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

Abstract

Intermittent flight through flap-gliding (alternating flapping phases and gliding phases with spread wings) or bounding (flapping and ballistic phases with wings folded against the body) are strategies to optimize aerial efficiency which are commonly used among small birds today. The broad morphological disparity 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 flight modes 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 have increased aerial efficiency through bounding flight, just as many small passerines and woodpeckers do today. Intermittent bounding appears to have evolved early in the evolutionary history of birds, at least 126 million years ago.

NewBohaiornis-like bird from the Early Cretaceous of China: enantiornithine interrelationships and flight performance

“…Our study also provides the first assessment of the flight properties of “bohaiornithid” enantiornithines. Key flight parameters inferred for these birds suggest ineffectiveness for performing intermittent flight (either flap-gliding or bounding) that was inferred for other enantiornithines (Liu et al, 2017, 2019; Serrano et al, 2017, 2018). Instead, these parameters indicate that Gretcheniao sinensis and other “bohaiornithids” were morphologically suited for flying through continuous flapping, although not able to perform prolonged flights.…”

“…This negative power margin (i.e., P av < P mec ; see Table 4) rules out the possibility that Gretcheniao sinensis and other “bohaiornithids” could have performed long flights through either sustained flapping or bounding. Thus, unlike other early Cretaceous enantiornithines for which intermittent flight has been inferred, either bounding or flap-gliding (Serrano et al, 2017, 2018; Liu et al, 2017, 2019), Gretcheniao sinensis and other “bohaiornithids” probably flew through continuous flapping. However, our results suggest that they would have been unable to generate sufficient power to sustain a prolonged flight.…”

“…Despite the fact that the interrelationships of these extinct birds continue to be contentious, recent studies have identified a number of distinct Jehol clades including Pengornithidae (Zhou, Clarke & Zhang, 2008; O’Connor et al, 2016), Longipterygidae (Chiappe et al, 2007; O’Connor et al, 2009), and Bohaiornithidae (Hu et al, 2011; Wang et al, 2014), the monophyly of which needs to be further tested. Recent studies on these birds have also begun to explore their aerodynamic properties (Liu et al, 2017, 2019; Serrano et al, 2017, 2018; Chiappe et al, 2014) suggesting that early in their evolutionary history, enantiornithines developed various styles of intermittent flight (e.g., bounding, flap-gliding).…”

Multiphase progenetic development shaped the brain of flying archosaurs

“…Although recent results propose that even Archaeopteryx may already have been capable of flight 30 , its brain was probably not yet capable of controlling the complex volancy seen in most modern birds. Enantiornithes were probably proficient flyers 71–73 , and the basal ornithurine Cerebavis (circa 122 Ma) already featured clear flight-related adaptations in the cranium 14 . However, the fossil record surrounding the origin of Neornithes 74 , as well as generally limited aerial performance across the basalmost extant neornithine clades, suggests that the last Mesozoic ancestors of modern birds were likely much less capable flyers.…”

The effect of long-term atmospheric changes on the macroevolution of birds

“…Some components of these calculations are difficult to measure experimentally in flying birds while flapping (i.e., CDb, k, Cpro, Sb). In fossils, calculation of these components requires a number of assumptions (see Serrano et al, 2018). Body drag coefficient (CDb), the most influential of these components, was calculated from the equation Sb CDb = 0.01 SL (Taylor et al, 2016) instead of using the constant value (0.1) given by Pennycuick (2008); Taylor et al…”