Discovery of a rare pterosaur bone bed in a cretaceous desert with insights on ontogeny and behavior of flying reptiles

Cranial and postcranial anatomy of a juvenile baurusuchid (Notosuchia, Crocodylomorpha) and the taxonomical implications of ontogeny

Baurusuchidae comprises a clade of top-tier terrestrial predators and are among the most abundant crocodyliforms found in the Adamantina Formation, Bauru Basin, Brazil (Campanian-Maastrichtian). Here, we provide a detailed description of the cranial and postcranial osteology and myology of the most complete juvenile baurusuchid found to date. Although the preservation of juvenile individuals is somewhat rare, previously reported occurrences of baurusuchid egg clutches, a yearling individual, and larger, but skeletally immature specimens, comprise a unique opportunity to track anatomical changes throughout their ontogenetic series. Its cranial anatomy was resolved with the aid of a three-dimensional model generated by the acquisition of computed tomography data, and its inferred adductor mandibular musculature was compared to that of mature specimens in order to assess possible ontogenetic shifts. A subsequent phylogenetic analysis included the scoring of Gondwanasuchus scabrosus, the smallest baurusuchid species known to date, to evaluate its phylogenetic relations relative to a known juvenile. We find considerable differences between juveniles and adults concerning skull ornamentation and muscle development, which might indicate ontogenetic niche partitioning, and also anatomical and phylogenetic evidence that G. scabrosus corresponds to a young semaphoront lacking mature cranial features.

A new toothless pterosaur from the Early Cretaceous Jehol Biota with comments on the Chaoyangopteridae

The Chaoyangopteridae is a clade of azhdarchoid pterosaurs that stands out in China, particularly in the Jehol Biota, as a Cretaceous group of medium-sized and high-crested pterosaurs. Herein, we describe a new species, Meilifeilong youhao gen. et sp. nov., based on two specimens, one tentatively referred to this taxon. This new species represents the most complete and well-preserved chaoyangopterid recorded to date. Along with a set of characters (low premaxillary crest above the nasoantorbital fenestra extending posteriorly, posterior premaxillary process arched and curving posteriorly, a slightly convex sternal articulation surface of coracoid, and a fibular shaft close to proximal articulation strongly arched posteriorly), this species also provides new information both on the unknown palatal region of this clade, and on the rarely preserved (in place) ear portion with stapes. Moreover, M. youhao sheds light on paleoecological aspects, while also giving new information about the taxonomic diversity of this peculiar group of Jiufotang pterosaurs.

A taxonomic revision of the Sinopterus complex (Pterosauria, Tapejaridae) from the Early Cretaceous Jehol Biota, with the new genus Huaxiadraco

Tapejarids are edentulous pterosaurs particularly abundant in the Chinese Jiufotang Formation, counting with over 10 described specimens and dozens of undescribed ones. A total of seven nominal tapejarid species (within two genera) have been proposed, though it is disputed how many of those are valid instead of sexual or ontogenetic morphs of fewer, or a single, species. However, detailed revisions of the matter are still lacking. In the present work, we provide a specimen-level survey of anatomical variation in previously described Jiufotang tapejarid specimens, as well as of six new ones. We present qualitative and morphometric comparisons, aiming to provide a basis for a taxonomic reappraisal of the complex. Our results lead us to interpret two Jiufotang tapejarid species as valid: Sinopterus dongi and Huaxiadraco corollatus (gen. et comb. nov.). Our primary taxonomic decisions did not rely around cranial crest features, which have typically been regarded as diagnostic for most of these proposed species albeit ever-growing evidence that these structures are highly variable in pterosaurs, due to ontogeny and sexual dimorphism. However, a reassessment of premaxillary crest variation in the Sinopterus complex reveals that while much of the observed variation (crest presence and size) can easily be attributed to intraspecific (ontogenetic and sexual) variation, some of it (crest shape) does seem to represent interspecific variation indeed. A phylogenetic analysis including the species regarded as valid was also performed.

Novel information on the cranial anatomy of the tapejarine pterosaur Caiuajara dobruskii

Caiuajara dobruskii is a tapejarid pterosaur from the Cretaceous of the 'Cemitério dos Pterossauros' (pterosaur graveyard) site, a unique pterosaur bonebed which is located at the municipality of Cruzeiro do Oeste (Paraná, Brazil). Preliminary inferences on Caiuajara morphology were founded on a few partial skeletons, with no detail on the skull anatomy. Here we describe a new specimen from the pterosaur graveyard site, which corresponds to the most complete skull of Caiuajara dobruskii known so far. Furthermore, we describe and compare other specimens including the holotype, a paratype, and several other undescribed specimens. The new specimen preserves the posterior portion of the skull, allowing a better comprehension of its morphology and provides an appreciation of the anatomic structures of the basicranium, enabling better interpretation of this region. We also described the lower jaw of Caiuajara, reporting a unique feature of its symphyseal which adds to the diagnosis for the species. A variability in the premaxillary crest is also noted in different specimens of Caiuajara, which might be interpreted as sexual dimorphism or ontogenetic variability. Therefore, those new findings allow a better comprehension of its skull and enables a more precise comparison between the skulls of those extinct flying reptiles.

A new wing skeleton of the Jehol tapejarid Sinopterus and its implications for ontogeny and paleoecology of the Tapejaridae

The tapejarid pterosaurs flourished in the Jehol Biota with an abundance of immature individuals and a rarity of individuals at skeletal maturity. Most of these individuals plot well on an ontogenetic series based on the proportions of limb elements, but this has lacked histological evidence until now. Here, a new wing skeleton of Sinopterus was thin-sectioned to provide the first histological data about the ontogeny of the Jehol tapejarids. Histologically, the new specimen is an immature individual at a late juvenile stage prior to sexual maturity. It is grouped with medium-sized and medium-crested individuals, which are distinct from the small-sized and crestless individuals as well as the rare large-sized and large-crested individuals at skeletal maturity, supporting the presence of the premaxillary crest as an ontogenetic feature in the Jehol tapejarids. Furthermore, this histology indicates that the largest skeletally immature individuals might have reached the sexual maturity. Enigmatically, there is a size gap between sexual and skeletal maturity, which is at about 79% of the large size, implying a ontogenetic strategy comparable with Pteranodon and possibly with the Brazilian tapejarid Caiuajara. This size gap is consistent with lack of the larger sexually mature individuals in the Jehol Biota, which is hypothesized to be a migratory habitat for the Jehol tapejarids.

The first edentulous ceratosaur from South America

The recognition of ontogenetic edentulism in the Jurassic noasaurid Limusaurus inextricabilis shed new light on the dietary diversity within Ceratosauria, a stem lineage of non-avian theropod dinosaurs known for peculiar craniomandibular adaptations. Until now, edentulism in Ceratosauria was exclusive to adult individuals of Limusaurus. Here, an exceptionally complete skeleton of a new toothless ceratosaur, Berthasaura leopoldinae gen. et sp. nov., is described from the Cretaceous aeolian sandstones of the Bauru Basin, Southern Brazil. The specimen resembles adult individuals of Limusaurus by the absence of teeth but based on the unfused condition of several elements (e.g., skull, vertebral column) it clearly represents an ontogenetically immature individual, indicating that it might never have had teeth. The phylogenetic analysis performed here has nested Berthasaura leopoldinae as an early-divergent Noasauridae, not closely related to Limusaurus. It represents the most complete non-avian theropod from the Brazilian Cretaceous and preserves the most complete noasaurid axial series known so far. Moreover, the new taxon exhibits many novel osteological features, uncommon in non-avian theropods, and unprecedented even among South American ceratosaurs. These include not only toothless jaws but also a premaxilla with cutting occlusal edge, and a slightly downturned rostral tip. This indicate that B. leopoldinae unlikely had the same diet as other ceratosaurs, most being regarded as carnivorous. As the ontogenetically more mature specimens of Limusaurus, Berthasaura might have been herbivorous or at least omnivorous, corroborating with an early evolutionary divergence of noasaurids from the ceratosaurian bauplan by disparate feeding modes.

A new specimen of Sinopterus dongi (Pterosauria, Tapejaridae) from the Jiufotang Formation (Early Cretaceous, China)

The Tapejarinae are edentulous pterosaurs that are relatively common in Cretaceous continental deposits in South America, North Africa, Europe, and China (mostly Early Cretaceous). The Chinese Jiufotang Formation is particularly rich in tapejarine specimens, having yielded over 10 described specimens and dozens of undescribed ones. For the Jiufotang Formation, a total of seven nominal tapejarid species and two genera have been proposed. Some debate exists over how many of those are valid or, alternatively, sexual or ontogenetic morphs of fewer (or even a single) species. Despite the abundance of specimens and the relevant taxonomic problems involved, detailed revisions of the matter are still lacking. This is partly due to the relatively scarce knowledge on the comparative osteology of the Sinopterus complex, which is hampered by the fact that most specimens have been only preliminarily described. In this contribution, we present a new postcranial specimen, D3072, which we attribute to the type-species of the genus, Sinopterus dongi. This new specimen helps shed some new light in the osteology of Sinopterus dongi, hopefully serving as a basis for future comparative studies involving further specimens and other proposed species and, subsequently, taxonomic revisions.

A taxonomic approach on diagnostic characters used to define new pterosaur taxa and an estimation of pterosaur diversity

Diagnostic characters from 227 pterosaur species were listed, separated into cranial or post-cranial elements and counted. From 21 post-cranial and 23 cranial elements, most diagnostic characters were related to phalanges (15%) and rostrum. Post-cranial characters comprise 44.23%, and cranial characters 55.77% of all characters used in pterosaur diagnoses. The highest correlation between diagnostic features occurs between the coracoid and the scapula. 25.11% and 28.63% of sampled taxa were diagnosed with 3-4 and 5-6 characters, respectively. The mean number of 6.79 characters was found in specimens with both cranial and post-cranial elements, and 4.86 and 4.17 in those with just cranial or post-cranial elements, respectively. 31 from 227 species (13.7%) were erected based on single elements, which are most frequently complete or partial mandibles (n=18). We estimate that 23.4% of the total pterosaur genera are currently known, with 90% of this diversity to be unveiled up to 2145. As the requirements of broad and cautious revision of genus/group must be undertaken, and some deposits will provide mostly fragmented and incomplete material, the assignment of fairly incomplete specimens to the most inclusive taxonomic level is feasible. Tracing this scenario can guide future works on the description of new pterosaur taxa.

Osteology of an exceptionally well-preserved tapejarid skeleton from Brazil: Revealing the anatomy of a curious pterodactyloid clade

A remarkably well-preserved, almost complete and articulated new specimen (GP/2E 9266) of Tupandactylus navigans is here described for the Early Cretaceous Crato Formation of Brazil. The new specimen comprises an almost complete skeleton, preserving both the skull and post-cranium, associated with remarkable preservation of soft tissues, which makes it the most complete tapejarid known thus far. CT-Scanning was performed to allow the assessment of bones still covered by sediment. The specimen can be assigned to Tupa. navigans due to its vertical supra-premaxillary bony process and short and rounded parietal crest. It also bears the largest dentary crest among tapejarine pterosaurs and a notarium, which is absent in other representatives of the clade. The new specimen is here regarded as an adult individual. This is the first time that postcranial remains of Tupa. navigans are described, being also an unprecedented record of an articulated tapejarid skeleton from the Araripe Basin.

Powered flight in hatchling pterosaurs: evidence from wing form and bone strength

Competing views exist on the behaviour and lifestyle of pterosaurs during the earliest phases of life. A 'flap-early' model proposes that hatchlings were capable of independent life and flapping flight, a 'fly-late' model posits that juveniles were not flight capable until 50% of adult size, and a 'glide-early' model requires that young juveniles were flight-capable but only able to glide. We test these models by quantifying the flight abilities of very young juvenile pterosaurs via analysis of wing bone strength, wing loading, wingspan and wing aspect ratios, primarily using data from embryonic and hatchling specimens of Pterodaustro guinazui and Sinopterus dongi. We argue that a young Sinopterus specimen has been mischaracterised as a distinct taxon. The humeri of pterosaur juveniles are similar in bending strength to those of adults and able to withstand launch and flight; wing size and wing aspect ratios of young juveniles are also in keeping with powered flight. We therefore reject the 'fly-late' and 'glide-early' models. We further show that young juveniles were excellent gliders, albeit not reliant on specialist gliding. The wing forms of very young juveniles differ significantly from larger individuals, meaning that variation in speed, manoeuvrability, take-off angle and so on was present across a species as it matured. Juveniles appear to have been adapted for flight in cluttered environments, in contrast to larger, older individuals. We propose on the basis of these conclusions that pterosaur species occupied distinct niches across ontogeny.

An early juvenile of Kunpengopterus sinensis (Pterosauria) from the Late Jurassic in China

The Wukongopteridae is a transitional clade between the long- and short-tailed pterosaur groups, and at least ten specimens have been studied without a determined juvenile specimen. Here, we described a small-sized Kunpengopterus sinensis, less than half the size of the holotype, which is the smallest specimen in wukongopterids. Based on unossified small elements, unfused cranial and postcranial elements, and grooves on the bone surface, this specimen is thought to be at least an early juvenile or even a late hatchling. By comparing the juvenile and subadult specimens of K. sinensis, we have found that the mid region of the upper and lower jaws had a higher growth rate than the anterior part, and that the growth rates were similar in most postcranial elements except for a higher rate in the caudal vertebrae. We revised the previous diagnosis of K. sinensis and specified that two characteristics, nasoantorbital fenestra approximately 40% of the skull length and a thin and relatively short maxillary process of the jugal, should be diagnostic in subadult or adult specimens. We have also found that pedal features are stable during ontogeny and can be diagnostic in juvenile, subadult or adult specimens in K. sinensis.

Assessing ontogenetic maturity in extinct saurian reptiles

Morphology forms the most fundamental level of data in vertebrate palaeontology because it is through interpretations of morphology that taxa are identified, creating the basis for broad evolutionary and palaeobiological hypotheses. Assessing maturity is one of the most basic aspects of morphological interpretation and provides the means to study the evolution of ontogenetic changes, population structure and palaeoecology, life-history strategies, and heterochrony along evolutionary lineages that would otherwise be lost to time. Saurian reptiles (the least-inclusive clade containing Lepidosauria and Archosauria) have remained an incredibly diverse, numerous, and disparate clade through their ~260-million-year history. Because of the great disparity in this group, assessing maturity of saurian reptiles is difficult, fraught with methodological and terminological ambiguity. We compiled a novel database of literature, assembling >900 individual instances of saurian maturity assessment, to examine critically how saurian maturity has been diagnosed. We review the often inexact and inconsistent terminology used in saurian maturity assessment (e.g. 'juvenile', 'mature') and provide routes for better clarity and cross-study coherence. We describe the various methods that have been used to assess maturity in every major saurian group, integrating data from both extant and extinct taxa to give a full account of the current state of the field and providing method-specific pitfalls, best practices, and fruitful directions for future research. We recommend that a new standard subsection, 'Ontogenetic Assessment', be added to the Systematic Palaeontology portions of descriptive studies to provide explicit ontogenetic diagnoses with clear criteria. Because the utility of different ontogenetic criteria is highly subclade dependent among saurians, even for widely used methods (e.g. neurocentral suture fusion), we recommend that phylogenetic context, preferably in the form of a phylogenetic bracket, be used to justify the use of a maturity assessment method. Different methods should be used in conjunction as independent lines of evidence when assessing maturity, instead of an ontogenetic diagnosis resting entirely on a single criterion, which is common in the literature. Critically, there is a need for data from extant taxa with well-represented growth series to be integrated with the fossil record to ground maturity assessments of extinct taxa in well-constrained, empirically tested methods.

Osteohistology and growth dynamics of the Brazilian noasaurid Vespersaurus paranaensis Langer et al., 2019 (Theropoda: Abelisauroidea)

Although the knowledge of bone histology of non-avian theropods has advanced considerably in recent decades, data about the bone tissue patterns, growth dynamics and ontogeny of some taxa such as abelisauroids are still limited. Here we describe the bone microstructure and growth dynamics of the Brazilian noasaurine Vespersaurus paranaensis using five femora and six tibiae and quantify the annual growth marks through retrocalculation of missing ones to estimate ontogenetic ages. The femoral series comprises four femoral histological classes (FHC I-IV), varying from two annuli or LAGs to seven LAGs. Femora show that sexual maturity was achieved around the seventh to tenth year of life, whereas the tibiae suggest it was earlier (around three to five years old). Tibiae represent three histological classes (THC I-III) displaying from three to nine LAGs. Two tibiae (THC III) exhibit an external fundamental system indicating that these specimens reached full skeletal size. The heterogeneous maturity observed in Vespersaurus hind limb bones could result from differential allometry scaling between femora and tibiae length with the body length. The predominant parallel-fibered bone matrix suggests that Vespersaurus grew more slowly than most theropods, including other abelisauroids, in a pattern shared with the noasaurines Masiakasaurus knopfleri from Madagascar and CPPLIP 1490 from Brazil. This deviation from the typical theropod growth pattern may be mainly correlated with small body size, but also may related to resource limitation imposed by the arid climate prevailing in southwestern Gondwana during Cretaceous. Moreover, given the ecological and phylogenetic similarities among these taxa, such features would probably be apomorphic within Noasauridae.

A new toothless pterosaur (Pterodactyloidea) from Southern Brazil with insights into the paleoecology of a Cretaceous desert

The first pterosaur bone bed from Brazil was reported in 2014 at the outskirts of the town Cruzeiro do Oeste, Paraná State, in the Southern region of the country. Here named 'cemitério dos pterossauros' site, these outcrops were referred to the Goio-Erê Formation (Turonian-Campanian) of the Caiuá Group (Bauru Basin) and revealed the presence of hundreds of isolated or partially articulated elements of the tapejarine pterosaur Caiuajara and fewer amounts of a theropod dinosaur. Here we present a new tapejaromorph flying reptile from this site, Keresdrakon vilsoni gen. et sp. nov., which shows a unique blunt ridge on the dorsal surface of the posterior end of the dentary. Morphological and osteohistological features indicate that all recovered individuals represent late juveniles or sub-adults. This site shows the first direct evidence of sympatry in Pterosauria. The two distinct flying reptiles coexisted with a theropod dinosaur, providing a rare glimpse of a paleobiological community from a Cretaceous desert.

A new desert-dwelling dinosaur (Theropoda, Noasaurinae) from the Cretaceous of south Brazil

Noasaurines form an enigmatic group of small-bodied predatory theropod dinosaurs known from the Late Cretaceous of Gondwana. They are relatively rare, with notable records in Argentina and Madagascar, and possible remains reported for Brazil, India, and continental Africa. In south-central Brazil, the deposits of the Bauru Basin have yielded a rich tetrapod fauna, which is concentrated in the Bauru Group. The mainly aeolian deposits of the Caiuá Group, on the contrary, bear a scarce fossil record composed only of lizards, turtles, and pterosaurs. Here, we describe the first dinosaur of the Caiuá Group, which also represents the best-preserved theropod of the entire Bauru Basin known to date. The recovered skeletal parts (vertebrae, girdles, limbs, and scarce cranial elements) show that the new taxon was just over 1 m long, with a unique anatomy among theropods. The shafts of its metatarsals II and IV are very lateromedially compressed, as are the blade-like ungual phalanges of the respective digits. This implies that the new taxon could have been functionally monodactyl, with a main central weight-bearing digit, flanked by neighbouring elements positioned very close to digit III or even held free of the ground. Such anatomical adaptation is formerly unrecorded among archosaurs, but has been previously inferred from footprints of the same stratigraphic unit that yielded the new dinosaur. A phylogenetic analysis nests the new taxon within the Noasaurinae clade, which is unresolved because of the multiple alternative positions that Noasaurus leali can acquire in the optimal trees. The exclusion of the latter form results in positioning the new dinosaur as the sister-taxon of the Argentinean Velocisaurus unicus.

Caelestiventus hanseni gen. et sp. nov. extends the desert-dwelling pterosaur record back 65 million years

Pterosaurs are the oldest known powered flying vertebrates. Originating in the Late Triassic, they thrived to the end of the Cretaceous. Triassic pterosaurs are extraordinarily rare and all but one specimen come from marine deposits in the Alps. A new comparatively large (wing span >150 cm) pterosaur, Caelestiventus hanseni gen. et sp. nov., from Upper Triassic desert deposits of western North America preserves delicate structural and pneumatic details not previously known in early pterosaurs, and allows a reinterpretation of crushed Triassic specimens. It shows that the earliest pterosaurs were geographically widely distributed and ecologically diverse, even living in harsh desert environments. It is the only record of desert-dwelling non-pterodactyloid pterosaurs and predates all known desert pterosaurs by more than 65 Myr. A phylogenetic analysis shows it is closely allied with Dimorphodon macronyx from the Early Jurassic of Britain.

Morphometric assessment of pterosaur jaw disparity

Pterosaurs were a successful group of Mesozoic flying reptiles. They were the first vertebrate group to achieve powered flight and varied enormously in morphology and ecology, occupying a variety of niches and developing specialized feeding strategies. Ecomorphological principles suggest this variation should be reflected by great morphological diversity in the lower jaw, given that the mandible served as the primary apparatus for prey acquisition. Here we present the first study of mandibular shape disparity in pterosaurs and aim to characterize major aspects of variation. We use a combination of geometric morphometric approaches, incorporating both outline analysis using elliptical Fourier analysis and semi-landmark approaches. Our results show that morphological convergence is prevalent and many pterosaurs, belonging to diverse dietary groups and subclades, overlap in morphospace and possessed relatively simple 'rod-shaped' jaws. There is no clear trend of size distributions in pterosaur mandibular morphospace, and larger forms are widely distributed. Additionally, there is limited functional signal within pterosaur lower jaw morphospace. Instead, the development of a large anterior ventral crest represents the major component of disparity. This suggests that a socio-sexual trait was a key driver for innovation in pterosaur lower jaw shape.

Late Maastrichtian pterosaurs from North Africa and mass extinction of Pterosauria at the Cretaceous-Paleogene boundary

Pterosaurs were the first vertebrates to evolve powered flight and the largest animals to ever take wing. The pterosaurs persisted for over 150 million years before disappearing at the end of the Cretaceous, but the patterns of and processes driving their extinction remain unclear. Only a single family, Azhdarchidae, is definitively known from the late Maastrichtian, suggesting a gradual decline in diversity in the Late Cretaceous, with the Cretaceous–Paleogene (K-Pg) extinction eliminating a few late-surviving species. However, this apparent pattern may simply reflect poor sampling of fossils. Here, we describe a diverse pterosaur assemblage from the late Maastrichtian of Morocco that includes not only Azhdarchidae but the youngest known Pteranodontidae and Nyctosauridae. With 3 families and at least 7 species present, the assemblage represents the most diverse known Late Cretaceous pterosaur assemblage and dramatically increases the diversity of Maastrichtian pterosaurs. At least 3 families—Pteranodontidae, Nyctosauridae, and Azhdarchidae—persisted into the late Maastrichtian. Late Maastrichtian pterosaurs show increased niche occupation relative to earlier, Santonian-Campanian faunas and successfully outcompeted birds at large sizes. These patterns suggest an abrupt mass extinction of pterosaurs at the K-Pg boundary.

Pterosaurs were winged cousins of the dinosaurs and lived from around 200 million years ago to 66 million years ago, when the last pterosaurs disappeared during the Cretaceous-Paleogene extinction that wiped out the dinosaurs. The pterosaurs are thought to have declined in diversity before their final extinction, suggesting that gradual processes played a major role in their demise. However, pterosaur fossils are very rare, and thus, it is unclear whether pterosaurs were really low in diversity at this time or whether these patterns merely result from a paucity of fossils. We describe new pterosaur fossils from the end of the Cretaceous in Morocco, including as many as 7 species. They represent 3 different families and show a large range of variation in size and skeletal proportions, suggesting that they occupied a wide range of ecological niches.

New anatomical information of the wukongopterid Kunpengopterus sinensis Wang et al., 2010 based on a new specimen

The Wukongopteridae compose a non-pterodactyloid clade of pterosaurs that are the most abundant flying reptiles in the deposits of the Middle-Late Jurassic Yanliao Biota. Until now, five species of three genera and two additional unnamed specimens have been described. Here we report on a new material, IVPP V 23674, that can be referred to the wukongopterid Kunpengopterus sinensis due to several features such as a comparably short nasoantorbital fenestra, the dorsally rising posterodorsal margin of the ischium, and the very short first pedal phalanx of digit V relative to metatarsal IV. IVPP V 23674 provides the first view of a wukongopterid palate, which differs from all other pterosaurs by having a very large postpalatine fenestra and laterally compressed choanae, indicating that the evolution of the pterosaur palate was more complex than previously thought. Sesamoid bones at the dorsal side of manual unguals are present and are reported for the first time in a wukongopterid suggesting an arboreal life-style for these pterosaurs.

The toothless pterosaur Jidapterus edentus (Pterodactyloidea: Azhdarchoidea) from the Early Cretaceous Jehol Biota and its paleoecological implications

BACKGROUND

In the Early Cretaceous Jehol Biota, the toothless pterosaurs flourished with the chaoyangopterids and tapejarids playing a key role in understanding the early diversity and evolution of the Azhdarchoidea. Unlike the more diverse tapejarids, the rarer chaoyangopterids are characterized by a long and low rostrum, supporting a close relationship with the huge azhdarchids. Unfortunately, our knowledge is still limited in the osteology, paleoecology, and taxonomy of the Chaoyangopteridae. As one of the best preserved skeletons, the type and only specimen of Jidapterus edentus provides an opportunity to understand the morphology and paleoecology of the chaoyangopterids.

RESULTS

Our study of the osteology of Jidapterus edentus reveals valuable information about the morphology of the Chaoyangopteridae such as a rostrum with a curved dorsal profile, high Rostral Index (RI), larger angle between the dorsal and postorbital processes of the jugal, sequentially shorter fourth to seventh cervical vertebrae, sternum with a plate wider than long, contact of the metacarpal I with the distal syncarpal, pneumatic foramen on first wing phalanx, hatchet-like postacetabular process with unconstricted neck and small dorsal process, distinctly concave anterior margin of pubis, subrectangular pubic plate with nearly parallel anterior and posterior margins, longer proximal phalanges of pedal digits III and IV, as well as reduced and less curved pedal unguals. These features further support the validity of Jidapterus edentus as a distinct species and the close relationship of the chaoyangopterids with the azhdarchids. Paleoecologically, the chaoyangopterids are probably like the azhdarchids, more terrestrial than the contemporaneous and putatively arboreal tapejarids, which may have been limited to the forest-dominated ecosystem of the Jehol Biota.

DISCUSSION

The osteology of Jidapterus edentus further supports the close relationship of the Chaoyangopteridae with the Azhdarchidae in sharing a high RI value and reduced and mildly-curved pedal unguals, and it also implies a possible paleoecological similarity in their terrestrial capability. Combined with the putatively arboreal and herbivorous tapejarids, this distinct lifestyle of the chaoyangopterids provides new insights into the diversity of pterosaurs in the ecosystem of the Jehol Biota.

Anhanguera taxonomy revisited: is our understanding of Santana Group pterosaur diversity biased by poor biological and stratigraphic control?

BACKGROUND

Anhanguerids comprise an important clade of pterosaurs, mostly known from dozens of three-dimensionally preserved specimens recovered from the Lower Cretaceous Romualdo Formation (northeastern Brazil). They are remarkably diverse in this sedimentary unit, with eight named species, six of them belonging to the genus Anhanguera. However, such diversity is likely overestimated, as these species have been historically diagnosed based on subtle differences, mainly based on the shape and position of the cranial crest. In spite of that, recently discovered pterosaur taxa represented by large numbers of individuals, including juveniles and adults, as well as presumed males and females, have crests of sizes and shapes that are either ontogenetically variable or sexually dimorphic.

METHODS

We describe in detail the skull of one of the most complete specimens referred to Anhanguera, AMNH 22555, and use it as a case study to review the diversity of anhanguerids from the Romualdo Formation. In order to accomplish that, a geometric morphometric analysis was performed to assess size-dependent characters with respect to the premaxillary crest in the 12 most complete skulls bearing crests that are referred in, or related to, this clade, almost all of them analyzed first hand.

RESULTS

Geometric morphometric regression of shape on centroid size was highly statistically significant (p = 0.0091) and showed that allometry accounts for 25.7% of total shape variation between skulls of different centroid sizes. Premaxillary crests are both taller and anteroposteriorly longer in larger skulls, a feature consistent with ontogenetic growth. A new diagnosis is proposed for Anhanguera, including traits that are nowadays known to be widespread within the genus, as well as ontogenetic changes. AMNH 22555 cannot be referred to "Anhanguera santanae" and, in fact, "Anhanguera santanae", "Anhanguera araripensis", and "Anhanguera robustus" are here considered nomina dubia.

DISCUSSION

Historically, minor differences in crest morphology have been used in the definition of new anhanguerid species. Nowadays, this practice resulted in a considerable difficulty in referring well-preserved skulls into known taxa. When several specimens are analyzed, morphologies previously believed to be disparate are, in fact, separated by a continuum, and are thus better explained as individual or temporal variations. Stratigraphically controlled excavations on the Romualdo Formation have showed evidence for faunal turnover regarding fish communities. It is thus possible that some of the pterosaurs from this unit were not coeval, and might even represent anagenetic morphotypes. Unfortunately, amateur collecting of Romualdo Formation fossils, aimed especially at commerce, resulted in the lack of stratigraphic data of virtually all its pterosaurs and precludes testing of these further hypotheses.

Anomalously high variation in postnatal development is ancestral for dinosaurs but lost in birds

Compared with all other living reptiles, birds grow extremely fast and possess unusually low levels of intraspecific variation during postnatal development. It is now clear that birds inherited their high rates of growth from their dinosaurian ancestors, but the origin of the avian condition of low variation during development is poorly constrained. The most well-understood growth trajectories of later Mesozoic theropods (e.g., Tyrannosaurus, Allosaurus) show similarly low variation to birds, contrasting with higher variation in extant crocodylians. Here, we show that deep within Dinosauria, among the earliest-diverging dinosaurs, anomalously high intraspecific variation is widespread but then is lost in more derived theropods. This style of development is ancestral for dinosaurs and their closest relatives, and, surprisingly, this level of variation is far higher than in living crocodylians. Among early dinosaurs, this variation is widespread across Pangaea in the Triassic and Early Jurassic, and among early-diverging theropods (ceratosaurs), this variation is maintained for 165 million years to the end of the Cretaceous. Because the Late Triassic environment across Pangaea was volatile and heterogeneous, this variation may have contributed to the rise of dinosaurian dominance through the end of the Triassic Period.

A Basal Tapejarine (Pterosauria; Pterodactyloidea; Tapejaridae) from the Crato Formation, Early Cretaceous of Brazil

A three-dimensional and almost complete pterosaur mandible from the Crato Formation (Early Cretaceous of Northeastern Brazil), Araripe Basin, is described as a new species of a tapejarine tapejarid. Tapejarines are a particular group of toothless pterosaurs, characterized by well-developed cranial crests, downturned rostra, and have been proposed to represent frugivorous flying reptiles. Though comparatively well represented and distributed, the evolutionary history of the group is still poorly known, and the internal relationships of its members are not well understood. The new species here reported, named Aymberedactylus cearensis gen. et sp. nov., adds new data concerning the evolution of the group, concerning their morphology and geographical origin. It differs from known tapejarids due to its unusually elongate retroarticular process and a shallow fossa on the splenial exhibiting distinctive rugose texture. Furthermore, it exhibits a suite of basal and derived conditions within the Tapejaridae, demonstrating how their morphological traits probably evolved and that these forms were even more diverse than already acknowledged. The discovery of Aymberedactylus cearensis sheds new light on the evolutionary history of the Tapejarinae.

A small azhdarchoid pterosaur from the latest Cretaceous, the age of flying giants

Pterosaur fossils from the Campanian-Maastrichtian of North America have been reported from the continental interior, but few have been described from the west coast. The first pterosaur from the Campanian Northumberland Formation (Nanaimo Group) of Hornby Island, British Columbia, is represented here by a humerus, dorsal vertebrae (including three fused notarial vertebrae), and other fragments. The elements have features typical of Azhdarchoidea, an identification consistent with dominance of this group in the latest Cretaceous. The new material is significant for its size and ontogenetic stage: the humerus and vertebrae indicate a wingspan of ca 1.5 m, but histological sections and bone fusions indicate the individual was approaching maturity at time of death. Pterosaurs of this size are exceedingly rare in Upper Cretaceous strata, a phenomenon commonly attributed to smaller pterosaurs becoming extinct in the Late Cretaceous as part of a reduction in pterosaur diversity and disparity. The absence of small juveniles of large species-which must have existed-in the fossil record is evidence of a preservational bias against small pterosaurs in the Late Cretaceous, and caution should be applied to any interpretation of latest Cretaceous pterosaur diversity and success.

New information on the Wukongopteridae (Pterosauria) revealed by a new specimen from the Jurassic of China

The Wukongopteridae is an important pterosaur group discovered from Yanliao Biota, because it combines character states seen in non-pterodactyloid and pterodactyloid pterosaurs. So far, the Wukongopteridae contains three genera: Wukongopterus, Darwinopterus and Kunpengopterus; representing five species. Here we report on a new specimen, IVPP V 17959, that can be undoubtedly referred to the Wukongopteridae based on the presence of a confluent nasoantorbital fenestra, elongated cervical vertebrae (convergent with Pterodactyloidea) and a long tail enclosed by rod-like bony extensions of the zygapophyses. Traits distinguishing this new specimen from other wukongopterid pterosaurs include a premaxilla with a low ossified anterodorsal crest, a nasal bearing the most elongated process known in the Wukongopteridae, and a lacrimal that has a foramen in its middle portion. The new kind of premaxillary crest preserved in IVPP V 17959 suggests that the presence or absence of a premaxillary crest might be an interspecific feature within the Wukongopteridae. A phylogenetic analysis including all wukongopterid pterosaurs recovers IVPP V 17959 in a polytomy with Wukongopterus and the species of Darwinopterus, having Kunpengopterus in a more basal position. The postcranial skeleton of IVPP V 17959 has ontogenetically mature characteristics including a completely fused scapula and coracoid, fused proximal and distal carpal series, and an ossified extensor tendon process of the first wing phalanx, allowing its classification as ontogenetic stage five. Furthermore, the atlas and axis are separated in IVPP V 17959, which indicates that these two bones probably are not fused in skeletally mature wukongopterid individuals.

Preservational bias controls the fossil record of pterosaurs

Pterosaurs, a Mesozoic group of flying archosaurs, have become a focal point for debates pertaining to the impact of sampling biases on our reading of the fossil record, as well as the utility of sampling proxies in palaeodiversity reconstructions. The completeness of the pterosaur fossil specimens themselves potentially provides additional information that is not captured in existing sampling proxies, and might shed new light on the group's evolutionary history. Here we assess the quality of the pterosaur fossil record via a character completeness metric based on the number of phylogenetic characters that can be scored for all known skeletons of 172 valid species, with averaged completeness values calculated for each geological stage. The fossil record of pterosaurs is observed to be strongly influenced by the occurrence and distribution of Lagerstätten. Peaks in completeness correlate with Lagerstätten deposits, and a recovered correlation between completeness and observed diversity is rendered non-significant when Lagerstätten species are excluded. Intervals previously regarded as potential extinction events are shown to lack Lagerstätten and exhibit low completeness values: as such, the apparent low diversity in these intervals might be at least partly the result of poor fossil record quality. A positive correlation between temporal patterns in completeness of Cretaceous pterosaurs and birds further demonstrates the prominent role that Lagerstätten deposits have on the preservation of smaller bodied organisms, contrasting with a lack of correlation with the completeness of large-bodied sauropodomorphs. However, we unexpectedly find a strong correlation between sauropodomorph and pterosaur completeness within the Triassic-Jurassic, but not the Cretaceous, potentially relating to a shared shift in environmental preference and thus preservation style through time. This study highlights the importance of understanding the relationship between various taphonomic controls when correcting for sampling bias, and provides additional evidence for the prominent role of sampling on observed patterns in pterosaur macroevolution.

Comments on Triassic pterosaurs with discussion about ontogeny and description of new taxa

Eudimorphodon ranzii was the first Triassic pterosaur to be described and several specimens have been referred to this taxon mainly based on the presence of multicuspid teeth. Since this dental feature has been observed in several other pterosaurs, the revision of some specimens assigned to Eudimorphodon shows that they represent new taxa as follows: Arcticodactylus cromptonellus (comb. nov.), Austriadraco dallavecchiai (gen. et sp. nov.) and Bergamodactylus wildi (gen. et sp. nov.). A preliminary analysis of pterosaur ontogeny resulted in the recognition of six distinct ontogenetic stages (OS1-6). According to this classification, the holotype of Arcticodactylus cromptonellus has reached OS2, and although being ontogenetically much younger than others, the conspicuous anatomical differences lead to its exclusion from Eudimorphodon. The holotypes of Austriadraco dallavecchiai, Bergamodactylus wildi and Carniadactylus rosenfeldi have reached at least OS5, which demonstrates that the anatomical differences among them cannot be explained by ontogeny. Moreover, Bergamodactylus wildi reaches about 60% of the maximized wingspan of Carniadactylus rosenfeldi and further concurs that these specimens collected in distinct Triassic Islands of Europe are not conspecific. The present study increases the diversity of Triassic flying reptiles and further pushes the origins of this clade back to at least the Middle Triassic.

A stem acrodontan lizard in the Cretaceous of Brazil revises early lizard evolution in Gondwana

Iguanians are one of the most diverse groups of extant lizards (>1,700 species) with acrodontan iguanians dominating in the Old World, and non-acrodontans in the New World. A new lizard species presented herein is the first acrodontan from South America, indicating acrodontans radiated throughout Gondwana much earlier than previously thought, and that some of the first South American lizards were more closely related to their counterparts in Africa and Asia than to the modern fauna of South America. This suggests both groups of iguanians achieved a worldwide distribution before the final breakup of Pangaea. At some point, non-acrodontans replaced acrodontans and became the only iguanians in the Americas, contrary to what happened on most of the Old World. This discovery also expands the diversity of Cretaceous lizards in South America, which with recent findings, suggests sphenodontians were not the dominant lepidosaurs in that continent as previously hypothesized.

Iguanians are a diverse group of lizards. Here, the authors report an acrodontan iguanian from the Late Cretaceous of Brazil, which suggests that this group achieved a global distribution during the Mesozoic but was replaced by non-acrodontans in the Americas.

How the pterosaur got its wings

Throughout the evolutionary history of life, only three vertebrate lineages took to the air by acquiring a body plan suitable for powered flight: birds, bats, and pterosaurs. Because pterosaurs were the earliest vertebrate lineage capable of powered flight and included the largest volant animal in the history of the earth, understanding how they evolved their flight apparatus, the wing, is an important issue in evolutionary biology. Herein, I speculate on the potential basis of pterosaur wing evolution using recent advances in the developmental biology of flying and non-flying vertebrates. The most significant morphological features of pterosaur wings are: (i) a disproportionately elongated fourth finger, and (ii) a wing membrane called the brachiopatagium, which stretches from the posterior surface of the arm and elongated fourth finger to the anterior surface of the leg. At limb-forming stages of pterosaur embryos, the zone of polarizing activity (ZPA) cells, from which the fourth finger eventually differentiates, could up-regulate, restrict, and prolong expression of 5'-located Homeobox D (Hoxd) genes (e.g. Hoxd11, Hoxd12, and Hoxd13) around the ZPA through pterosaur-specific exploitation of sonic hedgehog (SHH) signalling. 5'Hoxd genes could then influence downstream bone morphogenetic protein (BMP) signalling to facilitate chondrocyte proliferation in long bones. Potential expression of Fgf10 and Tbx3 in the primordium of the brachiopatagium formed posterior to the forelimb bud might also facilitate elongation of the phalanges of the fourth finger. To establish the flight-adapted musculoskeletal morphology shared by all volant vertebrates, pterosaurs probably underwent regulatory changes in the expression of genes controlling forelimb and pectoral girdle musculoskeletal development (e.g. Tbx5), as well as certain changes in the mode of cell-cell interactions between muscular and connective tissues in the early phase of their evolution. Developmental data now accumulating for extant vertebrate taxa could be helpful in understanding the cellular and molecular mechanisms of body-plan evolution in extinct vertebrates as well as extant vertebrates with unique morphology whose embryonic materials are hard to obtain.