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Abstract

Several new specimens of pterodactyloid pterosaurs attributed to the Ornithocheiroidea and Azhdarchoidea and housed within the State Museum of Natural History Karlsruhe are described. Knowledge of their anatomy, morphometrics, joint mechanics, and extent of the soft tissue membrane were subsequently used to create models that tested the aerodynamic characteristics of the wing, body and head.

Two specimens are herein erected as holotypes, the ornithocheirid Barbosania gracilirostris and the azhdarchoid Microtuban altivolans. The former of these, uncovered from the Romualdo member of the Santana Formation of NE Brazil, preserves an unusually advanced state of skeletal fusion where the suture between the extensor tendon process and the proximal articular surface of the first wing finger phalanx is partially closed. The fossil further advances the cause that crestless ornithocheiroids should not be considered as juvenile morphs of pre-established taxa. The second specimen, Microtuban altivolan was unearthed from the Upper Cretaceous Lagerstätten of northern Lebanon and represents a non-azhdarchid azhdarchoid displaying unusual proportions between the wing finger phalanges. The hyper reduction without loss of the fourth wing finger phalanx is shown to be more widespread within the Azhdarchoidea. Additional specimens presented here are attributed to the ornithocheirid Coloborhynchus robustus and the azhdarchoids Tapejara wellnhoferi and cf. Tupuxuara.

The “crocodilian-like” sequence of suture closure between the neural arches and vertebral bodies of the thoracic vertebrae is confirmed within the azhdarchoid pterosaurs, indicating that the developmental timing between the Azhdarchoidea and Ornithocheiroidea did not significantly differ. A possible sexual dimorphism, where the pelvic girdle lacks a symphysis and remains open even in large adults is observed within Coloborhynchus robustus, while a single preaxial metacarpal is observed to contact the distal carpus with cf Tupuxuara, indicating that this feature was widespread within Azhdarchoidea.

The primary flight membrane is reconstructed with an ankle attachment of the trailing edge, a configuration that was never fundamentally altered throughout the evolutionary history of the group. By adopting heavier estimates of mass and increasing wing load, horizontal/vertical flight velocities and circling radii are shown to increase. Maximum range speed for the study subject C. robustus varies between 15 – 21 ms, depending on the methodology, along with maximum L/D ratios of 13-23. Body drag of the small azhdarchoid Aurorazhdarcho micronyx is estimated at <0.015 while a CFD analysis of C. robustus indicates a coefficient of 0.022 for the large ornithocheiroid. Despite the presence of an often enlarged head, this feature contributes only 13-16% of the total parasite drag coefficient when orientated directed into the flow. Yawing of the head, however, results in increases of up to 20-91% by the relatively low angle of 40°. The crest of Nyctosaurus gracilis is found to flutter in low to moderate flow velocities, resulting in higher than expected drag coefficients. While the head and crest are found to influence the aerodynamics of the animal a primarily aerodynamic function is rejected.