Pterosaurs, extinct flying reptiles that thrived during the Mesozoic era, represent one of the most remarkable evolutionary achievements in the history of vertebrate flight. Spanning from the Late Triassic to the Cretaceous-Paleogene extinction event, these creatures developed wingspans that surpassed those of the largest modern birds, making them the earliest vertebrates to evolve powered flight. Despite their extensive presence in the fossil record, understanding the flight mechanics of pterosaurs has been challenging due to the rarity of well-preserved skeletal remains. Recent discoveries of new pterosaur remains from the Late Cretaceous of Afro-Arabia provide valuable insights into the flight capacity of these large pterosaurs, shedding light on their adaptation and ecological niches.
Discovery and Description of New Specimens
Recent fieldwork conducted by the University of Michigan and the Natural Resources Authority of Jordan in Upper Cretaceous deposits uncovered two new large-bodied pterosaur specimens. The first specimen, attributed to the species Arambourgiania philadelphiae, represents a giant azhdarchoid pterosaur with an estimated wingspan of about 10 meters. The second specimen, identified as a new species named Inabtanin alarabia, features a smaller wingspan of approximately 5 meters. These specimens were recovered from different sites in Jordan, including the phosphate mines of Ruseifa and the Muwaqqar Formation near Tal Inab, offering a rare opportunity to study well-preserved, three-dimensional wing elements of pterosaurs.
Morphological Analysis and Flight Adaptations
The new specimens were analyzed using high-resolution micro-computed tomography (µCT) scans to reconstruct the internal structure of their humeri. The humeral bones of both species exhibited distinct adaptations indicative of their flight capabilities. The humerus of Arambourgiania displayed a series of helical ridges formed along the cortical bone, similar to the bone structure observed in modern soaring birds. This feature suggests a flight style that relied on gliding and dynamic soaring, allowing the pterosaur to cover vast distances with minimal energetic expenditure.
In contrast, the humerus of Inabtanin exhibited a denser pattern of hollow struts within the bone, resembling the internal morphology seen in flapping birds. This structural adaptation suggests that Inabtanin was more capable of active, flapping flight compared to Arambourgiania. The contrasting flight styles inferred from the bone structure highlight the diverse evolutionary strategies employed by pterosaurs to exploit different ecological niches.
Geological Context and Preservation
The specimens were found in sedimentary deposits indicative of marine and coastal environments. The Muwaqqar Formation, where Inabtanin was discovered, is characterized by alternating layers of chalk, limestone, marl, and chert, suggesting deposition in an open marine environment with low oxygen levels at the seafloor. The exceptional preservation of pterosaur bones in these deposits, including detailed internal structures, is attributed to the rapid infilling of bone cavities by limestone matrix, which protected the bones from post-mortem compression and degradation.
The Ruseifa Phosphate Mines, where Arambourgiania was found, have previously yielded isolated pterosaur remains. The new finds expand the known pterosaur diversity in the region and provide crucial data on the skeletal adaptations that enabled these large pterosaurs to thrive in their respective environments.
Implications for Pterosaur Flight Mechanics
The internal bone structures observed in the humeri of Arambourgiania and Inabtanin offer important insights into the biomechanics of pterosaur flight. The helical ridges in the humerus of Arambourgiania suggest a reinforcement mechanism that would have reduced torsional stress during soaring, aligning with the flight dynamics of modern large seabirds such as albatrosses. This adaptation would have been advantageous for long-distance travel and foraging over open water, where sustained flapping would be energetically costly.
On the other hand, the dense struts in Inabtanin’s humerus indicate a bone structure adapted to withstand the repetitive forces of active flapping. This flight style would have allowed Inabtanin to maneuver more effectively, potentially enabling it to exploit different prey or habitats compared to the soaring Arambourgiania. These findings highlight how variations in internal bone morphology among pterosaurs reflect their ecological adaptations and flight strategies.
Systematic Paleontology
The new species, Inabtanin alarabia, is classified within the Azhdarchoidea, a clade known for its long-necked, large-bodied pterosaurs. The holotype consists of a partial skeleton, including the upper and lower jaws, cervical vertebrae, scapulocoracoid, humerus, and nearly complete wing elements. Inabtanin is distinguished from other azhdarchoids by its unique combination of morphological features, such as a deep, laterally compressed lower jaw and short cervical vertebrae. The species name reflects its discovery location near Tal Inab in Jordan and incorporates elements of Arabic language and culture.
Conclusion
The discovery of new pterosaur remains from the Late Cretaceous of Afro-Arabia represents a significant contribution to our understanding of pterosaur flight mechanics and diversity. The contrasting internal bone structures of Arambourgiania and Inabtanin reveal how these large pterosaurs adapted their flight capabilities to different ecological contexts, providing new insights into the evolutionary pathways that shaped the success of these remarkable flying reptiles. Further studies on these specimens, including biomechanical modeling and comparative analysis with extant volant vertebrates, will continue to illuminate the complex dynamics of pterosaur flight and their role in the ecosystems of the Late Cretaceous.
References
Rosenbach, K. L., Goodvin, D. M., Albshysh, M. G., Azzam, H. A., Smadi, A. A., Mustafa, H. A., Zalmout, I. S. A., & Wilson Mantilla, J. A. (2024). New pterosaur remains from the Late Cretaceous of Afro-Arabia provide insight into flight capacity of large pterosaurs. Journal of Vertebrate Paleontology. https://doi.org/10.1080/02724634.2024.2385068
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