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Post-Triassic theropod, sauropodomorph, and ornithischian dinosaurs are readily recognized based on the set of traits that typically characterize each of these groups. On the contrary, most of the early members of those lineages lack such specializations, but share a range of generalized traits also seen in more basal dinosauromorphs. Here, we report on a new Late Triassic dinosaur from the Santa Maria Formation of Rio Grande do Sul, southern Brazil. The specimen comprises the disarticulated partial skeleton of a single individual, including most of the skull bones. Based on four phylogenetic analyses, the new dinosaur fits consistently on the sauropodomorph stem, but lacks several typical features of sauropodomorphs, showing dinosaur plesiomorphies together with some neotheropod traits. This is not an exception among basal dinosaurs, the early radiation of which is characterized by a mosaic pattern of character acquisition, resulting in the uncertain phylogenetic placement of various early members of the group.
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... Members of the clade recorded from Carnian beds have relatively short necks or just slightly elongated cervical vertebrae when compared to non-dinosaur dinosauriforms (Bronzati et al., 2017;Müller, Langer, Bronzati, et al., 2018;Sereno et al., 2013). The condition is unknown in forms from strata that immediately overlap these beds (e.g., Cabreira et al., 2011;Pretto et al., 2019). Therefore, the fossil record displays a gap between the short neck of earliest members (±233 Ma) and the elongated neck of forms from early Norian (±225 Ma). ...
... These strata are Carnian in age (±233 Ma; Langer et al., 2018). The younger strata revealed forms that are slightly larger, with dental modifications related to an omnivorous to herbivorous diet: Pampadromaeus barberenai (Cabreira et al., 2011) and Bagualosaurus agudoensis . Whereas these layers were not radioisotopic dated, putative coeval strata from Argentina are approximately 288 Ma in age (Desojo et al., 2020). ...
... It was excavated from the "V arzea do Agudo" (= "Janner"; Figure 1b) site (29 39 0 10.89 00 S, 53 17 0 34.20 00 W), which is situated within the municipality of Agudo, Rio Grande do Sul, Brazil (Figure 1a). This site is the type locality of P. barberenai (Cabreira et al., 2011) and B. agudoensis . The site strata belong to the lower to middle portion of the Candel aria Sequence of the Santa Maria Supersequence, Paran a Basin (Horn et al., 2014;Zerfass et al., 2003). ...
Article
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Discoveries from South America have increased our knowledge on the early evolutionary history of sauropodomorph dinosaurs. The dietary shift from faunivorous to herbivorous creatures and the increasing body size are both widely documented in the fossil record. Conversely, the initial evolution of the elongated neck is poorly known. It is one of the most diagnostic features of Sauropodomorpha. There is a gap between the record of short‐necked sauropodomorphs from Carnian (±233 Ma) and long‐necked forms from early Norian (±225 Ma). As a consequence, it is unknown if the cervical vertebrae became long gradually or abruptly. In the present study, we present a new specimen excavated from strata that belong to this time interval (±228 Ma). CAPPA/UFSM 0352 comprises a series of five cervical vertebrae unearthed from the Late Triassic of Southern Brazil. The vertebrae are proportionately longer than that of older forms and proportionately shorter than that of younger ones. Therefore, our results demonstrate that the elongation of the neck of sauropodomorphs is an example of gradual evolutionary process. Except by its elongated shape, the general anatomy of the cervical elements resembles that of the earliest forms (i.e., have a conservative anatomy). Combined with previous data, it is possible to conclude that the shape of the skull and teeth, as well as the neck proportions, were the first structures to clearly differ derived sauropodomorphs from early diverging forms. Finally, some of the recovered phylogenetic scenarios favor the origins of the elongated neck in the clade Bagualosauria.
... Carnian sauropodomorphs recognised after Sat. tupiniquim ( Fig. 1)w e r e described in the last ten years or so (Martínez and Alcober 2009;Ezcurra 2010;Cabreira et al. 2011Cabreira et al. , 2016Pretto et al. 2019), namely Panphagia protos, Chromogisaurus novasi, Buriolestes schultzi, Pampadromaeus barberenai, and Bagualosaurus agudoensis. The latter three were found in the Alemoa Member of the Santa Maria Formation, in south Brazil, which also yielded Sat. ...
... When early sauropodomorph phylogeny is arranged in a more pectinate fashion, Sat. tupiniquim most frequently nests closer to bagualosaurs than to other Carnian forms (Martínez and Alcober 2009;Alcober and Martínez 2010;Cabreira et al. 2011Cabreira et al. , 2016Martínez et al. 2012b;Bittencourt et al. 2015;McPhee et al. 2015;Müller et al. 2016aMüller et al. , b, 2017aMüller et al. , b, 2018aWang et al. 2017;Agnolín and Rozadilla 2018;Pretto et al. 2017;Bronzati et al. 2017Bronzati et al. , 2019aZhang et al. 2018;Marsola et al. 2018 Pretto et al. (2019) was the only so far not to find Sat. tupiniquim as a sauropodomorph, but instead forming a Guaibasauridae clade outside Eusaurischia. ...
... The holotype and both referred specimens of Pam. barberenai were collected in the site known as 'Sítio Janner' or 'Várzea do Agudo' (Fig. 3; Cabreira et al. 2011;;D aR o s a2015; Pretto et al. 2015Pretto et al. , 2019 that is located about two kilometres to the west of the town of Agudo (coordinates: 53°17 ′ 34.20 ′′ W, 29°39 ′ 10.89 ′′ S). In the site, fossils are concentrated in the upper half of the massive to laminate, red mudstones interpreted to have accumulated in a distal floodplain palaeoenvironment, overlaid in erosive contact by a light-coloured, cross-bedded sandstone that represents a river channel (Pretto et al. 2015;DaRosa2015). ...
Chapter
Carnian (Late Triassic) deposits of South America provide the oldest unequivocal dinosaur records worldwide, most of which has been assigned to the sauropodomorph lineage. This includes Eoraptor lunensis, Panphagia protos, and Chromogisaurus novasi, from the Ischigualasto Formation, Argentina, and Saturnalia tupiniquim, Pampadromaeus barberenai, Buriolestes schultzi, and Bagualosaurus agudoensis, from the Santa Maria Formation, Brazil. Here, we demonstrate that their holotypes anatomically differ from one another, supporting the taxonomic validity of the species. In addition, a morphological disparity analysis, with significant statistical support, clustered some of the better-known specimens of E. lunensis, Sat. tupiniquim, and Bu. schultzi, with the respective holotypes. For the latter two taxa, this was corroborated by a specimen-level phylogenetic analysis that also found Ba. agudoensis as the sister taxon to post-Carnian sauropodomorphs. Our results also suggest that Bu. schultzi and E. lunensis are the earliest branching sauropodomorphs and that Sa. tupiniquim and Pam. barberenai are closer to Bagualosauria. A species-level phylogenetic analysis further suggests that Bu. schultzi and E. lunensis form a clade, that Sa. tupiniquim is the sister taxon to Bagualosauria, and that Pan. protos and Ch. novasi are also more highly nested, forming a clade with Pam. barberenai.
... Until recently, the evolution of body size in the earliest sauropodomorphs has remained obscure. However, increased fieldwork has yielded several important finds (e.g., Cabreira et al., 2011Cabreira et al., , 2016Apaldetti et al., 2018;Müller et al., 2018b;Pretto et al., 2018) that have reshaped our knowledge of their early evolution (Novas et al., 2021;Pol et al., 2021). Among these deposits, those from southern Brazil provide clues to the first steps of the sauropodomorph radiation via three distinct horizons (Müller and Garcia, 2020) that encompass a ∼8 Ma time interval . ...
... These animals were small (femur ∼15 cm long), bipedal, and faunivorous Bronzati et al., 2017Bronzati et al., , 2019Müller et al., 2021). The next-youngest stratigraphic horizons (middle, Santa Maria Formation, precise age unknown) contain sauropodomorphs displaying dental changes related to an omnivorous or mostly herbivorous diet, such as Pampadromaeus barberenai (Cabreira et al., 2011) and Bagualosaurus agudoensis (Pretto et al., 2018). The latter species reveals a slight increase in body size, with femoral length over 20 cm (Pretto et al., 2018). ...
... Regarding cynodonts, the most abundant taxon is the traversodontid Exaeretodon riograndensis (Oliveira et al., 2007;Liparini et al., 2013;Müller et al., 2020a), whereas specimens of the ecteniniid Trucidocynodon riograndensis were rare (Oliveira et al., 2010;Stefanello et al., 2018). On the other hand, archosauromorphs are represented by dinosaurs (e.g., Pampadromaeus barberenai and Bagualosaurus agudoensis; Cabreira et al., 2011;Pretto et al., 2018), as well as the ornithosuchid Dynamosuchus collisensis (Müller et al., 2020b). Furthermore, rhynchosaur remains attributed to Hyperodapedon sp. were collected (Langer et al., 2007a), however, with the discovery of the taxon Teyumbaita sulcognathus (Montefeltro et al., 2010) occurring in stratigraphic levels above Hyperodapedon in several sites from both Brazil and Argentina (Desojo et al., 2020), the assignment of these remains to Hyperodapedon should be considered carefully until they are properly reviewed. ...
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Whereas sauropod dinosaurs from the Jurassic and Cretaceous Periods were the largest land animals that ever lived, some of their early relatives evolved relatively large bodies during the Triassic Period. The evolutionary pathways followed by the earliest sauropodomorphs towards the acquisition of massive bodies are poorly understood. However, new finds from South America and Africa are reshaping our knowledge of this issue. Here, we describe a new early and relatively large sauropodomorph represented by a partial postcranial skeleton excavated from Carnian-aged beds (Upper Triassic) of southern Brazil. The new specimen is recovered as a sauropodomorph more closely related to bagualosaurians than saturnaliids or other early-diverging forms in two phylogenetic analyses. The new specimen is generically indeterminate but provides important evidence of an early increase in body size in Sauropodomorpha, being significantly larger than that of coeval or older forms (except Bagualosaurus agudoensis). Furthermore, the specimen is about 3.2 times heavier than Buriolestes schultzi, the earliest-branching Sauropodomorph. The slender hind limbs and typical cursorial proportions present in the earliest sauropodomorphs are mostly maintained in the new specimen despite its larger body size.
... In the present study, the shape and variations in the anterolateral scar in early dinosaur sauropodomorphs; Pampadromaeus barberenai (Cabreira et al., 2011) and Buriolestes schultzi (Cabreira et al., 2016) are presented. These dinosaurs are particularly significant because of their phylogenetic positioning as basal members of the clade, and because they are coeval with the oldest dinosaurs worldwide (Cabreira et al., 2011(Cabreira et al., , 2016Müller et al., 2018a, b;Bronzati et al., 2019;Langer et al., 2019). ...
... In the present study, the shape and variations in the anterolateral scar in early dinosaur sauropodomorphs; Pampadromaeus barberenai (Cabreira et al., 2011) and Buriolestes schultzi (Cabreira et al., 2016) are presented. These dinosaurs are particularly significant because of their phylogenetic positioning as basal members of the clade, and because they are coeval with the oldest dinosaurs worldwide (Cabreira et al., 2011(Cabreira et al., , 2016Müller et al., 2018a, b;Bronzati et al., 2019;Langer et al., 2019). Distribution of the anterolateral scar in other archosaurs remains an important topic of discussion. ...
Article
The anterolateral scar is a raised and generally rounded ossification on the anterolateral face of the femoral head of certain archosaurs, located anterior to the ‘greater trochanter’ and posterior to the femoral head. The presence and shape of this structure in early dinosaurs is still poorly understood. In the present study, the shape and variation of the anterolateral scar is preserved in two early sauropodomorph dinosaurs Pampadromaeus barberenai and Buriolestes schultzi from the Upper Triassic of Brazil. These sauropodomorphs are particularly significant because of their phylogenetic position as basal members of the clade and because they were coeval with the oldest of dinosaurs. Upon analysis, the specimens revealed distinct surface morphologies related to the anterolateral scar throughout their femoral series. Small specimens (putative juvenile individuals) of each species lack any sign of an anterolateral scar. On the other hand, the structure is well-developed in larger specimens (putatively adult individuals). Thus, an absence/presence of the anterolateral scar on the femora of early dinosaurs is affected by ontogeny, as observed in silesaurids. The presence of the anterolateral scar seems more widely distributed in ornithodirans than previously thought. Further, the absence of a raised anterolateral scar in massopodan sauropodomorphs appears to be a neotenic trait, since putatively immature early sauropodomorph individuals share this absence, while full adults develop a remarkable scar.
... These characters are discussed and illustrated thoroughly in Nesbitt (2011) and this dataset has been used recursively in part in several other datasets that deal with early dinosaur evolution, such as Cabreira et al. (2011Cabreira et al. ( , 2016 and Baron et al. (2017b). ...
... This character refers to the location of the supratemporal fossa, so here each character state corresponds to the bones where the temporal muscles extend to. In Cabreira et al. (2011) only ...
Thesis
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Non-sauropod sauropodomorphs, also known as 'basal sauropodomorphs' or 'prosauropods', have been thoroughly studied in recent years. Several hypotheses on the interrelationships within this group have been proposed, ranging from a complete paraphyly, where the group represents a grade from basal saurischians to Sauropoda, to a group on its own. The grade-like hypothesis is the most accepted; however, the relationships between the different taxa are not consistent amongst the proposed scenarios. These inconsistencies have been attributed to missing data and unstable (i.e., poorly preserved) taxa, nevertheless, an extensive comparative cladistic analysis has found that these inconsistencies instead come from the character coding and character selection, plus the strategies on merging data sets. Furthermore, a detailed character analysis using information theory and mathematical topology as an approach for character delineation is explored here to operationalise characters and reduce the potential impact of missing data. This analysis also produced the largest and most comprehensive matrix after the reassessment and operationalisation of every character applied to this group far. Additionally, partition analyses performed on this data set have found consistencies in the interrelationships within non-sauropod Sauropodomorpha and has found strong support for smaller clades such as Plateosauridae, Riojasauridae, Anchisauridae, Massospondylinae and Lufengosarinae. The results of these analyses also highlight a different scenario on how quadrupedality evolved, independently originating twice within the group, and provide a better framework to understand the palaeo-biogeography and diversification rate of the first herbivore radiation of dinosaurs.
... So far, Stenoscelida aurantiacus and Dynamosuchus collisensis comprise the only carnivorous archosauriforms from this site, with the ectetniniid cynodont Trucidocynodon riograndensis (Oliveira et al. 2010) adding to this context. Other occurrences at the site belong to herbivorous/omnivorous animals: the archosauromorph Hyperodapedon sp., the traversodontid cynodont Exaeretodon, and the sauropodomorph dinosaurs Pampadromaeus barberenai (Cabreira et al. 2011) and Bagualosaurus agudoensis (Pretto et al. 2019). ...
Article
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Characterized by an elongated snout, proterochampsids are carnivorous non-archosaur archosauriforms. The clade is endemic to South America and its fossil record extends from the early Carnian to the late Carnian/early Norian. Nesting close to Archosauria, it is a key clade for understanding the origin and evolution of archosaurian traits. Unfortunately, hind limb elements are usually poorly preserved for the group. Therefore, the hind limb anatomy of proterochampsids still lacks detailed descriptions. In the present study, we partially fill this gap with the description of a new proterochampsid represented by a complete and well-preserved hind limb. Stenoscelida aurantiacus gen. et sp. nov. was excavated from the late Carnian/early Norian (Late Triassic) beds of southern Brazil. A phylogenetic investigation recovers the new taxon as a non-rhadinosuchine proterochampsid. The species bears an unusual set of traits for the group, which provides clues on the evolutionary origins of some muscle attachment structures. For instance, the femur of Stenoscelida aurantiacus gen. et sp. nov. possesses an anterior trochanter and an anterolateral scar. So far, these features have not been reported in other non-archosaurian archosauriforms. Therefore, the new specimen indicates that some typical archosaurian features evolved earlier than previously thought. The taxon also carries additional uncommon features for proterochampsids, such as an iliofibularis tubercle on the anterior margin of the fibula and a vestigial phalanx in digit V. In sum, Stenoscelida aurantiacus has one of the best-preserved hind limbs within Proterochampsidae and sheds light on the polarization of important traits regarding the evolutionary context of Archosauria. http://zoobank.org/urn:lsid:zoobank.org:pub:C78B7CE3-AB9B-4543-833E-B2A3FEA957D9
... Sauropodomorpha is one of the main lineages of dinosaurs that had diversified by the Carnian [12][13][14][15][16][17], becoming ecologically diverse and globally widespread by the latest Triassic [18][19][20]. Early members of the clade were small to medium-sized gracile bipeds that later experienced a stepwise trend towards increased body sizes, eventually giving rise to the gigantic quadrupedal sauropods [21,22]. ...
Article
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Dinosaur evolution is marked by numerous independent shifts from bipedality to quadrupedality. Sauropodomorpha is one of the lineages that transitioned from small bipedal forms to graviportal quadrupeds, with an array of intermediate postural strategies evolving in non-sauropodan sauropodomorphs. This locomotor shift is reflected by multiple modifications of the appendicular skeleton, coupled with a drastic rearrangement of the limb musculature. Here, we describe the osteological correlates of appendicular muscle attachment of the Late Triassic sauropodomorph Thecodontosaurus antiquus from multiple well-preserved specimens and provide the first complete forelimb and hindlimb musculature reconstruction of an early-branching sauropodomorph. Comparisons with other sauropodomorphs and early dinosaurs reveal a unique combination of both plesiomorphic and derived musculoskeletal features. The diversity of appendicular osteological correlates among early dinosaurs and their relevance in muscle reconstruction are discussed. In line with previous evidence, aspects of the limb muscle arrangement, such as conspicuous correlates of lower limb extensors and flexors and low moment arms of hip extensors and flexors, suggest Thecodontosaurus was an agile biped. This reconstruction helps to elucidate the timing of important modifications of the appendicular musculature in the evolution of sauropodomorphs which facilitated the transition to quadrupedalism and contributed to their evolutionary success.
Article
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The origin and evolutionary relationships of ornithischian dinosaurs are topics that have undergone a series of substantial revisions. At present there are several competing hypotheses concerning the relationship between Ornithischia and the other principal clades of Dinosauria. Some hypotheses have posited a tree topology within Dinosauria that imply a ‘ghost-lineage’ for Ornithischia (whose representatives make their first unambiguous appearance in the Hettangian) that extends through a substantial portion of Triassic time. In contrast, other hypotheses have placed conventionally Triassic dinosauromorph (stem-lineage Dinosauria) taxa within the clade Ornithischia. Recently, a large-scale phylogenetic analysis recovered an array of taxa, known as ‘silesaurids’, as a paraphyletic assemblage of taxa (referred to in this article using the informal terms silesaurs or silesaurians) on the branch leading to the clade Ornithischia. This latter hypothesis of relationships would account for the apparent absence of Triassic ornithischians, because stem-lineage ornithischians (silesaurs in this article) are exclusively Triassic. However, the analysis that produced this novel topology used a dataset that, in its original form, did not include all early representatives of Ornithischia (sensu lato), and did not incorporate all the anatomical characters that have been suggested to unite Ornithischia with other dinosaurian clades (Theropoda and Sauropodomorpha). Nor did the initial study go on to expand upon some important taxonomic, palaeobiological and evolutionary implications of a topology that links a paraphyletic array of silesaurs to the clade Ornithischia. The present article addresses these latter issues by expansion and re-analysis of the original dataset. The results find further support for the hypothesis that silesaurs comprise a paraphyletic grouping of taxa on the stem of Ornithischia and that successive silesaur taxa acquire anatomical characters anagenetically in a process that culminates in the assembly of what may be described as a ‘traditional’ ornithischian. The overall topology of the consensus tree remains but little changed from the original analysis, despite the addition of new taxa and characters. To provide stability to this area of the tree and to preserve the most important of the relevant taxonomic names, we suggest a revised taxonomic framework for ornithischians that is consistent with this new topology. We retain the name Ornithischia for the total-group (traditional Ornithischia and its stem-lineage), while we resuscitate a name originally proposed by Richard Owen, Prionodontia (= ‘coarse edged teeth’) for the clade containing only the so-called traditional ornithischian (= ‘bird-hipped’) dinosaurs. We also erect Parapredentata as a more exclusive subclade in Ornithischia. This novel taxonomic framework is intended to provide phylogenetic clarity and a degree of stability in Ornithischia and Dinosauria as further analyses and new data continue to refine and re-shape the tree. The data presented in this study represent a stage in our attempt to establish an early dinosaur dataset in which character definitions and character scores are agreed upon and used consistently.
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A literature review showed that there is not a defined consensus on what specimens belong to Plateosaurus in current phylogenetic analyses, and after the assignation of SMNS 13200 as the neotype for Plateosaurus, the specimen composition of Plateosaurus as an operational taxonomic unit (OTU) needs to be addressed in further iterations of phylogenetic analyses. At least one of the specimens used to illustrate plateosaurian anatomy contains several characters identified in more derived sauropodomorphs commonly referred to as massopodans. This partial skeleton, traditionally known as specimen ‘GPIT IV’, was found in the lower dinosaur bone bed of the Obere Mühle, a Trossingen Formation outcrop, during an excavation in 1922 near the city of Tübingen, Germany. The holotype of Plateosaurus trossingensis and several other specimens referred to as this species were found in this level, which was initially interpreted as a synchronic deposit of animals. However, the current understanding of the Trossingen Formation indicates that this bed was probably a constant accumulation of carcasses through miring and transport down a river for hundreds of years. In this work, a framework to compare phylogenetic signals with morphological and histological data is provided to help in the species delineation of Plateosaurus, and support is found to refer the historic specimen ‘GPIT IV’ as a new genus and a new species.
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Many recent studies of theropod relationships have been focused on the phylogeny of coelurosaurs and the question of the origin of birds, but the interrelationships and evolution of basal theropods are still poorly understood. Thus, this paper presents a phylogenetic analysis of all theropods, but focuses on the basal members of this clade. The result supports the inclusion of Eoraptor and herrerasaurids in the Theropoda, but differs from other recent studies in two main aspects: (1) The taxa usually grouped as ceratosaurs form two monophyletic clades that represent successively closer outgroups to tetanurans. The more basal of these clades, the Coelophysoidea, comprise the majority of Late Triassic and Early Jurassic theropods. The other clade of basal theropods that are usually included in the Ceratosauria comprises Ceratosaurus, Elaphrosaurus, and abelisaurids. (2) Two monophyletic groups of basal tetanurans are recognized: the Spinosauroidea and the Allosauroidea. In contrast to other recent phylogenetic hypotheses, both clades are united in a monophyletic Carnosauria. The branching pattern of the present cladogram is in general accordance with the stratigraphic occurrence of theropod taxa. Despite the differences in recent analyses, there is a significant level of consensus in theropod phylogeny. At least four different radiations of non-avian theropods can be recognized. These radiations show different patterns in Laurasia and Gondwana, and there are increasing differences between the theropod faunas of the two hemispheres from the Triassic to the Cretaceous.
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Ceratosauria represents the first widespread and diverse radiation of theropod dinosaurs comprising two main sister clades, Neoceratosauria and Coelophysoidea. This chapter discusses the diagnostic features, phylogenetic placement, and paleobiology of ceratosaurians. The fossil record for Ceratosauria spans a minimum of 155 million years, from the late Carnian of the Late Triassic to the end of the Cretaceous. Ceratosaurs had an essentially global distribution, their remains being found on every continent except Australia and Antarctica. Ceratosaurs evolved into a broad range of sizes and body forms, from lightly built, diminutive taxa such as Segisaurus (1 to 1.5 m in length) to the large abelisaurids, such as Carnotaurus (10 to 11 m). Several coelophysoid taxa were collected from mass burials, where multiple individuals were preserved together. In particular, Syntarsus rhodesiensis is known from at least thirty individuals found at localities in Zimbabwe and South Africa.
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This chapter discusses the anatomy, evolution, biogeography, taphonomy, paleoecology, and paleobiology of prosauropaud dinosaurs. Prosauropods have been found on all the major continents, including Antarctica. They were medium- to large-sized, bipedal, facultatively bipedal or quadrupedal sauropodomorphs with long necks and tails. Prosauropods were probably the slowest of the bipedal dinosaurs but better runners than most other quadrupedal dinosaurs. Among prosauropods, Saturnalia and Thecodontosaurus are considered fully bipedal. Riojasaurus and other melanorosaurids were fully quadrupedal and the remaining prosauropods were probably only facultatively bipedal.
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The continental Triassic succession of southernmost Brazil comprises two second-order depositional sequences-the Sanga do Cabral (Early Triassic) and the Santa Maria (Middle to Late Triassic) supersequences. The first one includes ephemeral, low-sinuosity fluvial deposits developed on a low gradient plain. Based on fossil tetrapods, especially procolophonids, an Upper Induan age is estimated for this sequence. Facies association of the Santa Maria Supersequence indicates low-sinuosity fluvial rivers, deltas and lakes. This supersequence can be further subdivided into three third-order sequences (age provided by palaeovertebrate biostratigraphic data) as follows: Santa Maria I (Ladinian), Santa Maria 2 (Carman to Early Norian) and Santa Maria 3 (probably Raethian or Early Jurassic) sequences. The Gondwanides paroxysms I and 11 in the Sierra de la Ventana-Cape Fold Belt are directly related to the development of both supersequences. The source area of the Sanga do Cabral Supersequence was located to the south. It consisted of an uplifted peripheral bulge situated landward of the retro-foreland system, from where older sedimentary rocks were eroded. The source area of the Santa Maria Supersequence was also positioned southwards and related to the uplifted Sul-Rio-Grandense and Uruguayan shields. The Santa Maria Supersequence stratigraphic architecture is comparable to the Triassic rift basins of Western Argentina. Diagenesis, facies and palacontology of the studied succession suggest a dominantly semiarid climate during the Triassic.
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The early evolutionary history of Ornithodira (avian-line archosaurs) has hitherto been documented by incomplete (Lagerpeton) or unusually specialized forms (pterosaurs and Silesaurus). Recently, a variety of Silesaurus-like taxa have been reported from the Triassic period of both Gondwana and Laurasia, but their relationships to each other and to dinosaurs remain a subject of debate. Here we report on a new avian-line archosaur from the early Middle Triassic (Anisian) of Tanzania. Phylogenetic analysis places Asilisaurus kongwe gen. et sp. nov. as an avian-line archosaur and a member of the Silesauridae, which is here considered the sister taxon to Dinosauria. Silesaurids were diverse and had a wide distribution by the Late Triassic, with a novel ornithodiran bauplan including leaf-shaped teeth, a beak-like lower jaw, long, gracile limbs, and a quadrupedal stance. Our analysis suggests that the dentition and diet of silesaurids, ornithischians and sauropodomorphs evolved independently from a plesiomorphic carnivorous form. As the oldest avian-line archosaur, Asilisaurus demonstrates the antiquity of both Ornithodira and the dinosaurian lineage. The initial diversification of Archosauria, previously documented by crocodilian-line archosaurs in the Anisian, can now be shown to include a contemporaneous avian-line radiation. The unparalleled taxonomic diversity of the Manda archosaur assemblage indicates that archosaur diversification was well underway by the Middle Triassic or earlier.