Lísie Vitória Soares Damke

Nowadays, Lepidosauria is a diverse group represented by squamates and the rhynchocephalian tuatara. However, their origins date back to the end of the Permian Period, when the stem lineages Lepidosauromorpha and Archosauromorpha diverged. Within the lepidosauromorph stem lineage, a few species have been described with unstable phylogenetic placements. In Brazilian strata, the only representative of this lineage is the rare species Cargninia enigmatica . The taxon was found in Norian beds (upper portion of the Candelária Sequence) and is known from the posterior end of a dentary and a tentatively referred partial maxilla. Here, we describe a new specimen (CAPPA/UFSM 0519) referred to Cargninia enigmatica , consisting of a partial dentary recovered from the type locality. The specimen provides new anatomical information on the anterior portion of the dentary. In addition, for the first time, the phylogenetic placement of Cargninia enigmatica was investigated in a computational framework, and the results are congruent with previous suggestions that it represents a non‐lepidosaur lepidosauromorph. Finally, the new specimen reveals details of the anatomy of the mandibular ramus of the trigeminal nerve, demonstrating that it shares a similar condition with its extant relatives.

There is a growing consensus that pterosaurs and the flightless Lagerpetidae are closely related. This relationship is supported by apomorphies throughout the skeleton, including endocranial character states such as a well‐developed floccular fossa and a tall anterior semicircular canal. Our knowledge of lagerpetid anatomy has been improved by recent discoveries. Among them, the Brazilian record plays a significant role, having produced two described species, Ixalerpeton polesinensis and Venetoraptor gassenae , and several more fragmentary specimens. In this study, we used an x‐ray micro‐computed tomographic scan to describe the endocranial anatomy of the holotype of Venetoraptor gassenae . The endocranial anatomy of Venetoraptor gassenae is similar in shape to that of other described lagerpetids, and we reach the following conclusions: (1) in pterosaurs, the metotic foramen exits posteriorly, whereas in lagerpetids and dinosauromorphs it exits through the lateral wall of the braincase; and (2) Venetoraptor gassenae is unique among lagerpetids in having only one exit for cranial nerve XII, expanding its differential diagnosis. These differences highlight that the braincase anatomy of lagerpetids is aligned with the anatomical disparity observed in the group. Finally, we discuss why future studies should focus on comprehending patterns of braincase pneumaticity in avemetatarsalians.

Introdução. A variação intraespecífica refere-se às diferenças morfológicas ou comportamentais observadas entre indivíduos de uma mesma espécie, sendo determinadas por diversos fatores, como mudanças ontogenéticas; dimorfismo sexual; variação individual e condições patológicas devido a doenças ou lesões. Objetivo. O presente estudo apresenta, de forma breve, os principais fatores que geram a variação intraespecífica nos primeiros dinossauros, bem como os meios de analisá-la (e.g., investigação da morfologia externa, morfometria, histologia). Metodologia. A investigação envolveu uma revisão sistemática da literatura especializada. Resultados. No campo da Paleontologia, estudos indicam que a falha em reconhecer esse tipo de variação intraespecífica pode ser um fator responsável pela instabilidade nas inferências filogenéticas relacionadas aos dinossauros. Conclusão. Ressalta-se que o detalhamento da variação intraespecífica em dinossauros necessita de um número adequado de indivíduos com certa variabilidade no seu tamanho, forma e deposição óssea, mas há um cenário promissor para esse campo de estudos, uma vez que diferentes grupos de pesquisa têm dedicado esforços tanto à descoberta de novos materiais.

Dinosaurs arose in the Late Triassic and diversified during the subsequent periods of the Mesozoic Era. The oldest unequivocal dinosaurs come from Carnian deposits of Brazil, Argentina, India, and Zimbabwe, with sauropodomorphs representing the bulk of this record. Saturnalia tupiniquim was described from Brazilian strata in 1999 as the first Carnian member of that group. Although several new species and specimens of coeval sauropodomorphs have been described in recent years, no new material has been formally assigned to that species. In this contribution, we describe an association of at least three partially preserved individuals of S. tupiniquim (UFSM 11660), which was excavated from the S. tupiniquim type-locality (Late Triassic of the Santa Maria Formation) and preserves cranial and postcranial elements, including the first rostrum known for the species. Assigned to S. tupiniquim according to several lines of evidence, the new specimen has a proportionally short rostrum, compared to that of coeval sauropodomorphs, providing evidence for a reduced skull in S. tupiniquim. In addition, we investigated the intraspecific variation in S. tupiniquim, highlighting the need to understand the morphological limits of such variations among the earliest dinosaurs, in order to properly explore their alpha diversity.

The phylogenetic affinities of early dinosaurs are a controversial topic. There are disputing scenarios aiming to explain the evolutionary tree of these reptiles. A number of factors play a role on this issue. High levels of intraspecific variation experienced by the earliest forms are pointed by distinct authors as one of the main sources of phylogenetic biases. In the present study, we performed experimental analyses incorporating skeletally immature individuals as distinct operational taxonomic units in order to investigate the effect of ontogeny on the phylogeny and morphospace of early Late Triassic sauropodomorphs. The results support an “artificial” grouping of skeletally immature individuals of early dinosaurs in the phylogenetic trees, which is controlled by ontogenetic development. Such results are interpreted as the effect of ontogenetic control on the states of certain morphological characters, producing false synapomorphies. In addition, the morphological disparity analysis indicated a significant difference between the skeletally immature and mature individuals, corroborating previous assumptions. At this point, we suggest caution during the scoring process of early dinosaurs. Some approaches that avoid ontogenetically sensitive characters revealed a putative solution. Nevertheless, additional specimens and alternative tools are mandatory in order to properly deal with this issue.

Buriolestes schultzi is a small sauropodomorph dinosaur from Carnian beds (ca., 233 Ma) of southern Brazil. It is one of the earliest members of that lineage and is a key taxon to investigate the initial evolution of Sauropodomorpha. Here, we attribute a new specimen to B. schultzi from Late Triassic of southern Brazil, which represents the first occurrence of the taxon outside the type locality. The new specimen comprises a disarticulated and partial skeleton, including cranial and postcranial elements. It is tentatively regarded as an additional specimen of B. schultzi according to a unique combination of traits (including autapomorphies). Conversely, the new specimen is stouter than the other specimens of B. schultzi, as shown by femoral Robustness Index. Based on femoral circumference, the estimated body mass of the new specimen is approximately 15 kg, which is far higher than the previous estimations for other specimens of B. schultzi (i.e., approximately 7 kg). In fact, the new specimen and some specimens of Eoraptor lunensis and Saturnalia tupiniquim were found to be significantly stouter than coeval sauropodomorphs. Therefore, instead of all being constructed as gracile, the earliest sauropodomorphs experienced an unappreciated intraspecific variation in robustness. This is interesting because more precise data on species body mass are crucial in order to better understand the complex terrestrial ecosystems in which dinosaurs originated.

The lineage of sauropodomorph dinosaurs raised some of the most impressive animals that ever walked on Earth. However, the massive titans of the Mesozoic Era originated from far smaller dinosaurs. The Triassic beds from Brazil yielded the earliest part of this evolutionary history. Despite the diverse fossil record of early sauropodomorphs, juvenile specimens, as well as certain species are poorly sampled. This is the case for Unaysaurus tolentinoi, an unaysaurid sauropodomorph from Caturrita Formation (ca. 225 Ma; early Norian, Late Triassic). The holotype and only specimen of U. tolentinoi was excavated from the Água Negra Locality (São Martinho da Serra, Rio Grande do Sul, Brazil) in 1998. More than two decades later, no other fossil vertebrates have been reported from the same fossiliferous site. Here we describe a skeletally immature specimen which was found in association with the holotype of U. tolentinoi. The specimen was discovered after a first‐hand examination of the holotype and comprises some isolated vertebrae and elements from the posterior autopodium. According to linear regressions, its metatarsal I is approximately 41.7 mm in length, compared to approximately 75.9 mm in the holotype. The repeated elements and reduced size indicates that it does not belong to the elements originally used to erect U. tolentinoi. Rather, the specimen is assigned to U. tolentinoi by topotypy and shared morphology. In addition to the reduced size, distinct lines of evidence (e.g., neurocentral sutures; bone texture) support its assignment to a skeletally immature individual. In sum, the new material expands the record of U. tolentinoi, and represents an additional juvenile dinosaur from the Caturrita Formation.

Discoveries from South America have increased our knowledge on the early evolutionary history of sauropodomorph dinosaurs. The dietary shift from faunivorous to herbivorous creatures and the increasing body size are both widely documented in the fossil record. Conversely, the initial evolution of the elongated neck is poorly known. It is one of the most diagnostic features of Sauropodomorpha. There is a gap between the record of short‐necked sauropodomorphs from Carnian (±233 Ma) and long‐necked forms from early Norian (±225 Ma). As a consequence, it is unknown if the cervical vertebrae became long gradually or abruptly. In the present study, we present a new specimen excavated from strata that belong to this time interval (±228 Ma). CAPPA/UFSM 0352 comprises a series of five cervical vertebrae unearthed from the Late Triassic of Southern Brazil. The vertebrae are proportionately longer than that of older forms and proportionately shorter than that of younger ones. Therefore, our results demonstrate that the elongation of the neck of sauropodomorphs is an example of gradual evolutionary process. Except by its elongated shape, the general anatomy of the cervical elements resembles that of the earliest forms (i.e., have a conservative anatomy). Combined with previous data, it is possible to conclude that the shape of the skull and teeth, as well as the neck proportions, were the first structures to clearly differ derived sauropodomorphs from early diverging forms. Finally, some of the recovered phylogenetic scenarios favor the origins of the elongated neck in the clade Bagualosauria.