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The origin of Pterosaurs

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Abstract

Our understanding of the pterosaurs' place within the reptilian lineage has had a long and complex history. The unusual morphology of pterosaurs, which is inextricably linked to their habit of powered flight, has generated numerous proposals over the years regarding their exact origin and systematic position. Though it was concluded early on in pterosaur research history that these animals represented a group of derived flying reptiles, their exact origination remained mysterious for a long time and is still somewhat controversial. A rough consensus has now been reached that pterosaurs are derived archosaurs and are likely close relatives of the dinosaurs, united with them in the clade Ornithodira, though some still challenge this view. The anatomical evidence in support of this position close to Dinosauria is also admittedly fairly limited at present, largely owing to a lack of any clear-cut transitional ‘proto-pterosaur’ taxa (albeit that some fragmentary specimens have been suggested to represent exactly this). Differing hypotheses have also recently been put forward as to the exact interrelationships between the pterosaurs and other non-dinosaurian and dinosaurian ornithodirans. Here the previous hypotheses of where pterosaurs fit into the reptilian lineage and the anatomical evidence in support of the current hypotheses are reviewed. Results of new analyses are included that looked to test the origin and systematic position of the Pterosauria using an expanded version of a large anatomical dataset of archosaurs, within which several previously unconsidered early pterosaur taxa and a suit of new anatomical characters were considered. The analyses in this study support the close affinities between pterosaurs and dinosauriforms within Ornithodira; Pterosauria is recovered as the sister-taxon to Lagerpetidae. Such a result suggests that the clade Pterosauria belongs with Lagerpetidae as part of a broader Pterosauromorpha that then, with Dinosauriformes, falls within Ornithodira. The anatomical evidence in support of this position within Ornithodira is also discussed in detail.

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... The anatomy, biomechanics, biology, and evolution of the group were exhaustively investigated (e.g., Aires et al., 2021;Kellner, 2003;Palmer & Dyke, 2010;Yang et al., 2019). Nevertheless, its origins and early evolution are poorly known (Baron, 2021;Ezcurra et al., 2020). Whereas the identity of the sister group of Pterosauria was a mystery for centuries, lagerpetids were thought to be dinosaur precursors, or nondinosauriform dinosauromorphs (Baron et al., 2017;Cabreira et al., 2016;Garcia et al., 2019;Irmis et al., 2007;Müller et al., 2018;Nesbitt, 2011;Sereno & Arcucci, 1993). ...
... Characterized by elongate and gracile hindlimbs, much of the skeletal anatomy of lagerpetids remains unknown (Langer et al., 2013;Müller et al., 2018). However, our knowledge of the osteology of this group was recently improved by new discoveries and interpretations of additional bony elements (Baron, 2021;Cabreira et al., 2016;Ezcurra et al., 2020;Kammerer et al., 2020;Martz & Small, 2019;McCabe & Nesbitt, 2021). These new data supplied a new interpretation regarding the phylogenetic affinities of lagerpetids and pterosaurs (Baron, 2021;Ezcurra et al., 2020;Kammerer et al., 2020). ...
... However, our knowledge of the osteology of this group was recently improved by new discoveries and interpretations of additional bony elements (Baron, 2021;Cabreira et al., 2016;Ezcurra et al., 2020;Kammerer et al., 2020;Martz & Small, 2019;McCabe & Nesbitt, 2021). These new data supplied a new interpretation regarding the phylogenetic affinities of lagerpetids and pterosaurs (Baron, 2021;Ezcurra et al., 2020;Kammerer et al., 2020). Instead of dinosaur precursors, the new hypothesis places these animals as the sister group of pterosaurs. ...
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Exquisite discoveries and new interpretations regarding an enigmatic group of cursorial avemetatarsalians led to a new phylogenetic hypothesis regarding pterosaur affinities. Previously thought to be dinosaur precursors, lagerpetids are now considered to be the closest relatives to pterosaurs. This new hypothesis sheds light on a new explorable field, especially regarding the character acquisition and evolution within the pterosaur lineage. In the present study, the morphospace occupation of distinct skeletal regions of lagerpetids within the morphological spectrum of avemetatarsalians is investigated. This approach indicates which portions of the skeleton are more similar to the anatomy of pterosaurs and which portions present different homoplastic signals. The analyses demonstrate that the craniomandibular traits of lagerpetids are pterosaur‐like, the pectoral girdle and forelimb are dinosauromorph‐like and the axial skeleton and the pelvic girdle and hindlimb are unique and highly specialized among the analyzed sample. So, despite the close phylogenetic relationships, the postcranial skeleton of lagerpetids and pterosaurs are very different. The occurrence of two distinct and highly specialized groups of pterosauromorphs coexisting with a wide ecological range of dinosauromorphs during the Triassic suggests pressure for new niches occupation.
... The interpretation that Lagerpeton represented the earliest-diverging member of the dinosaur lineage was unanimously followed by subsequent authors that studied dinosaur origins (e.g., Bittencourt et al., 2015;Brusatte et al., 2010;Cabreira et al., 2016;Ezcurra, 2006Ezcurra, , 2016Irmis et al., 2007;Langer et al., 2010Langer et al., , 2013Nesbitt, 2011;Nesbitt et al., 2010;Novas, 1996). More recently, Lagerpeton and its kin (i.e., Lagerpetidae) were re-interpreted as the sister group to Pterosauria, forming the clade Pterosauromorpha with them (e.g., Baron, 2021;Ezcurra, Nesbitt, Bronzati, et al., 2020;Foffa et al., 2022Foffa et al., , 2023Kellner et al., 2022;Müller et al., 2023). ...
... We follow the phylogenetic hypothesis proposed by Ezcurra, Nesbitt, Bronzati, et al. (2020) (see also Baron, 2021;Foffa et al., 2022;Kellner et al., 2022;Müller et al., 2023), which regard Lagerpetidae as the sister group to Pterosauria, within the avemetatarsalian clade Pterosauromorpha. ...
Article
Lagerpeton chanarensis is an early avemetatarsalian from the lower Carnian (lowermost Upper Triassic) levels of the Chañares Formation, La Rioja Province, Argentina. Lagerpeton and its kin were traditionally interpreted as dinosaur precursors of cursorial habits, with a bipedal posture and parasagittal gait. Some authors also speculated saltatorial capabilities for this genus. Recent analyses indicate that lagerpetids are early‐diverging pterosauromorphs, a hypothesis that invites a review of most aspects of their anatomy and function. A revision of available specimens and additional preparation of previously known individuals indicate that Lagerpeton lacked a parasagittal gait and was probably a sprawling archosaur. This latter inference is based on the femoral head articulation with the acetabulum. The acetabular rim has a strongly laterally projected posteroventral antitrochanteric corner, which results in a position of the legs that recalls that of sprawling living reptiles, such as lizards, and departs from the parasagittally positioned limbs of dinosaurs. This may indicate that early pterosauromorphs had a sprawling posture of their hindlegs, casting doubts on the significance of bipedal posture and parasagittal gait for the radiation of early ornithodirans, given that both traits have been regarded as key features that triggered the ecological and evolutionary success of the clade. Our results bolster recent claims of a high ecomorphological diversity among early avemetatarsalians.
... The inclusion of V. gassenae in the most comprehensive phylogenetic analyses of archosauromorph relationships, using both maximum parsimony and Bayesian inference as optimality criteria, nests the new species within Lagerpetidae and lends support to the sister group relationship between Lagerpetidae and Pterosauria 8,17,28 . Under maximum parsimony, Venetoraptor is the sister taxon to the North American 'D.' gregorii in the reduced strict consensus tree ( Fig. 2a and Extended Data Fig. 5). ...
... Whereas the phylogenetic relationships of lagerpetids have received considerable attention recently 8,11,16,28 , their biology and ecological role remain obscure. The presence of Venetoraptor in the same fossiliferous site that yielded Ixalerpeton represents the first robust evidence of sympatric lagerpetid species. ...
Article
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Dinosaurs and pterosaurs have remarkable diversity and disparity through most of the Mesozoic Era1–3. Soon after their origins, these reptiles diversified into a number of long-lived lineages, evolved unprecedented ecologies (for example, flying, large herbivorous forms) and spread across Pangaea4,5. Recent discoveries of dinosaur and pterosaur precursors6–10 demonstrated that these animals were also speciose and widespread, but those precursors have few if any well-preserved skulls, hands and associated skeletons11,12. Here we present a well-preserved partial skeleton (Upper Triassic, Brazil) of the new lagerpetid Venetoraptor gassenae gen. et sp. nov. that offers a more comprehensive look into the skull and ecology of one of these precursors. Its skull has a sharp, raptorial-like beak, preceding that of dinosaurs by around 80 million years, and a large hand with long, trenchant claws that firmly establishes the loss of obligatory quadrupedalism in these precursor lineages. Combining anatomical information of the new species with other dinosaur and pterosaur precursors shows that morphological disparity of precursors resembles that of Triassic pterosaurs and exceeds that of Triassic dinosaurs. Thus, the ‘success’ of pterosaurs and dinosaurs was a result of differential survival among a broader pool of ecomorphological variation. Our results show that the morphological diversity of ornithodirans started to flourish among early-diverging lineages and not only after the origins of dinosaurs and pterosaurs.
... Os pterossauros não são considerados pertencentes ao grupo dos dinossauros (Ezcurra, 2016), como erroneamente propagam diversos textos e representações de educação e divulgação científica. Somente nos últimos anos, com importante contribuição de paleontólogos brasileiros, eles foram associados a um grupo extinto de répteis parecidos com pequenos lagartos, os lagerpetídeos (Ezcurra et al., 2020, Baron, 2021, Müller et al., 2023. Dentro da classificação atual (Fig. 2), os pterossauros, junto a outros grupos de arcossauros derivados, além dos dinossauros, formam o grupo Ornithodira, que compreende Lagerpetidae, Pterosauria, Silesauridae e Dinosauria . ...
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Introdução. A Paleontologia integra conceitos de outras áreas das Ciências da Natureza para tratar da evolução e mudanças ambientais no tempo Geológico. A despeito da sua importância, o rico registro fossilífero brasileiro é raramente tratado em sala de aula. Objetivos. Este trabalho propõe o jogo de tabuleiro “Qual é o Pterossauro?” como ferramenta adicional para o ensino de Paleontologia no Ensino Básico. Metodologia. As regras e as ilustrações são autorais e inéditas, e se basearam na literatura científica. Após a exposição ao tema em formato de uma aula, o jogo foi aplicado com alunos e posteriormente avaliado por formulário. Resultados. O jogo foi considerado como boa experiência educativa por 92 crianças de duas escolas públicas da Zona Leste da Cidade de São Paulo. Conclusão. A originalidade do jogo e de todas as ilustrações que incluem representações de pterossauros brasileiros se destacam por se tratarem de material original e autoral. O jogo se demonstrou viável para apresentar conceitos de Paleontologia e pterossauros brasileiros, como ferramenta para o ensino de Geociências no Ensino Básico e valorização do patrimônio fossilífero do nosso país.
... Lagerpetidae is a clade of small and enigmatic forms within Avemetatarsalia (=Pan-Aves sensu Ezcurra et al., 2020), the lineage of Archosauria including birds (Sereno, 1991). These animals were previously understood as nondinosaurian dinosauromorphs (e.g., Cabreira et al., 2016;Ezcurra, 2016;Irmis et al., 2007;Nesbitt, 2011;Novas, 1996;Sereno & Arcucci, 1993), but recent phylogenetic hypotheses indicate that lagerpetids are the closest relatives of pterosaurs ( Figure 1; Baron, 2021;Ezcurra et al., 2020;Foffa et al., 2022;Kellner et al., 2022;Müller et al., 2023). Lagerpetid fossils have been found in Upper Triassic (around 236-200 Ma) deposits of North-(e.g., Irmis et al., 2007;) and South America (e.g., Cabreira et al., 2016;Martínez et al., 2016;Romer, 1971;Arcucci, 1986), in Middle/Late Triassic beds of Madagascar (Kammerer et al., 2020), and perhaps in the Late Triassic of Scotland (Foffa et al., 2022). ...
Article
The anatomy of the braincase and associated soft tissues of the lagerpetid Dromomeron gregorii (Archosauria: Avemetatarsalia) from the Late Triassic of the United States is here described. This corresponds to the first detailed description of cranial materials of Lagerpetidae, an enigmatic group of Late Triassic (c. 236–200 Million years ago) animals that are the closest known relatives of pterosaurs, the flying reptiles. The braincase of D. gregorii is characterized by the presence of an anteriorly elongated laterosphenoid and a postparietal, features observed in stem‐archosaurs but that were still unknown in early members of the avian lineage of archosaurs. Using micro‐computed tomography (CT‐scan data), we present digital reconstructions of the brain and endosseous labyrinth of D. gregorii . The brain of D. gregorii exhibits a floccular lobe of the cerebellum that projects within the space of the semicircular canals. The semicircular canals are relatively large when compared to other archosauromorphs, with the anterior canal exhibiting a circular shape. These features of the sensory structures of D. gregorii are more similar to those of pterosaurs than to those of other early avemetatarsalians. In sum, the braincase anatomy of D. gregorii shows a combination of plesiomorphic and apomorphic features in the phylogenetic context of Archosauria and suggests that the still poorly understood early evolution of the braincase in avemetatarsalians is complex, with a scenario of independent acquisitions and losses of character states.
... The fossil record is crucial for understanding the mode and tempo of these ecological transitions. Body fossils of sarcopterygians (Tiktaalik), basal pterosaurs (Preondactylus), and winged dinosaurs (Archaeopteryx) have provided crucial insights into the Devonian transition from water to land (3) and the Triassic-Jurassic colonization of the air (4,5). Biogenic sedimentary structures (trace fossils) are remarkable for our knowledge of ecological transitions because of their high preservation potential, providing the earliest evidence for land colonization by vertebrates (6) and recording the invasion of the marine realm by mammals (7). ...
Article
Vertebrate macroevolution has been punctuated by fundamental habitat transitions from shallow marine origins to terrestrial, freshwater, and aerial environments. Invasion of the deep sea is a less well-known ecological shift because of low fossilization potential and continual loss of abyssal fossil record by ocean floor subduction. Therefore, there has been a lack of convincing evidence of bottom-living vertebrates from pre-Paleogene deep seas. Here, we describe trace fossils from abyssal plain turbidites of the Tethys Ocean, which, combined with nannofossil dating, indicate that fishes have occupied the deep seafloor since at least the Early Cretaceous (Hauterivian-Barremian). These structures are identical to those produced by modern demersal fishes that feed by either scratching the substrate or expose their prey by water flow generated by suction or jetting. The trace fossils suggest activity of at least three fish species exploiting a productive abyssal invertebrate sediment fauna. These observations are consistent with Early Cretaceous vertebrate transition to the deep sea triggered by the availability of new food sources. Our results anticipate the appearance of deep-seafloor fishes in the fossil record by over 80 My while reassessing the mode of vertebrate colonization of the deep sea.
... Benton's (2004) dataset was later iterated by Li et al. (2006). dataset was later iterated by several authors (Butler et al., 2011(Butler et al., , 2014Nesbitt et al., 2011Nesbitt et al., , 2013aNesbitt et al., , c, 2014Nesbitt et al., , 2017Nesbitt et al., , 2018aNesbitt et al., , b, 2020Li et al., 2012Li et al., , 2016Lecuona, 2013;Nesbitt & Butler, 2013;Sues & Schoch, 2013;Baczko et al., 2014Baczko et al., , 2020Raugust, 2014;Sookias et al., 2014a, b;Lautenschlager & Rauhut, 2015;Zanno et al., 2015;Cabreira et al., 2016;Lacerda et al., 2016Lacerda et al., , 2018Lecuona et al., 2016;Lessner et al., 2016;Niedźwiedzki et al., 2016;Roberto˗da˗Silva et al., 2016Nesbitt & Desojo, 2017;Roberto˗da˗Silva, 2017;Stocker et al., 2017;Müller et al., 2018;Sarıgül et al., 2018;Garcia et al., 2019Garcia et al., , 2021Barrett et al., 2020;Kammerer et al., 2020;Marsh et al., 2020;Baron, 2021;DallaVecchia, 2021;Tolchard et al., 2021;Parker et al., 2021;Damke et al., 2022; ) and many of them including modifications/corrections and inserting new taxa. With few exceptions (e.g., Li et al., 2012Li et al., , 2016 the combined score of the lectotype plus the Sanga Pascoal specimen (UFRGS-PV 156T) was the standard sequence used in their phylogenetic analyses for "Prestosuchus chiniquensis" terminal. ...
Article
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The nominal genus Prestosuchus Huene was originally proposed comprising two nominal species but without a valid indication of the type-species. According to the International Code of Zoological Nomenclature, this indication is essential for proposals after the year 1930. Consequently, both nominal species, although valid, have a very uncomfortable situation. Therefore, a new nominal genus, Huenesuchus, is here proposed to correct this nomenclatural situation to be used in the new combination Huenesuchus chiniquensis. In addition, it is noted that two class-group names that have been used lately in the literature are previously occupied. The first, Suchia Krebs, is previously occupied by Simpson. The second, Loricata Merrem, is previously occupied by Schumacher. Therefore, two substitute names are here proposed: Holosuchia for the first and Loricatosuchia for the second. Keywords: Archosauria, Prestosuchus, Huenesuchus, Santa Maria Formation, Triassic.
... As such, comparisons between the Gondwanan and Laurasian pterosaur palaeobiogeography are provisional. Nevertheless, despite the description of new material, and revision of holotype specimens, the origins and biogeographical history of the Pterosauria remains controversial (Andres, 2012;Baron, 2021;Unwin, 1996). At present, the earliest definitive pterosaurs are Norian in age, with non-pterodactyloid pterosaurs predominantly known from the Northern Hemisphere (see Martínez et al., 2022 and references therein). ...
Article
The Gondwanan pterosaur record is scarce when compared with that of Laurasia and is reviewed here. The majority of Gondwanan pterosaur remains are derived from South America; however, the relative richness of the South American record compared with other Gondwanan continents is largely a result of the ‘Lagerstätten’ effect. Nevertheless, the South American pterosaur assemblage represents the most speciose and diverse known from Gondwana, with several lineages represented, including the Raeticodactylidae, Rhamphorhynchoidea, Darwinoptera, Ctenochasmatidae, Gnathosaurinae, Nyctosauridae, Ornithocheiridae, Tapejaridae, Thalassodromidae, Dsungaripteridae, Chaoyangopteridae and Azhdarchidae. Gondwanan pterosauromorphs are known only from South America. From Africa rhamphorhynchids, archaeopterodactyloids, pteranodontians, nyctosaurids, ornithocheirids, tapejarids, dsungaripteroids, chaoyangopterids, and azhdarchids have been reported. The Arabian Peninsula has produced nyctosaurids, an istiodactyliform, ornithocheirids and azhdarchids. Non-pterodactyloid pterosaurs have been reported from India. A possible azhdarchid has been reported from Madagascar and rhamphorhynchids are known from isolated teeth. The Antarctic pterosaur assemblage also comprises isolated remains of indeterminate pterodactyloids, and a possible indeterminate rhamphorhynchoid. The pterosaur record from East Gondwana comprises ornithocheirids, azhdarchids and a possible ctenochasmatoid from Australia, as well as azhdarchids from New Zealand. Although our understanding of Gondwanan pterosaurs has greatly improved within the last three decades, the discovery and description of more specimens, particularly from Antarctica and East Gondwana, will enhance our understanding of pterosaurian biodiversity and palaeobiogeography.
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Pterosaurs, remarkable for their extensive evolutionary history and role as the first vertebrates to achieve active flight, have long intrigued paleontologists and the public alike. Spanning over 150 million years and vanishing at the end of the Mesozoic Era, pterosaurs represent a major evolutionary radiation within terrestrial ecosystems. Despite their prominence, the origins of pterosaurs have remained a complex puzzle in paleontology for over 200 years. We present a comprehensive catalog of pterosaur precursors specimens from the Upper Triassic of the Candelária Sequence within the Santa Maria Supersequence in southern Brazil and discuss their significance for understanding pterosauromorph radiation and the origins of Pterosauria. Additionally, we carried out a phylogenetic analysis to investigate the hypothesis that lagerpetids are closely related to pterosaurs, incorporating new data into the most comprehensive dataset of Triassic dinosauromorphs. Our results support the hypothesis that lagerpetids are pterosauromorphs, offering new insights into the evolutionary relationships between non-pterosaur pterosauromorphs and their better known volant relatives. This study highlights the importance of detailed anatomical and phylogenetic analyses in resolving the complex origins of pterosaurs and underscores the value of the Triassic fossil record in understanding the early evolution of pterosauromorphs.
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Take-off is a vital part of powered flight which likely constrains the size of birds, yet extinct pterosaurs are known to have reached far larger sizes. Three different hypothesised take-off motions (bipedal burst launching, bipedal countermotion launching, and quadrupedal launching) have been proposed as explanations for how pterosaurs became airborne and circumvented this proposed morphological limit. We have constructed a computational musculoskeletal model of a 5 m wingspan ornithocheiraean pterosaur, reconstructing thirty-four key muscles to estimate the muscle moment arms throughout the three hypothesised take-off motions. Range of motion constrained hypothetical kinematic sequences for bipedal and quadrupedal take-off motions were modelled after extant flying vertebrates. Across our simulations we did not find higher hindlimb moment arms for bipedal take-off motions or noticeably higher forelimb moment arms in the forelimb for quadrupedal take-off motions. Despite this, in all our models we found the muscles utilised in the quadrupedal take-off have the largest total launch applicable moment arms throughout the entire take-off sequences and for the take-off pose. This indicates the potential availability of higher leverage for a quadrupedal take-off than hypothesised bipedal motions in pterosaurs pending further examination of muscle forces.
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Müller et al.1 recently described a Late Triassic partial skeleton they named Venetoraptor gassena. The authors linked their find to the origin of dinosaurs and pterosaurs while omitting three Middle and Late Triassic taxa that share more traits pterosaurs. Coseaurus, Sharovipteryx and Longisquama (Figs. 1, 2) are known from articulated fossils that preserve bones and soft tissues otherwise only reported in pterosaurs. Unfortunately, the omission of these pertinent taxa in the search for pterosaur ancestors has been an academically approved tradition documented in the following timeline of pterosaur origin studies.
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Fossils provide the only direct evidence we have of ancient life, and fossil insects are a window into the evolutionary history of insects [...]
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Pterosaurs were the first vertebrates to evolve powered flight¹ and comprised one of the main evolutionary radiations in terrestrial ecosystems of the Mesozoic era (approximately 252–66 million years ago), but their origin has remained an unresolved enigma in palaeontology since the nineteenth century2–4. These flying reptiles have been hypothesized to be the close relatives of a wide variety of reptilian clades, including dinosaur relatives2–8, and there is still a major morphological gap between those forms and the oldest, unambiguous pterosaurs from the Upper Triassic series. Here, using recent discoveries of well-preserved cranial remains, microcomputed tomography scans of fragile skull bones (jaws, skull roofs and braincases) and reliably associated postcrania, we demonstrate that lagerpetids—a group of cursorial, non-volant dinosaur precursors—are the sister group of pterosaurs, sharing numerous synapomorphies across the entire skeleton. This finding substantially shortens the temporal and morphological gap between the oldest pterosaurs and their closest relatives and simultaneously strengthens the evidence that pterosaurs belong to the avian line of archosaurs. Neuroanatomical features related to the enhanced sensory abilities of pterosaurs⁹ are already present in lagerpetids, which indicates that these features evolved before flight. Our evidence illuminates the first steps of the assembly of the pterosaur body plan, whose conquest of aerial space represents a remarkable morphofunctional innovation in vertebrate evolution.
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Pterosaurs, the first vertebrates to evolve active flight, lived between 210 and 66 million years ago. They were important components of Mesozoic ecosystems, and reconstructing pterosaur diets is vital for understanding their origins, their roles within Mesozoic food webs and the impact of other flying vertebrates (i.e. birds) on their evolution. However, pterosaur dietary hypotheses are poorly constrained as most rely on morphological-functional analogies. Here we constrain the diets of 17 pterosaur genera by applying dental microwear texture analysis to the three-dimensional sub-micrometre scale tooth textures that formed during food consumption. We reveal broad patterns of dietary diversity (e.g. Dimorphodon as a vertebrate consumer; Austriadactylus as a consumer of 'hard' invertebrates) and direct evidence of sympatric niche partitioning (Rhamphorhynchus as a piscivore; Pterodactylus as a generalist invertebrate consumer). We propose that the ancestral pterosaur diet was dominated by invertebrates and later pterosaurs evolved into piscivores and carnivores, shifts that might reflect ecological displacements due to pterosaur-bird competition.
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Present knowledge of Late Triassic tetrapod evolution, including the rise of dinosaurs, relies heavily on the fossil-rich continental deposits of South America, their precise depositional histories and correlations. We report on an extended succession of the Ischigualasto Formation exposed in the Hoyada del Cerro Las Lajas (La Rioja, Argentina), where more than 100 tetrapod fossils were newly collected, augmented by historical finds such as the ornithosuchid Venaticosuchus rusconii and the putative ornithischian Pisanosaurus mertii. Detailed lithostratigraphy combined with high-precision U–Pb geochronology from three intercalated tuffs are used to construct a robust Bayesian age model for the formation, constraining its deposition between 230.2 ± 1.9 Ma and 221.4 ± 1.2 Ma, and its fossil-bearing interval to 229.20 + 0.11/− 0.15–226.85 + 1.45/− 2.01 Ma. The latter is divided into a lower Hyperodapedon and an upper Teyumbaita biozones, based on the ranges of the eponymous rhynchosaurs, allowing biostratigraphic correlations to elsewhere in the Ischigualasto-Villa Unión Basin, as well as to the Paraná Basin in Brazil. The temporally calibrated Ischigualasto biostratigraphy suggests the persistence of rhynchosaur-dominated faunas into the earliest Norian. Our ca. 229 Ma age assignment to Pi. mertii partially fills the ghost lineage between younger ornithischian records and the oldest known saurischians at ca. 233 Ma.
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The pterosaurs first appear in the fossil record in the middle of the Late Triassic. Their earliest representatives are known from Northern Hemisphere localities but, by the end of the Jurassic Period, this clade of flying reptiles achieved a global distribution, as well as high levels of diversity and disparity. Our understanding of early pterosaur evolution and the fundamental interrelationships within Pterosauria has improved dramatically in recent decades. However, there is still debate about how the various pterosaur subgroups relate to one another and about which taxa comprise these. Many recent phylogenetic analyses, while sampling well from among the known Triassic and Early Jurassic pterosaurs, have not included many non-pterosaurian ornithodirans or other avemetatarsalians. Given the close relationship between these groups of archosaurs, the omission of other ornithodirans and avemetatarsalians has the potential to adversely affect the results of phylogenetic analyses, in terms of character optimisation and ingroup relationships recovered. This study has addressed this issue and tests the relationships between the early diverging pterosaur taxa following the addition of avemetatarsalian taxa and anatomical characters to an existing early pterosaur dataset. This study has, for the first time, included taxa that represent the aphanosaurs, lagerpetids, silesaurids and dinosaurs, in addition to early pterosaurs. Anatomical characters used in other recent studies of archosaurs and early dinosaurs have also been incorporated. By expanding the outgroup taxa and anatomical character coverage in this pterosaur dataset, better resolution between the taxa within certain early pterosaur subclades has been achieved and stronger support for some existing clades has been found; other purported clades of early pterosaurs have not been found in this analysis—for example there is no support for a monophyletic Eopterosauria or Eudimorphodontidae. Further support has been found for a sister-taxon relationship between Peteinosaurus zambelli and Macronychoptera, a clade here named Zambellisauria (clade nov.), as well as for a monophyletic and early diverging Preondactylia. Some analyses also support the existence of a clade that falls as sister-taxon to the zambellisaurs, here named Caviramidae (clade nov.). Furthermore, some support has been found for a monophyletic Austriadraconidae at the base of Pterosauria. Somewhat surprisingly, Lagerpetidae is recovered outside of Ornithodira sensu stricto , meaning that, based upon current definitions at least, pterosaurs fall within Dinosauromorpha in this analysis. However, fundamental ornithodiran interrelationships were not the focus of this study and this particular result should be treated with caution for now. However, these results do further highlight the need for broader taxon and character sampling in phylogenetic analyses, and the effects of outgroup choice on determining ingroup relationships.
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The six known specimens of Scleromochlus taylori and casts made from their negative impressions were examined to reassess the osteological evidence that has been used to interpret Scleromochlus’ s locomotion and phylogenetic relationships. It was found that the trunk was dorsoventrally compressed. The upper temporal fenestra was on the lateral surface of skull and two-thirds the size of the lower, the jaw joint posteriorly placed with short retroarticular process, and teeth short and subconical, but no evidence of external nares or antorbital fossae was found. The posterior trunk was covered with ~20 rows of closely spaced transversely elongate dorsal osteoderms. The coracoid was robust and elongate. The acetabulum was imperforate and the femoral head hemispherical and only weakly inturned such that the hip joint was unsuited to swinging in a parasagittal plane. The presence of four distal tarsals is confirmed. The marked disparity of tibial and fibular shaft diameters and of proximal tarsal dimensions indicates that the larger proximal tarsal is the astragalus and the significantly smaller tarsal is the calcaneum. The astragalus and calcaneum bear little resemblance to those of Lagosuchus , and the prominent calcaneal tuber confirms that the ankle was crurotarsal. There is no evidence that preserved body and limb postures are unnatural, and most specimens are preserved in what is interpreted as a typical sprawling resting pose. A principal component analysis of skeletal measurements of Scleromochlus and other vertebrates of known locomotor type found Scleromochlus to plot with frogs, and that finding combined with skeletal morphology suggests Scleromochlus was a sprawling quadrupedal hopper. Phylogenetic analyses found that Scleromochlus was not an ornithodiran, but was either within the Doswelliidae or outside the clade consisting of the most recent common ancestor of the Erythrosuchidae and Archosauria and all its descendants.
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The skull of the holotype of the Late Triassic diapsid reptile Megalancosaurus preonensis is described for the first time. Its study revealed affinities with archosauromorph reptiles along with striking similarities with basal pterosaurs, apart for the absence of an antorbital fenestra.
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Discoveries of fossil reptiles in the sea cliffs of south-western England helped to consolidate ideas of 'deep time' and extinction by revealing ancient worlds whose unfamiliar and bizarre inhabitants had no living counterparts. Many of these fossils were from the Lower and Upper Lias Groups, suites of rocks laid down in the shallow seas that covered much of southern England during the Early Jurassic period (around 201-174 million years ago). Sir Richard Owen (1804–92) was one of several anatomists who provided extensive descriptions of these animals. His monograph on the Liassic Reptilia (published in three parts in 1861–81) includes the first, and so far only, detailed description of the early armoured dinosaur Scelidosaurus (the first dinosaur known from an almost complete skeleton), an important account of Dimorphodon (the first flying reptile named from the United Kingdom), and critical information on two marine reptile groups, the plesiosaurs and ichthyosaurs.
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Two recent studies have independently recovered Pisanosaurus mertii – long thought to represent the oldest known member of Ornithischia – within Silesauridae. These finds are expanded upon here, as are the implications of this hypothesis. Based upon these finds, it now appears that Ornithischia was absent in the Triassic Period entirely, which constitutes a major incongruence between the fossil record and current phylogenetic hypotheses, particularly the traditional model of dinosaur interrelationships in which Ornithischia and Saurischia are sister-taxa. It has been suggested previously that Ornithischia was simply a rare component of Late Triassic faunas, or that perhaps the clade’s ecology or geographic distribution were not conducive to producing a fossil record. Here I propose that phylogeny could hold the solution to this problem. I examine how an alternative position for Ornithischia – nested either within Theropoda or Sauropodomorpha – could be the reason behind their later appearance and relative rarity in the Early Jurassic. An Early Jurassic origin of Ornithischia would force us to consider that the anatomical similarities between ornithischians and Early Jurassic taxa might not be convergences, and to broaden the current datasets of early dinosaurs to test these ideas.
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For 130 years, dinosaurs have been divided into two distinct clades—Ornithischia and Saurischia. Here we present a hypothesis for the phylogenetic relationships of the major dinosaurian groups that challenges the current consensus concerning early dinosaur evolution and highlights problematic aspects of current cladistic definitions. Our study has found a sister-group relationship between Ornithischia and Theropoda (united in the new clade Ornithoscelida), with Sauropodomorpha and Herrerasauridae (as the redefined Saurischia) forming its monophyletic outgroup. This new tree topology requires redefinition and rediagnosis of Dinosauria and the subsidiary dinosaurian clades. In addition, it forces re-evaluations of early dinosaur cladogenesis and character evolution, suggests that hypercarnivory was acquired independently in herrerasaurids and theropods, and offers an explanation for many of the anatomical features previously regarded as notable convergences between theropods and early ornithischians.
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Effigia okeeffaee is named based on a well-preserved nearly complete skeleton from the Upper Triassic (?Rhaetian) "siltstone member" at Ghost Ranch, northern New Mexico. The skull is described and compared to other suchian and basal archosaurs. The maxilla and premaxilla are edentulous, and a rhamphotheca was possibly present in life. Effigia conclusively indicates that the skull of Shuvosaurus and the postcrania of "Chatterjeea" belong to the same taxon. Furthermore, the close relationship between Shuvosaurus and Effigia indicates that both taxa are nested within the suchian clade and not within Ornithomimisauria. However, the similarity in features in the skull and postcrania of Effigia and ornithomimids suggests extreme convergence occurred between the two clades. A clade containing Arizonasaurus, Bromsgroveia, Poposaurus, Sillosuchus, Shuvosaurus, and Effigia is suggested based solely on shared derived character states. Additionally, a clade (Clade Y) containing Sillosuchus, Shuvosaurus, and Effigia is well supported by further derived character states. The distribution and temporal pattern of members of Group Y suggest that members of Group Y are present in the early Middle Triassic through the Latest Triassic of North America, and one member of the clade, Sillosuchus, was present in South America.
Chapter
Dinosaurs belong within Archosauria, a wide group of extinct and extant reptiles that also includes modern crocodilians as well as pterosaurs and various basal groups of Triassic age. This chapter considers the origin of the dinosaurs in terms of phylogeny and the timing of events. It discusses the cladistic analysis of Archosauria, followed by an account of the evolutionary events that led to the radiation of the dinosaurs.
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The extremely well-preserved tarsus of the tapejarid Tapejara sp. and the anhanguerid Anhanguera piscator (Pterosauria, Pterodactyloidea) are described and regarded as representative of the ankle structure of Pterosauria. The pterosaur ankle joint (PAJ) shows the following features: astragalus mediolaterally elongated forming a hemicylinder; proximal part of the astragalocalcaneal contact characterized by a ridge bordered on each side by a depression on the astragalus that has a perfect counterpart in the calcaneum, and distal part that is concavoconvex, with the concavity present in the astragalus; calcaneum extremely reduced not reaching the posterior portion of the tarsus; absence of an astragalar posterior groove, perforating foramen, calcaneal tuber, and astragalar ascending process; proximal tarsals fusing very early in ontogeny, forming a tibiotarsus. The main movement between the crus and foot in the PAJ occurs between the proximal and distal tarsals as in the advanced mesotarsal-reversed joint (AM-R). The main differences from the latter are the lack of an ascending process and the extreme reduction of the calcaneum that make the PAJ unique. The absence of an astragalar groove and the reduction of the calcaneum reinforce the hypothesis that pterosaurs are basal ornithodirans and closely related to the Dinosauromorpha. As has been demonstrated by this and other studies, the ankle structure (a complex of characters) is phylogenetically informative and, in the light of characters from other parts of the animal's body, can contribute to a better understanding of archosaur relationships.
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Tyrannosauroids are among the most distinctive and best known of Mesozoic theropods. Diagnostic skeletal material for Tyrannosauridae is at present limited to the last part of the Late Cretaceous of eastern and central Asia (China and Mongolia) and North America; the more inclusive Tyrannosauroidea includes taxa from the Late Jurassic of Europe and North America and the Early Cretaceous of Europe and Asia. Tyrannosaurids include some of the largest known theropod taxa (up to 13 m long and weighing six or more tonnes). The five most completely known species (Tyrannosaurus rex, Tarbosaurus bataar, Daspletosaurus torosus, Albertosaurus sarcophagus, and Gorgosaurus libratus) are all represented by individuals with femora more than 100 cm in length, reaching 138 cm in the largest Tyrannosaurus rex.