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The Triassic was a key period in the evolution of vertebrates, and reptiles in particular, giving rise to a plethora of successful lineages, some of which are still extant. One of the groups that flourished during the early Mesozoic were the tanysaurians (Archosauromorpha: Tanysauria). They had elongate neck vertebrae that in some genera reached extreme proportions. Here, we provide the first comprehensive description of the internal structure of these extraordinary elements, focusing on the famously bizarre Tanystropheus. Through computed tomography and sectioning, we were able to reveal some intriguing features comparable to those seen in pterosaurs and birds. However, contrary to what we see in pneumatic bones, cervicals of tanysaurians contain a singular voluminous cavity. This results in a cylindrical structure in these vertebrae, which likely provided durability, while contributing less to the weight of the neck. These insights are relevant for better understanding of a unique and extreme anatomy among tetrapods, which evolved as a result of very strict selection for some particular function. Importantly, our findings demonstrate that major modifications of the internal anatomy of vertebrae were not unique to derived avemetatarsalians (pterosaurs and dinosaurs), but more widespread among reptiles. [ABSTRACT FROM AUTHOR]

This paper discusses the geology of the unique Mansurovo tetrapod and trace fossil locality in the Orenburg Region of Russia (Gostevskaya Formation, Lower Olenekian Substage, Ustmylian Horizon). Sections of 16 trenches are described bed-by-bed and correlated throughout. Based on fossils (Wetlugasaurus malachovi grouping of the Wetlugasaurus Fauna) and lithology, the Mansurovo section correlates with the middle part of the stratotype section of the Gostevskaya Formation (Buzuluk Depression of the East European Platform). The site geology suggests that the four recognized geological members of the section were formed in a varying channel-floodplain environment during alternating depositional cycles. The depositional settings were reconstructed based on rock structure and texture and microlithological examination of thin sections. The tetrapod faunal assemblages, macrofloral remains and unique trace fossil assemblages are also studied. Based on the lithology and facies analysis, the depositional environment is reconstructed for the locality, showing the irregular riverine depositional pattern due to the wandering of river channels and their periodic drying out in a hot and semi-arid climate during the Early Olenekian. Taphonomy of fossil occurrences suggests that the burial took place in a riverine depositional environment affected by strong currents, and that the Temnospondyli probably died in subaquatic conditions. [ABSTRACT FROM AUTHOR]

Abstract Some of the earliest members of the archosaur-lineage (i.e., non-archosauriform archosauromorphs) are characterised by an extremely elongated neck. Recent fossil discoveries from the Guanling Formation (Middle Triassic) of southern China have revealed a dramatic increase in the known ecomorphological diversity of these extremely long-necked archosauromorphs, including the fully marine and viviparous Dinocephalosaurus orientalis. These recent discoveries merit a reinvestigation of enigmatic Triassic diapsid fossils from contemporaneous European deposits housed in historical collections. Here, we provide a redescription of Trachelosaurus fischeri, represented by a single, disarticulated specimen first described in 1918. Due to its unique morphology, which includes short, bifurcating cervical ribs, and a high presacral vertebral count, this taxon has been referred to either as a “protorosaurian” archosauromorph or a sauropterygian. Our revision clearly shows that Trachelosaurus represents the first unambiguous Dinocephalosaurus-like archosauromorph known from outside the Guanling Formation. Our finding has important systematic implications. Trachelosauridae Abel, 1919 represents the senior synonym for the recently identified Dinocephalosauridae Spiekman, Fraser and Scheyer, 2021. Based on our phylogenetic analyses, which employ two extensive datasets, we also corroborate previous findings that tanystropheids and trachelosaurids represent two families within a larger monophyletic group among non-crocopodan archosauromorphs, which is here named Tanysauria (clade nov.). Trachelosauridae is minimally composed of Trachelosaurus fischeri, Dinocephalosaurus orientalis, Pectodens zhenyuensis, and Austronaga minuta, but one of our analyses also found a probably taxonomically broader clade that may also include Gracilicollum latens and Fuyuansaurus acutirostris. Trachelosaurus fischeri considerably expands the known spatial and temporal range of Trachelosauridae to the earliest Anisian and the Central European Basin. Our findings add to the growing evidence for the presence of a diverse group of fully marine reptiles during the Middle Triassic among Tanysauria. These trachelosaurids possess flipper-like limbs, high vertebral counts, and elongate necks, thus superficially resembling long-necked Jurassic and Cretaceous plesiosaurs in some regards.

The Triassic radiation of vertebrates saw the emergence of the modern vertebrate groups, as well as numerous extinct animals exhibiting conspicuous, unique anatomical characteristics. Among these, members of Tanystropheidae (Reptilia: Archosauromorpha) displayed cervical vertebral elongation to an extent unparalleled in any other vertebrate. Tanystropheids were exceptionally ecologically diverse and had a wide spatial and temporal distribution. This may have been related to their neck anatomy, yet its evolution and functional properties remain poorly understood. We used geometric morphometrics to capture the intraspecific variation between the vertebrae comprising the cervical column among early archosauromorphs, to trace the evolutionary history of neck elongation in these animals. Our results show that the cervical series of these reptiles can be divided into modules corresponding to those of extant animals. Tanystropheids achieved neck elongation through somite elongation and a shift between cervical and thoracic regions, without presacral vertebrae count increase—contrary to crown archosaurs. This suggests a peculiar developmental constraint that strongly affected the evolution of tanystropheids. The data obtained just at the base of the archosauromorph phylogenetic tree are crucial for further studies on the modularity of vertebral columns of not only Triassic reptile groups but extant and other extinct animals as well.

Prolacerta broomi is one of the most important of fossil reptiles. First considered as one of the earliest members of squamates, this basal archosauromorph has been used as a model for diapsid morphological evolution ever since its discovery, playing a pivotal role in hypotheses on the origin of diapsid reptiles. The holotype of Prolacerta broomi (UCMZ 2003.41R) is known from a mostly complete skull, but the original description is limited to the superficial features of the skull roof and palate. Since then, many other specimens of Prolacerta broomi have been recovered that potentially account for this limited access to anatomical information, but it remains unclear whether these aspects correspond well to the known material of the holotype. Here, the skull morphology of the holotype of Prolacerta broomi is revisited through the use of µCT scans. The identifications of some cranial elements have been corrected, such as the left prefrontal and lacrimal, and several new elements are revealed, including the epi- and ectopterygoids, prearticular, coronoid, and braincase bones. The orbitonasal region is described in detail and significantly shows a contribution of the lacrimal to the dorsal alveolar canal. Finally, the addition of the holotype as an independent OTU in recently published analyses indicate conflicts with the current knowledge on Prolacerta broomi phylogenetic affinity and taxonomy. First, it points to potential taxonomic inconsistency since the holotype does not form a monophyletic group with other Prolacerta broomi OTUs in any of the analyses and, second, it suggests a more basal position for the holotype than that recovered in some studies, more basal than rhynchosaurs and close to the origin of Crocopoda. Together, these findings indicate areas of future research interest in the study of early evolving archosauromorphs.

Proterosuchidae represents the oldest substantial diversification of Archosauromorpha and plays a key role in understanding the biotic recovery after the end-Permian mass extinction. Proterosuchidae was long treated as a wastebasket taxon, but recent revisions have reduced its taxonomic content to five valid species from the latest Permian of Russia and the earliest Triassic (Induan) of South Africa and China. In addition to these occurrences, several isolated proterosuchid bones have been reported from the Induan Panchet Formation of India for over 150 years. Following the re-study of historical specimens and newly collected material from this unit, we erect the new proterosuchid species Samsarasuchus pamelae, which is represented by most of the presacral vertebral column. We also describe cf. proterosuchid and proterosuchid cranial, girdle and limb bones that are not referred to Samsarasuchus pamelae. Phylogenetic analyses recovered Samsarasuchus pamelae within the new proterosuchid clade Chasmatosuchinae. The taxonomic diversity of Proterosuchidae is substantially expanded here, with at least 11 nominal species and several currently unnamed specimens, and a biogeographical range encompassing present-day South Africa, China, Russia, India, Brazil, Uruguay and Australia. This indicates a broader taxonomic, phylogenetic and biogeographic diversification of Proterosuchidae than previously thought in the aftermath of the end-Permian mass extinction.

Prolacerta broomi is one of the most important of fossil reptiles. First considered as one of the earliest members of squamates, this basal archosauromorph has been used as a model for diapsid morphological evolution ever since its discovery, playing a pivotal role in hypotheses on the origin of diapsid reptiles. The holotype of Prolacerta broomi (UCMZ 2003.41R) is known from a mostly complete skull, but the original description is limited to the superficial features of the skull roof and palate. Since then, many other specimens of Prolacerta broomi have been recovered that potentially account for this limited access to anatomical information, but it remains unclear whether these aspects correspond well to the known material of the holotype. Here, the skull morphology of the holotype of Prolacerta broomi is revisited through the use of μCT scans. The identifications of some cranial elements have been corrected, such as the left prefrontal and lacrimal, and several new elements are revealed, including the epi- and ectopterygoids, prearticular, coronoid, and braincase bones. The orbitonasal region is described in detail and significantly shows a contribution of the lacrimal to the dorsal alveolar canal. Finally, the addition of the holotype as an independent OTU in recently published analyses indicate conflicts with the current knowledge on Prolacerta broomi phylogenetic affinity and taxonomy. First, it points to potential taxonomic inconsistency since the holotype does not form a monophyletic group with other Prolacerta broomi OTUs in any of the analyses and, second, it suggests a more basal position for the holotype than that recovered in some studies, more basal than rhynchosaurs and close to the origin of Crocopoda. Together, these findings indicate areas of future research interest in the study of early evolving archosauromorphs. [ABSTRACT FROM AUTHOR]

The Upper Triassic Dockum Group of Garza County, Texas (lower, middle, and upper Cooper Canyon Formation) captures the radiation of Triassic non-marine tetrapods by preserving a variety of Late Triassic taxa from the southwestern United States. Our understanding of the vertebrate assemblage from these strata largely comes from a single site, the Post Quarry (lower Cooper Canyon Formation), with previous research documenting a variety of temnospondyls, sphenodontians, non-archosauriform archosauromorphs, and archosauriforms including a phytosaur, three species of aetosaurs, a poposauroid, a rauisuchid, a crocodylomorph, and several dinosauromorphs. To more completely reconstruct the vertebrate assemblage of the Dockum Group of Garza County we use an apomorphy-based approach to identify morphologically similar disarticulated and fragmentary elements from a variety of localities that span the entire Cooper Canyon Formation (Norian-Rhaetian), allowing assignments from the large clade level to the species level. Many skeletal elements are incomplete yet diagnostic and are assigned to the least inclusive clade if discrete character states do not allow for an unambiguous species-level identification. We identify new specimens referable to numerous clades including Tanystropheidae, Allokotosauria + Prolacerta + Archosauriformes, Vancleavea + Litorosuchus, Phytosauria, Paracrocodylomorpha, Dinosauriformes, and Saurischia, in addition to additional species identifications of the aetosaur Scutarx deltatlyus, and the dinosauromorph Dromomeron gregorii. Our study of this material demonstrates the utility of an apomorphy-based approach in making testable and repeatable observations for identifying small, isolated fragmentary fossil tetrapod material to reconstruct a more accurate faunal hypothesis for a portion of the Late Triassic of Texas. Previous claims of the earliest dinosaurs from near the base of the Dockum Group do not pass the apomorphy-based identification test, and the question of whether the oldest known North American dinosaurs are present in the Chinle Formation or Dockum Group can be resolved by utilizing vertebrate biostratigraphic correlation. Our revision of these fossil assemblages supports the hypothesis that early diapsids, early archosauromorphs, and non-dinosaurian dinosauromorphs were more common, diverse, and widespread in low latitudes during this time than previously thought.

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. [ABSTRACT FROM AUTHOR]

We provide a detailed description of the poorly known reptile Eifelosaurus triadicus Jaekel, 1904 from the Upper Buntsandstein (Triassic: early Anisian) of Oberbettingen in the southwestern Eifel region of Rhineland-Palatinate, Germany. The holotype and only known specimen is a partial postcranial skeleton exposed in ventral view. Since its original description Eifelosaurus triadicus has been almost completely ignored in the literature. Our phylogenetic analysis recovered this taxon within Rhynchosauria and Rhynchosauridae, as the sister taxon to the clade comprising Stenaulorhynchinae and hyperodapedontine-line rhynchosaurids. A unique combination of character states allows distinguishing Eifelosaurus triadicus from other rhynchosaur species with preserved matching postcranial bones. Thus, we tentatively consider this taxon valid until more information about the postcrania of other Early to Middle Triassic rhynchosaurs becomes available. Eifelosaurus triadicus represents a paleobiogeographically important record, showing that rhynchosaurs had already attained a broad paleolatitudinal distribution by the early Middle Triassic. [ABSTRACT FROM AUTHOR]

Little is known about the large‐scale evolutionary patterns of skull size relative to body size, and the possible drivers behind these patterns, in Archosauromorpha. For example, the large skulls of erythrosuchids, a group of non‐archosaurian archosauromorphs from the Early and Middle Triassic, and of theropod dinosaurs are regarded as convergent adaptations for hypercarnivory. However, few investigations have explicitly tested whether erythrosuchid and theropod skulls are indeed disproportionately large for their body size, and whether this trend is driven by hypercarnivory. Here, we investigate archosauromorph relative skull size evolution, examining the scaling relationships between skull and body size of Palaeozoic and Mesozoic archosauromorphs using a robust phylogenetic framework and assessing the influence of potential drivers, such as taxonomy, diet, locomotory mode and inhabited biotope. Our results show that archosauromorph relative skull sizes are largely determined by phylogeny and that the other drivers have much weaker levels of influence. We find negative allometric scaling of skull size with respect to body size when all studied archosauromorphs are analysed. Within specific groups, skull size scales with positive allometry in non‐archosaurian archosauromorphs and, interestingly, scales isometrically in theropods. Ancestral reconstructions of skull–femur size ratio reveal a disproportionately large skull at the base of Erythrosuchidae and proportionately sized skulls at the bases of Theropoda, Carnosauria and Tyrannosauroidea. Relative skull sizes of erythrosuchids and theropods are therefore distinct from each other, indicating that disproportionately large skulls are not a prerequisite for hypercarnivory in archosauromorphs, and that erythrosuchids exhibit a bauplan unique among terrestrial Mesozoic carnivores. [ABSTRACT FROM AUTHOR]

An important parameter in studying the macroevolutionary history of a clade is the variation of its body size. However, the analysis of this parameter in archosauromorphs has been restricted to Archosauria, and the disparity in body size has not been exhaustively explored. In the present work, we study the variation in body size of more than 400 known Permian-Early Jurassic archosauromorph species in the context of their early evolutionary radiation. We analysed the disparity of body size over time and the relationship between this parameter and the palaeolatitudinal distribution of species. From these analyses, it was found that the disparity of body size of archosauromorphs increased after the Permian/Triassic boundary. In the case of Pseudosuchia and Pan-Aves (=Avemetatarsalia), the Triassic/Jurassic extinction shows a pattern of selective extinction of medium to large-sized forms, and their body size disparity decreased significantly. In contrast, dinosaurs increased their body size and their disparity did not change significantly after the Triassic/Jurassic extinction event. Regarding the relationship between body size and geographic distribution, pseudosuchians show a pattern of body size decrease towards higher palaeolatitudes, i.e., a converse Bergmann's rule. These results could be linked to physiological factors since many groups of extant ectothermic animals show a similar pattern. These analyses help to elucidate the complex body size evolutionary dynamics in the early radiation of Archosauromorpha, as indicated by the different patterns observed across its subclades. [ABSTRACT FROM AUTHOR]

The Chañares Formation exhibits one of the most important archosauriform records of early Carnian ecosystems. Here we present new data on the palaeohistology of Chañares archosauriforms and provide new insights into their paleobiology, as well as possible phylogenetically informative traits. Bone microstructure of Lagerpeton chanarensis and Tropidosuchus romeri is dominated by fibro-lamellar tissue and dense vascularization. On the other hand, Chanaresuchus bonapartei is more densely vascularized, but with cyclical growth characterized by alternate fibro-lamellar, parallel-fibered and lamellar-zonal tissues. Dense vascularization and fibro-lamellar tissue imply fast growth and high metabolic rates for all these taxa. These histological traits may be tentatively interpreted as a possible adaptative advantage in front of Chañares Formation environmental conditions.

Adaptive radiations have played a major role in generating modern and deep-time biodiversity. The Triassic radiation of the Archosauromorpha was one of the most spectacular vertebrate radiations, giving rise to many highly ecomorphologically varied lineages—including the dinosaurs, pterosaurs, and stem-crocodylians—that dominated the larger-bodied land fauna for the following 150 Ma, and ultimately gave rise to today’s > 10,000 species of birds and crocodylians. This radiation provides an outstanding testbed for hypotheses relating to adaptive radiations more broadly. Recent studies have started to characterize the tempo and mode of the archosauromorph early adaptive radiation, indicating very high initial rates of evolution, non-competitive niche-filling processes, and previously unrecognized morphological disparity even among non-crown taxa. However, these analyses rested primarily either on discrete characters or on geometric morphometrics of the cranium only, or even failed to fully include phylogenetic information. Here we expand previous 2D geometric morphometric cranial datasets to include new taxa and reconstructions, and create an analogous dataset of the pelvis, thereby allowing comparison of anatomical regions and the transition from “sprawling” to “upright” posture to be examined. We estimated morphological disparity and evolutionary rates through time. All sampled clades showed a delayed disparity peak for sum of variances and average nearest neighbor distances in both the cranium and pelvis, with disparity likely not saturated by the end of the studied time span (Late Jurassic); this contrasts with smaller radiations, but lends weight to similar results for large, ecomorphologically-varied groups. We find lower variations in pelvic than cranial disparity among Triassic-Jurassic archosaurs, which may be related to greater morphofunctional constraints on the pelvis. Contrasting with some previous work, but also confirming some previous findings during adaptive radiations, we find relatively widespread evidence of correlation between sampled diversity and disparity, especially at the largest phylogenetic scales and using average displacement rather than sum of variances as disparity metric; this also demonstrates the importance of comparing disparity metrics, and the importance of phylogenetic scale. Stem and crown archosauromorphs show a morphological diversification of both the cranium and pelvis with higher initial rates (Permian–Middle Triassic and at the base of major clades) followed by lower rates once diversification into niches has occurred (Late Triassic–Jurassic), indicating an “early burst” pattern sensu lato. Our results provide a more detailed and comprehensive picture of the early archosauromorph radiation and have significant bearing on the understanding of deep-time adaptive radiations more broadly, indicating widespread patterns of delayed disparity peaks, initial correlation of diversity and disparity, and evolutionary early bursts.

The radiation of archosauromorph reptiles in the Triassic Period produced an unprecedented collection of diverse and disparate forms with a mix of varied ecologies and body sizes. Some of these forms were completely unique to the Triassic, whereas others were converged on by later members of Archosauromorpha. One of the most striking examples of this is with Triopticus primus, the early dome‐headed form later mimicked by pachycephalosaurid dinosaurs. Here we fully describe the cranial anatomy of Triopticus primus, but also recognize a second dome‐headed form from a Upper Triassic deposit in present‐day India. The new taxon, Kranosaura kuttyi gen. et sp. nov., is likely the sister taxon of Triopticus primus based on the presence of a greatly expanded skull roof with a deep dorsal opening (possibly the pineal opening) through the dome, similar cranial sculpturing, and a skull table that is expanded more posterior than the posterior extent of the basioccipital. However, the dome of Kranosaura kuttyi gen. et sp. nov. extends anterodorsally, unlike that of any other archosauromorph. Histological sections and computed tomographic reconstructions through the skull of Kranosaura kuttyi gen. et sp. nov. further reveal the uniqueness of the dome of these early archosauromorphs. Moreover, our integrated analysis further demonstrates that there are many ways to create a dome in Amniota. The presence of 'dome‐headed' archosauromorphs at two localities on the western and eastern portions of Pangea suggests that these archosauromorphs were widespread and are likely part of more assemblages than currently recognized. [ABSTRACT FROM AUTHOR]

The historical clade “Protorosauria” represents an important group of archosauromorph reptiles that had a wide geographic distribution between the Late Permian and Late Triassic. “Protorosaurs” are characterized by their long necks, which are epitomized in the genus Tanystropheus and in Dinocephalosaurus orientalis. Recent phylogenetic analyses have indicated that “Protorosauria” is a polyphyletic clade, but the exact relationships of the various “protorosaur” taxa within the archosauromorph lineage is currently uncertain. Several taxa, although represented by relatively complete material, have previously not been assessed phylogenetically. We present a new phylogenetic hypothesis that comprises a wide range of archosauromorphs, including the most exhaustive sample of “protorosaurs” to date and several “protorosaur” taxa from the eastern Tethys margin that have not been included in any previous analysis. The polyphyly of “Protorosauria” is confirmed and therefore we suggest the usage of this term should be abandoned. Tanystropheidae is recovered as a monophyletic group and the Chinese taxa Dinocephalosaurus orientalis and Pectodens zhenyuensis form a new archosauromorph clade, Dinocephalosauridae, which is closely related to Tanystropheidae. The well-known crocopod and former “protorosaur” Prolacerta broomi is considerably less closely related to Archosauriformes than was previously considered.

The historical clade "Protorosauria" represents an important group of archosauromorph reptiles that had a wide geographic distribution between the Late Permian and Late Triassic. "Protorosaurs" are characterized by their long necks, which are epitomized in the genus Tanystropheus and in Dinocephalosaurus orientalis. Recent phylogenetic analyses have indicated that "Protorosauria" is a polyphyletic clade, but the exact relationships of the various "protorosaur" taxa within the archosauromorph lineage is currently uncertain. Several taxa, although represented by relatively complete material, have previously not been assessed phylogenetically. We present a new phylogenetic hypothesis that comprises a wide range of archosauromorphs, including the most exhaustive sample of "protorosaurs" to date and several "protorosaur" taxa from the eastern Tethys margin that have not been included in any previous analysis. The polyphyly of "Protorosauria" is confirmed and therefore we suggest the usage of this term should be abandoned. Tanystropheidae is recovered as a monophyletic group and the Chinese taxa Dinocephalosaurus orientalis and Pectodens zhenyuensis form a new archosauromorph clade, Dinocephalosauridae, which is closely related to Tanystropheidae. The well-known crocopod and former "protorosaur" Prolacerta broomi is considerably less closely related to Archosauriformes than was previously considered. [ABSTRACT FROM AUTHOR]

The Triassic radiation of vertebrates saw the emergence of the modern vertebrate groups, as well as numerous extinct animals exhibiting conspicuous, unique anatomical characteristics. Among these, members of Tanystropheidae (Reptilia: Archosauromorpha) displayed cervical vertebral elongation to an extent unparalleled in any other vertebrate. Tanystropheids were exceptionally ecologically diverse and had a wide spatial and temporal distribution. This may have been related to their neck anatomy, yet its evolution and functional properties remain poorly understood. We used geometric morphometrics to capture the intraspecific variation between the vertebrae comprising the cervical column among early archosauromorphs, to trace the evolutionary history of neck elongation in these animals. Our results show that the cervical series of these reptiles can be divided into modules corresponding to those of extant animals. Tanystropheids achieved neck elongation through somite elongation and a shift between cervical and thoracic regions, without presacral vertebrae count increase-contrary to crown archosaurs. This suggests a peculiar developmental constraint that strongly affected the evolution of tanystropheids. The data obtained just at the base of the archosauromorph phylogenetic tree are crucial for further studies on the modularity of vertebral columns of not only Triassic reptile groups but extant and other extinct animals as well., Competing Interests: We declare we have no competing interests., (© 2024 The Authors.)

Teyujagua paradoxa is a remarkable early archosauromorph from the Lower Triassic Sanga do Cabral Formation, Brazil. The species was originally described from an almost complete skull and a few associated cervical vertebrae, and no further postcranial elements were known at that time. Additional fieldwork in the Sanga do Cabral Formation, however, was successful in recovering a fairly complete postcranial skeleton attributable to the holotype. Here, we describe this new postcranial material, which is composed of cervical, dorsal, sacral and caudal vertebrae, limbs, pectoral and pelvic girdles, ribs, and gastralia. The description of its postcranial skeleton makes T. paradoxa one of the best-known early-diverging archosauromorphs. The cladistic analysis performed after the scoring of postcranial data recovered T. paradoxa in the same position initially described, close to the node that defines the Archosauriformes. Teyujagua paradoxa shares morphological features with representatives of early-diverging archosauromorphs and archosauriforms, with certain traits demonstrating a mosaic of plesiomorphic and apomorphic character states. We also performed partitioned morphospace and disparity analysis to elucidate the morphological disparity and evolutionary patterns among archosauromorphs. Teyujagua paradoxa occupies a notable position, suggesting an intermediate morphology between early archosauromorphs and proterosuchids. Disparity estimates highlighted Pseudosuchia and Avemetatarsalia as having the highest median disparity, reflecting their diverse cranial and postcranial morphologies, respectively. These findings offer valuable insights into archosauromorph macroevolution and adaptation., (© 2024 American Association for Anatomy.)

The postcranial morphology of the extremely long-necked Tanystropheus hydroides is well-known, but observations of skull morphology were previously limited due to compression of the known specimens. Here we provide a detailed description of the skull of PIMUZ T 2790, including a partial endocast and endosseous labyrinth, based on synchrotron microtomographic data, and compare its morphology to that of other early Archosauromorpha. In many features, such as the wide and flattened snout and the configuration of the temporal and palatal regions, Tanystropheus hydroides differs strongly from other early archosauromorphs. The braincase possesses a combination of derived archosaur traits, such as the presence of a laterosphenoid and the ossification of the lateral wall of the braincase, but also differs from archosauriforms in the morphology of the ventral ramus of the opisthotic, the horizontal orientation of the parabasisphenoid, and the absence of a clearly defined crista prootica. Tanystropheus hydroides was a ram-feeder that likely caught its prey through a laterally directed snapping bite. Although the cranial morphology of other archosauromorph lineages is relatively well-represented, the skulls of most tanystropheid taxa remain poorly understood due to compressed and often fragmentary specimens. The recent descriptions of the skulls of Macrocnemus bassanii and now Tanystropheus hydroides reveal a large cranial disparity in the clade, reflecting wide ecological diversity, and highlighting the importance of non-archosauriform Archosauromorpha to both terrestrial and aquatic ecosystems during the Triassic.

Tetrapod remains are extremely rare in the early Carnian (Late Triassic) Calcare del Predil Formation on the Italian side of the Julian Alps (Friuli Venezia Giulia Autonomous Region), which yielded the Raibl fossil assemblage including the famous "Raibl ichthyofauna". A new tanystropheid archosauromorph, Raibliania calligarisi, is here named based on a partial skeleton found in this formation along the Prasnig Brook. The new taxon is similar to Tanystropheus, sharing with it the very elongated cervical vertebrae, but is characterized by the presence of relatively large button-like teeth; apex of the neural spines not transversely thickened; articular facets on the upper corners of the neural spines of the dorsal vertebrae; short and distally pointed pleurapophyses of the second and last 'lumbar' vertebra; ilium with a long preacetabular process bearing a robust and transversely thick tuberosity and a medial ridge bordering the entire ventral part of the iliac blade; and pubis with a cranial process. Tanystropheids lived in the present day Alps and Prealps of Friuli Venezia Giulia Region from the late Anisian to the mid-late Norian and were an important component of the coastal reptile faunas, although they were less common than eusauropterygians and placodonts during the early Carnian. Tanystropheids with extremely elongated cervical vertebrae are reported in this area from the upper Anisian to the lower Carnian.

Tanystropheidae is a clade of early archosauromorphs with a reported distribution ranging from the Early to the Late Triassic of Asia, Europe, and North America. Although some specimens with possible tanystropheid affinities from the Lower Triassic beds of Brazil have been previously attributed to “Protorosauria”, little is known about the tanystropheid record in Gondwana. Here, two new and one previously reported specimen from the Sanga do Cabral Formation (Induan–Olenekian) of Brazil are described and interpreted as ?Tanystropheidae. These records, together with other tetrapods previously reported for the Sanga do Cabral Formation, increase the knowledge of the biotic diversification during the beginning of the Triassic. This contribution reinforces that the archosauromorph diversification occurred shortly after the Permo-Triassic extinction, making the Sanga do Cabral Formation an important unit for the study of early Mesozoic faunas.

Two isolated teeth, a dorsal vertebra, fragments of a humerus and femur, a fragmentary pubic “boot” and part of an ischium shaft, identified here as belonging to a large predatory archosaur were discovered in the Upper Triassic site at Marciszów near Zawiercie (southern Poland). Comparisons of the new fossils from Marciszów with the dorsal vertebrae, pubic “boot”, ischium and femur of the theropod-like Smok wawelski from Lisowice (Silesia) reveal that the two taxa are very similar. Nevertheless, due to the lack of more diagnostic elements (e.g., braincase or cranial elements), we prefer to consider all described specimens from Marciszów as Smok sp. Smok sp. shares a low mound-like, anterior trochanter with trochanteric shelf on the femur, a massive pubic “boot” with a distinct depression (= bevelled area), and a transversely lenticular ischium shaft in cross-section with S. wawelski. Some observed characters of the dorsal vertebra (e.g., lack of some lamina, shape and position of zygapophyses), however, are different from S. wawelski and may also suggest that the new findings represent a second species of the genus in the Upper Triassic of Poland. The discovery of Smok sp. at Marciszów is significant because it is the second example of the co-occurrence of this genus with: (i) bones of a large dicynodont; and (ii) record of gnawed tetrapod bones. The discovery of Smok sp. and the lack of significant morphologic divergence from S. wawelski suggest that this taxon is the only large-bodied predator currently known from the Upper Triassic of Poland. This new evidence expands the record of the genus and contributes, in some measure, to our knowledge of the stratigraphical distribution of large predatory archosaurs from the Polish Upper Triassic bone-bearing levels.

Rhynchosaurs were quadrupedal, bulky herbivorous archosauromorph diapsids with a highly specialized dental apparatus. This group is restricted to the Triassic Period and became extremely abundant worldwide during the late Carnian, numerically dominating some of the first dinosaur-bearing assemblages. Despite their high abundance in upper Carnian beds of South America, rhynchosaurs are restricted to a handful of specimens in the latest Ladinian–early Carnian tetrapod assemblages of this continent. Here, we improve the record of one of the oldest rhynchosaur assemblages of South America with the detailed description of all the rhynchosaur specimens currently known from the Tarjadia Assemblage Zone (AZ) (late Ladinian–?earliest Carnian) of the Chañares Formation (Ischigualasto-Villa Unión Basin, La Rioja Province). Most of these specimens were only preliminarily reported before, and as part of this revision we name the new taxon Elorhynchus carrolli gen. et sp. nov. based on one of these specimens, which represents the first new taxon for the Chañares Formation in 22 years. Elorhynchus carrolli and three more rhynchosaur specimens from the Chañares Formation are identified as stenaulorhynchine rhynchosaurs based on the presence of a crowded field of numerous lingual teeth in the dentary and the presence of small occlusal teeth in the maxillary tooth plate. Although their morphology is congruent, we did not refer the other stenaulorhynchine specimens to Elorhynchus carrolli because they lack diagnostic overlapping character states between them. Nevertheless, there is no current evidence for the presence of more than one rhynchosaur species in the Chañares Formation. The description of Elorhynchus carrolli and the other stenaulorhynchines from the Chañares Formation reinforces biostratigraphical links with the Dinodontosaurus AZ (Santa Maria Supersequence) of southern Brazil and the Lifua Member of the Manda Beds of Tanzania. [ABSTRACT FROM AUTHOR]

Proterochampsids are one of the several diapsid groups that originated, flourished and became extinct during the Triassic Period. The current fossil record of this group indicates that its species were restricted to continental assemblages of the early Late Triassic of South America. The recent description of new rhadinosuchine proterochampsid specimens from the Chañares Formation (early Carnian, Argentina) increased the morphological diversity of the group and cast doubts on their current taxonomic scheme. Previous authors have pointed out that available diagnoses do not allow specimens to be referred unambiguously to the different rhadinosuchine species. Here we redescribe, figure and compare in detail the holotype of one of these rhadinosuchine species, Chanaresuchus bonapartei from the Chañares Formation. The new information provided here allows us to discuss the degree of post-mortem deformation present in the specimen and check the character scorings for the proterochampsid species sampled in the most comprehensive phylogenetic data set currently available for Permo–Triassic archosauromorphs. Our new cladistic analyses find stronger support than previous studies for the monophyly of Rhadinosuchinae and the clades that include Doswelliidae + Proterochampsidae and Tropidosuchus + Rhadinosuchinae. Doswelliids are recovered within Proterochampsidae, as the sister taxon to the genus Proterochampsa, in some analyses under implied weights. Some characters present a phylogenetic signal consistent with the latter grouping, but one additional step is required to force it in the analysis under equal weights. We consider that the new anatomical and phylogenetic information provided here is a step towards a necessary taxonomic revision of Rhadinosuchinae and further research on the interrelationships of proterochampsian archosauriforms. [ABSTRACT FROM AUTHOR]

Tanystropheus and other possible archosauromorph fossils have been discovered from Middle to Upper Triassic shallow marine sedimentary sections in Villány (Villány Hills, southern Hungary). Four fragmentary cervical vertebrae can be assigned to Tanystropheus sp. based on characteristic features including the strongly elongate and hollow vertebral body with extremely reduced neural spine. Besides the cervicals, various teeth, classified into four different morphotypes including longitudinally striated, carinated and ziphodont ones, are thought to belong to archosauromorphs, since they markedly differ from the frequently found teeth of fish and sauropterygians. In addition, three enigmatic cranial bones that might represent some circumorbital elements, have been found as well, and are referred to here as Sauropsida indet. These fossils, originated from the same tectonic unit as those from the Anisian of Bihor (Romania), are of great importance for a better understanding of the poorly known semi-aquatic to terrestrial vertebrate fauna of the Middle to Late Triassic of central Europe. [ABSTRACT FROM AUTHOR]

Archosauriformes are a major group of fossil and living reptiles that include the crown group Archosauria (birds, crocodilians and their extinct relatives) and closely related taxa. Archosauriformes are characterized by a highly diagnostic skull architecture, which is linked to the predatory habits of their early representatives, and the development of extensive cranial pneumaticity associated with the nasal capsule. The evolution of the archosauriform skull from the more plesiomorphic configuration present ancestrally in the broader clade Archosauromorpha was, until recently, elusive. This began to change with the discovery and description of Teyujagua paradoxa , an early archosauromorph from the Lower Triassic Sanga do Cabral Formation of Brazil. Here, we provide a detailed osteological description of the holotype and, thus far, only known specimen of T. paradoxa. In addition to providing new details of the anatomy of T. paradoxa , our study also reveals an early development of skull pneumaticity prior to the emergence of the antorbital fenestra. We use these new data to discuss the evolution of antorbital openings within Archosauriformes. Reappraisal of the phylogenetic position of T. paradoxa supports previous hypotheses of a close relationship with Archosauriformes. The data presented here provide new insights into character evolution during the origin of the archosauriform skull. [ABSTRACT FROM AUTHOR]

The Chañares Formation exhibits one of the most important archosauriform records of early Carnian ecosystems. Here we present new data on the palaeohistology of Chañares archosauriforms and provide new insights into their paleobiology, as well as possible phylogenetically informative traits. Bone microstructure of Lagerpeton chanarensis and Tropidosuchus romeri is dominated by fibro-lamellar tissue and dense vascularization. On the other hand, Chanaresuchus bonapartei is more densely vascularized, but with cyclical growth characterized by alternate fibro-lamellar, parallel-fibered and lamellar-zonal tissues. Dense vascularization and fibro-lamellar tissue imply fast growth and high metabolic rates for all these taxa. These histological traits may be tentatively interpreted as a possible adaptative advantage in front of Chañares Formation environmental conditions. [ABSTRACT FROM AUTHOR]

The homology and evolution of the archosaur ankle is a controversial topic that has been deeply studied using evidence from both extinct and extant taxa. In early stem archosaurs, the astragalus and calcaneum form the ancestral proximal tarsus and a single ossification composes the centrale series. In more recent stem archosaurs, the centrale is incorporated to the proximal row of tarsals laterally contacting the astragalus. This bone is subsequently lost as an independent ossification before the last common ancestor of birds and crocodilians, but the evolutionary fate of this element remains mostly unexplored. Here, we integrate embryological and palaeontological data with morphogeometric analyses to test the hypothesis of loss of the centrale or, alternatively, its incorporation into the archosaurian astragalus. Our results support the latter hypothesis, indicating that the astragalus developed ancestrally from two ossification centres in stem archosaurs and that the supposed tibiale of bird embryos represents a centrale. This conclusion agrees with previous embryological studies that concluded that the tibiale never develops in diapsids. [ABSTRACT FROM AUTHOR]

Tetrapod remains are extremely rare in the early Carnian (Late Triassic) Calcare del Predil Formation on the Italian side of the Julian Alps (Friuli Venezia Giulia Autonomous Region), which yielded the Raibl fossil assemblage including the famous "Raibl ichthyofauna". A new tanystropheid archosauromorph, Raibliania calligarisi, is here named based on a partial skeleton found in this formation along the Prasnig Brook. The new taxon is similar to Tanystropheus, sharing with it the very elongated cervical vertebrae, but is characterized by the presence of relatively large button-like teeth; apex of the neural spines not transversely thickened; articular facets on the upper corners of the neural spines of the dorsal vertebrae; short and distally pointed pleurapophyses of the second and last 'lumbar' vertebra; ilium with a long preacetabular process bearing a robust and transversely thick tuberosity and a medial ridge bordering the entire ventral part of the iliac blade; and pubis with a cranial process. Tanystropheids lived in the present day Alps and Prealps of Friuli Venezia Giulia Region from the late Anisian to the mid-late Norian and were an important component of the coastal reptile faunas, although they were less common than eusauropterygians and placodonts during the early Carnian. Tanystropheids with extremely elongated cervical vertebrae are reported in this area from the upper Anisian to the lower Carnian. [ABSTRACT FROM AUTHOR]

Erythrosuchidae is a clade of early archosauriform reptiles, which were apex predators in many late Early and Middle Triassic ecosystems, following the Permo-Triassic mass extinction. Erythrosuchids had a worldwide distribution, with well-preserved fossil material known from South Africa, European Russia, and China. We here redescribe the anatomy and revise the taxonomy of Guchengosuchus shiguaiensis, which is one of the stratigraphically oldest erythrosuchids and is known from a single partial skeleton from the lowermost Middle Triassic (lower Anisian) lower Ermaying Formation of Shaanxi Province, China. We provide a new differential diagnosis for Guchengosuchus shiguaiensis, and identify a series of autapomorphies relating to the morphologies of the skull roof and vertebrae. Incorporating updated anatomical information for Guchengosuchus into the most comprehensive morphological phylogenetic analysis available for early archosauromorphs recovers it as an early branching member of Erythrosuchidae, outside of the clade formed by Garjainia, Erythrosuchus, Chalishevia, and Shansisuchus. Fugusuchus hejiapanensis, from the uppermost Lower Triassic to lower Middle Triassic Heshanggou Formation of China, is recovered as the earliest branching member of Erythrosuchidae.

Rhynchosaurs are a clade of quadruped, herbivorous stem-archosaur diapsids restricted to the Triassic Period. The group became globally distributed and the numerically dominant tetrapods of several terrestrial ecosystems before their extinction. Derived rhynchosaurs are characterized by a specialized masticatory apparatus, composed of a blade-and-groove occlusion with multiple longitudinal maxillary tooth rows. The morphology of the maxillary tooth plate has shown to be taxonomically and phylogenetically informative. So far, two rhynchosaur maxillary tooth plate morphotypes are known in Argentina, one belonging to an unnamed stenaulorhynchine from the Chañares Formation and the other to the hyperodapedontine Hyperodapedon sanjuanensis, the single rhynchosaur species currently name for the Ischigualasto Formation. Here we describe a new rhynchosaur maxillary tooth plate morphotype based on an indeterminate hyperodapedontine specimen from the Ischigualasto Formation. This maxillary tooth plate (PVL 2728) possesses a single longitudinal groove that divides symmetric lateral and medial tooth-bearing areas with relatively large tooth crowns, which is an uncommon combination of features among hyperodapedontines. These qualitative observations in addition to quantitative analyses show that the morphology of PVL 2728 differs from that of, at least, other sampled South American rhynchosaurs. Therefore, this specimen expands the morphological disparity of rhynchosaurs in northwest Argentina and southwestern Pangaea. [ABSTRACT FROM AUTHOR]

Teraterpeton hrynewichorum is an unusual archosauromorph reptile from the Upper Triassic (Carnian) Evangeline Member of the Wolfville Formation in Nova Scotia (Canada). Its long snout has transversely broad, cusped 'molariform' teeth posteriorly and lacks teeth anteriorly. The temporal region of the cranium is 'euryapsid' with large upper and closed lower temporal fenestrae. A previously undescribed specimen referable to Teraterpeton includes a nearly complete pelvic girdle and both hind limbs. The ilium has a long, dorsoventrally deep anterior process similar to that of derived rhynchosaurs. The pelvis has a well-developed thyroid fenestra, a feature shared only by Tanystropheidae among Archosauromorpha. Metatarsal V is proximodistally short, resembling the condition in Tanystropheidae. The pedal unguals of Teraterpeton are strongly flattened mediolaterally, dorsoventrally deep and weakly curved, much like the manual unguals. We performed a phylogenetic analysis of a matrix comprising 61 taxa of Permo-Triassic diapsid reptiles and 337 characters, which supports the position of Teraterpeton as the sister-taxon of Trilophosaurus + Spinosuchus. In the current phylogeny, parsimony-based character optimization of the aforementioned character-states in Teraterpeton indicate that all were acquired independently from other saurian lineages. The unusual combination of postcranial features in Teraterpeton underscores the critical importance of comprehensive taxon sampling for understanding the mode of character change among Triassic diapsid reptiles and careful apomorphy-based identifications to faunal analyses. [ABSTRACT FROM AUTHOR]

Many traits have been linked to extinction risk among modern vertebrates, including mode of life and body size. However, previous work has indicated there is little evidence that body size, or any other trait, was selective during past mass extinctions. Here, we investigate the impact of the Triassic–Jurassic mass extinction on early Archosauromorpha (basal dinosaurs, crocodylomorphs and their relatives) by focusing on body size and other life history traits. We built several new archosauromorph maximum‐likelihood supertrees, incorporating uncertainty in phylogenetic relationships. These supertrees were then employed as a framework to test whether extinction had a phylogenetic signal during the Triassic–Jurassic mass extinction, and whether species with certain traits were more or less likely to go extinct. We find evidence for phylogenetic signal in extinction, in that taxa were more likely to become extinct if a close relative also did. However, there is no correlation between extinction and body size, or any other tested trait. These conclusions add to previous findings that body size, and other traits, were not subject to selection during mass extinctions in closely‐related clades, although the phylogenetic signal in extinction indicates that selection may have acted on traits not investigated here. [ABSTRACT FROM AUTHOR]

Erythrosuchids are Early–Middle Triassic bulky, quadrupedal archosauromorphs with proportionally large heads, and they were among the first archosauromorphs to occupy the role of terrestrial hypercarnivores. Recent work has expanded anatomical and phylogenetic knowledge of erythrosuchids, but a thorough understanding is still lacking, and Erythrosuchus africanus is the only species for which a thorough anatomical description of most of the skeleton has been published. Garjainia prima, from the upper Olenekian of Russia, represents one of the oldest known erythrosuchids and includes the best-preserved skull of an Early Triassic erythrosuchid. Here, we expand understanding of erythrosuchid anatomy by providing the first detailed and comprehensive description of the holotype of Garjainia prima. We consider ' Vjushkovia triplicostata ' to be a junior synonym of Garjainia prima, because of their extremely similar morphology, with the two character states that differ between them being variable intraspecifically in some other diapsids. A new phylogenetic analysis recovered a monophyletic Garjainia as sister to Middle Triassic erythrosuchids and recovered Fugusuchus hejiapanensis as sister to all other erythrosuchids. Branch support for Erythrosuchidae is low, but the Middle Triassic erythrosuchid clade is well supported by characters with low homoplasy, indicating that their morphology was specialized in ways rarely explored by other Triassic archosauromorphs. [ABSTRACT FROM AUTHOR]

Erythrosuchidae is a clade of early archosauriform reptiles, which were apex predators in many late Early andMiddle Triassic ecosystems, following the Permo-Triassic mass extinction. Erythrosuchids had a worldwide distribution, with well-preserved fossil material known from South Africa, European Russia, and China. We here redescribe the anatomy and revise the taxonomy of Guchengosuchus shiguaiensis, which is one of the stratigraphically oldest erythrosuchids and is known from a single partial skeleton from the lowermost Middle Triassic (lower Anisian) lower Ermaying Formation of Shaanxi Province, China. We provide a new differential diagnosis for Guchengosuchus shiguaiensis, and identify a series of autapomorphies relating to the morphologies of the skull roof and vertebrae. Incorporating updated anatomical information for Guchengosuchus into the most comprehensive morphological phylogenetic analysis available for early archosauromorphs recovers it as an early branching member of Erythrosuchidae, outside of the clade formed by Garjainia, Erythrosuchus, Chalishevia, and Shansisuchus. Fugusuchus hejiapanensis, from the uppermost Lower Triassic to lower Middle Triassic Heshanggou Formation of China, is recovered as the earliest branching member of Erythrosuchidae. [ABSTRACT FROM AUTHOR]

Several partially articulated specimens and numerous isolated bones of Ozimek volans gen. et sp. nov., from the late Carnian lacustrine deposits exposed at Krasiejów in southern Poland, enable a reconstruction of most of the skeleton. The unique character of the animal is its enlarged plate-like coracoids presumably fused with sterna. Other aspects of the skeleton seem to be comparable to those of the only known specimen of Sharovipteryx mirabilis from the latest Middle Triassic of Kyrgyzstan, which supports interpretation of both forms as protorosaurians. One may expect that the pectoral girdle of S. mirabilis, probably covered by the rock matrix in its only specimen, was similar to that of O. volans gen. et sp. nov. The Krasiejów material shows sharp teeth, low crescent scapula, three sacrals in a generalized pelvis (two of the sacrals being in contact with the ilium) and curved robust metatarsal of the fifth digit in the pes, which are unknown in Sharovipteryx. Other traits are plesiomorphic and, except for the pelvic girdle and extreme elongation of appendages, do not allow to identify any close connection of the sharovipterygids within the Triassic protorosaurians.

The first osteohistological study focused exclusively on rhynchosaurs (non-archosauriform archosauromorphs), based on the hyperodapedontines Teyumbaita sulcognathus and Hyperodapedon sp., from the Upper Triassic of Southern Brazil, indicates a relatively rapid growth rate in early ontogeny shown by the fibrolamellar complex, with a change to slow intermittent growth during late ontogeny represented by parallel-fibred bone with several growth marks. Contrary to previous studies, which described a typical non-archosaur reptilian bone tissue pattern for rhynchosaurs, with growth marks extending across the entire cortex, we demonstrate that, in both studied taxa, the initial growth rate was faster in comparison to the later. This suggests that the ability of rapid growth at high rates was already present in basal non-archosauriform archosauromorphs.

Proterosuchidae represents the oldest substantial diversification of Archosauromorpha and plays a key role in understanding the biotic recovery after the end-Permian mass extinction. Proterosuchidae was long treated as a wastebasket taxon, but recent revisions have reduced its taxonomic content to five valid species from the latest Permian of Russia and the earliest Triassic (Induan) of South Africa and China. In addition to these occurrences, several isolated proterosuchid bones have been reported from the Induan Panchet Formation of India for over 150 years. Following the re-study of historical specimens and newly collected material from this unit, we erect the new proterosuchid species Samsarasuchus pamelae , which is represented by most of the presacral vertebral column. We also describe cf. proterosuchid and proterosuchid cranial, girdle and limb bones that are not referred to Samsarasuchus pamelae . Phylogenetic analyses recovered Samsarasuchus pamelae within the new proterosuchid clade Chasmatosuchinae. The taxonomic diversity of Proterosuchidae is substantially expanded here, with at least 11 nominal species and several currently unnamed specimens, and a biogeographical range encompassing present-day South Africa, China, Russia, India, Brazil, Uruguay and Australia. This indicates a broader taxonomic, phylogenetic and biogeographic diversification of Proterosuchidae than previously thought in the aftermath of the end-Permian mass extinction., Competing Interests: We declare we have no competing interests., (© 2023 The Authors.)

Three small and gracile jaw fragments are recovered from the Boren Quarry, one of the lowest fossil quarries of the Upper Triassic Dockum Group of Texas. The specimens are referred to archosauromorphs, where the morphology of the dentary and teeth of two specimens resemble what is observed in basal saurischians. Growing numbers of early dinosaur fossils from the lowest quarries of the Dockum Group of Texas which correspond to the lowermost Norian raises doubts concerning early dinosaur dispersal during the late Carnian-early Norian interval and the first occurrence of North American dinosaurs which might have happened earlier than previously suggested. [ABSTRACT FROM AUTHOR]

Tanystropheidae is a clade of early archosauromorphs with a reported distribution ranging from the Early to the Late Triassic of Asia, Europe, and North America. Although some specimens with possible tanystropheid affinities from the Lower Triassic beds of Brazil have been previously attributed to "Protorosauria", little is known about the tanystropheid record in Gondwana. Here, two new and one previously reported specimen from the Sanga do Cabral Formation (Induan-Olenekian) of Brazil are described and interpreted as Tanystropheidae. These records, together with other tetrapods previously reported for the Sanga do Cabral Formation, increase the knowledge of the biotic diversification during the beginning of the Triassic. This contribution reinforces that the archosauromorph diversification occurred shortly after the Permo-Triassic extinction, making the Sanga do Cabral Formation an important unit for the study of early Mesozoic faunas. [ABSTRACT FROM AUTHOR]

Two isolated teeth, a dorsal vertebra, fragments of a humerus and femur, a fragmentary pubic "boot" and part of an ischium shaft, identified here as belonging to a large predatory archosaur were discovered in the Upper Triassic site at Marciszów near Zawiercie (southern Poland). Comparisons of the new fossils from Marciszów with the dorsal vertebrae, pubic "boot", ischium and femur of the theropod-like Smok wawelski from Lisowice (Silesia) reveal that the two taxa are very similar. Nevertheless, due to the lack of more diagnostic elements (e.g., braincase or cranial elements), we prefer to consider all described specimens from Marciszów as Smok sp. Smok sp. shares a low mound-like, anterior trochanter with trochanteric shelf on the femur, a massive pubic "boot" with a distinct depression (= bevelled area), and a transversely lenticular ischium shaft in cross-section with S. wawelski. Some observed characters of the dorsal vertebra (e.g., lack of some lamina, shape and position of zygapophyses), however, are different from S. wawelski and may also suggest that the new findings represent a second species of the genus in the Upper Triassic of Poland. The discovery of Smok sp. at Marciszów is significant because it is the second example of the co-occurrence of this genus with: (i) bones of a large dicynodont; and (ii) record of gnawed tetrapod bones. The discovery of Smok sp. and the lack of significant morphologic divergence from S. wawelski suggest that this taxon is the only large-bodied predator currently known from the Upper Triassic of Poland. This new evidence expands the record of the genus and contributes, in some measure, to our knowledge of the stratigraphical distribution of large predatory archosaurs from the Polish Upper Triassic bone-bearing levels. [ABSTRACT FROM AUTHOR]

One of the key faunal transitions in Earth history occurred after the Permo- Triassic mass extinction (ca 252.2 Ma), when the previously obscure archosauromorphs (which include crocodylians, dinosaurs and birds) become the dominant terrestrial vertebrates. Here, we place all known middle Permian--early Late Triassic archosauromorph species into an explicit phylogenetic context, and quantify biodiversity change through this interval. Our results indicate the following sequence of diversification: a morphologically conservative and globally distributed post-extinction 'disaster fauna'; a major but cryptic and poorly sampled phylogenetic diversification with significantly elevated evolutionary rates; and a marked increase in species counts, abundance, and disparity contemporaneous with global ecosystem stabilization some 5 million years after the extinction. This multiphase event transformed global ecosystems, with far-reaching consequences for Mesozoic and modern faunas. [ABSTRACT FROM AUTHOR]

This report describes two adjacent, longitudinally-fused anterior cervical vertebrae from a basal archosauromorph. The specimen was collected from the Denwa Formation, Satpura Gondwana Basin, India. The differential diagnosis of the fusion includes genetic or environmentally-mediated congenital malformations, nonspecific spondyloarthopathy, and various infectious agents. These observations represent the first published recognition of archosauromorph vertebral pathology from specimens that were discovered in India. The observations affirm that basal archosauromorphs suffered from disorders that have been observed in later dinosaurs and modern-day vertebrates. Considering the process of orderly differential diagnosis is an important aspect of understanding lesions of ancient bones. [ABSTRACT FROM AUTHOR]

The origin of the avian hand, with its reduced and fused carpals and digits, from the five-fingered hands and complex wrists of early dinosaurs represents one of the major transformations of manus morphology among tetrapods. Much attention has been directed to the later part of this transition, from four- to three-fingered taxa. However, earlier anatomical changes may have influenced these later modifications, possibly paving the way for a later frameshift in digit identities. We investigate the five- to four-fingered transition among early dinosaurs, along with changes in carpus morphology. New three-dimensional reconstructions from computed tomography data of the manus of the Triassic and Early Jurassic theropod dinosaurs Coelophysis bauri and Megapnosaurus rhodesiensis are described and compared intra- and interspecifically. Several novel findings emerge from these reconstructions and comparisons, including the first evidence of an ossified centrale and a free intermedium in some C. bauri specimens, as well as confirmation of the presence of a vestigial fifth metacarpal in this taxon. Additionally, a specimen of C. bauri and an unnamed coelophysoid from the Upper Triassic Hayden Quarry, New Mexico, are to our knowledge the only theropods (other than alvarezsaurs and birds) in which all of the distal carpals are completely fused together into a single unit. Several differences between the manus of C. bauri and M. rhodesiensis are also identified. We review the evolution of the archosauromorph manus more broadly in light of these new data, and caution against incorporating carpal characters in phylogenetic analyses of fine-scale relationships of Archosauromorpha, in light of the high degree of observed polymorphism in taxa for which large sample sizes are available, such as the theropod Coelophysis and the sauropodomorph Plateosaurus. We also find that the reduction of the carpus and ultimate loss of the fourth and fifth digits among early dinosaurs did not proceed in a neat, stepwise fashion, but was characterized by multiple losses and possible gains of carpals, metacarpals and phalanges. Taken together, the high degree of intra- and interspecific variability in the number and identities of carpals, and the state of reduction of the fourth and fifth digits suggest the presence of a 'zone of developmental variability' in early dinosaur manus evolution, from which novel avian-like morphologies eventually emerged and became channelized among later theropod clades. [ABSTRACT FROM AUTHOR]