Esaú Victor de Araújo

The enantiornithes, a group of Mesozoic birds, have morphological features suggesting a precocial mode of development; however, their detailed physiological characteristics, particularly hatchling metabolic rates, have yet to be explored. Here, we retrodicted metabolic rates for four Lower Cretaceous enantiornithines: one hatchling, one adult from Las Hoyas, one early post-hatching juvenile and one post-juvenile individual from the Jehol Biota, using phylogenetic comparative analyses and a comprehensive dataset of extant birds spanning the altricial–precocial spectrum. By examining vascular density (related to resting metabolic rate (RMR)) and nutrient foraminal size (proportional to blood flow rate) as proxies, we inferred the metabolic scope of the hatchling enantiornithine and determined that it fell toward the precocial end of the altricial–precocial spectrum. The RMR values of the two enantiornithine chicks were retrodicted as 0.67 mlO2 h–1 g–0.93. The peak metabolic rate (PMR) retrodicted is twice the resting metabolism for the Las Hoyas hatchling. These results are consistent with a semi-precocial/precocial development characterized by independent locomotion by climbing using the wing claws soon after hatching. However, flapping flight may have been delayed, owing to incomplete ossification of the sternum, as observed in one hatchling specimen.

Studies on paleophysiology and thermoregulation are central topics in fossil vertebrate paleobiology because they allow inferences about extinct organismal function beyond anatomical description. Pterosaur thermophysiology remains actively debated. Evidence such as relatively rapid growth and elevated metabolic rate estimates has been used to argue for endothermic-like physiologies consistent with the energetic demands of powered flight, whereas reproductive traits, including burial incubation and precocial development, have led some authors to propose ectothermic strategies more akin to those of extant non-avian diapsids. Here, we provide quantitative estimates of resting metabolic rate (RMR) for the tapejarid pterosaur Caiuajara dobruskii using phylogenetic eigenvector maps and osteocyte lacunar density as proxy. Analysis of six histological sections from three appendicular elements (femur, tibia, humerus) at different ontogenetic stages (adult and juvenile) yielded mass-independent RMR estimates of 0.24–0.76 ml O ₂ h ⁻¹ g ^−0.86 , substantially higher than those of lepidosaurs but lower than typical mammalian and avian values. The retrodicted mass-independent maximum metabolic rate (MMR) of 5.68 ml O ₂ h ⁻¹ g ^−0.87 falls between values for highly active reptiles and birds, suggesting sufficient aerobic capacity to sustain powered flight without fully matching the maximal performance of small endotherms. Together, these results suggest active-flighted pterosaurs fall among a metabolically intermediate continuum, limiting straightforward actualistic comparisons for inferring their thermoregulatory strategy.

More than fifty years after the first discoveries of pterosaurs in the Araripe Basin, this sedimentary unit remains one of the most informative windows into the diversity and biology of these fantastic flying reptiles. With dozens of proposed species from two different Lagerstätten, the exceptional preservation of Araripe fossils offers a detailed view of the anatomy, function, and ecology of Cretaceous pterosaurs. These fossils reveal complex faunal assemblages populated by these animals, providing rare snapshots of ancient ecosystems. Today, Araripe pterosaur diversity appears to have reached a plateau, with fewer new taxa and more specimens assigned to known species. This situation calls for a comprehensive reassessment of Araripe pterosaur diversity. Here, we present an in-depth, richly illustrated taxonomic review of all taxa proposed for the basin, along with a synthesis of available paleobiological data. This work aims to establish a solid foundation for future research and proposes guidelines for advancing our understanding of Araripe pterosaurs, especially from biostratigraphic and paleoecological perspectives—areas severely affected by the ongoing threat of illegal collecting and fossil trade.

The Araripe Basin in northeastern Brazil is a key site for Cretaceous pterosaur fossils from Gondwanan deposits. Most discoveries are concentrated in its northern portion, particularly in Ceará state, within the Crato and Romualdo formations. In contrast, records from the southern part of the basin, especially in Piauí and Pernambuco, remain scarce. This study reports the first pterosaur fossils from the Romualdo Formation in Piauí, represented by two three-dimensionally preserved, incomplete wing phalanges: LPP Pt-002 and LPP Pt-005. Osteohistological analysis of LPP Pt-002 reveals a cortex composed of parallel-fibered bone, with endosteal lamellae and an external fundamental system (EFS), indicating skeletal maturity. In contrast, LPP Pt-005 displays a cortex of woven bone and circumferential lamellae, with a highly vascularized matrix and no evidence of EFS or endosteal lamellae, suggesting a post-juvenile stage. These differences indicate that the specimens represent distinct individuals. Although the reasons for the lower abundance of pterosaur remains in the southern Araripe Basin are unclear, these findings expand the known geographic range of Pterosauria within the basin and underscore the importance of further paleontological exploration in underrepresented regions to better understand pterosaur diversity and distribution during the Cretaceous.

Powered flight has evolved separately in three tetrapod clades: pterosaurs, birds (avian dinosaurs), and bats. To meet the challenges of powered flight, tetrapods acquired structural, mechanical, and physiological adaptations. Circumferential vascular canals, forming laminar bone, have been proposed to be an adaptation linked to withstanding torsional loading during flight in birds. However, whether laminarity serves as an indicator of biomechanical torsion in pterosaurs, remains to be elucidated. Through a comparative statistical approach, we investigate the association between cortical bone laminarity and skeletal stress in pterosaur flight. For the first time, the presence of laminarity in pterosaur bones was analyzed to observe torsion in bones associated with flight, using thirty-five thin sections of the tapejarid Caiuajara dobruskii, Anhangueridae, and Dsungaripteroidea pterosaurs. We conclude that adaptive relationships arise between bone microstructure and biomechanical function, with forelimb elements (humerus, ulna, and wing phalanges) exhibiting higher laminarity rates compared to hindlimb bones. Additionally, the results provide insights into the possible flight style of these pterosaurs through comparison with bird groups. The presence of laminarity in pterosaurs and birds, but not in bats, highlights that this feature, once considered exclusive to birds, may have convergently evolved in pterosaurs and birds.

Animal Conquest é um jogo de tabuleiro que se apropria da temática paleontológica, a fim de auxiliar no processo de ensino e aprendizagem de diferentes conceitos relacionados à história natural e à evolução dos vertebrados. A proposta explora a grande atratividade da Paleontologia junto aos jovens, e do fato de ser uma ciência interdisciplinar para auxiliar na compreensão de conceitos relacionados às Geociências (Geologia e Geografia) e às Biociências (Evolução, Zoologia, Botânica e Ecologia). O jogo foi criado em computador com o programa Adobe Photoshop CS6, tendo um formato de tapete pedagógico de grandes proporções. Durante o jogo, os jogadores podem conhecer a história, desde a transição entre os ambientes aquático e terrestre, vislumbrando a ascensão e declínio dos dinossauros não-avianos, até a irradiação dos mamíferos, e as transformações antrópicas causadas ao planeta Terra. O produto pedagógico é uma ferramenta de ensino complementar que busca aproximar a Paleontologia e a educação básica.

Caimaninae is a South American lineage of crocodylians widely distributed in Brazil and composed of six species within three genera. Currently, there is insufficient information regarding growth strategies, growth rates, and ecology extracted from the bone microstructure. Here we present the first osteohistological study of both Caiman yacare and an unidentified fossil Caiman. Long bones of one specimen of C. yacare and of one fossil Caiman found at Solimões Formation (Acre Basin), were used to prepare the histological slides. The microstructure of C. yacare shows fibrolamellar complex present in the femur and tibia, while the humerus and radius of both C. yacare and the fossil Caiman revealed a slow-growing bone matrix with gradual decrease and effective stops. According to the results found here, Caimaninae seem to have the capability to adjust their growth rates in response to seasonal changes. The extant Caiman is classified as juvenile, but for the fossilized specimen no ontogenetic stage can be determined. Caiman yacare shows the presence of intraskeletal variability regarding the record of bone growth. We conclude that Caimaninae likely have been experiencing cyclical changes in growth rates in direct correlation to changes in seasons and environmental conditions since the Miocene.