal jaw joint was a key step in mammalian evolution^1–5. Although this innovation has received decades of study, questions remain over when and how frequently a mammalian-like skull–jaw contact evolved, hindered by a paucity of three-dimensional data spanning the non-mammaliaform cynodont–mammaliaform transition. New discoveries of derived non-mammaliaform probainognathian cynodonts from South America have much to offer to this discussion. Here, to address this issue, we used micro-computed-tomography scanning to reconstruct the jaw joint anatomy of three key probainognathian cynodonts: Brasilodon quadrangularis, the sister taxon to Mammaliaformes^6–8, the tritheledontid-related Riograndia guaibensis⁹ and the tritylodontid Oligokyphus major. We find homoplastic evolution in the jaw joint in the approach to mammaliaforms, with ictidosaurs (Riograndia plus tritheledontids) independently evolving a dentary–squamosal contact approximately 17 million years before this character first appears in mammaliaforms of the Late Triassic period^10–12. Brasilodon, contrary to previous descriptions^6–8, lacks an incipient dentary condyle and squamosal glenoid and the jaws articulate solely using a plesiomorphic quadrate–articular joint. We postulate that the jaw joint underwent marked evolutionary changes in probainognathian cynodonts. Some probainognathian clades independently acquired ‘double’ craniomandibular contacts, with mammaliaforms attaining a fully independent dentary–squamosal articulation with a conspicuous dentary condyle and squamosal glenoid in the Late Triassic. The dentary–squamosal contact, which is traditionally considered to be a typical mammalian feature, therefore evolved more than once and is more evolutionary labile than previously considered.

Investigating the evolutionary trajectory of synapsid sensory and cephalic systems is pivotal for understanding the emergence and diversification of mammals. Recent studies using CT‐scanning to analyze the rostral foramina and maxillary canals morphology in fossilized specimens of probainognathian cynodonts have contributed to clarifying the homology and paleobiological interpretations of these structures. In the present work, μCT‐scannings of three specimens of Riograndia guaibensis, an early Norian cynodont from southern Brazil, were analyzed and revealed an incomplete separation between the lacrimal and maxillary canals, with points of contact via non‐ossified areas. While the maxillary canal exhibits a consistent morphological pattern with other Prozostrodontia, featuring three main branches along the lateral region of the snout, the rostral alveolar canal in Riograndia displays variability in the number of extra branches terminating in foramina on the lateral surface of the maxilla, showing differences among individuals and within the same skull. Additionally, pneumatization is observed in the anterior region of the skull, resembling similar structures found in reptiles and mammals. Through this pneumatization, certain branches originating from the maxillary canal extend to the canine alveolus. Further investigation is warranted to elucidate the functionality of this structure and its occurrence in other cynodont groups.