Flight in slow motion: aerodynamics of the pterosaur wing

Abstract

The flight of pterosaurs and the extreme sizes of some taxa have long perplexed evolutionary biologists. Past reconstructions of flight capability were handicapped by the available aerodynamic data, which was unrepresentative of possible pterosaur wing profiles. I report wind tunnel tests on a range of possible pterosaur wing sections and quantify the likely performance for the first time. These sections have substantially higher profile drag and maximum lift coefficients than those assumed before, suggesting that large pterosaurs were aerodynamically less efficient and could fly more slowly than previously estimated. In order to achieve higher efficiency, the wing bones must be faired, which implies extensive regions of pneumatized tissue. Whether faired or not, the pterosaur wings were adapted to low-speed flight, unsuited to marine style dynamic soaring but adapted for thermal/slope soaring and controlled, low-speed landing. Because their thin-walled bones were susceptible to impact damage, slow flight would have helped to avoid injury and may have contributed to their attaining much larger sizes than fossil or extant birds. The trade-off would have been an extreme vulnerability to strong or turbulent winds both in flight and on the ground, akin to modern-day paragliders.

Does postcranial palaeoneurology provide insight into pterosaur behaviour and lifestyle? New data from the azhdarchoid Vectidraco and the ornithocheirids Coloborhynchus and Anhanguera

“…We take this as evidence that it may have been a proficient terrestrial locomotor, a hypothesis consistent with data from azhdarchoids in general (Witton & Naish , ; Witton ). In contrast, the larger brachial enlargement (with respect to the lumbosacral enlargement) seen in ornithocheirids is consistent with data indicating that these animals spent little time on land and were highly aerial, perhaps being on par with extant frigatebirds (Palmer ). Such forelimb‐dominance is consistent with substantial innervation of the wings.…”

Understanding selection for long necks in different taxa

“…However if they were adapted to low‐speed flight (e.g. Palmer, 2011) they may have been able to take off from the water surface and this potentially allows a much larger range of feeding behaviour, as seen in extant long‐necked fish‐eating birds: diving from the water surface as in cormorants or plunge diving as in the (superficially pterosaur shaped) brown pelican Pelecanus occidentalis Linnaeus (Nelson, 2005). Clearly the question ‘could pterosaurs take off easily from the water surface?’ is a key one for pterosaur biology—if the answer is ‘yes’ then many of the selection pressures that apply to modern fish‐eating birds are likely to be relevant to pterosaurs.…”

Constraints on the wing morphology of pterosaurs

“…This is maximized by flying at the lowest descent (sink) speed, which does not coincide exactly with the maximum lift : drag ratio. However, in practice, it is generally the case that increases in lift : drag ratio tend also to reduce sink rates [21].…”