Aerodynamics Show Membrane-Winged Theropods Were a Poor Gliding Dead-end

Abstract

The bizarre scansoriopterygid theropods Yi and Ambopteryx had skin stretched between elongate fingers that form a potential membranous wing. This wing is thought to have been used in aerial locomotion, but this has never been tested. Using laser-stimulated fluorescence imaging, we re-evaluate their anatomy and perform aerodynamic calculations covering flight potential, other wing-based behaviors, and gliding capabilities. We find that Yi and Ambopteryx were likely arboreal, highly unlikely to have any form of powered flight, and had significant deficiencies in flapping-based locomotion and limited gliding abilities. Our results show that Scansoriopterygidae are not models for the early evolution of bird flight, and their structurally distinct wings differed greatly from contemporaneous paravians, supporting multiple independent origins of flight. We propose that Scansoriopterygidae represents a unique but failed flight architecture of non-avialan theropods and that the evolutionary race to capture vertebrate aerial morphospace in the Middle to Late Jurassic was dynamic and complex.

‘Dinosaur-bird’ macroevolution, locomotor modules and the origins of flight

“…1). The astonishing wealth of fossil discoveries in the past decades have increased our knowledge about the origins of flight in maniraptoran dinosaurs and how different groups (not only birds) exploited this new locomotion behaviour (Brusatte, 2017;Dececchi et al, 2020;Pei et al, 2020). According to this new evidence, it is unquestionable that non-avialan maniraptoran theropods already possessed features that were once thought to be unique to modern flying birds, such as feathers, asymmetrical feathers building wings, and air-filled bones that lightened body mass, among other anatomical traits.…”

“…Further, some members of the bizarre paravian Jurassic clade Scansoriopterygidae, with genus such as Yi and Ambopteryx, possessed extra novel elements in their hands that supported a characteristic membranous patagium along their extremely elongated hands, similarly to the building of the wing in pterosaurs or bats, allegedly qualifying them for a potential flying performance (Wang et al, 2019;Xu et al, 2015). Nevertheless, recent evidence suggests that these small non-avialan maniraptorans were not able to perform powered flight or flapping-based aerial locomotion, being limited to be arboreal gliders and, therefore, showing a completely different pattern of aerial performance compared to any crown birds (Dececchi et al, 2020). Thus, the fossil record reveals that increased anatomical variation and its expression as morphological disparity is linked to multiple origins of different flying capacities in Maniraptora.…”

“…Coloured symbols show macroevolutionary events related to each lineage (legend at the top right shows the meaning of each symbol). Flight capacity is based onPei et al (2020) andDececchi et al (2020). Evolutionary radiations are based onBenson et al (2014) andPuttick et al (2014).…”

Independent origins of powered flight in paravian dinosaurs?

“…USA. 3 Area of Paleontology, Faculty of Sciences, Universidad de Malaga, Malaga, Spain. *E-mail: fjsa@uma.es…”

Response to Serrano and Chiappe

“…There remains the potential to detect obligate gliders among 'marginal' taxa that we recovered as not capable of powered fl ight. This could be the case for taxa that were arboreal or scansorial, as shown for scansoriopterygids 3 .…”