Flight reconstruction of two European enantiornithines (Aves, Pygostylia) and the achievement of bounding flight in Early Cretaceous birds

Birds today follow different aerial strategies to deal with the high costs of flapping flight. Intermittent flight, through either flap-gliding or bounding, is commonly used among small birds as a strategy to optimize aerial efficiency. The broad morphological disparity of the different lineages of Mesozoic birds suggests that a range of aerial strategies could have evolved early in avian evolution. Based on biomechanics and aerodynamic theory, this study reconstructs the flying properties of two small enantiornithines from the Lower Cretaceous fossil site of Las Hoyas (Spain), Concornis lacustris and Eoalulavis hoyasi. Our results show that the short length of their wings in relation to their body masses were suitable for flying through strict flapping and intermittent bounds, but not through facultative glides. Aerodynamic models indicate that the power margins of these birds were sufficient to sustain bounding flight. Our results thus suggest that C. lacustris and E. hoyasi would h...