The Aerodynamics of the British Late Triassic Kuehneosauridae

Abstract

The Kuehneosauridae (Late Triassic, Britain, USA) had remarkable adaptations, most notably their elongate mid-dorsal ribs that were presumably covered with a skin membrane in life. These lateral 'wings' have always been linked with some form of gliding adaptation, but quantitative studies have been limited. Here, we provide a thorough aerodynamic analysis of both genera of British kuehneosaurids based on theory and on experiments with life-sized models in a wind tunnel. Of the two genera, Kuehneosuchus, with elongate 'wings', was a glider, and Kuehneosaurus, with much shorter 'wings', was a parachutist. Kuehneosuchus most probably had highly cambered wings and no additional skin membranes on hands or feet, nor did it have a cruropatagium. Lappets on the hyoid apparatus, as seen in Draco, were probably present to enhance pitch control. Kuehneosuchus was capable of gliding at angles (h) between 13 and 16 degrees, at speeds between 7 and 9 m ⁄ s, and was probably very manoeuvrable when airborne. Kuehneosaurus was capable of parachuting (h > 45 degrees) at speeds between 10 and 12 m ⁄ s. It is unclear whether the British kuehneosaurid material represents two genera, as assumed here, two species of one genus, or sexual dimorphs of a single species, where the gliding Kuehneosuchus was the male, which used its gliding and perhaps highly coloured 'wings' to display to the parachuting Kuehneosaurus.

How lizards fly: A novel type of wing in animals

“…These adjustments certainly have an influence on the aerodynamic properties of the aerofoil, but their significance remains to be studied in detail. Also, the role of the throat lappets which are extended laterally in some but not all gliding flights (Figs 1 – 5 ; S1 – S3 Fig ) and which have been interpreted as canards [ 20 ] or smaller and secondary anterior aerofoils [ 6 ] remains to be investigated in detail.…”

“…A number of extinct lineages, including the Late Permian Coelurosauravus , the Late Triassic Kuehneosaurus , Kuehneosuchus and Icarosaurus , the Late Triassic Mecistotrachelos , and the Early Cretaceous Xianglong , possess elongated ribs or bony rib-like structures that are hypothesized to have supported a patagial membrane and thus to resemble the glide-associated morphological modifications of the modern Draco [ 20 , 26 – 30 ]. These fossil taxa are assumed to have glided through the air with the forelimbs extended forwardly and to have changed direction by unilateral adjustments of the aerofoil through contractions of the trunk musculature [ 6 , 20 , 27 , 28 ]. Since Draco apparently uses the forelimbs to control the patagium, it is reasonable to propose that the extinct gliders formed a similar connection and might have regulated their glide path in a similar way.…”

Tooth and cranial disparity in the fossil relatives of Sphenodon (Rhynchocephalia) dispute the persistent ‘living fossil’ label

“…For example, all four clevosaurs plot near each other with respect to other taxa such as the pleurosaurs. All three outgroup taxa (stem lepidosaurs) plot near one another despite representing animals of different palaeoecological role: Sophineta being a small scansorial animal (Evans & Borsuk-Białynicka, 2009), Marmoretta being an aquatic predator (Waldman & Evans, 1994) and Kuehneosaurus being a parachuter/glider (Robinson, 1962;Stein et al, 2008). However, in the sample as a whole, evolutionary paths are not very parsimonious.…”

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

“…Extant gliding taxa tend to have smaller maximum body masses and lower wing loading values than powered flyers ( Tables S3 and S8 ): maximum body mass between 2.5 and 3 kg ( Dial, 2003 ) and wing loading values in extant gliders ranging from 9–143 Nm −2 . The Triassic fossil amniote Kuehneosaurus possibly extends the range of the latter to ~157 Nm −2 , though the gliding ability of this taxon has been questioned ( Stein et al., 2008 ; McGuire and Dudley, 2011 ). Yi and Ambopteryx are both within these ranges, suggesting gliding flight was possible assuming a bat and pterosaur wing model ( Figure 6 ), except at the highest mass estimate for Yi .…”