THE GLIDING HINDLIMB CONFIGURATION OF SHAROVIPTERYX MIRABILIS, THE WORLD’S ONLY HINDLIMB GLIDER AND THE FIRST KNOWN GLIDING VERTEBRATE

Sharovipteryx mirabilis, the earliest proposed gliding vertebrate in the fossil record, displays a unique hindlimb gliding membrane. Since the only known specimen from the Late Triassic Madygen Lägerstatte in Kyrgyzstan lacks preserved forelimbs, the glide ability of this strange organism remains enigmatic. Every other terrestrial gliding vertebrate has a forelimb gliding membrane, so, in the absence of additional Sharovipteryx specimens, prior modeling and computational work has assumed a forelimb gliding membrane would be required for functional gliding. However, the Sharovipteryx hindlimb membrane is more substantial than any other known vertebrate glider, and it is possible Sharovipteryx relied solely on a hindlimb gliding membrane.

To determine if gliding with only a hindlimb membrane was feasible, we created life models with accurate limb ratios and body mass estimates for Sharovipteryx mirabilis based on fossil evidence. From these life models, we then constructed physical glide models with three different hindlimb configurations: a delta-wing configuration based on Dyke et al.’s study from 2006 (the D model), a sprawling configuration based on the Gans et al. description of the holotype in 1987 (the G model), and a novel hyperextended model based on a combination of Sharov’s original reconstruction and the Gans et al. description (the H model). These models were launched repeatedly via a custom-made gravity-assisted catapult to determine which configuration offered the most efficient glide in terms of distance traveled. Results after 50 glides suggested the novel H model outperformed the D model and the G model, gliding an average distance of 240.76 cm while the D model glided an average 235.56 cm and the G model glided an average 226.60 cm. A significant Bartlett test also indicated the H model and the G models provided less variable glide distances than the D model, suggesting they were more aerodynamically stable. Based on these results, Sharovipteryx could have glided without a forelimb gliding membrane, but the models’ steep descent angles suggest none of the reconstructions were efficient gliders compared to modern organisms and other fossil gliders. This leaves open the possibility that Sharovipteryx was a parachuting organism rather than a true glider, with or without a forelimb membrane.