The Early Radiation of Sauropodomorphs in the Carnian (Late Triassic) of South America

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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.

Section: Discussionmentioning

confidence: 99%

The elongated neck of sauropodomorph dinosaurs evolved gradually

Damke

Bem

Doering

et al. 2022

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“…CAPPA/UFSM 0244, and some specimens of E. lunensis and S. tupiniquim fall above the confidence interval of the RI analysis for non-bagualosaurian F I G U R E 1 9 Phylogenetic analyses by dataset of Langer et al (2022). Strict consensus tree of the "specimen-based" analysis (a), strict consensus tree of the "combined" analysis (b).…”

Section: Femoral Circumference Analysis Of Sauropodomorphamentioning

confidence: 97%

“…An additional set of analyses was conducted scoring CAPPA/UFSM 0244 in the dataset of Langer et al (2022). The final dataset comprises 25 OTUs and 771 morphological characters.…”

Section: Phylogenetic Analysismentioning

confidence: 99%

“…The final dataset comprises 25 OTUs and 771 morphological characters. The multistate characters were ordered according to Langer et al (2022). All characters received the same weight.…”

Section: Phylogenetic Analysismentioning

confidence: 99%

“…The increasing number of described early sauropodomorph specimens in recent years has expanded the understanding of the early evolution of the group as a whole, but also brought some uncertainty regarding its alpha taxonomy (Langer et al, 2019, 2022; Müller & Garcia, 2020a). A detailed taxonomic review of early sauropodomorphs supports the hypothesis that these taxa are anatomically distinct from one another (Langer et al, 2022), but phylogenetic hypotheses vary among authors (Baron et al, 2017; Cabreira et al, 2016; Langer & Benton, 2006; Marsola et al, 2019; Müller, 2020; Novas et al, 2011; Pacheco et al, 2019). The description of new specimens is mandatory in order to fill anatomical gaps and produce more reliable phylogenetic inferences.…”

Section: Introductionmentioning

confidence: 99%

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An unusually robust specimen attributed to Buriolestes schultzi (Dinosauria: Sauropodomorpha) from the Late Triassic of southern Brazil

Moro,

Damke,

Müller

et al. 2023

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.

On a skeletally immature individual of Unaysaurus tolentinoi (Dinosauria: Sauropodomorpha) from the upper Triassic of southern Brazil

Müller,

Garcia,

Bem

et al. 2023

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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.