The Cretaceous Neornithine record and new Vegaviidae specimens from the López de Bertodano Formation (Upper Maastrichthian) of Vega Island, Antarctic Peninsula.

A worldwide revision of the Cretaceous record of Neornithes (crown birds) revealed that unambiguous neornithine taxa are extremely scarce, with only a few showing diagnostic features to be confidently assigned to that group. Here we report two new neornithine specimens from Vega Island (López de Bertodano Formation). The first is a synsacrum (MN 7832-V) that shows a complex pattern of transversal diverticula intercepting the canalis synsacri, as in extant neornithines. Micro-CT scanning revealed a camerate pattern of trabeculae typical of neornithines. It further shows the oldest occurrence of lumbosacral canals in Neornithes, which are related to a balance sensing system acting in the control of walking and perching. The second specimen (MN 7833-V) is a distal portion of a tarsometatarsus sharing with Vegavis iaai a straight apical border of the crista plantaris lateralis. Osteohistologically the tarsometatarsus shows a thick and highly vascularized cortex that lacks any growth marks, resembling Polarornis gregorii. The cortex is osteosclerotic as in other extinct and extant diving neornithines. These new specimens increase the occurrences of the Cretaceous avian material recovered from the Upper Cretaceous strata of the James Ross Sub-Basin, suggesting that a Vegaviidae-dominated avian assemblage was present in the Antarctic Peninsula during the upper Maastrichtian.

First record of insect-plant interaction in Late Cretaceous fossils from Nelson Island (South Shetland Islands Archipelago), Antarctica.

Despite the enormous paleobotanical record on different islands of the Antarctic Peninsula, the evidence of insect activity associated with fossilized plants is scarce. Here we report the first evidence of insect-plant interaction from Cretaceous deposits, more precisely from a new locality at the Rip Point area, Nelson Island (Antarctic Peninsula). The macrofossil assemblage includes isolated Nothofagus sp. leaf impressions, a common component of the Antarctic paleoflora. Two hundred leaves were examined, of which 15 showed evidence of insect activity, displaying variations in size, shape, and preservation. Two types of interaction damage, galls and mines, were identified. A single specimen retained a circular scar recognized as galling scar, while meandering tracks were considered mines. These traces of herbivore insect activity, correspond to the oldest known record of this type of interaction of West Antarctica and the oldest record of insect-plant interaction in Nothofagus sp. reported so far.

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.

Paleoenvironment of the Cerro Negro Formation (Aptian, Early Cretaceous) of Snow Island, Antarctic Peninsula.

A study of macro and microfacies, palynoflora and palynofacies of the non-marine Cerro Negro Formation at President Head Peninsula, Snow Island, northwest of the Antarctic Peninsula, was developed. Two assemblages were recognized: Palynofacies assemblage 1 (P1) at the base of the section with a dominance of fern spores and conifer pollen grains, and facies association consisting of a clastic layer, with the predominance of mudstones; and Palynofacies assemblage 2 (P2) at the top of the section, with remarkable abundance of AOM/Pseudoamorphous particles, associated with facies that includes tuffs. The complete section shows in some levels the presence of freshwater algae and translucent phytoclasts. The integrated data characterizes a fluvial-lacustrine environment, what is reinforced by the occurrence of freshwater algae (Botryococcus) in some levels of P1 and P2. We could verify an increase in volcanic activity towards the top of the section that apparently has played an important role in the collapse of the palynoflora. The occurrence of the spore species Muricingulisporis annulatus, Sotasporites elegans, S. triangularis, Foraminisporis wonthaggiensis, and F. asymmetricus in the Cerro Negro Formation allows the correlation with sections in South America and Australia, suggesting an Aptian age for these deposits.

Shell and long-bone histology, skeletochronology, and lifestyle of Araripemys barretoi (Testudines: Pleurodira), a side-necked turtle of the Lower Cretaceous from Brazil.

In this study we provide a comprehensive investigation of the microanatomical and microstructural aspects of the carapace and limb bones of the Early Cretaceous side-necked turtle, Araripemys barretoi, from the Araripe Basin, Brazil. Inter-elemental histovariability reveals different secondary remodelling of the skeletal elements within the same individual. The vascularisation is scarce and mainly longitudinal, also it ceases towards the bone surface, forming an avascular parallel-fibred bone with closely spaced LAGs. These traits indicate a late ontogenetic stage and a slow growth rate for one of the two A. barretoi specimens. The high cortical thickness of the costal plate suggests an increase of the shell stiffness. The elevated relative bone wall thickness of the ulna compared to other limb bones indicates a case of local pachyosteosclerosis, possibly to improve body stability in the aquatic environment.

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.

Pterodactyloid pterosaur bones from Cretaceous deposits of the Antarctic Peninsula.

Fossil vertebrates from Antarctica are considerably rare, hampering our understanding of the evolutionary history of the biota from that continent. For several austral summers, the PALEOANTAR project has been carrying out fieldwork in the Antarctic Peninsula in search for fossils, particularly Cretaceous vertebrates. Among the specimens recovered so far are two bones referable to Pterosauria, more specifically to the Pterodacyloidea, the first volant reptiles from Antarctica to be fully described. MN 7800-V (part and counterpart) was recovered from a moraine at the Abernathy Flats (Santa Marta Formation, Lachman Crags Member, Santonian-Campanian) on James Ross Island. It is interpreted as the distal articulation of a first phalanx of the wing finger, representing an animal with an estimated wingspan between 3 and 4 m. The second specimen (MN 7801-V) comes from Vega Island (Snow Hill Island Formation, Maastrichtian) and is identified as a wing metacarpal IV of an animal with an estimated wingspan from 4 to 5 m. These occurrences show that pterodactyloids inhabited the Antarctic Peninsula at least during the Upper Cretaceous and demonstrate that large pterosaurs were widespread through all parts of the planet during that period.

First complete pterosaur from the Afro-Arabian continent: insight into pterodactyloid diversity.

Despite being known from every continent, the geological record of pterosaurs, the first group of vertebrates to develop powered flight, is very uneven, with only a few deposits accounting for the vast majority of specimens and almost half of the taxonomic diversity. Among the regions that stand out for the greatest gaps of knowledge regarding these flying reptiles, is the Afro-Arabian continent, which has yielded only a small number of very fragmentary and incomplete materials. Here we fill part of that gap and report on the most complete pterosaur recovered from this continent, more specifically from the Late Cretaceous (~95 mya) Hjoûla Lagerstätte of Lebanon. This deposit is known since the Middle Ages for the exquisitely preserved fishes and invertebrates, but not for tetrapods, which are exceedingly rare. Mimodactylus libanensis gen. et sp. nov. differs from the other Afro-Arabian pterosaur species named to date and is closely related to the Chinese species Haopterus gracilis, forming a new clade of derived toothed pterosaurs. Mimodactylidae clade nov. groups species that are related to Istiodactylidae, jointly designated as Istiodactyliformes (clade nov.). Istiodactyliforms were previously documented only in Early Cretaceous sites from Europe and Asia, with Mimodactylus libanensis the first record in Gondwana.

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.

Egg accumulation with 3D embryos provides insight into the life history of a pterosaur.

Fossil eggs and embryos that provide unique information about the reproduction and early growth of vertebrates are exceedingly rare, particularly for pterosaurs. Here we report on hundreds of three-dimensional (3D) eggs of the species Hamipterus tianshanensis from a Lower Cretaceous site in China, 16 of which contain embryonic remains. Computed tomography scanning, osteohistology, and micropreparation reveal that some bones lack extensive ossification in potentially late-term embryos, suggesting that hatchlings might have been flightless and less precocious than previously assumed. The geological context, including at least four levels with embryos and eggs, indicates that this deposit was formed by a rare combination of events, with storms acting on a nesting ground. This discovery supports colonial nesting behavior and potential nesting site fidelity in the Pterosauria.

Paleohistology of Susisuchus anatoceps (Crocodylomorpha, Neosuchia): Comments on Growth Strategies and Lifestyle.

Susisuchus anatoceps is a neosuchian crocodylomorph lying outside the clade Eusuchia, and associated with the transition between basal and advanced neosuchians and the rise of early eusuchians. The specimen MPSC R1136 comprises a partially articulated postcranial skeleton and is only the third fossil assigned to this relevant taxon. Thin sections of a right rib and right ulna of this specimen have been cut for histological studies and provide the first paleohistological information of an advanced non-eusuchian neosuchian from South America. The cross-section of the ulna shows a thick cortex with 17 lines of arrested growth (LAGs), a few scattered vascular canals, and primary and secondary osteons. This bone has a free medullary cavity and a spongiosa is completely absent. Thin sections of the rib show that remodeling process was active when the animal died, with a thin cortex and a well-developed spongiosa. In the latter, few secondary osteons and 4 LAGs were identified. According to the observed data, Susisuchus anatoceps had a slow-growing histological microstructure pattern, which is common in crocodylomorphs. The high number of ulnar LAGs and the active remodeling process are indicative that this animal was at least a late subadult, at or past the age of sexual maturity. This contradicts previous studies that interpreted this and other Susisuchus anatoceps specimens as juveniles, and suggests that full-grown adults of this species were relatively small-bodied, comparable in size to modern dwarf crocodiles.

Eggshell and Histology Provide Insight on the Life History of a Pterosaur with Two Functional Ovaries.

The counterpart of a previously described non-pterodactyloid pterosaur with an egg revealed the presence of a second egg inside the body cavity of this gravid female. It clearly shows that pterosaurs had two functional oviducts and demonstrates that the reduction of one oviduct was not a prerequisite for developing powered flight, at least in this group. Compositional analysis of one egg suggests the lack of a hard external layer of calcium carbonate. Histological sections of one femur lack medullary bone and further demonstrate that this pterosaur reached reproductive maturity before skeletal maturity. This study shows that pterosaurs laid eggs even smaller than previously thought and had a reproductive strategy more similar to basal reptiles than to birds. Whether pterosaurs were highly precocial or needed parental care is still open to debate.

A new toothed pterosaur (Pterodactyloidea: Anhangueridae) from the Early Cretaceous Romualdo Formation, NE Brazil.

A new species of pterosaur, Maaradactylus kellneri gen. nov., sp. nov. (Archosauria: Pterosauria) from the Romualdo Formation (Aptian/Albian), is herein described. The specimen (MPSC R 2357) was found at Sítio São Gonçalo, Santana do Cariri city (State of Ceará, northeast Brazil) and consists of the skull, atlas and axis, and represents one of the largest skulls of the Anhangueridae from the Araripe Basin described. The autapomorphies of the new pterosaur include the following characters: a premaxillary sagittal crest that is relatively long and high, beginning at the anterior part of the skull (rostrum) and extending to the 22nd pair of alveoli, not covering the nasoantorbital fenestra or the choanaes, and also the presence of 35 pairs of alveoli; smooth palatal ridge, which starts on the 5th pair of alveoli and ends on the 13th pair; palate is convex shaped in the anterior region; choanae not extending laterally; small and convex palatal elevation; the 5th, 6th and 7th alveoli smaller than the 4th and 8th; the alveoli decreasing in size from the 9th to the 12th and increasing from the 13th to 18th, and from the 18th to the 35th they are arranged in triplets. Furthermore, the lateral surface of the premaxillary crest shows grooves and tridimensional structures that may have housed blood vessels.

A new angiosperm from the Crato Formation (Araripe Basin, Brazil) and comments on the Early Cretaceous monocotyledons.

The Crato Formation paleoflora is one of the few equatorial floras of the Early Cretaceous. It is diverse, with many angiosperms, especially representatives of the clades magnoliids, monocotyledons and eudicots, which confirms the assumption that angiosperm diversity during the last part of the Early Cretaceous was reasonably high. The morphology of a new fossil monocot is studied and compared to all other Smilacaceae genus, especially in the venation. Cratosmilax jacksoni gen. et sp. nov. can be related to the Smilacaceae family, becoming the oldest record of the family so far. Cratosmilax jacksoni is a single mesophilic leaf with entire margins, ovate shape, with acute apex and base, four venation orders and main acrodromous veins. It is the first terrestrial monocot described for the Crato Formation, monocots were previously described for the same formation, and are considered aquatics. Cratosmilax jacksoni is the first fossil record of Smilacaceae in Brazil, and the oldest record of this family.

The largest flying reptile from Gondwana: a new specimen of Tropeognathus cf. T. mesembrinus Wellnhofer, 1987 (Pterodactyloidea, Anhangueridae) and other large pterosaurs from the Romualdo Formation, Lower Cretaceous, Brazil.

A very large pterosaur (MN 6594-V) from the Romualdo Formation (Aptian/Albian), Santana Group, Araripe Basin, is described. The specimen is referred to Tropeognathus cf. T. mesembrinus mainly due to the presence of a low and blunt frontoparietal crest, the comparatively low number of teeth and the inclined dorsal part of the occipital region. Two distinct wingspan measurements for pterosaurs are introduced: the maximized wingspan (maxws), which essentially consists of doubling the addition of all wing elements and the length of the scapula or the coracoid (the smaller of the two), and the normal wingspan (nws), which applies a reducing factor (rfc) to the maximized wingspan to account for the natural flexures of the wing. The rfc suggested for pteranodontoids is 5%. In the case of MN 6594-V, the maxws and nws are 8.70 m and 8.26 m, respectively, making it the largest pterosaur recovered from Gondwana so far. The distal end of a larger humerus (MCT 1838-R) and a partial wing (MPSC R 1395) are also described showing that large to giant flying reptiles formed a significant part of the pterosaur fauna from the Romualdo Formation. Lastly, some comments on the nomenclatural stability of the Santana deposits are presented.

New evidence of feathers in the Crato Formation supporting a reappraisal on the presence of Aves.

The preservation of delicate structures such as feathers is very rare in the paleontological record, due to the fragility of their components. Fossil feathers have been reported from approximately 50 deposits around the world, from the Late Jurassic to the Pleistocene. In Brazil initial findings consisted of a primary feather of a large bird found in the Tremembé Formation. Other occurrences are preserved in the Crato Formation, where several symmetrical and one single asymmetrical feather was found. Based on three new specimens and reassessing further feather occurrences we cannot confirm the presence of volant Aves in this deposit. The presence of an asymmetrical feather without barbules and hooks hints at the previous existence of a flightless animal within this deposit, possibly a flightlessness bird or a non-avian theropod. Conversely, the presence of a feather from morphotype II present in Tyrannosauroidea, Compsognathidae, Therizinosauroidea and Dromeosauridae, points to a non-theropod origin. Since there are no confirmed records of birds and other feathered archosaurs in the region to date, more evidence is required to identify the animal from which these structures originated.

New evidence of feathers in the Crato Formation supporting a reappraisal on the presence of Aves

The preservation of delicate structures such as feathers is very rare in the paleontological record, due to the fragility of their components. Fossil feathers have been reported from approximately 50 deposits around the world, from the Late Jurassic to the Pleistocene. In Brazil initial findings consisted of a primary feather of a large bird found in the Tremembé Formation. Other occurrences are preserved in the Crato Formation, where several symmetrical and one single asymmetrical feather was found. Based on three new specimens and reassessing further feather occurrences we cannot confirm the presence of volant Aves in this deposit. The presence of an asymmetrical feather without barbules and hooks hints at the previous existence of a flightless animal within this deposit, possibly a flightlessness bird or a non-avian theropod. Conversely, the presence of a feather from morphotype II present in Tyrannosauroidea, Compsognathidae, Therizinosauroidea and Dromeosauridae, points to a non-theropod origin. Since there are no confirmed records of birds and other feathered archosaurs in the region to date, more evidence is required to identify the animal from which these structures originated.

A fossilização de estruturas de revestimento delicadas como as penas constitui um processo extremamente raro, principalmente pela fragilidade de seus componentes. São conhecidos apenas cinquenta depósitos com esta natureza de registro (do Jurássico ao Terciário). No Brasil a primeira referência data de 1916, descrevendo uma pena de vôo com características plumáceas da Formação Tremembé (Bacia de Taubaté). Outras evidências, são provenientes dos calcários laminados da Formação Crato, apresentando registros de penas assimétricas e apenas uma simétrica. Com base em novos achados e reavaliando penas previamente descritas, verificou-se que não se pode afirmar a presença de Aves voadoras nestes depósitos. Isto se deve a ausência de estruturas exclusivas deste tipo de hábito, a exemplo de penas assimétricas com bárbulas e ganchos. Ao contrário disso, verificou-se que os registros apontam mais para a presença de animais emplumados não voadores, como terópodes não avianos ou Aves que tenham perdido secundariamente o voo. Reforçando esta ideia está a presença de uma pena pertencente ao morfótipo do estágio II encontrado até o momento em Tyrannosauroidea, Compsognathidae, Therizinosauroidea e Dromeosauridae. A ausência de registros confirmados de aves ou de outros arcossauros emplumados na região até o momento, geram expectativas sobre novos registros que apontem para os organismos detentores das penas encontradas neste depósito.