Non-technical Summary

Dinosaurs are among the most iconic animals to have ever lived, yet their origins remain one of the most challenging chapters in the history of life on Earth. Before becoming the dominant land animals of the Jurassic and Cretaceous Periods, dinosaur precursors evolved during the Triassic Period, approximately 240 million years ago, in ecosystems largely dominated by other reptile groups and distant mammal relatives. South America, especially Argentina and Brazil, plays a particularly important role in understanding the emergence of dinosaurs. Fossil sites in the state of Rio Grande do Sul of southern Brazil preserve an exceptional record of dinosaur precursors and early dinosaurs. This fossil record documents a nearly continuous presence of dinosauromorphs over more than 10 million years, including forms closely related to dinosaurs as well as some of the earliest true dinosaurs. These fossils capture key evolutionary transitions, such as the rise of the first predatory dinosaurs and the transformation of small, meat-eating ancestors into larger, plant-eating forms that later gave rise to giant long-necked dinosaurs. Many of the fossils from southern Brazil are exceptionally well preserved, including complete skulls and nearly entire skeletons. This level of preservation allows us to reconstruct anatomy, lifestyles, and ecological roles in remarkable detail. Although some questions remain regarding exact ages and evolutionary relationships, the Triassic fossils of southern Brazil provide one of the clearest windows into how dinosaurs originated and began to diversify. Ongoing discoveries and improved geological studies are expected to further clarify when, how, and under what conditions dinosaurs first evolved.

Geological setting

The Triassic record of dinosauromorphs in Brazil occurs in the Santa Maria Supersequence (Fig. 3, 4; Table 1), which includes the Santa Maria and the Caturrita Formations (Zerfass et al., Reference Zerfass, Lavina, Schultz, Garcia, Faccini and Chemale2003). The oldest records came from the Pinheiros-Chiniquá Sequence (sensu Horn et al., Reference Horn, Melo, Schultz, Philipp, Kloss and Goldberg2014), which includes silesaurids (Pretto et al., Reference Pretto, Müller, Moro, Garcia, Neto and Da Rosa2022; Müller, Reference Müller2025) and indeterminate dinosauromorphs (Müller and Garcia, Reference Müller and Garcia2022). These records are Ladinian in age (Philipp et al., Reference Philipp, Faccini, Schultz, Zvirtes and Bruckmann2023) and represent the oldest dinosauromorphs from South America. Fossils of the Pinheiros-Chiniquá Sequence are associated with the Dinodontosaurus Assemblage Zone (AZ), which is dominated by large dicynodonts, traversodontid cynodonts, and giant loricatan pseudosuchians (Schultz et al., Reference Schultz, Martinelli, Soares, Pinheiro, Kerber, Horn, Pretto, Müller and Melo2020). The overlying Santa Cruz Sequence is early Carnian in age (Philipp et al., Reference Philipp, Schultz, Kloss, Horn, Soares and Basei2018) and has provided a scarce record of dinosauromorphs, which is limited to one silesaurid (Paes-Neto et al., Reference Paes‐Neto, Lacerda, Ezcurra, Raugust, Trotteyn, Soares, Schultz, Pretto, Francischini and Martinelli2024). The fossil record of this sequence is dominated by traversodontid cynodonts associated with the Santacruzodon AZ (Schultz et al., Reference Schultz, Martinelli, Soares, Pinheiro, Kerber, Horn, Pretto, Müller and Melo2020). The lower portion of the Candelária Sequence has yielded the oldest unequivocal dinosaurs from Brazil, which are mid to Late Carnian in age (Langer et al., Reference Langer, Ramezani and Da-Rosa2018). This Sequence includes silesaurids, herrerasaurians, sauropodomorphs, and debated records of theropods (Colbert, Reference Colbert1970; Langer et al., Reference Langer, Abdala, Richter and Benton1999; Cabreira et al., Reference Cabreira, Schultz, Bittencourt, Soares, Fortier, Silva and Langer2011, Reference Cabreira, Kellner, Dias-da-Silva, Roberto-da-Silva and Bronzati2016; Pacheco et al., Reference Pacheco, Müller, Langer, Pretto, Kerber and da Silva2019; Pretto et al., Reference Pretto, Langer and Schultz2019; Müller and Garcia, Reference Müller and Garcia2023). The fossil record from this unit belongs to the Hyperodapedon AZ, which is dominated by rhynchosaurs, with some levels dominated by traversodontid cynodonts (Schultz et al., Reference Schultz, Martinelli, Soares, Pinheiro, Kerber, Horn, Pretto, Müller and Melo2020). Just over the typical layers of the Hyperodapedon AZ, there is a peculiar fauna dominated by the traversodontid cynodont Siriusgnathus niemeyerorum Pavanatto et al., Reference Pavanatto, Pretto, Kerber, Müller, Da-Rosa and Dias-da-Silva2018 (Miron et al., Reference Miron, Pavanatto, Pretto, Müller, Dias-da-Silva and Kerber2020; Roese-Miron et al., Reference Roese-Miron, Abdala, Pretto, Müller, Michelotti da Costa, Sánchez-Villagra and Kerber2025). This fauna, which is attributed to a transitional moment between the Carnian and Norian (Doering et al., Reference Doering, Ezcurra, Schiefelbein, Garcia and Müller2024), has yielded records of silesaurids, putative sauropodomorphs, and theropod dinosaurs (Müller, Reference Müller2021; Doering et al., Reference Doering, Ezcurra, Schiefelbein, Garcia and Müller2024). Finally, the upper portion of the Candelária Sequence is early Norian in age (Langer et al., Reference Langer, Ramezani and Da-Rosa2018) and its fossiliferous content is associated with the Riograndia AZ (Schultz et al., Reference Schultz, Martinelli, Soares, Pinheiro, Kerber, Horn, Pretto, Müller and Melo2020). The record of dinosauromorphs from these layers includes silesaurids, sauropodomorphs, and putative theropod dinosaurs (Bonaparte et al., Reference Bonaparte1999; Leal et al., Reference Leal, Azevedo, Kellner and Da Rosa2004; Ferigolo and Langer, Reference Ferigolo and Langer2007; Pinheiro, Reference Pinheiro2016; Müller et al., Reference Müller, Langer and Dias-da-Silva2018b). The fossil content of this AZ is dominated by small cynodonts and rhynchocephalians (Schultz et al., Reference Schultz, Martinelli, Soares, Pinheiro, Kerber, Horn, Pretto, Müller and Melo2020). Most of these AZs are biostratigraphically correlated with deposits from Argentina (Ezcurra et al., Reference Ezcurra, Fiorelli, Martinelli, Rocher, von Baczko, Ezpeleta, Taborda, Hechenleitner, Trotteyn and Desojo2017; Novas et al., Reference Novas, Agnolín, Ezcurra, Müller, Martinelli and Langer2021; Hechenleitner et al., Reference Hechenleitner, Martinelli, Rocher, Fiorelli, Juarez, Taborda and Desojo2025), and together these South American records highlight the important role of South America in understanding the origin and early evolution of dinosauromorphs.

Figure 3.

Location and general view of the main fossiliferous sites yielding Triassic dinosauromorph remains in the state of Rio Grande do Sul, Brazil. (1) Central region of Rio Grande do Sul highlighting some of the main dinosauromorph-bearing sites: a, Picada do Gama; b, Água Negra; c, Cerro da Alemoa; d, Linha São Luiz; e, Marchezan and Predebon; f, Piche; g, Buriol; h, Wachholz; i, Várzea do Agudo (= Janner); j, Niemeyer complex; k, Linha Várzea 2 (Becker); l, Cerro Botucararí; m, Schoenstatt. (2) General view of the Váreza do Agudo (= Janner) site, lower portion of the Candelária Sequence. (3) General view of the upper portion of the Niemeyer complex, Candelária Sequence. (4) General view of the Cerro da Alemoa site, lower portion of the Candelária Sequence.

Figure 3. Long description

Panel 1: A geographical map of the central region of Rio Grande do Sul, Brazil. A scale bar indicates 25 km. The map shows a network of blue rivers and gray roads. Red circular markers labeled ‘a’ through ‘m’ indicate fossiliferous sites. From West to East, sites include: a (Picada do Gama), b (Água Negra), c (Cerro da Alemoa), d (Faxinal do Soturno), e (Marchezan and Predebon), f (Piche), g (Buriol), h (Wachholz), i (Várzea do Agudo), j (Niemeyer complex), k (Linha Várzea 2), l (Cerro Botucaraí), and m (Schoenstatt). To the left of the main map, an inset shows the location of Brazil within South America and the state of Rio Grande do Sul within Brazil.

Panel 2: A wide-angle photograph of the Várzea do Agudo site. The foreground consists of dry grass leading to a large, eroded red sandstone cliff with vertical gullies. Green trees line the top of the cliff under a clear blue sky.

Panel 3: A photograph of the Niemeyer complex. The foreground shows a sloped, sandy red earth surface where two researchers are kneeling. In the background, a small body of water is visible to the left, with trees and distant hills under a hazy sky.

Panel 4: An aerial photograph of the Cerro da Alemoa site. It shows a large, deeply eroded red sandstone formation with intricate drainage patterns and ridges. The formation is surrounded by dense green forest on all sides.

Figure 4.

Stratigraphic distribution of major dinosaur groups in the Triassic of southern Brazil. Silhouettes were constructed based on artwork by Caio Fantini, Márcio L. Castro, and Matheus F. Gadelha.

Figure 4. Long description

A stratigraphic column and fossil distribution chart.

Vertical Axes (Left):

* Far left: Triassic period divided into Middle (247.2 to 237 M a) and Upper (237 to 227 M a).

* Stages: Anisian, Ladinian, Carnian (subdivided into 236 and 233 M a), and Norian (225 M a).

* Santa Maria Supersequence: Divided into Pinheiros-Chiniquá Sequence (bottom), Santa Cruz Sequence (middle), and Candelária Sequence (top).

Assemblage Zones (A Z) and Levels (Center):

* Dinodontosaurus A Z (Ladinian).

* Santacruzodon A Z (Carnian).

* Hyperodapedon A Z (Carnian), including the Hyperodapedon acme zone and Exaeretodon sub-zone.

* Siriusgnathus level (boundary of Carnian and Norian).

* Riograndia A Z (Norian).

Biological Distribution (Right):

Four vertical lineages are shown with red circles indicating species count (small for 1 species, large for greater than or equal to 2 species, and circles with question marks for ambiguous records). Silhouettes at the top and bottom identify the groups:

* Silesauridae: Present from Ladinian through Norian.

* Sauropodomorpha: Present from Carnian through Norian.

* Herrerasauridae: Present in the Carnian.

* Theropoda: Present from Carnian through Norian.

Table 1.

Triassic avemetatarsalian species recorded from Brazil; species not mentioned in the text: Spondylosoma absconditum von Huene, Reference von Huene1942, Faxinalipterus minimus Bonaparte, Schultz, and Soares, Reference Bonaparte, Schultz, Soares and Bandyopadhyay2010, Unaysaurus tolentinoi Leal et al., Reference Leal, Azevedo, Kellner and Da Rosa2004

Table 1. Long description

The table contains 20 entries organized into four columns: Species, Clade, Sequence, and Age.

* Spondylosoma absconditum: Aphanosauria, Pinheiros-Chiniquá, Ladinian.

* Faxinalipterus minimus: Lagerpetidae, Candelária (upper), early Norian.

* Ixalerpeton polesinensis: Lagerpetidae, Candelária (lower), Carnian.

* Venetoraptor gassenae: Lagerpetidae, Candelária (lower), Carnian.

* Gondwanax paraisensis: Silesauridae, Pinheiros-Chiniquá, Ladinian.

* Gamatavus antiquus: Silesauridae, Pinheiros-Chiniquá, Ladinian.

* Itaguyra occulta: Silesauridae, Santa Cruz, early Carnian.

* Amanasaurus nesbitti: Silesauridae, Candelária (lower), Carnian.

* Sacisaurus agudoensis: Silesauridae, Candelária (upper), early Norian.

* Staurikosaurus pricei: Herrerasauridae, Candelária (lower), Carnian.

* Gnathovorax cabreirai: Herrerasauridae, Candelária (lower), Carnian.

* Nhandumirim waldsangae: Sauropodomorpha, Candelária (lower), Carnian.

* Saturnalia tupiniquim: Sauropodomorpha, Candelária (lower), Carnian.

* Pampadromaeus barberenai: Sauropodomorpha, Candelária (lower), Carnian.

* Buriolestes schultzi: Sauropodomorpha, Candelária (lower), Carnian.

* Bagualosaurus agudoensis: Sauropodomorpha, Candelária (lower), Carnian.

* Guaibasaurus candelariensis: Sauropodomorpha, Candelária (upper), early Norian.

* Unaysaurus tolentinoi: Sauropodomorpha, Candelária (upper), early Norian.

* Macrocollum itaquii: Sauropodomorpha, Candelária (upper), early Norian.

* Erythrovenator jacuiensis: Theropoda, Candelária (upper), early Norian.

Despite the scarce dinosauromorph record in some sequences of the Santa Maria Supersequence, evidence of the presence of the group in each sequence (Fig. 4) indicates a continuous occurrence even through different depositional environments. For a more in-depth review of the geological context related to the fossil record of dinosauromorphs in Brazil see Da-Rosa (Reference Da-Rosa2015) and Corecco et al. (Reference Corecco, Kohn and Schultz2024).

Finally, a note regarding the age of the Triassic deposits of Brazil is warranted. Although collective efforts have been undertaken to obtain more precise age constraints for these deposits (e.g., Langer et al., Reference Langer, Ramezani and Da-Rosa2018; Philipp et al., Reference Philipp, Schultz, Kloss, Horn, Soares and Basei2018, Reference Philipp, Faccini, Schultz, Zvirtes and Bruckmann2023), the detrital nature of the zircons results in age distributions that inherently include some degree of uncertainty, requiring caution when interpreting the ages of Brazilian stratigraphic units. A major constraint on the accuracy of this story is the limited chronological resolution of Brazilian Triassic deposits. Accordingly, future investigations aimed at refining their age should focus on dating specific fossiliferous sites and improving the biostratigraphical framework at the site level, rather than relying solely on broad, basin-scale correlations.

Re-rooting the evolutionary tree

For many years, the tiny Argentine archosaur Lagerpeton chanarensis Romer, Reference Romer1971, was regarded as one of the basalmost members of the clade Dinosauromorpha (Sereno and Arcucci, Reference Sereno and Arcucci1994a; Novas, Reference Novas1996). Known from early Carnian deposits dated to approximately 237 million years ago (Marsicano et al., Reference Marsicano, Irmis, Mancuso, Mundil and Chemale2016), this small and slender archosaur was widely used to infer the anatomy of the ancestor of the lineage that later gave rise to dinosaurs (Fig. 5.3; Langer et al., Reference Langer, Nesbitt, Bittencourt and Irmis2013). Subsequent discoveries from other parts of the world (Irmis et al., Reference Irmis, Nesbitt, Padian, Smith, Turner, Woody and Downs2007; Nesbitt et al., Reference Nesbitt, Irmis, Parker, Smith, Turner and Rowe2009a; Kammerer et al., Reference Kammerer, Nesbitt, Flynn, Ranivoharimanana and Wyss2020), including Brazil (Cabreira et al., Reference Cabreira, Kellner, Dias-da-Silva, Roberto-da-Silva and Bronzati2016; Müller et al., Reference Müller, Ezcurra, Garcia, Agnolín, Stocker, Novas, Soares, Kellner and Nesbitt2023; Garcia et al., Reference Garcia, Fonseca, Doering, da Rosa and Müller2024a), revealed similar reptiles, all of which were included within a clade known as Lagerpetidae (Arcucci, Reference Arcucci1986). These animals are characterized by proximodistally short pubes and ischia, as well as elongated hind limbs (Fig. 5.1, 5.2), with a unique configuration of the pedal digits (Sereno and Arcucci, Reference Sereno and Arcucci1994a; Nesbitt et al., Reference Nesbitt, Irmis, Parker, Smith, Turner and Rowe2009a; Müller et al., Reference Müller, Ezcurra, Garcia, Agnolín, Stocker, Novas, Soares, Kellner and Nesbitt2023; Agnolín et al., Reference Agnolín, Novas, Ezcurra, Miner and Müller2024). The combination of postcranial traits indicates that at least some members of this clade adopted a posture unique among archosaurs, characterized by sprawling hind limbs and a digitigrade pedal posture (Agnolín et al., Reference Agnolín, Novas, Ezcurra, Miner and Müller2024). However, the limited understanding of lagerpetid anatomy, particularly of the cranial region, has hindered development of a clearer picture of these potential precursors of dinosaurs (Müller et al., Reference Müller, Langer and Dias-da-Silva2018c). It was only later, largely through fossils from Brazil and Argentina, that new anatomical information revealed an unexpected result: rather than being precursors of dinosaurs, lagerpetids appear to represent precursors of pterosaurs (Fig. 5.4; Ezcurra et al., Reference Ezcurra, Nesbitt, Bronzati, Dalla Vecchia, Agnolín, Benson, Brissón Egli, Cabreira, Evers and Gentil2020).

Figure 5.

General anatomy and alternative phylogenetic hypotheses of Lagerpetidae. (1) Skeleton of a lagerpetid based on Venetoraptor gassenae Müller et al., Reference Müller, Ezcurra, Garcia, Agnolín, Stocker, Novas, Soares, Kellner and Nesbitt2023. (2) Life reconstruction of Venetoraptor gassenae by Matheus F. Gadelha. (3) Lagerpetids as dinosauromorphs. (4) Lagerpetids as the sister group to Pterosauria. (5) “Lagerpetids” as a paraphyletic assemblage leading to Pterosauria. Life reconstructions by Matheus F. Gadelha.

Figure 5. Long description

Panel 1 shows a skeletal reconstruction of Venetoraptor gassenae in profile, facing left, with a long tail and slender limbs. To its right is a detailed lateral view of the skull and lower jaw. Panel 2 is a full-color life reconstruction of the same animal, depicted with brown and grey fur-like integument and a striped tail.

Panels 3, 4, and 5 present phylogenetic trees rooted at Avemetatarsalia.

* Panel 3 depicts Lagerpetidae as a sister group to Dinosauria, both nested within Dinosauromorpha. Pterosauria is the outgroup to this clade.

* Panel 4 depicts Lagerpetidae as the sister group to Pterosauria, both nested within Pterosauromorpha. Dinosauria is the outgroup to this clade.

* Panel 5 depicts Lagerpetidae as a paraphyletic assemblage. One branch leads to Pterosauria, while another branch, also labeled Lagerpetidae, is more closely related to Pterosauromorpha. Dinosauromorpha is the outgroup.

In all trees, Lagerpetidae and Pterosauromorpha labels are highlighted in red text.

This new hypothesis reshaped the base of the dinosaur evolutionary tree because lagerpetids could no longer be used to infer the ancestral morphology of dinosaurs and their closest lineages properly. Although, according to the new hypothesis, lagerpetids are more closely related to pterosaurs than to dinosaurs, their position as avemetatarsalians is still maintained in recent studies (Baron, Reference Baron2020; Ezcurra et al., Reference Ezcurra, Nesbitt, Bronzati, Dalla Vecchia, Agnolín, Benson, Brissón Egli, Cabreira, Evers and Gentil2020; Müller et al., Reference Müller, Ezcurra, Garcia, Agnolín, Stocker, Novas, Soares, Kellner and Nesbitt2023). This raises the possibility that some traits of the dinosaurian ancestor may still be present in lagerpetids as plesiomorphic conditions. Even more recently, a new study positioned lagerpetids as a paraphyletic assemblage leading to the pterosaur clade (Fig. 5.5; Garcia and Müller, Reference Garcia and Müller2025), reinforcing their affinities with pterosaurs while suggesting a more gradual evolutionary history, with typical lagerpetids progressively accumulating characteristic pterosaur traits throughout the Triassic.

Despite advances in our understanding of lagerpetid anatomy and phylogenetic affinities, these taxa remain comparatively poorly known relative to other Triassic avemetatarsalians. To date, few specimens preserving substantial portions of the skeleton are known, and no complete skull has yet been recovered. Nevertheless, taxa such as Ixalerpeton polesinensis Cabreira et al., Reference Cabreira, Kellner, Dias-da-Silva, Roberto-da-Silva and Bronzati2016, and Venetoraptor gassenae Müller et al., Reference Müller, Ezcurra, Garcia, Agnolín, Stocker, Novas, Soares, Kellner and Nesbitt2023, both from the Carnian of southern Brazil, constitute some of the most informative sources of anatomical data for these unusual archosaurs (Fig. 6). Examination of these materials suggests that at least some lagerpetids possessed a raptorial, beak-like structure formed by the premaxilla (Müller et al., Reference Müller, Ezcurra, Garcia, Agnolín, Stocker, Novas, Soares, Kellner and Nesbitt2023). Both taxa also display the unexpected retention of a well-developed postfrontal bone in the skull (Cabreira et al., Reference Cabreira, Kellner, Dias-da-Silva, Roberto-da-Silva and Bronzati2016; Müller et al., Reference Müller, Ezcurra, Garcia, Agnolín, Stocker, Novas, Soares, Kellner and Nesbitt2023). The manus of Venetoraptor gassenae indicates that, in at least some lagerpetids, manual digit IV was longer than the remaining digits, a condition shared with pterosaurs and markedly distinct from that observed in early dinosaurs (Müller et al., Reference Müller, Ezcurra, Garcia, Agnolín, Stocker, Novas, Soares, Kellner and Nesbitt2023). Furthermore, computed tomography-based reconstructions of the neurocranial soft tissues indicate that the endocranial morphology of Ixalerpeton polesinensis and Venetoraptor gassenae shares several features with pterosaurs, including laterally positioned optic lobes, yet lacks other characters typical of these volant reptiles, most notably an expanded floccular lobe (Bronzati et al., Reference Bronzati, Watanabe, Benson, Müller and Witmer2025; Damke et al., Reference Damke, Kerber, Bronzati, Garcia, Ezcurra, Nesbitt and Müller2026).

Figure 6.

Examples of fossils of Triassic lagerpetids from southern Brazil. (1) Right forelimb of Venetoraptor gassenae (CAPPA/UFSM 0356) from the lower portion of the Candelária Sequence. (2) Axial skeleton of Ixalerpeton polesinensis (ULBRA-PVT059) from the lower portion of the Candelária Sequence. (3) Right dentary of Ixalerpeton polesinensis (ULBRA-PVT059) from the lower portion of the Candelária Sequence. Specimens not to scale.

Although having been excluded from the base of the dinosaur lineage, lagerpetids remain critical for elucidating avemetatarsalian evolution during the Triassic, and a substantial portion of current knowledge of the group derives from discoveries made in Brazil (e.g., Cabreira et al., Reference Cabreira, Kellner, Dias-da-Silva, Roberto-da-Silva and Bronzati2016; Kellner et al., Reference Kellner, Holgado, Grillo, Pretto and Kerber2022; Müller et al., Reference Müller, Ezcurra, Garcia, Agnolín, Stocker, Novas, Soares, Kellner and Nesbitt2023; Garcia and Müller, Reference Garcia and Müller2025; Damke et al., Reference Damke, Kerber, Bronzati, Garcia, Ezcurra, Nesbitt and Müller2026). Although the Brazilian record to date is dominated by incomplete material (Garcia and Müller, Reference Garcia and Müller2025), it is highly likely that more complete specimens will be discovered in the near future.

With the reassignment of lagerpetids from Dinosauromorpha to Pterosauromorpha, Lagosuchus talampayensis Romer, Reference Romer1971, became the only unambiguous non-dinosaurian dinosauromorph consistently recovered in phylogenetic analyses (e.g., Ezcurra et al., Reference Ezcurra, Nesbitt, Bronzati, Dalla Vecchia, Agnolín, Benson, Brissón Egli, Cabreira, Evers and Gentil2020; Müller et al., Reference Müller, Ezcurra, Garcia, Agnolín, Stocker, Novas, Soares, Kellner and Nesbitt2023; Fonseca et al., Reference Fonseca, Reid, Venner, Duncan, Garcia and Müller2024; Garcia et al., Reference Garcia, Cabreira, da Silva, Pretto and Müller2024b). Although it was originally described as a pseudosuchian (Romer, Reference Romer1971), its position close to, but outside, Dinosauria has remained largely undisputed. As a result, this Argentine taxon from the Chañares Formation provides key information about the body plan of the archosaurs most closely related to dinosaurs.

Lagosuchus talampayensis was a small and gracile bipedal dinosauromorph (Romer, Reference Romer1971; Bonaparte, Reference Bonaparte1975; Sereno and Arcucci, Reference Sereno and Arcucci1994b; Langer et al., Reference Langer, Nesbitt, Bittencourt and Irmis2013; Agnolín and Ezcurra, Reference Agnolín and Ezcurra2019; Otero et al., Reference Otero, Bishop and Hutchinson2025). Its low and elongated maxilla bears ziphodont teeth, suggesting a faunivorous diet. The axial vertebrae are proportionally short compared to those of dinosaurs, and the sacrum is composed of only two vertebrae. The forelimbs are much shorter than the hindlimbs. The pelvic girdle includes an ilium with a well-developed medial wall, resulting in a closed acetabulum. The pubis is short compared to those of early dinosaurs. The ischium differs from that of early dinosaurs in possessing a long lamina extending along most of its shaft. Although the femur bears an anterior trochanter and a trochanteric shelf, the fourth trochanter is asymmetrical. The tibia is longer than the femur and bears a well-developed cnemial crest. Metatarsal III is the longest metatarsal.

So far, no forms closely related to the Argentine taxon have been identified in Brazilian Triassic-aged deposits. However, considering the recent discovery of new Ladinian and early Carnian outcrops, fossils of dinosauromorphs related to Lagosuchus talampayensis may be discovered in the coming years.

The challenging silesaurids

It is not surprising that the earliest branches of the dinosaur evolutionary tree remain obscure and marked by conflicting topologies. This issue is not solely a consequence of the recent repositioning of lagerpetids. Rather, it has affected, to varying degrees, the placement of nearly all major dinosaur groups and their closest relatives (Langer and Ferigolo, Reference Langer and Ferigolo2013; Cabreira et al., Reference Cabreira, Kellner, Dias-da-Silva, Roberto-da-Silva and Bronzati2016; Baron et al., Reference Baron, Norman and Barrett2017; Langer et al., Reference Langer, Ezcurra, Rauhut, Benton, Knoll, McPhee, Novas, Pol and Brusatte2017; Müller and Garcia, Reference Müller and Garcia2020a; Novas et al., Reference Novas, Agnolín, Ezcurra, Müller, Martinelli and Langer2021). At the center of these debates, a peculiar group of dinosauromorphs stands out: the Silesauridae. These dinosauromorphs were first introduced to the literature in 2003 with the description of Silesaurus opolensis Dzik, Reference Dzik2003. Since then, an explosion of discoveries worldwide (Ferigolo and Langer, Reference Ferigolo and Langer2007; Nesbitt et al., Reference Nesbitt, Sidor, Irmis, Angielczyk, Smith and Tsuji2010; Kammerer et al., Reference Kammerer, Nesbitt and Shubin2011; Martínez et al., Reference Martínez, Apaldetti, Alcober, Colombi, Sereno, Fernandez, Malnis, Correa and Abelín2013; Peecook et al., Reference Peecook, Sidor, Nesbitt, Smith, Steyer and Angielczyk2013; Martz and Small, Reference Martz and Small2019; Müller, Reference Müller2025; Paes-Neto et al., Reference Paes Neto, Pretto, Martinelli, Battista and Garcia2025), along with re-evaluations of previously described forms (Ezcurra, Reference Ezcurra2006; Irmis et al., Reference Irmis, Nesbitt, Padian, Smith, Turner, Woody and Downs2007; Agnolín and Rozadilla, Reference Agnolín and Rozadilla2018), has revealed that these taxa formed part of a group with a remarkably complex evolutionary history throughout the Triassic. They first appeared in the fossil record during the Middle Triassic (Nesbitt et al., Reference Nesbitt, Sidor, Irmis, Angielczyk, Smith and Tsuji2010; Peecook et al., Reference Peecook, Sidor, Nesbitt, Smith, Steyer and Angielczyk2013; Pretto et al., Reference Pretto, Müller, Moro, Garcia, Neto and Da Rosa2022; Müller, Reference Müller2025, Reference Müller2026) and persisted until close to the end of the Triassic (Irmis et al., Reference Irmis, Nesbitt, Padian, Smith, Turner, Woody and Downs2007; Martz and Small, Reference Martz and Small2019). During this time interval, the group retained a broadly consistent and characteristic body plan, yet exhibited a certain degree of disparity, particularly with respect to the masticatory apparatus and dietary strategies. Although basalmost forms have been interpreted as carnivorous (Müller and Garcia, Reference Müller and Garcia2020a), early in the evolutionary history of the group, adaptations associated with an omnivorous diet are already evident, which subsequently became increasingly specialized toward herbivory (Nesbitt et al., Reference Nesbitt, Sidor, Irmis, Angielczyk, Smith and Tsuji2010; Martz and Small, Reference Martz and Small2019).

There is no consensus regarding the placement of Lewisuchus admixtus Romer, Reference Romer1972, as a definitive member of Silesauridae. However, except for this taxon, most other silesaurids represented by sufficiently well-preserved material exhibit a set of highly characteristic features, such as the presence of a beak-like projection at the anterior end of the dentary (Nesbitt et al., Reference Nesbitt, Sidor, Irmis, Angielczyk, Smith and Tsuji2010). This unusual structure was initially thought to represent an early version of the predentary bone of ornithischians (Dzik, Reference Dzik2003; Ferigolo and Langer, Reference Ferigolo and Langer2007). Another typical feature of silesaurids is their elongated and slender forelimbs, which confer a distinctive morphology among early dinosauromorphs. Furthermore, the group is also characterized by its femoral anatomy, including a relatively poorly expanded femoral head and an elongated popliteal fossa (Nesbitt et al., Reference Nesbitt, Sidor, Irmis, Angielczyk, Smith and Tsuji2010; Langer and Ferigolo, Reference Langer and Ferigolo2013; Müller and Garcia, Reference Müller and Garcia2020a). In general, silesaurids are represented as quadrupedal organisms with slender limbs (Fig. 7.1, 7.2) and body size ranging from 1 to approximately 3 meters in length (Dzik, Reference Dzik2003; Langer et al., Reference Langer, Nesbitt, Bittencourt and Irmis2013; Barrett et al., Reference Barrett, Nesbitt and Peecook2015; Peecook et al., Reference Peecook, Steyer, Tabor and Smith2017; Marsh and Parker, Reference Marsh and Parker2020; Lovegrove et al., Reference Lovegrove, Chapelle, Peecook, Upchurch and Barrett2025; Marsh, Reference Marsh2025; Müller, Reference Müller2026).

Figure 7.

General anatomy and alternative phylogenetic hypotheses of Silesauridae. (1) Skeleton of a silesaurid based on several specimens (modified from Müller, Reference Müller2025). (2) Life reconstruction of Amanasaurus nesbitti by Matheus F. Gadelha. (3) Silesaurids as non-dinosaur dinosauromorphs. (4) Silesaurids as the sister group to “traditional ornithischians”. (5) “Silesaurids” as a paraphyletic assemblage leading to “traditional ornithischians”. Life reconstructions by Caio Fantini, Márcio L. Castro, and Matheus F. Gadelha.

Figure 7. Long description

The image consists of five numbered panels.

* Panel 1: A skeletal reconstruction of a silesaurid in profile facing left. The skeleton is shown in white against a black silhouette, highlighting a long neck, slender limbs, and a long tail. To the right is a detailed line drawing of the skull and lower jaw.

* Panel 2: A life reconstruction of Amanasaurus nesbitti. It is a quadrupedal animal with textured, brownish-grey skin, a small head, and a robust body.

* Panel 3: A phylogenetic tree showing Silesauridae in red as a sister group to Dinosauria. Dinosauria branches into Ornithischia and Saurischia. The root node is labeled Dinosauromorpha in red.

* Panel 4: A phylogenetic tree showing Silesauridae in red as the sister group to traditional ornithischians. Together, they form the clade Ornithischia, which is the sister group to Saurischia. The root node is labeled Dinosauria.

* Panel 5: A phylogenetic tree depicting Silesauridae as a paraphyletic group. Two separate branches labeled Silesauridae lead sequentially toward traditional ornithischians. This combined group is the sister clade to Saurischia. The root node is labeled Dinosauria.

Each tree includes small silhouette icons of the animals above their respective taxonomic labels.

Although the fossil record of silesaurids has been progressively expanding, few specimens preserve substantial portions of the skeleton. In fact, to date, there is no single specimen that can be considered complete. As a result, much of what is known about the group is based on composite reconstructions derived from different individuals, making its true proportions relatively poorly understood. Perhaps for this reason, the phylogenetic affinities of silesaurids remain one of the most debated and attention-drawing aspects of these dinosauromorphs. There are two main hypotheses regarding the phylogenetic position of the group. One places silesaurids as the sister group to Dinosauria (Fig. 7.3; Ezcurra, Reference Ezcurra2006; Irmis et al., Reference Irmis, Nesbitt, Padian, Smith, Turner, Woody and Downs2007; Nesbitt et al., Reference Nesbitt, Sidor, Irmis, Angielczyk, Smith and Tsuji2010; Nesbitt, Reference Nesbitt2011; Ezcurra et al., Reference Ezcurra, Nesbitt, Bronzati, Dalla Vecchia, Agnolín, Benson, Brissón Egli, Cabreira, Evers and Gentil2020), whereas the other recovers silesaurids as ornithischian dinosaurs (Langer and Ferigolo, Reference Langer and Ferigolo2013; Cabreira et al., Reference Cabreira, Kellner, Dias-da-Silva, Roberto-da-Silva and Bronzati2016; Müller and Garcia, Reference Müller and Garcia2020a; Norman et al., Reference Norman, Baron, Garcia and Müller2022; Cau, Reference Cau2024; Fonseca et al., Reference Fonseca, Reid, Venner, Duncan, Garcia and Müller2024). This latter hypothesis can be subdivided into two alternative scenarios: one in which silesaurids are recovered as the sister group of traditional ornithischians (Fig. 7.4; Langer and Ferigolo, Reference Langer and Ferigolo2013; Cabreira et al., Reference Cabreira, Kellner, Dias-da-Silva, Roberto-da-Silva and Bronzati2016), and another in which silesaurids form a paraphyletic assemblage leading to the clade that includes traditional ornithischians (Fig. 7.5; Müller and Garcia, Reference Müller and Garcia2020a; Norman et al., Reference Norman, Baron, Garcia and Müller2022). Because this is a relatively recent and actively debated topic, each of these hypotheses carries important implications for our understanding of the origin of dinosaurs. However, to avoid reiterating arguments that have already been explored in more detailed studies on this subject (e.g., Müller and Garcia, Reference Müller and Garcia2020a; Norman et al., Reference Norman, Baron, Garcia and Müller2022, Reference Norman, Baron, Garcia and Müller2024), these issues are not discussed further here.

Despite the phylogenetic uncertainties, current evidence indicates that several aspects of silesaurid skeletal anatomy are well documented. The morphology of the premaxilla varies from an almost edentulous condition in Asilisaurus kongwe Nesbitt et al., Reference Nesbitt, Sidor, Irmis, Angielczyk, Smith and Tsuji2010 (Nesbitt et al., Reference Nesbitt, Langer and Ezcurra2020) to the presence of four teeth in Silesaurus opolensis (Dzik, Reference Dzik2003). The narial fossa is consistently rimmed posteroventrally by the posterodorsal process of the premaxilla. The maxilla bears a short antorbital fossa and lacks a longitudinal ridge on the lateral surface of its posterior process. The main body of the jugal is tall and ornamented by a longitudinal ridge on the lateral surface. Unlike lagerpetids (Cabreira et al., Reference Cabreira, Kellner, Dias-da-Silva, Roberto-da-Silva and Bronzati2016; Müller et al., Reference Müller, Ezcurra, Garcia, Agnolín, Stocker, Novas, Soares, Kellner and Nesbitt2023), the postfrontal bone became evolutionarily lost. A supratemporal fossa excavates the dorsal surface of the posterior region of the frontal (Nesbitt et al., Reference Nesbitt, Langer and Ezcurra2020). In addition to the beak-like anterior end of the dentary, this element is generally tall, and the external mandibular fenestra is relatively small (Dzik and Sulej, Reference Dzik and Sulej2007).

The axial skeleton of silesaurids lacks invasive pneumatic features. The vertebrae bear fossae delimited by laminae. The cervical series is relatively short, contrasting with the proportionally longer necks of most sauropodomorphs and some neotheropods. However, the cervical vertebrae of silesaurids are proportionately longer than those of lagerpetids. The dorsal vertebrae resemble those of most early dinosaurs, except for the characteristic anteroposteriorly short vertebrae observed in herrerasaurids (Novas, Reference Novas1994; Garcia et al., Reference Garcia, Müller, Pretto, Da-Rosa and Dias-da-Silva2021). The sacrum varies from two vertebrae in the basalmost forms to three or four vertebrae (depending on the interpretation of some material) in late-diverging members of the group (Müller, Reference Müller2025). One of the most peculiar features of the sacral region is the presence of an “inserted” vertebra between the first and second primordial sacral vertebrae (Nesbitt, Reference Nesbitt2011; Müller, Reference Müller2025).

The forelimb of silesaurids represents one of the most unique anatomical structures among early dinosauromorphs. The humerus is elongated and slender, with a weak deltopectoral crest that does not extend beyond one quarter of the total length of the bone. Additionally, the humeral shaft is arched, with the concave surface facing medially (Breeden et al., Reference Breeden, Irmis, Nesbitt, Smith and Turner2025). The radius and ulna are also gracile and long, resulting in a quite elongated fore limb. The manus of these animals is poorly known.

The pelvic girdle is well documented. The ilium is anteroposteriorly short and usually exhibits a concave dorsal margin of the iliac blade. The preacetabular process varies from short in the most basal forms to markedly elongated in more derived taxa. The medial wall of the acetabulum is large in most species, whereas it is partially open in more derived forms. The pubis is long, anteroventrally directed, and lacks a distal pubic boot. The ischium bears a medial wall between the iliac and pubic peduncles; its shaft is elongated and includes a weak ventral obturator plate that is continuous with the main body of the bone. The femur is sigmoid in both anterior and lateral views. A distinct notch is present at the transition between the femoral shaft and the ventral surface of the femoral head. In late-diverging forms, the anterior trochanter is wing-like. The fourth trochanter is symmetrical, and the popliteal fossa is markedly elongated. The tibia bears a well-developed cnemial crest, and its distal end is circular in distal view.

Concerning the fossil record of silesaurids from Brazil, the group was restricted to the early Norian Sacisaurus agudoensis Ferigolo and Langer, Reference Ferigolo and Langer2007, until recently. However, several new specimens have been described over the last few years (Fig. 8; Pretto et al., Reference Pretto, Müller, Moro, Garcia, Neto and Da Rosa2022; Mestriner et al., Reference Mestriner, Marsola, Nesbitt, Da-Rosa and Langer2023; Müller and Garcia, Reference Müller and Garcia2023; Doering et al., Reference Doering, Ezcurra, Schiefelbein, Garcia and Müller2024; Campo et al., Reference Campo, da Silva, Neto, Ferigolo and Ribeiro2025; Müller, Reference Müller2025, Reference Müller2026; Paes-Neto et al., Reference Paes Neto, Pretto, Martinelli, Battista and Garcia2025). This record includes specimens from the Middle to Late Triassic of the Santa Maria Supersequence. The oldest Brazilian silesaurids come from Ladinian-aged deposits and comprise two species: Gamatavus antiquus Pretto et al., Reference Pretto, Müller, Moro, Garcia, Neto and Da Rosa2022, and Gondwanax paraisensis Müller, Reference Müller2025. The slightly younger Itaguyra occulta Paes-Neto et al., Reference Paes Neto, Pretto, Martinelli, Battista and Garcia2025, was described from early Carnian beds, whereas Amanasaurus nesbitti Müller and Garcia, Reference Müller and Garcia2023, was discovered in mid to late Carnian deposits. Together with the Norian record of Sacisaurus agudoensis, silesaurid remains from Brazil comprise an almost continuous distribution from the Middle to the Late Triassic. Although these materials are usually fragmentary, this continuous distribution provides important evidence for the evolutionary history of the group, indicating the persistence of silesaurids in southwestern Gondwana despite the faunal turnovers that occurred in Gondwana during the Triassic. In addition, the Brazilian silesaurid record continues to expand, with more complete specimens currently under study, suggesting a positive outlook for future research.

Figure 8.

Examples of fossils of Triassic silesaurids from southern Brazil. (1) Right ilium of Gamatavus antiquus (UFSM 11348) from the Pinheiros-Chiniquá Sequence. (2) Proximal portion of the right femur of Amanasaurus nesbitti (CAPPA/UFSM 0374) from the lower portion of the Candelária Sequence. (3) Right femur of Gondwanax paraisensis Müller, Reference Müller2025 (CAPPA/UFSM 0417) from the Pinheiros-Chiniquá Sequence. Specimens not to scale.

The first apex predatory dinosaurs

Dinosaurs evolved within ecosystems dominated by well-established crocodile-line archosaurs and synapsids (Bonaparte, Reference Bonaparte1982, Reference Bonaparte1995; Langer et al., Reference Langer, Ezcurra, Bittencourt and Novas2010; Benton et al., Reference Benton, Forth and Langer2014). Although some of these archosaurs attained large body sizes (>500 kg; Turner and Nesbitt, Reference Turner and Nesbitt2013), most early dinosaurs were small-bodied, typically weighing no more than 10 kg (Müller et al., Reference Müller, Ferreira, Pretto, Bronzati and Kerber2021; Moro et al., Reference Moro, Damke, Müller, Kerber and Pretto2024). An important exception to this pattern is the peculiar clade of early dinosaurs known as the Herrerasauridae. This clade was erected by Benedetto (Reference Benedetto1973) to include Herrerasaurus ischigualastensis Reig, Reference Reig1963, and Staurikosaurus pricei Colbert, Reference Colbert1970. Fifty years later, at least two additional species, Sanjuansaurus gordilloi Alcober and Martínez, Reference Alcober and Martínez2010, and Gnathovorax cabreirai Pacheco et al., Reference Pacheco, Müller, Langer, Pretto, Kerber and da Silva2019, both from South America, are currently regarded as valid and are unequivocally assigned to Herrerasauridae (Alcober and Martínez, Reference Alcober and Martínez2010; Pacheco et al., Reference Pacheco, Müller, Langer, Pretto, Kerber and da Silva2019). Herrerasaurids appear in the fossil record contemporaneously with the oldest unequivocal dinosaurs yet discovered (ca. 231 Ma; Martínez et al., Reference Martínez, Sereno, Alcober, Colombi, Renne, Montañez and Currie2011; Langer et al., Reference Langer, Ramezani and Da-Rosa2018; Novas et al., Reference Novas, Agnolín, Ezcurra, Müller, Martinelli and Langer2021). In contrast to other coeval dinosaurs, herrerasaurids were relatively large, with some specimens reaching approximately 5–6 m in total length (e.g., PVSJ 53; Novas, Reference Novas1986). Equipped with jaws bearing nearly 80 ziphodont teeth and elongated mani with three large, recurved claws (Sereno, Reference Sereno1994; Sereno and Novas, Reference Sereno and Novas1994; Pacheco et al., Reference Pacheco, Müller, Langer, Pretto, Kerber and da Silva2019), herrerasaurids represent the earliest dinosaurs to occupy the apex predator niche (Garcia et al., Reference Garcia, Müller, Pretto, Da-Rosa and Dias-da-Silva2021). Curiously, this clade disappeared around the Carnian–Norian boundary (ca. 227 Ma). Following their extinction, neotheropods and morphoraptorans (non-herrerasaurian herrerasaurids) replaced herrerasaurids as apex predatory dinosaurs, a role they maintained until the end of the Mesozoic (Langer et al., Reference Langer, Ezcurra, Bittencourt and Novas2010; Pacheco et al., Reference Pacheco, Müller, Langer, Pretto, Kerber and da Silva2019; Srivastava and Nesbitt, Reference Srivastava and Nesbitt2026).

The overall body plan of herrerasaurids (Fig. 9.1, 9.2) is conservative across species, with only minor variation in skeletal proportions and specific anatomical traits. Their skeletons combine plesiomorphic features with unique synapomorphies and characters shared exclusively with theropods (Sereno, Reference Sereno1994; Sereno and Novas, Reference Sereno and Novas1994; Novas, Reference Novas1994; Pacheco et al., Reference Pacheco, Müller, Langer, Pretto, Kerber and da Silva2019; Garcia et al., Reference Garcia, Müller, Pretto, Da-Rosa and Dias-da-Silva2021; Novas et al., Reference Novas, Agnolín, Ezcurra, Müller, Martinelli and Langer2021). This unusual mosaic of characters has resulted in long-standing phylogenetic controversy. Some authors have placed the clade outside Dinosauria (e.g., Gauthier and Padian, Reference Gauthier, Padian, Hecht, Ostrom, Viohl and Wellnhofer1985; Novas, Reference Novas1992; Fraser et al., Reference Fraser, Padian, Walkden and Davis2002; Baron and Williams, Reference Baron and Williams2021), whereas others have supported theropod affinities (Fig. 9.3; Sereno and Novas, Reference Sereno and Novas1992; Novas, Reference Novas1996; Rauhut, Reference Rauhut2003; Nesbitt et al., Reference Nesbitt, Smith, Irmis, Turner, Downs and Norell2009b; Martínez et al., Reference Martínez, Sereno, Alcober, Colombi, Renne, Montañez and Currie2011; Sues et al., Reference Sues, Nesbitt, Berman and Henrici2011) or interpreted herrerasaurids as early-diverging saurischians (Fig. 9.4; Langer, Reference Langer, Weishampel, Dodson and Osmólska2004; Langer and Benton, Reference Langer and Benton2006; Irmis et al., Reference Irmis, Nesbitt, Padian, Smith, Turner, Woody and Downs2007; Martínez and Alcober, Reference Martínez and Alcober2009; Ezcurra, Reference Ezcurra2010; Müller and Garcia, Reference Müller and Garcia2020a; Novas et al., Reference Novas, Agnolín, Ezcurra, Müller, Martinelli and Langer2021; Ezcurra et al., Reference Ezcurra, Garcia, Novas, Müller, Agnolín and Chatterjee2025). Additional hypotheses recover traditional herrerasaurids as a paraphyletic assemblage leading to core theropods (Nesbitt, Reference Nesbitt2011; Nesbitt et al., Reference Nesbitt, Butler, Ezcurra, Barrett and Stocker2017) or as the sister group to Sauropodomorpha (Baron et al., Reference Baron, Norman and Barrett2017). Some comprehensive studies have placed Herrerasauridae within Herrerasauria (sensu Langer, Reference Langer, Weishampel, Dodson and Osmólska2004), as the sister group to a clade composed of North American taxa (Novas et al., Reference Novas, Agnolín, Ezcurra, Müller, Martinelli and Langer2021; Srivastava and Nesbitt, Reference Srivastava and Nesbitt2026). Under this hypothesis, Herrerasauria is recovered as the sister group to Eusaurischia (i.e., Theropoda + Sauropodomorpha). Large-scale phylogenetic analyses including early dinosaurs and closely related forms have provided further support for Herrerasauridae as early diverging saurischians rather than alternative placements (Ezcurra et al., Reference Ezcurra, Nesbitt, Bronzati, Dalla Vecchia, Agnolín, Benson, Brissón Egli, Cabreira, Evers and Gentil2020, Reference Ezcurra, Garcia, Novas, Müller, Agnolín and Chatterjee2025; Norman et al., Reference Norman, Baron, Garcia and Müller2022; Garcia et al., Reference Garcia, Cabreira, da Silva, Pretto and Müller2024b).

Figure 9.

General anatomy and alternative phylogenetic hypotheses of Herrerasauridae. (1) Skeleton of a herrerasaurid based on Gnathovorax cabreirai (modified from Pacheco et al., Reference Pacheco, Müller, Langer, Pretto, Kerber and da Silva2019). (2) Life reconstruction of Gnathovorax cabreirai by Caio Fantini. (3) Herrerasaurids as theropods. (4) Herrerasaurids as non-eusaurischian saurischians. Life reconstructions by Caio Fantini, Márcio L. Castro, and Matheus F. Gadelha.

Figure 9. Long description

The top half contains two panels. Panel 1 shows a skeletal reconstruction of Gnathovorax cabreirai in profile, facing left, with white bones against a black silhouette and a separate detailed skull diagram below the neck. Panel 2 shows a full-color life reconstruction of the same dinosaur by Caio Fantini, depicted as a bipedal carnivore with brown and tan patterned skin and a long tail.

The bottom half contains two phylogenetic trees. Panel 3 illustrates the hypothesis of Herrerasaurids as theropods. The tree branches from a Dinosauria root into Ornithischia and Saurischia. Saurischia further splits into Sauropodomorpha and a clade labeled Theropoda in red, which contains Herrerasauridae and other theropods. Panel 4 illustrates the hypothesis of Herrerasaurids as non-eusaurischian saurischians. In this tree, Dinosauria splits into Ornithischia and a red-labeled Saurischia node. This Saurischia node branches first into Herrerasauridae and then into a sister clade containing Sauropodomorpha and Theropoda. Both trees use small dinosaur silhouettes to represent the terminal taxa: Ornithischia, Sauropodomorpha, Herrerasauridae, and Theropoda.

Regarding the general skeletal anatomy of herrerasaurids, the skull is large, being almost as long as the femoral length. The rostrum is rectangular in lateral view. The premaxilla bears a well-developed posterolateral process that excludes the maxilla from the posterior margin of the external naris. The number of premaxillary teeth ranges from three to four (Sereno and Novas, Reference Sereno and Novas1994; Pacheco et al., Reference Pacheco, Müller, Langer, Pretto, Kerber and da Silva2019). The maxilla is stout and bears approximately 18 teeth. The extension of the antorbital fossa in the maxilla is reduced. Herrerasaurids lack a promaxillay fenestra. There is no row of foramina perforating the lateral surface of the posterior ramus of the maxilla. Distinct from some theropods, the nasal is flat, lacking any kind of crest or related features. Moreover, the nasal does not form a laterally facing shelf, distinct from early suropodomorphs. The jugal is robust with a smooth ridge on the lateral surface. The ventral ramus of the squamosal is short and robust. There is no evidence of palatal teeth. Conversely, palatal teeth are present in early theropods (Martínez et al., Reference Martínez, Sereno, Alcober, Colombi, Renne, Montañez and Currie2011) and early sauropodomorphs (Cabreira et al., Reference Cabreira, Schultz, Bittencourt, Soares, Fortier, Silva and Langer2011; Sereno et al., Reference Sereno, Martínez and Alcober2013; Müller et al., Reference Müller, Bronzati, Pacheco, Cabreira, Langer and Dias-da-Silva2018a). The anterior tip of the dentary is rounded and perforated by several foramina. The retroarticular process is strongly directed upward. All herrerasaurids bear ziphodont teeth, with some degree of variation regarding the occurrence of enlarged teeth in the anterior half of the maxilla.

The vertebrae lack pneumatic features (Aureliano et al., Reference Aureliano, Ghilardi, Müller, Kerber, Pretto, Fernandes, Ricardi-Branco and Wedel2022). The cervical vertebrae are not elongated, the neural spine is anteroposteriorly short and there are epipophyses on the dorsal surface of the postzygapophyses. The dorsal vertebrae are characterized by marked shortening in anteroposterior direction, as a result of which, the centrum is usually taller than long. The neural spine is tall and straight. It is “H-shaped” in cross-section and bears spine tables on its distal end. An intervertebral articulation named “hyposphene-hypantrum” is recorded in the dorsal series. In addition, the neural arch of the dorsal vertebrae carries a set of laminae bordering fossae. The sacrum is composed by two primordial vertebrae (Novas, Reference Novas1994). The anteriormost caudal vertebrae are anteroposteriorly short and have straight neural spines. The prezygapophysis of the middle to posterior caudal vertebrae is elongated, forming an enlarged contact with the neural arch of the preceding vertebra.

The pectoral girdle is particularly interesting and unique in herrerasaurids. The scapular blade is slender. The distal end of the scapular blade is variable among the species, ranging from non-expanded to relatively expanded (Sereno, Reference Sereno1994; Pacheco et al., Reference Pacheco, Müller, Langer, Pretto, Kerber and da Silva2019). The forelimb is elongated and slender. The deltopectoral crest of the humerus is less than 50% of the total length of the bone. The ulna bears a well-developed olecranon process. The manus is composed of three elongated digits with trenchant claws (I, II, and III) and two vestigial digits with no claws (IV and V).

The pelvic girdle is characterized by a semi-perforated acetabulum. The ilium is anteroposteriorly short, with a short postacetabular ala that lacks a ventrally facing brevis fossa. The orientation of the main shaft of the pubis varies in herrerasaurids (Bittencourt and Kellner, Reference Bittencourt and Kellner2009; Pacheco et al., Reference Pacheco, Müller, Langer, Pretto, Kerber and da Silva2019). In some species it is ventrally directed, whereas in other species it is posteroventrally directed. In addition, the distal end of the pubis is expanded. The ischium of herrerasaurids lacks a notch between the ventral margin of the obturator plate and the ischial shaft. The femur is sigmoid and bears an asymmetrical fourth trochanter. In some specimens, a posteromedial tuber on the proximal portion of the femur is present, whereas in others it is absent. In most specimens, the tibia is shorter than the femur. The astragalus and calcaneum are unfused. Pedal digit I is relatively elongated.

The earliest stages of the evolutionary history of Herrerasauridae are documented in Triassic deposits of South America (Reig, Reference Reig1963; Colbert, Reference Colbert1970; Alcober and Martínez, Reference Alcober and Martínez2010; Pacheco et al., Reference Pacheco, Müller, Langer, Pretto, Kerber and da Silva2019). In particular, rich Carnian assemblages from the Ischigualasto Formation of Argentina and the Candelária Sequence of Brazil provide the most comprehensive fossil record of herrerasaurs worldwide (Novas et al., Reference Novas, Agnolín, Ezcurra, Müller, Martinelli and Langer2021). Notably, Herrerasaurus ischigualastensis is the most abundant dinosaur taxon from the Ischigualasto Formation of Argentina, with more than 50 specimens recovered to date (Martínez et al., Reference Martínez, Apaldetti, Alcober, Colombi, Sereno, Fernandez, Malnis, Correa and Abelín2013). This represents an overwhelming abundance compared with other herrerasaurid species. This disparity highlights the need for a thorough reassessment of the alpha taxonomy of Herrerasauridae. For example, it remains unclear whether all specimens currently referred to Herrerasaurus ischigualastensis are taxonomically homogeneous. Some specimens were originally assigned to distinct taxa (e.g., “Frenguellisaurus ischigualastensis” Novas, Reference Novas1986; “Ischisaurus cattoi” Reig, Reference Reig1963) but were subsequently regarded as junior synonyms of Herrerasaurus ischigualastensis.

Despite the abundance of herrerasaur remains from the Ischigualasto Formation, the most complete single specimen is known from Carnian-aged deposits of the Candelária Sequence of Brazil. The holotype (CAPPA/UFSM 0009) of Gnathovorax cabreirai comprises a complete and exceptionally well-preserved skeleton of a single individual approximately 3 m in total length (Pacheco et al., Reference Pacheco, Müller, Langer, Pretto, Kerber and da Silva2019). The excellent preservation of bone surfaces in CAPPA/UFSM 0009 (Fig. 10.1), together with minimal deformation caused by sedimentary compression, provides a reliable anatomical basis for understanding these early predatory dinosaurs. To date, this specimen represents one of the best-preserved early dinosaurs known and ranks among the most significant discoveries of the recent wave of finds from Brazil.

Figure 10.

Examples of fossils of Triassic herrerasaurids from southern Brazil. (1) Skull of Gnathovorax cabreirai (CAPPA/UFSM 0009) from the lower portion of the Candelária Sequence. (2) Disarticulated skeleton of a herrerasaurid (CAPPA/UFSM 0433) under study from the lower portion of the Candelária Sequence. Specimens not to scale.

Figure 10. Long description

A two-panel vertical layout of fossil specimens.

Panel 1, at the top, is a photo of the skull of Gnathovorax cabreirai (C A P P A forward slash U F S M 0009). The skull is oriented with the snout pointing toward the bottom right. It features a large, elongated cranium with visible orbital and antorbital fenestrae. A detached lower jaw bone sits in the foreground, showing several sharp, recurved teeth. The fossil has a light tan and reddish-brown coloration against a plain grey surface.

Panel 2, at the bottom, is a photo of a disarticulated herrerasaurid skeleton (C A P P A forward slash U F S M 0433). The bones are embedded in a thick, textured block of reddish-brown sedimentary matrix. Various long bones, including possible limb elements and vertebrae, are scattered across the uneven surface. The bones appear light grey or off-white, contrasting with the dark red earth. The specimen is shown in situ within its protective plaster jacket or excavation block.

In recent years, additional herrerasaur specimens have been described from Carnian-aged deposits of Brazil. Garcia et al. (Reference Garcia, Müller, Pretto, Da-Rosa and Dias-da-Silva2021) reported a large individual (UFSM 11330) composed of both cranial and postcranial remains. Although this specimen is approximately 50% larger than the holotype of Gnathovorax cabreirai (Garcia et al., Reference Garcia, Müller, Pretto, Da-Rosa and Dias-da-Silva2021), it remains smaller than the largest known specimen of Herrerasaurus ischigualastensis (PVSJ 53; Novas, Reference Novas1986). The absence of a diagnostic set of traits has hindered the assignment of UFSM 11330 to any known herrerasaur species. Furthermore, Garcia et al. (Reference Garcia, Müller and Dias-da-Silva2019a) suggested a putative additional specimen of Staurikosaurus pricei based on the reinterpretation of previously indeterminate dinosauromorph remains (BSPG AS XXV 53 and BSPG AS XXV 54). More fragmentary specimens have also been described from other coeval fossiliferous sites in Brazil (Silva et al., Reference Silva, Martinelli, Ferigolo and Ribeiro2023; Garcia et al., Reference Garcia, Cabreira, da Silva, Pretto and Müller2024b; Campo et al., Reference Campo, da Silva, Neto, Ferigolo and Ribeiro2025). Although some of these materials have been interpreted as non-herrerasaurid herrerasaurians (CAPPA/UFSM 0373; Garcia et al., Reference Garcia, Cabreira, da Silva, Pretto and Müller2024b), they nevertheless provide important insights into the broader clade that includes Herrerasauridae.

Until recently, the fossil record of Herrerasauridae in Brazil was limited to the long-known Staurikosaurus pricei (Colbert, Reference Colbert1970; Bittencourt and Kellner, Reference Bittencourt and Kellner2009). This understanding has changed markedly over the last decade with the discovery and reinterpretation of the specimens mentioned above. In addition, several promising specimens are currently under study (Fig. 10.2), including a nearly complete skeleton, which will undoubtedly provide substantially more data on this unusual group of predators that lived for a relatively brief interval at the dawn of the dinosaur era.

The humble origins of majestic creatures

Sauropods are the largest terrestrial animals that have ever existed on Earth. These creatures roamed the Earth for much of the Mesozoic and had a relatively conservative body plan. However, before acquiring their typical body plan, characterized by a long neck, columnar limbs with a quadrupedal gait, and enormous bodies (Sander et al., Reference Sander, Christian, Clauss, Fechner and Gee2011), the precursors of sauropods had a very different morphology. In fact, the earliest members of the clade Sauropodomorpha were the structural opposite of sauropods (Müller et al., Reference Müller, Bronzati, Pacheco, Cabreira, Langer and Dias-da-Silva2018a). The oldest unequivocal sauropodomorphs are recorded from Carnian-aged deposits of South America and Africa (Griffin et al., Reference Griffin, Wynd, Munyikwa, Broderick, Zondo, Tolan, Langer, Nesbitt and Taruvinga2022; Langer et al., Reference Langer, Marsola, Müller, Bronzati, Bittencourt, Apaldetti, Ezcurra, Apaldetti and Pol2022). These forms were small-bodied (< 2 m in length), bipedal, cursorial, and carnivorous (Fig. 11.1; Sereno et al., Reference Sereno, Martínez and Alcober2013; Cabreira et al., Reference Cabreira, Kellner, Dias-da-Silva, Roberto-da-Silva and Bronzati2016). Soon after its origin, the group evolved a suite of traits that would continue to be exaggerated throughout its evolutionary history (Fig. 11.2), including a proportionally small skull (Pretto et al., Reference Pretto, Langer and Schultz2019; Damke et al., Reference Damke, Langer, Da-Rosa and Müller2024a), an elongated neck (Müller et al., Reference Müller, Langer and Dias-da-Silva2018b; Damke et al., Reference Damke, Bem, Doering, Piovesan and Müller2024b; Hechenleitner et al., Reference Hechenleitner, Martinelli, Rocher, Fiorelli, Juarez, Taborda and Desojo2025), an herbivorous diet (Müller and Garcia, Reference Müller and Garcia2020b; Ballell et al., Reference Ballell, Benton and Rayfield2022), a quadrupedal stance (McPhee et al., Reference McPhee, Benson, Botha-Brink, Bordy and Choiniere2018), and large body size (Pol and Powell, Reference Pol and Powell2007; Apaldetti et al., Reference Apaldetti, Martínez, Cerda, Pol and Alcober2018).

Figure 11.

General anatomy and macroevolutionary trends in Sauropodomorpha. (1) Skeleton of Buriolestes schultzi by Maurício S. Garcia. (2) Phylogenetic relationships and evolutionary trends in early sauropodomorphs, with a focus on Brazilian taxa. Life reconstructions by Márcio L. Castro.

Figure 11. Long description

Panel 1 shows a skeletal reconstruction of Buriolestes schultzi in profile, facing right. The skeleton is rendered in white against a black silhouette. It features a small skull, a long neck, a slender torso with a prominent rib cage, and long hind limbs positioned for a bipedal stance. The tail is elongated and extends horizontally to the left.

Panel 2 is a phylogenetic tree illustrating evolutionary trends. The tree begins at a basal node labeled Saurischia. A branch to the left leads to Theropoda, depicted as a small bipedal dinosaur. The main lineage continues to a red node labeled Sauropodomorpha. From this node, the tree branches upward and to the right through several taxa, each accompanied by a life reconstruction.

1. Buriolestes: Small, bipedal, and carnivorous.

2. Bagualosaurus: Larger bipedal form, marking the transition to omnivorous or herbivorous diets and cranial reduction.

3. Macrocollum: Shows a gradual increase in body size and gradual neck elongation.

4. Sauropoda: The final branch, representing gigantic quadrupedal forms with extremely long necks and massive bodies.

Text labels along the branches highlight macroevolutionary trends including bipedal carnivorous origins, omnivorous or herbivorous transitions, cranial reduction, gradual neck elongation, gradual increase in body size, and the emergence of quadrupedal gigantic forms.

The origin and early evolution of sauropodomorphs are well documented in Triassic deposits of South America, with a particularly remarkable record from Brazil and Argentina (Pol et al., Reference Pol, Otero, Apaldetti and Martínez2021; Langer et al., Reference Langer, Marsola, Müller, Bronzati, Bittencourt, Apaldetti, Ezcurra, Apaldetti and Pol2022). Discoveries made over the past three decades form the foundation of our current understanding of the earliest members of the clade (Langer et al., Reference Langer, Abdala, Richter and Benton1999; Martínez and Alcober, Reference Martínez and Alcober2009; Ezcurra, Reference Ezcurra2010; Cabreira et al., Reference Cabreira, Schultz, Bittencourt, Soares, Fortier, Silva and Langer2011, Reference Cabreira, Kellner, Dias-da-Silva, Roberto-da-Silva and Bronzati2016; Pretto et al., Reference Pretto, Langer and Schultz2019; Hechenleitner et al., Reference Hechenleitner, Martinelli, Rocher, Fiorelli, Juarez, Taborda and Desojo2025). Nevertheless, it was during the last decade that a growing number of discoveries (Fig. 12) have shed light on most aspects of the anatomy, diet, development, and behavior of these early dinosaurs (e.g., Cabreira et al., Reference Cabreira, Kellner, Dias-da-Silva, Roberto-da-Silva and Bronzati2016; Bronzati et al., Reference Bronzati, Rauhut, Bittencourt and Langer2017; Reference Bronzati, Müller and Langer2019; Garcia et al., Reference Garcia, Pretto, Dias-da-Silva and Müller2019b; Müller et al., Reference Müller, Pacheco, Langer and Dias-da-Silva2019, Reference Müller2021; Langer et al., Reference Langer, Marsola, Müller, Bronzati, Bittencourt, Apaldetti, Ezcurra, Apaldetti and Pol2022; Moro et al., Reference Moro, Damke, Müller, Kerber and Pretto2024; Hechenleitner et al., Reference Hechenleitner, Martinelli, Rocher, Fiorelli, Juarez, Taborda and Desojo2025). Emerging in ecosystems dominated by rhynchosaurs (Novas et al., Reference Novas, Agnolín, Ezcurra, Müller, Martinelli and Langer2021), the earliest sauropodomorphs were small-bodied predators that likely did not compete directly with fully grown herrerasaurids for prey, but may have competed with the earliest theropod dinosaurs and juvenile herrerasaurids. Gracile jaws, neurocranial features, and elongate hindlimbs indicate that they were agile predators (Bronzati et al., Reference Bronzati, Rauhut, Bittencourt and Langer2017; Müller et al., Reference Müller, Ferreira, Pretto, Bronzati and Kerber2021).

Figure 12.

Examples of fossils of Triassic sauropodomorphs from southern Brazil. (1) Skull of Buriolestes schultzi (CAPPA/UFSM 0035) from the from the lower portion of the Candelária Sequence. (2) Skull and neck of Macrocollum itaquii (CAPPA/UFSM 0001a) from the from the upper portion of the Candelária Sequence. (3) Skull of Saturnalia tupiniquim (UFSM 11660A) from the from the lower portion of the Candelária Sequence. Specimens not to scale.

Figure 12. Long description

This three-panel collection of photos displays fossilized remains of early dinosaurs.

* Panel 1 at the top shows a researcher holding the small, elongated skull of Buriolestes schultzi (C A P P A / U F S M 0035) in their hand. The skull is light brown and white, viewed from the side, showing a row of small, sharp teeth along the upper jaw and a large orbital opening for the eye.

* Panel 2 at the bottom-left shows the skull and articulated neck vertebrae of Macrocollum itaquii (C A P P A / U F S M 0001a) embedded in a reddish-brown sedimentary rock matrix. The neck curves downward and to the right from the skull, which is positioned on the left side of the frame.

* Panel 3 at the bottom-right shows a close-up of the skull of Saturnalia tupiniquim (U F S M 11660A). The fossil is partially encased in chunky red rock. The side view highlights the lower jaw with several distinct, pointed teeth visible and the textured surface of the cranial bones.

The study of Carnian sauropodomorphs began with description of the Brazilian dinosaur Saturnalia tupiniquim Langer et al., Reference Langer, Abdala, Richter and Benton1999, from deposits of the lower portion of the Candelária Sequence. At that time, other dinosaurs of similar age were generally regarded as theropods, including Eoraptor lunensis as well as the herrerasaurids Herrerasaurus ischigualastensis and Staurikosaurus pricei (Sereno et al., Reference Sereno, Forster, Rogers and Monetta1993; Novas, Reference Novas1996). Consequently, when it was described by Langer et al. (Reference Langer, Abdala, Richter and Benton1999), Saturnalia tupiniquim was considered the oldest sauropodomorph then known and became the cornerstone for studies addressing the origin of the group. However, unlike the current view, the body plan of the species was initially interpreted as being more similar to that of post-Carnian sauropodomorphs. As a result, Saturnalia tupiniquim was long depicted as a dinosaur with a relatively long neck and a quadrupedal posture (Langer et al., Reference Langer, Abdala, Richter and Benton1999). Nevertheless, following more detailed descriptions of Saturnalia tupiniquim material (Langer, Reference Langer2003; Langer et al., Reference Langer, França and Gabriel2007; Bronzati et al., Reference Bronzati, Langer and Rauhut2018, Reference Bronzati, Müller and Langer2019), as well as the discovery of new specimens (Damke et al., Reference Damke, Langer, Da-Rosa and Müller2024a), the current interpretation of this sauropodomorph is markedly different, closely resembling other Carnian sauropodomorphs.

Subsequent discoveries from Carnian-aged deposits of Brazil (Cabreira et al., Reference Cabreira, Schultz, Bittencourt, Soares, Fortier, Silva and Langer2011) and Argentina (Martínez and Alcober, Reference Martínez and Alcober2009; Ezcurra, Reference Ezcurra2010) expanded the record of the oldest sauropodomorphs in the years following the description of Saturnalia tupiniquim. In addition, a study published by Martínez et al. (Reference Martínez, Sereno, Alcober, Colombi, Renne, Montañez and Currie2011) placed Eoraptor lunensis as an early sauropodomorph rather than a theropod. At that point, at least five Carnian sauropodomorphs were known from South American deposits. Subsequently, two new species were described from Brazil (Cabreira et al., Reference Cabreira, Kellner, Dias-da-Silva, Roberto-da-Silva and Bronzati2016; Pretto et al., Reference Pretto, Langer and Schultz2019) and, more recently, another from Argentina (Hechenleitner et al., Reference Hechenleitner, Martinelli, Rocher, Fiorelli, Juarez, Taborda and Desojo2025). Currently, eight valid species of Carnian sauropodomorphs are recognized from these deposits: Eoraptor lunensis Sereno et al., Reference Sereno, Forster, Rogers and Monetta1993; Saturnalia tupiniquim Langer et al., Reference Langer, Abdala, Richter and Benton1999; Panphagia protos Martínez and Alcober, Reference Martínez and Alcober2009; Chromogisaurus novasi Ezcurra, Reference Ezcurra2010; Pampadromaeus barberenai Cabreirai et al., Reference Cabreira, Schultz, Bittencourt, Soares, Fortier, Silva and Langer2011; Buriolestes schultzi Cabreira et al., Reference Cabreira, Kellner, Dias-da-Silva, Roberto-da-Silva and Bronzati2016; Bagualosaurus agudoensis Pretto et al., Reference Pretto, Langer and Schultz2019; and Huayracursor jaguensis Hechenleitner et al., Reference Hechenleitner, Martinelli, Rocher, Fiorelli, Juarez, Taborda and Desojo2025.

Most phylogenetic analyses support consistent patterns regarding these oldest forms (Müller et al., Reference Müller, Langer and Dias-da-Silva2018b; Langer et al., Reference Langer, Marsola, Müller, Bronzati, Bittencourt, Apaldetti, Ezcurra, Apaldetti and Pol2022; Fonseca et al., Reference Fonseca, Bem and Müller2025; Hechenleitner et al., Reference Hechenleitner, Martinelli, Rocher, Fiorelli, Juarez, Taborda and Desojo2025), in which Buriolestes schultzi and Eoraptor lunensis are recovered as the basalmost members of Sauropodomorpha, whereas Bagualosaurus agudoensis and Huayracursor jaguensis occupy more derived positions among Carnian-aged taxa. The remaining Carnian-aged species are typically nested within low-diversity clades that fall between the basalmost Buriolestes schultzi and Eoraptor lunensis and the more derived Bagualosaurus agudoensis and Huayracursor jaguensis. This phylogenetic pattern also indicates major changes in the body plan of early sauropodomorphs. Intermediate forms began to exhibit features associated with a shift from a carnivorous diet to an omnivorous one, as evinced by dental morphology (Cabreira et al., Reference Cabreira, Kellner, Dias-da-Silva, Roberto-da-Silva and Bronzati2016; Müller and Garcia, Reference Müller and Garcia2020b). A trend towards a relative reduction in skull size is also observed (Bronzati et al., Reference Bronzati, Müller and Langer2019; Damke et al., Reference Damke, Langer, Da-Rosa and Müller2024a). In the more derived Carnian forms, an increase in overall body size (Pretto et al., Reference Pretto, Langer and Schultz2019; Müller and Garcia, Reference Müller and Garcia2021; Hechenleitner et al., Reference Hechenleitner, Martinelli, Rocher, Fiorelli, Juarez, Taborda and Desojo2025) and a gradual elongation of the neck are likewise evident (Damke et al., Reference Damke, Bem, Doering, Piovesan and Müller2024b; Hechenleitner et al., Reference Hechenleitner, Martinelli, Rocher, Fiorelli, Juarez, Taborda and Desojo2025).

The general skeletal anatomy of the earliest sauropodomorphs shows some degree of variation (Langer et al., Reference Langer, Marsola, Müller, Bronzati, Bittencourt, Apaldetti, Ezcurra, Apaldetti and Pol2022), but several features are consistently observed across most species. Skull size varies among taxa, being relatively large in the basalmost forms (e.g., Buriolestes schultzi; Cabreira et al., Reference Cabreira, Kellner, Dias-da-Silva, Roberto-da-Silva and Bronzati2016) and proportionally smaller in more derived species (e.g., Bagualosaurus agudoensis; Pretto et al., Reference Pretto, Langer and Schultz2019). The external naris is typically large and associated with an enlarged narial fossa. The premaxilla bears four tooth positions, and its alveolar margin is usually anteroventrally inclined relative to the maxilla. A row of foramina perforates the lateral surface of the maxilla, and the antorbital fossa extends over a wide portion of the ascending process of that element. The lateral surface of the nasal is well developed and forms a broad roof over the antorbital fenestra. The jugal has slender proportions, and the orbit is large and subcircular. The ventral process of the squamosal is slender and elongated. The craniomandibular articulation is displaced slightly ventral to the maxillary tooth row. The dorsal surface of the anterior tip of the dentary is ventrally inclined, and a short edentulous area is present at its anterior end.

The dentition of the earliest forms is typically ziphodont (Cabreira et al., Reference Cabreira, Kellner, Dias-da-Silva, Roberto-da-Silva and Bronzati2016). In addition, palatal teeth are present on the pterygoid of Pampadromaeus barberenai (Cabreira et al., Reference Cabreira, Schultz, Bittencourt, Soares, Fortier, Silva and Langer2011), Eoraptor lunensis (Sereno et al., Reference Sereno, Martínez and Alcober2013), and Buriolestes schultzi (Müller et al., Reference Müller, Bronzati, Pacheco, Cabreira, Langer and Dias-da-Silva2018a). In Pampadromaeus barberenai and Bagualosaurus agudoensis, some tooth serrations form oblique angles relative to the main axis of the tooth. This feature is more common among post-Carnian sauropodomorphs.

The axial skeleton of Carnian-aged sauropodomorphs lacks pneumatic features invading the vertebrae (Aureliano et al., Reference Aureliano, Ghilardi, Müller, Kerber, Pretto, Fernandes, Ricardi-Branco and Wedel2022). The neck is relatively short in the basalmost forms, but the cervical vertebrae become progressively more elongate in derived taxa (Damke et al., Reference Damke, Bem, Doering, Piovesan and Müller2024b; Hechenleitner et al., Reference Hechenleitner, Martinelli, Rocher, Fiorelli, Juarez, Taborda and Desojo2025). The dorsal vertebrae bear laminae and fossae, as well as an intervertebral articulation of the hyposphene-hypantrum type. The sacrum is composed of three vertebrae, two of which are primordial sacrals, whereas the additional element may be derived either from the dorsal series (Sereno et al., Reference Sereno, Martínez and Alcober2013) or from the caudal series (Cabreira et al., Reference Cabreira, Kellner, Dias-da-Silva, Roberto-da-Silva and Bronzati2016).

The pectoral girdle is relatively robust, at least when compared to that of herrerasaurids. The humerus of the earliest sauropodomorphs is more gracile than that of post-Carnian forms. The ulna usually bears a well-developed olecranon process, and the first phalanx of digit I of the manus is rotated relative to its main axis. The acetabulum of the pelvic girdle is only slightly perforated and retains well-developed medial walls. The postacetabular process of the ilium is elongate and bears rugosities on its dorsolateral surface. The pubis and ischium are elongated. The distal end of the pubis lacks a well-developed pubic boot; however, a slight expansion is present. The femur is sigmoid and shorter than the tibia and fibula. Several muscle scars are present on the proximal and distal regions of the femur. As in other early dinosaurs, the astragalus and calcaneum are not fused. The pes is gracile, with an elongate digit I, whereas digit V is poorly developed.

In addition to these Carnian-aged sauropodomorphs, deposits from the upper portion of the Candelária Sequence in Brazil have also yielded sauropodomorphs that represent the next phase of the radiation of these dinosaurs (Leal et al., Reference Leal, Azevedo, Kellner and Da Rosa2004; Bittencourt et al., Reference Bittencourt, Leal, Langer and Azevedo2012, Reference Bittencourt, da Rosa, Schultz and Langer2013; Müller et al., Reference Müller, Langer and Dias-da-Silva2018b; Bem and Müller, Reference Bem and Müller2024). Among these records, one of the most remarkable is Macrocollum itaquii Müller et al., Reference Müller, Langer and Dias-da-Silva2018b. This dinosaur represents the first complete dinosaur ever discovered in Brazil. Furthermore, the holotype and paratypes were excavated in association, revealing at least four individuals that are nearly complete and articulated (Müller et al., Reference Müller, Da-Rosa, da Silva, Aires, Pacheco, Pavanatto and Dias-da-Silva2015). This species provides one of the best examples for the early stages at which sauropodomorphs became relatively large and evolved several adaptations for consuming vegetation. The body plan of these forms is characterized by proportionally small skulls with large external nares, a markedly elongated neck, robust forelimbs, a partially open acetabulum, an almost straight femur longer than the tibia, and a total body length exceeding 3 m (Leal et al., Reference Leal, Azevedo, Kellner and Da Rosa2004; Müller et al., Reference Müller, Langer and Dias-da-Silva2018b; Müller, Reference Müller2020; Fonseca et al., Reference Fonseca, Bem and Müller2025; Reference Fonseca, Bem, Dalle-Laste, Garcia and Müller2026). Most of these traits seem to be related to a dietary shift, in which sauropodomorphs adopted vegetation as an important component of their diet, becoming larger, more widespread, and more abundant. Notably, sauropodomorphs of similar age and morphology have also been recorded from other regions of the world, such as India (Novas et al., Reference Novas, Ezcurra, Chatterjee and Kutty2011; Ezcurra et al., Reference Ezcurra, Müller, Novas and Chatterjee2024), indicating that the radiation of unaysaurids extended beyond what is now South America.

In sum, Triassic-aged deposits from Brazil provide a key record of the earliest sauropodomorphs, as well as of subsequent stages in the evolutionary history of this group. From the basalmost members of the clade to the first typical “prosauropods”. Brazil preserves one of the most remarkable and informative records of early sauropodomorphs worldwide. Because much of the anatomy of the Brazilian forms is now well documented, future studies can focus on more in-depth investigations, such as development, behavior, biology, and the ecological roles of these precursors of the majestic giants.

The fragmentary record of the ancestors of the largest terrestrial predators

During their evolutionary history, predatory dinosaurs with trenchant claws and powerful jaws came to dominate terrestrial ecosystems. Although large theropods readily occupied the apex predator niche throughout the late Norian and the rest of the Mesozoic (Arcucci and Coria, Reference Arcucci and Coria2003; Cobos et al., Reference Cobos, Lockley, Gasco, Royo-Torres and Alcala2014; Hendrickx et al., Reference Hendrickx, Stiegler, Currie, Han, Xu, Choiniere and Wu2020; Holtz, Reference Holtz2021; Tanaka et al., Reference Tanaka, Anvarov, Zelenitsky, Ahmedshaev and Kobayashi2021), the origin of this lineage was far more modest (Fig. 13.1, 13.2). During the Carnian, herrerasaurids were top-tier predators (Novas, Reference Novas1986; Pacheco et al., Reference Pacheco, Müller, Langer, Pretto, Kerber and da Silva2019; Garcia et al., Reference Garcia, Müller, Pretto, Da-Rosa and Dias-da-Silva2021; Novas et al., Reference Novas, Agnolín, Ezcurra, Müller, Martinelli and Langer2021), whereas theropods were only beginning to diversify (Martínez et al., Reference Martínez, Sereno, Alcober, Colombi, Renne, Montañez and Currie2011, Reference Martínez, Colombi, Ezcurra, Abelín, Cerda and Alcober2025; Müller, Reference Müller2021). In contrast to their immediate sister group, Sauropodomorpha, the fossil record of theropods in Carnian-aged deposits is sparse (Novas et al., Reference Novas, Agnolín, Ezcurra, Müller, Martinelli and Langer2021).

Figure 13.

General anatomy and alternative phylogenetic hypotheses of Theropoda. (1) Skeleton of an early theropod by Maurício S. Garcia. (2) Life reconstruction of Erythrovenator jacuiensis by Márcio L. Castro. (3) Theropods as saurischians (sister group to Sauropodomorpha). (4) Theropods as ornithoscelidans (sister group to Ornithischia). Life reconstructions by Márcio L. Castro.

Figure 13. Long description

The diagram is divided into four numbered panels.

Panel 1 shows a skeletal reconstruction of an early theropod by Maurício S. Garcia. The skeleton is shown in profile facing left, with white bones highlighted against a black silhouette of the body. It features a long neck, slender limbs, and a long tail.

Panel 2 shows a life reconstruction of Erythrovenator jacuiensis by Márcio L. Castro. The dinosaur is depicted with brown and tan skin, dark vertical stripes along its back, and a light-colored underside. It is bipedal with three-toed feet and small forelimbs.

Panel 3 illustrates the Saurischia hypothesis. A phylogenetic tree rooted at Dinosauria splits into Ornithischia on the left and a clade on the right. This right clade, labeled Saurischia with a red dot at the node, branches into Sauropodomorpha and Theropoda. Theropoda is highlighted in red text.

Panel 4 illustrates the Ornithoscelida hypothesis. The tree rooted at Dinosauria splits into Sauropodomorpha on the left and a clade on the right. This right clade, labeled Ornithoscelida with a red dot at the node, branches into Ornithischia and Theropoda. Theropoda is again highlighted in red text.

Both trees use small life reconstructions by Márcio L. Castro to represent the terminal taxa: a robust quadrupedal Ornithischian, a long-necked Sauropodomorph, and a slender bipedal Theropod.

For nearly two decades after its description, the Argentinean Eoraptor lunensis was regarded as one of the earliest theropods (Sereno et al., Reference Sereno, Forster, Rogers and Monetta1993; Novas, Reference Novas1996; Baron et al., Reference Baron, Norman and Barrett2017). This small, bipedal, faunivorous dinosaur conformed well to expectations for an early theropod body plan and, consequently, was widely treated as a model taxon for the origin of Theropoda. However, the discovery of a new dinosaur skeleton from the same strata that yielded Eoraptor lunensis fundamentally altered this interpretation. This material was described as Eodromaeus murphi Martínez et al., Reference Martínez, Sereno, Alcober, Colombi, Renne, Montañez and Currie2011, another small and gracile dinosaur characterized by elongated hind limbs and ziphodont dentition, indicative of a cursorial predatory lifestyle. Since then, Eoraptor lunensis has been considered an early sauropodomorph (Cabreira et al., Reference Cabreira, Kellner, Dias-da-Silva, Roberto-da-Silva and Bronzati2016; Müller et al., Reference Müller, Bronzati, Pacheco, Cabreira, Langer and Dias-da-Silva2018a; Novas et al., Reference Novas, Agnolín, Ezcurra, Müller, Martinelli and Langer2021; Langer et al., Reference Langer, Marsola, Müller, Bronzati, Bittencourt, Apaldetti, Ezcurra, Apaldetti and Pol2022).

In contrast to Eoraptor lunensis, the morphology of the jaws and teeth, the configuration of the manus, and the presence of skeletal pneumaticity in Eodromaeus murphi suggested closer phylogenetic affinities with Theropoda (Martínez et al., Reference Martínez, Sereno, Alcober, Colombi, Renne, Montañez and Currie2011; Sereno et al., Reference Sereno, Martínez and Alcober2013). As a result, Eoraptor lunensis was removed from Theropoda and reinterpreted as an early sauropodomorph. At that time, no additional unequivocal theropods had been recovered from coeval Carnian-aged strata. Actually, Eodromaeus murphi has been recovered as a non-theropod saurischian dinosaur in several studies (e.g., Cabreira et al., Reference Cabreira, Kellner, Dias-da-Silva, Roberto-da-Silva and Bronzati2016; Langer et al., Reference Langer, Ezcurra, Rauhut, Benton, Knoll, McPhee, Novas, Pol and Brusatte2017; Pacheco et al., Reference Pacheco, Müller, Langer, Pretto, Kerber and da Silva2019; Müller and Garcia, Reference Müller and Garcia2020a; Fonseca et al., Reference Fonseca, Reid, Venner, Duncan, Garcia and Müller2024), rendering its phylogenetic placement as a theropod questionable. More recently, however, a new theropod species was described from the Ischigualasto Formation of Argentina. Anteavis crurilongus Martínez et al., Reference Martínez, Colombi, Ezcurra, Abelín, Cerda and Alcober2025, is represented by a partial skeleton including cranial remains and articulated postcranial elements. This new taxon provides additional insights into the earliest traits to evolve within Theropoda (Martínez et al., Reference Martínez, Colombi, Ezcurra, Abelín, Cerda and Alcober2025).

Based on the fossils of Eodromaeus murphi and Anteavis crurilongus, it is possible to obtain a relatively clear picture of the earliest members of the theropod lineage. Unlike most herrerasaurids, early theropods were small-bodied animals, reaching approximately 1.5 m in total length, and exhibited a gracile body plan with elongated limbs (Martínez et al., Reference Martínez, Sereno, Alcober, Colombi, Renne, Montañez and Currie2011, Reference Martínez, Colombi, Ezcurra, Abelín, Cerda and Alcober2025). These dinosaurs were carnivorous, as indicated by the presence of ziphodont teeth. In both species, a promaxillary foramen perforates the anterior margin of the antorbital fossa of the maxilla, a feature commonly observed in neotheropods. The maxilla bears fewer tooth positions than in early sauropodomorphs (~11 in Eodromaeus murphi versus 17 in Eoraptor lunensis; Martínez et al., Reference Martínez, Sereno, Alcober, Colombi, Renne, Montañez and Currie2011). The jugal is gracile, with the anterior ramus being slender. Unlike some early neotheropods, there is no evidence of any bony crest on the dorsal surface of the skull in Carnian-aged theropods. The first dentary tooth is located at the anterior end of the dentary, thus it lacks a short edentulous region.

In Eodromaeus murphi, some evidence of pneumaticity in the axial skeleton has been reported (Martínez et al., Reference Martínez, Sereno, Alcober, Colombi, Renne, Montañez and Currie2011), a condition that is not observed in the fossil material of Anteavis crurilongus (Martínez et al., Reference Martínez, Colombi, Ezcurra, Abelín, Cerda and Alcober2025). The neck is only slightly elongated, differing from that of some post-Carnian theropods. Laminae bordering fossae are present on the cervical and dorsal vertebrae. The sacrum of the earliest theropods is composed of three to four vertebrae. The forelimb is comparatively shorter than the hind limb.

The manus of Eodromaeus murphi is composed of three functional digits (I, II, and III) bearing ungual phalanges, whereas digits IV and V are strongly reduced. Unfortunately, a relatively complete manus is not yet known for Anteavis crurilongus. However, based on the manus of Eodromaeus murphi, it can be observed that there is no rotation of the main axis of phalanx 1 of digit I (Martínez et al., Reference Martínez, Sereno, Alcober, Colombi, Renne, Montañez and Currie2011). The pelvic girdle of Anteavis crurilongus also displays a combination of features typical of theropods, including the fusion of the ilium, pubis, and ischium, as well as the presence of a notch between the posterior ventral margin of the obturator process and the shaft of the ischium (Martínez et al., Reference Martínez, Colombi, Ezcurra, Abelín, Cerda and Alcober2025). Unlike several post-Triassic theropods, the astragalus and calcaneum are neither fused to each other nor to the tibia and fibula. Several other aspects of the anatomy of the earliest theropods are similar to those of the earliest sauropodomorphs (Cabreira et al., Reference Cabreira, Schultz, Bittencourt, Soares, Fortier, Silva and Langer2011, Reference Cabreira, Kellner, Dias-da-Silva, Roberto-da-Silva and Bronzati2016; Langer, Reference Langer2014; Müller et al., Reference Müller, Bronzati, Pacheco, Cabreira, Langer and Dias-da-Silva2018a; Novas et al., Reference Novas, Agnolín, Ezcurra, Müller, Martinelli and Langer2021).

Regarding the phylogenetic affinities of Theropoda, most recent studies agree on their placement within Saurischia, as the sister group to Sauropodomorpha (Fig. 13.3; Langer et al., Reference Langer, Ezcurra, Rauhut, Benton, Knoll, McPhee, Novas, Pol and Brusatte2017; Nesbitt et al., Reference Nesbitt, Butler, Ezcurra, Barrett and Stocker2017; Ezcurra et al., Reference Ezcurra, Nesbitt, Bronzati, Dalla Vecchia, Agnolín, Benson, Brissón Egli, Cabreira, Evers and Gentil2020; Müller and Garcia, Reference Müller and Garcia2020a). However, an alternative hypothesis places theropods as the sister group of Ornithischia, forming the clade Ornithoscelida (Fig. 13.4; Baron et al., Reference Baron, Norman and Barrett2017). Under this scenario, sauropodomorphs and herrerasaurids together constitute Saurischia, which no longer includes Theropoda. Ornithischians are at the center of this debate, as well as of the different hypotheses concerning the placement of silesaurids.

Historically, there are few records of Triassic-aged theropods from Brazilian deposits. According to Langer et al. (Reference Langer, Bittencourt and Schultz2011), one putative record is Guaibasaurus candelariensis Bonaparte, Ferigolo, and Ribeiro, Reference Bonaparte, Ferigolo and Ribeiro1999 (Fig. 14.1). This taxon is known from several partial skeletons and fragmentary material (Bonaparte et al., Reference Bonaparte1999, Reference Bonaparte, Brea, Schultz and Martinelli2007; Langer et al., Reference Langer, Bittencourt and Schultz2011). Nevertheless, its phylogenetic affinities have long been debated (Langer and Benton, Reference Langer and Benton2006; Novas et al., Reference Novas, Agnolín, Ezcurra, Müller, Martinelli and Langer2021), particularly because the available specimens are poorly preserved and lack cranial and cervical elements. Adding to this issue is the fact that the preserved elements of Guaibasaurus candelariensis are commonly subject to significant taphonomic alteration, including incomplete preservation of the ends of long bones and sedimentary compression. With advances in our understanding of early sauropodomorphs, most recent phylogenetic analyses support sauropodomorph, rather than theropodan, affinities for Guaibasaurus candelariensis (Baron et al., Reference Baron, Norman and Barrett2017; Müller and Garcia, Reference Müller and Garcia2020a; Norman et al., Reference Norman, Baron, Garcia and Müller2022; Fonseca et al., Reference Fonseca, Bem and Müller2025). Therefore, the contribution of this taxon to our understanding of the early evolutionary history of Theropoda remains ambiguous. Nevertheless, several discoveries over the last decade have highlighted the potential for future findings of Triassic-aged theropods in Brazil. Pinheiro (Reference Pinheiro2016) assigned the distal portion of a small left femur (MMACR 039 T), from the upper portion of the Candelária Sequence (Caturrita Formation), to a neotheropod. Similar to the case of Guaibasaurus candelariensis, new sauropodomorph material from the same geological units that yielded MMACR 039 T indicates that some putative theropod traits observed in this specimen are more widely distributed. Furthermore, the specimen shares a similar morphology with unaysaurid sauropodomorphs (e.g., Ezcurra et al., Reference Ezcurra, Müller, Novas and Chatterjee2024), a group that is recorded from the same beds (Leal et al., Reference Leal, Azevedo, Kellner and Da Rosa2004; Müller et al., Reference Müller, Langer and Dias-da-Silva2018b).

Figure 14.

Examples of fossils of Triassic putative theropods from southern Brazil. (1) Partial skeleton of Guaibasaurus candelariensis (UFRGS-PV0725T) from the from the upper portion of the Candelária Sequence. Note that most recent phylogenetic investigations have recovered this taxon as a sauropodomorph dinosaur. (2) Left femur of Erythrovenator jacuiensis Müller, Reference Müller2021 (CAPPA/UFSM 0157) from the from the Candelária Sequence. Specimens not to scale.

Figure 14. Long description

Panel 1 is a photo of the partial skeleton of Guaibasaurus candelariensis (U F R G S - P V 0 7 2 5 T) embedded in a reddish-brown sedimentary matrix. The fossil shows an articulated series of dorsal vertebrae and ribs curving across the top and right side. Below the ribs, long bones of the hind limb are visible. A small white rectangular scale card with a green and yellow logo is placed in the center for size reference. Panel 2 is a photo of the proximal portion of a left femur from Erythrovenator jacuiensis (C A P P A / U F S M 0 1 5 7). The fossil is dark brown and is being held between a person’s thumb and fingers. The number 0 1 5 7 is written in black ink on the rounded head of the femur. The background is dark and out of focus.

Another specimen attributed to Theropoda is the holotype (LPRP/USP 0651) of Nhandumirim waldsangae Marsola et al., Reference Marsola, Bittencourt, Butler, Da Rosa, Sayão and Langer2018. This taxon was described based on a skeletally immature individual from the lower portion of the Candelária Sequence (Santa Maria Formation; Marsola et al., Reference Marsola, Bittencourt, Butler, Da Rosa, Sayão and Langer2018). The beds that yielded Nhandumirim waldsangae are coeval with those from which the Argentine taxa Eodromaeus murphi and Anteavis crurilongus were recovered. If Nhandumirim waldsangae indeed belongs to Theropoda, it would represent the oldest record of the clade in Brazil. Conversely, the phylogenetic position of this taxon remains controversial (Novas et al., Reference Novas, Agnolín, Ezcurra, Müller, Martinelli and Langer2021), with several studies recovering it as a sauropodomorph (Pacheco et al., Reference Pacheco, Müller, Langer, Pretto, Kerber and da Silva2019; Norman et al., Reference Norman, Baron, Garcia and Müller2022; Fonseca et al., Reference Fonseca, Bem and Müller2025). The skeletally immature status of the holotype also adds further difficulties in assessing its phylogenetic affinities (Müller et al., Reference Müller, Damke and Terras2024).

Finally, the most recently described theropod from the Triassic of Brazil is Erythrovenator jacuiensis Müller, Reference Müller2021 (Fig. 14.2). As with most material attributed to Theropoda from Brazilian Triassic-aged strata, the holotype (CAPPA/UFSM 0157) is very incomplete, being limited to the proximal portion of a left femur (Müller, Reference Müller2021). The specimen was recovered from a locality assigned to the upper portion of the Candelária Sequence, regarded as lying between the Hyperodapedon and Riograndia Assemblage zones, and therefore close in age to the early Norian (Doering et al., Reference Doering, Ezcurra, Schiefelbein, Garcia and Müller2024; Dalle-Laste et al., Reference Dalle-Laste, Garcia, Aureliano, Ghilardi, Kerber and Müller2025; Roese-Miron et al., Reference Roese-Miron, Abdala, Pretto, Müller, Michelotti da Costa, Sánchez-Villagra and Kerber2025).

Better-preserved specimens are still necessary to construct a more reliable interpretation on these ambiguous theropods, highlighting the search for theropods as one of the most challenging aspects of studying the origins of dinosaurs in Brazil. Fortunately, the growing number of discoveries offers a promising outlook for the coming years.

Soft tissues and paleobiology

Recently excavated Triassic dinosaurs from Brazil have yielded exceptional anatomical information, including complete and articulated skeletons (e.g., Müller et al., Reference Müller, Langer and Dias-da-Silva2018b; Pacheco et al., Reference Pacheco, Müller, Langer, Pretto, Kerber and da Silva2019). The expansion of our knowledge of the anatomy of these early dinosaurs has not only established a robust basis for comparative anatomical studies but has also contributed to the development of more detailed and refined phylogenetic hypotheses. Nevertheless, these new discoveries have also helped elevate the study of dinosaur origins to a new level. Multiple lines of investigation have provided novel data on various aspects of the biology and life history of these animals (Bronzati et al., Reference Bronzati, Rauhut, Bittencourt and Langer2017; Müller et al., Reference Müller, Ferreira, Pretto, Bronzati and Kerber2021; Damke et al., Reference Damke, Langer, Da-Rosa and Müller2024a; Moro et al., Reference Moro, Damke, Müller, Kerber and Pretto2024; Garcia et al., Reference Garcia, Martínez and Müller2025), offering insights that were not accessible until relatively recently. Some of these research efforts, based on discoveries involving Triassic-aged dinosaur fossils from Brazil, are discussed below.

The brain anatomy of the earliest dinosaurs remained almost entirely unknown until the description of a cranial endocast of Saturnalia tupiniquim by Bronzati et al. (Reference Bronzati, Rauhut, Bittencourt and Langer2017). Using computed tomography techniques, the authors reconstructed a partial endocast that revealed a well-developed floccular and parafloccular lobe of the cerebellum. This condition was interpreted as indicating that Saturnalia tupiniquim may have been capable of maintaining visual focus on prey while coordinating rapid movements of the neck and skull (Bronzati et al., Reference Bronzati, Rauhut, Bittencourt and Langer2017). Thus, this study not only provided rare insights into soft-tissue anatomy, but also suggested aspects of the hunting behavior of this species. This behavior is consistent with the faunivorous diet indicated by the dental morphology of Saturnalia tupiniquim (Bronzati et al., Reference Bronzati, Rauhut, Bittencourt and Langer2017, Müller and Garcia, Reference Müller and Garcia2020b; Damke et al., Reference Damke, Langer, Da-Rosa and Müller2024a).

A second cranial endocast was described some years later by Müller et al. (Reference Müller2021) for the early sauropodomorph Buriolestes schultzi (Fig. 15). In contrast to the specimen of Saturnalia tupiniquim, this endocast was more complete, including the olfactory bulbs and tracts. Observations derived from this specimen corroborated the presence of a well-developed floccular and parafloccular lobe of the cerebellum. Similarly, Buriolestes schultzi also appears to have been capable of maintaining visual tracking of prey while executing rapid, coordinated movements of the head and neck (Fig. 16.1). Additionally, the endocast provided information on olfactory acuity, suggesting that olfaction played an important role during the early evolutionary history of sauropodomorphs (Müller, Reference Müller2022a).

Figure 15.

Digital cranial endocast of the early sauropodomorph Buriolestes schultzi, based on specimen CAPPA/UFSM 0035 (Müller et al., Reference Müller, Ferreira, Pretto, Bronzati and Kerber2021), from the lower portion of the Candelária Sequence. Endocasts in the upper portion of the figure are shown in dorsal view. Life reconstructions by Márcio L. Castro.

Figure 15. Long description

The diagram consists of five main visual components connected by blue curved arrows.

1. Bottom-right: A circular inset photo shows a hand holding the actual fossilized skull of Buriolestes schultzi, which is reddish-brown and white.

2. Center: A C T scan reconstruction of the skull in lateral view, rendered in off-white with the internal brain cavity highlighted in yellow and blue.

3. Top-left: A dorsal view of the skull reconstruction showing the blue endocast nested within the translucent bone structure.

4. Top-right: An isolated, high-detail blue digital endocast. Moving from the anterior (front) to posterior (back), the labels identify:

- olfactory bulb: the most anterior rounded structure.

- olfactory tract: the narrow bridge connecting the bulb to the main brain mass.

- cerebral hemisphere: the large, textured dorsal swelling.

- flocculus: a small lateral protrusion near the base.

- endosseous labyrinth: a pink-colored structure representing the inner ear, located at the postero-ventral corner.

5. Bottom-left: A life reconstruction of the dinosaur’s head and neck, showing a slender, bipedal reptile with brown pebbled skin and an open mouth revealing small teeth.

Figure 16.

Life reconstructions of dinosaurs illustrating behavioral traits inferred from anatomical, taphonomic, and paleoecological analyses of Triassic fossils from Rio Grande do Sul. (1) An individual of the early sauropodomorph Buriolestes schultzi exhibiting predatory behavior toward a lepidosauromorph. Artwork by Márcio L. Castro. (2) Individuals of the unaysaurid sauropodomorph Macrocollum itaquii exhibiting gregarious behavior while feeding on vegetation. Artwork by Márcio L. Castro. (3) Two individuals of herrerasaurid Gnathovorax cabreirai engaging in intraspecific combat. Artwork by Caio Fantini.

Figure 16. Long description

Panel 1 at the top shows a Buriolestes schultzi, a small bipedal dinosaur with a long tail and slender neck, lunging with an open mouth toward a small green lizard-like lepidosauromorph perched on a tree branch to the right. The setting is a lush forest with ferns in the foreground.

Panel 2 in the middle depicts a group of three Macrocollum itaquii. The central individual is shown in profile facing left with its long neck extended upward. Two other individuals are visible in the background, one grazing on the ground and another walking, illustrating social herding behavior in a misty coniferous forest.

Panel 3 at the bottom illustrates two Gnathovorax cabreirai engaged in a violent struggle. One individual stands over the other, biting down on the lower jaw of the pinned dinosaur. Both animals have scaly, blue-grey skin with striped patterns on their tails and are positioned in a dense, sun-dappled woodland environment.

Also, with respect to sauropodomorphs, the discovery of articulated skeletons of Macrocollum itaquii provided the oldest compelling evidence for gregarious behavior in dinosaurs (Fig. 16.2), suggesting that, at least within the sauropodomorph lineage, this clade had already developed such behavior by the early Norian (Müller et al., Reference Müller, Langer and Dias-da-Silva2018b). The increasing number of articulated and partially articulated skeletons of Buriolestes schultzi (Cabreira et al., Reference Cabreira, Kellner, Dias-da-Silva, Roberto-da-Silva and Bronzati2016; Müller et al., Reference Müller, Bronzati, Pacheco, Cabreira, Langer and Dias-da-Silva2018a) and Saturnalia tupiniquim (Langer et al., Reference Langer, Abdala, Richter and Benton1999; Damke et al., Reference Damke, Langer, Da-Rosa and Müller2024a) recovered from the same stratigraphic layers and localities may offer additional insights into this behavior.

The development of the earliest dinosaurs has also been a focus of investigation in recent years. Previous studies have demonstrated that early dinosaurs and their close relatives exhibited high levels of intraspecific variation throughout ontogeny (Piechowski et al., Reference Piechowski, Tałanda and Dzik2014; Griffin and Nesbitt, Reference Griffin and Nesbitt2016a, Reference Griffin and Nesbitt2016b; Griffin, Reference Griffin2018; Müller et al., Reference Müller, Pacheco, Langer and Dias-da-Silva2019; Barta et al., Reference Barta, Griffin and Norell2022). Data derived from Triassic-aged dinosaurs from Brazil provide further support for this pattern (Garcia et al., Reference Garcia, Pretto, Dias-da-Silva and Müller2019b; Müller et al., Reference Müller, Pacheco, Langer and Dias-da-Silva2019; Müller, Reference Müller2022b; Damke et al., Reference Damke, Langer, Da-Rosa and Müller2024a; Moro et al., Reference Moro, Damke, Müller, Kerber and Pretto2024). Notably, skeletally immature individuals of a given species were found to differ more markedly from conspecific adults than those adults differ from individuals of closely related species (Müller et al., Reference Müller, Pacheco, Langer and Dias-da-Silva2019). In addition, individuals within the same species could attain highly variable body masses, depending on overall skeletal robustness (Moro et al., Reference Moro, Damke, Müller, Kerber and Pretto2024). Consequently, skeletal plasticity in early dinosaurs was not restricted to the presence and morphology of specific muscle attachment sites, but also encompassed overall bone shape, ranging from gracile to robust morphotypes, with implications for their potential ecological roles.

In addition to skeletal plasticity, another important aspect of dinosaur physiology is the presence of an invasive air sac system (Farmer, Reference Farmer2006; Wedel, Reference Wedel2009). Although this condition is well documented in sauropods and theropods (Wedel, Reference Wedel2009; Sereno et al., Reference Sereno, Martinez, Wilson, Varricchio, Alcober and Larsson2008; Aureliano et al., Reference Aureliano, Almeida, Rasaona and Ghilardi2026a), its origin remains poorly understood. The first investigations aimed at assessing the presence or absence of an invasive air sac system in the axial skeleton of the earliest dinosaurs were conducted using exquisitely preserved Triassic specimens from Brazil. These studies revealed that the earliest sauropodomorphs (Buriolestes schultzi and Pampadromaeus barberenai) and herrerasaurids (Gnathovorax cabreirai) lack evidence for the presence of such features (Aureliano et al., Reference Aureliano, Ghilardi, Müller, Kerber, Pretto, Fernandes, Ricardi-Branco and Wedel2022). This finding indicated that invasive vertebral pneumaticity evolved independently within the dinosaur clades Theropoda and Sauropodomorpha. Subsequent investigations demonstrated the putative presence of an invasive air sac system in the Norian-aged sauropodomorph Macrocollum itaquii, representing the oldest known evidence of this condition within Dinosauria (Aureliano et al., Reference Aureliano, Ghilardi, Müller, Kerber, Fernandes, Ricardi-Branco and Wedel2024). Further analyses also documented the presence of pneumatic foramina and internal chambers in the dorsal vertebrae of the Brazilian lagerpetid Venetoraptor gassenae, indicating an even earlier origin of this condition within Pterosauromorpha than within Dinosauria (Aureliano et al., Reference Aureliano, Müller, Holgado, Kerber and Ghilardi2026b). Based on current evidence, an invasive air sac system in the axial skeleton likely evolved independently at least three times (i.e., pterosauromorpha, sauropodomorpha, and theropoda) during the early evolutionary history of avemetatarsalians (Aureliano et al., Reference Aureliano, Ghilardi, Müller, Kerber, Pretto, Fernandes, Ricardi-Branco and Wedel2022, Reference Aureliano, Ghilardi, Müller, Kerber, Fernandes, Ricardi-Branco and Wedel2024, Reference Aureliano, Müller, Holgado, Kerber and Ghilardi2026b).

More direct evidence of behavior in early dinosaurs was recently documented by Garcia et al. (Reference Garcia, Martínez and Müller2025), who described craniofacial lesions in herrerasaurid specimens from Brazil and Argentina. These cranial pathologies were interpreted as resulting from intraspecific agonistic interactions (Fig. 16.3; Garcia et al., Reference Garcia, Martínez and Müller2025), a behavioral pattern also documented in theropod dinosaurs from younger deposits (Tanke and Currie, Reference Tanke and Currie1998; Brown et al., Reference Brown, Currie and Therrien2022). The lesions identified in herrerasaurids represent the oldest known evidence of pathology in dinosaurs and provide important insights into the paleobiology and behavior of the earliest large-bodied predatory dinosaurs.

As previously mentioned, research on the earliest dinosaurs has moved beyond purely anatomical and phylogenetic investigations to explore more specific aspects of their biology. This research area is still in an early stage of development and frequently relies on exceptional discoveries or the application of advanced analytical and imaging techniques. With the growing number of discoveries, including exceptionally well-preserved fossils, it is expected that this field will continue to expand, providing access to progressively more detailed and informative insights into the biology and life history of the earliest dinosaurs.