The evolutionary origins of turtles remain poorly understood. Molecular systematics posit a sister relationship between turtles and archosaurs, but morphological studies return conflicting hypotheses of turtle relationships both to other living reptiles and to their closest fossil relatives. The middle Permian Eunotosaurus africanus has been widely regarded as the oldest stem turtle, which makes it instrumental in recent discussions of the origins of turtles and their highly transformed anatomy. Here, we use anatomical observations derived from X-ray computed microtomography (μCT) of Eunotosaurus and candidate stem turtles to evaluate phylogenetic hypotheses of turtle origins. Eunotosaurus has many plesiomorphies and lacks synapomorphies of crown reptiles, whereas Proganochelys, one of the oldest uncontentious stem turtles, shares similarities with archosauromorphs, especially in the endocranium. Our comprehensive phylogenetic analysis recovers Eunotosaurus as a millerettid stem reptile not related to turtles. This indicates that features shared by Eunotosaurus and turtles, notably including broadened dorsal ribs, evolved independently. These similarities are better explained by convergent evolution of fossorial ecologies rather than shared ancestry. Furthermore, we find strong support for the molecular phylogenetic hypothesis that turtles are sister to Archosauria among living reptiles, resolving long-standing conflicts between morphological and molecular datasets. By placing turtle origins among the earliest archosauromorphs in the late Permian, we provide new insights into the anatomical transformations involved in the origins of the distinct turtle body plan.

Archosauromorphs are a diverse clade of vertebrates that originated in the Early Triassic and persist today as crown birds (ornithodirans) and crocodilians (pseudosuchians). They exhibit markedly different life-history strategies, with ornithodirans characterized by rapid growth, and more crown-ward pseudosuchians with slower growth rates. Understanding how these patterns emerged requires further insight into growth dynamics among early archosauromorphs. We use synchrotron X-ray micro-computed tomography to investigate the bone microstructure in an assemblage of archosauromorphs from the Early Triassic locality Driefontein Farm 11 in the Olenekian-Anisian Langbergia-Garjainia subzone of the Cynognathus zone in the main Karoo Basin of South Africa. Our findings reveal that growth strategies among Early Triassic archosauromorphs already encompass both rapid and slow growth rates. We further deduce that the diversity in growth strategies observed in crown-ward archosaur lineages were not lineage-specific derived characteristics but rather inherited growth traits already present among their Early Triassic members.

Living reptiles including turtles, crocodilians, birds and squamates are descended from a common ancestor among the Neodiapsida that lived in the late Permian c . 257 million years ago. Their origin was preceded by key evolutionary changes to cranial architecture that are poorly understood due to the rarity of early neodiapsids in the fossil record. Here, we describe a monospecific aggregation of a new non-saurian neodiapsid from the late Permian of South Africa. Synchrotron microtomography of four complete skulls reveals a mosaic of classic ‘saurian’ features such as a tympanic fossa and cephalic condyle of the quadrate and an open lower temporal bar, alongside surprising plesiomorphies including a rectangular denticle field on the braincase and a comparatively robust stapes. Phylogenetic analysis finds the new taxon within the Younginidae, sister to Akkedops bremneri and Youngina capensis as the earliest-diverging neodiapsid lineage. Our results demonstrate that the mobile (strepostylic) quadrate evolved only shortly after the origin of the tympanic fossa and the loss of the lower temporal bar, among crownward stem reptiles. This suggests a functional evolutionary linkage between these important traits related to hearing and feeding during the rise of crown reptiles.

The maxillary canal system in Cynognathus and Diademodon is described. The hypothesis that expansion of the maxillary sinus represents a synapomorphy of the clade Cynognathia is supported. A trend towards the reduction of the inferior palpebral ramus is proposed.

Bioinspiration is an approach to innovation based on the observation of biological systems, of which only 0.1% remain since life began 3.7 billion years ago. Expanding the scope of bioinspiration to the fossil record greatly increases the diversity of potential biological "muses" and provides a means to understand the form, function and origins of current living systems. This extended approach, here termed "palaeo-bioinspiration", has already been applied to the fields of hydrodynamics, aeromechanics, actuators, protective technology and building construction. To reach its full potential, palaeo-bioinspiration has to overcome the misconception that fossils are "failures" or "primitive", and temper the widespread belief that extant biodiversity is inherently "optimised". By encouraging interdisciplinarity, investing in technical infrastructure and collaborating with both Natural Science institutions and industry, palaeo-bioinspiration could become a powerful asset within the bioinspiration domain.

The anatomy of the enigmatic stem-reptile Galesphyrus capensis (Middle-Late Permian, South Africa) is redescribed in detail. The validity of G. capensis is confirmed based on its holotype, but the other previously referred specimen is excluded from G. capensis based on skeletal differences. The new anatomical data described here are included in an expanded phylogenetic dataset, designed to examine the relationships of Permian reptiles. Both specimens are recovered as early-diverging members of a clade which includes Millerettidae, traditionally considered 'parareptiles' and Neodiapsida. Consequently, Parareptilia is paraphyletic, as Millerettidae occupies a more crownward position than any other parareptile, themselves not forming a clade. Our results also demonstrate that neodiapsids originated at least in the late Capitanian, prior to the Capitanian Mass Extinction, and highlight the diversity of Younginidae, which includes three South African taxa. The exquisitely preserved postcranium of G. capensis sheds light on postcranial evolution in Late Permian stem-reptiles, bringing additional support for sister-group relationship between millerettids and neodiapsids. Our new data on G. capensis and other stem-reptiles demonstrate that the evolutionary history of the foot was remarkably complex close to the origin of Sauria, with some of the prerequisites to the evolution of the saurian foot and gait having already appeared by the late Capitanian. These overlooked Middle and Late Permian stem-reptiles have the potential to further our understanding of the origin of the reptilian crown group.

The enigmatic neodiapsid Thadeosaurus colcanapi (Lower Sakamena Formation, southwestern Madagascar), sole species of the genus Thadeosaurus, is revised here. The attribution of 12 of the 21 referred specimens is confirmed, spanning all ontogenetic stages, and the anatomy of Thadeosaurus is redescribed in detail with comments on ontogenetical differences. This new anatomical information is included in an expanded phylogenetical dataset tailored to examine the relationships of Permo-Triassic diapsids. A stem-saurian neodiapsid position is confirmed here for all 'younginiforms', which are here recovered paraphyletic, with Youngina representing an earlier-diverging taxon. However, this topology is extremely labile, and the monophyly or paraphyly of 'younginiforms' could not be unequivocally supported. In contrast, our analyses provide good support for a monophyletic Tangasauridae including all other 'younginiforms'. Thadeosaurus is here recovered as a member of the Tangasauridae and as the sister-group to the putative semi-aquatic Tangasaurinae with a moderate degree of support, despite the large amounts of missing data in lesser-known tangasaurids partially obscuring our understanding of tangasaurid interrelationships. Last, Thadeosaurus is considered to have inhabited a nearshore, probably riparian, environment, although it remains unclear whether it was semi-aquatic or fully terrestrial. Further examinations of lesser-known tangasaurids, as well as a novel morphotype identified here in the Lower Sakamena Formation of Madagascar, could provide new evidence to deepen our understanding of the evolution and palaeoecology of the Tangasauridae.

The Late Permian Weigeltisauridae are the world's first gliding reptiles, but much remains unknown regarding the anatomy of their patagium (or wing), which, in turn, confounds our understanding of their gliding mechanism and paleobiology. Here, we examine the morphology and osteo-histology of the patagial skeleton of weigeltisaurids using an array of imaging techniques and several thin sections through the wing skeleton of a specimen of Weigeltisaurus from the Late Permian of Germany. We demonstrate that patagials and gastralia share a one-to-one articulation, permitted by the uniquely specialized anatomy of the lateral gastralia. We also show, based on skeletal anatomy, histology, and inferred musculoskeletal relationships, that patagials are likely neomorphic ossifications and are thus not strictly homologous to the gastralia. We provide the first reconstruction of the musculoskeletal anatomy of the weigeltisaurid wing, suggesting that the base of the patagials was likely embedded in the M. obliquus externus group. Similar to the condition in the extant flying lizard Draco, these muscles may have contributed to the unfolding of the patagium, which was likely supported by hooking the manual claws onto the leading edge of the patagium. This would have provided weigeltisaurids with a means to maintain the patagium expanded and under tension while gliding, as well as some measure of control of the dihedral angle of the wing, thereby offering a means to control stability and maneuverability in flight. Wing folding may have been permitted by muscular and tendinous connections between the elements of the patagial skeleton, generating elastic tension toward a folded state, as in Draco. Lastly, the cross sections of the patagials show a bimodal cortical distribution with much thicker cortices along their cross-sectional long axis than short axis. This made the patagials rigid, which likely helped prevent patagial collapse during gliding. This work represents a critical step toward understanding the wing structure and gliding mechanism in weigeltisaurids, paving the way for future morphofunctional or biomechanical studies on the locomotion of the world's first flying vertebrates.

The anatomy of Late Triassic drepanosauromorphs is re-examined, with a focus on the previously published surface models of the holotype of Avicranium renestoi from the Norian of North America. We comment on the cranial anatomy of this taxon and propose a new reconstruction of the skull and mandible. Contrary to previous interpretations, the entire rostrum and most of the palate are not preserved in this specimen. We also suggest that some proposed plesiomorphic characters may result from incomplete ossification due to immaturity. These new observations are compiled into a new morphological phylogenetic dataset designed to address the monophyly of 'Avicephala', the group comprising the Late Permian gliding reptiles Weigeltisauridae, and the Late Triassic chameleon-like Drepanosauromorpha. We recover Weigeltisauridae as stem-saurian diapsids and Drepanosauromorpha as sister-group to Trilophosauridae among archosauromorphs, thus implying the paraphyly of 'Avicephala'. Drepanosauromorphs and trilophosaurids are recovered as sister-taxa for the first time, as supported by several cranial and postcranial synapomorphies. This new phylogenetic position of Drepanosauromorpha reduces the group's ghost lineage that now does not necessarily cross the Permian-Triassic boundary. However, much remains unknown of the early history of trilophosaurids and drepanosauromorphs, and of the evolution of arboreality in Triassic archosauromorph reptiles.

The agamid lizards of the genusDracoare undoubtedly the most renown reptilian gliders, using their rib-supported patagial wings as lifting surfaces while airborne. Recent investigations into these reptiles highlighted the role of body posture during gliding, however, the aerodynamics of postural changes inDracoremain unclear. Here, we examine the aerodynamics and gliding performances ofDraco volansusing a numerical approach focusing on three postural changes: wing expansion, body camber, and limb positioning. To this aim, we conducted 70 three-dimensional steady-state computational fluid dynamics simulations of gliding flight and 240 two-dimensional glide trajectory calculations. Our results demonstrate that while airborne,D. volansgenerates a separated turbulent boundary layer over its wings characterized by a large recirculation cell that is kept attached to the wing surface by interaction with wing-tip vortices, increasing lift generation. This lift generating mechanism may be controlled by changing wing expansion and shape to modulate the generation of aerodynamic force. Furthermore, our trajectory simulations highlight the influence of body camber and orientation on glide range. This sheds light on howD. volanscontrols its gliding performance, and conforms to the observation that these animals plan their glide paths prior to take off. Lastly,D. volansis mostly neutral in pitch and highly maneuverable, similar to other vertebrate gliders. The numerical study presented here thus provides a better understanding of the lift generating mechanism and the influence of postural changes in flight in this emblematic animal and will facilitate the study of gliding flight in analogous gliding reptiles for which direct observations are unavailable.

The agamid lizards of the genus Draco are undoubtedly the most renown reptilian gliders, using their rib-supported patagial wings as lifting surfaces while airborne. Recent investigations into these reptiles highlighted the role of body posture during gliding, however, the aerodynamics of postural changes in Draco remain unclear. Here, we examine the aerodynamics and gliding performances of Draco volans using a numerical approach focusing on three postural changes: wing expansion, body camber, and limb positioning. To this aim, we conducted 70 three-dimensional steady-state computational fluid dynamics simulations of gliding flight and 240 two-dimensional glide trajectory calculations. Our results demonstrate that while airborne, D. volans generates a separated turbulent boundary layer over its wings characterized by a large recirculation cell that is kept attached to the wing surface by interaction with wing-tip vortices, increasing lift generation. This lift generating mechanism may be controlled by changing wing expansion and shape to modulate the generation of aerodynamic force. Furthermore, our trajectory simulations highlight the influence of body camber and orientation on glide range. This sheds light on how D. volans controls its gliding performance, and conforms to the observation that these animals plan their glide paths prior to take off. Lastly, D. volans is mostly neutral in pitch and highly maneuverable, similar to other vertebrate gliders. The numerical study presented here thus provides a better understanding of the lift generating mechanism and the influence of postural changes in flight in this emblematic animal and will facilitate the study of gliding flight in analogous gliding reptiles for which direct observations are unavailable.

Files 1-3: RTI interactive photographs of the skulls of the drepanosauromorphs Megalancosaurus preonensis Calzavara, Muscio and Wild, 1980 and Vallesaurus cenensis Renesto and Binelli, 2006 (Norian, Italy). Reflectance Transformation Imaging (RTI) is a method that computes an 'interactive specimen' on which the illumination can be oriented at will. Sets of 54 photographs under different LED sources were compiled using the RTIBuilder software. The RTI files can be opened using the RTI vewer software (both softwares are freely available at www.culturalheritageimaging.org). Files 4-6: Nexus files of phylogenetic taxon-character matrices and backbone constraints used in phylogenetic analyses. Currently only available upon request for reviewers, but will be made public after acceptance of article for publication.

Wapitisaurus problematicus was initially described as a member of the Weigeltisauridae, a clade of Late Permian gliding reptiles from Eurasia and Madagascar. However, the poor preservation of the holotype and only known specimen, from the lower Sulphur Mountain Formation at Ganoid Ridge (British Columbia, Canada), raised doubts about this assignment. Here, we redescribe W. problematicus and reassess its systematic position among diapsid reptiles. Comparison with all known weigeltisaurids, as well as contemporaneous reptiles from the Sulphur Mountain Formation, indicates that the taxon instead represents a thalattosauroid thalattosauriform, with noted similarities to Thalattosaurus and Paralonectes. This reidentification restricts weigeltisaurids to the Late Permian, with no occurrence in North America. Wapitisaurus problematicus potentially represents one of the oldest thalattosauriforms and increases our understanding of their diversity and disparity during the late Early and Middle Triassic. The close morphological similarities with later (thalattosauroid) thalattosauriforms and their high abundance in (shallow) marine settings may indicate an earlier invasion of this realm than previously assumed. This parallels observations in early ichthyopterygians with widespread opportunistic trophic niche diversification occurring relatively rapidly after the end-Permian mass extinction event.

The postcranial skeleton of the gliding neodiapsid reptile Coelurosauravus elivensis (Lower Sakamena Formation, ?upper Permian, southwestern Madagascar) is re-described in detail based on all previously referred specimens. The exquisite preservation of the material provides three-dimensional details of the individual bones, which are missing in the Laurasian weigeltisaurid material. A new skeletal reconstruction of C. elivensis is proposed including the first reconstruction of a weigeltisaurid reptile in lateral view. The re-examination of the material highlights interspecific differences in the postcranium of weigeltisaurids, in particular in the trunk and patagial spars. These animals have long been considered as arboreal and gliding reptiles. However, new information on the postcranium of C. elivensis reveals strong similarities with both extant and extinct quadrupeds specialized for a clinging arboreal lifestyle. Additionally, the presence of an additional phalanx in the fifth digit of the manus is now attested for all weigeltisaurids where this region is preserved. We suggest that this morphology could have allowed weigeltisaurids to grasp their patagium as observed in the extant gliding agamid Draco. Weigeltisaurids are thus the earliest known gliding vertebrates and some of the first tetrapods with an obligatory arboreal lifestyle, but also represent the only known vertebrates with a hyperphalangy aligned with a gliding apparatus.