Powered flight in hatchling pterosaurs: evidence from wing form and bone strength

Abstract

Competing views exist on the behaviour and lifestyle of pterosaurs during the earliest phases of life. A ‘flap-early’ model proposes that hatchlings were capable of independent life and flapping flight, a ‘fly-late’ model posits that juveniles were not flight capable until 50% of adult size, and a ‘glide-early’ model requires that young juveniles were flight-capable but only able to glide. We test these models by quantifying the flight abilities of very young juvenile pterosaurs via analysis of wing bone strength, wing loading, wingspan and wing aspect ratios, primarily using data from embryonic and hatchling specimens of Pterodaustro guinazui and Sinopterus dongi. We argue that a young Sinopterus specimen has been mischaracterised as a distinct taxon. The humeri of pterosaur juveniles are similar in bending strength to those of adults and able to withstand launch and flight; wing size and wing aspect ratios of young juveniles are also in keeping with powered flight. We therefore reject the ‘fly-late’ and ‘glide-early’ models. We further show that young juveniles were excellent gliders, albeit not reliant on specialist gliding. The wing forms of very young juveniles differ significantly from larger individuals, meaning that variation in speed, manoeuvrability, take-off angle and so on was present across a species as it matured. Juveniles appear to have been adapted for flight in cluttered environments, in contrast to larger, older individuals. We propose on the basis of these conclusions that pterosaur species occupied distinct niches across ontogeny.

A new wing skeleton of the Jehol tapejarid Sinopterus and its implications for ontogeny and paleoecology of the Tapejaridae

“…In addition, the Jehol tapejarids are all comparable in their postcranial skeleton and limb proportions, with the exception of “ Huaxiapterus ” benxiensis (Fig. 5 ) 1 , 13 , 14 . Therefore, a taxonomic revision has been proposed that most or even all the Jehol tapejarids should be synonymized as Sinopterus , but “ Huaxiapterus ” benxiensis needs to be further confirmed 1 , 7 , 8 , 12 , 14 .…”

“…In the Jehol Biota, the tapejarids are dominated by immature specimens. Their variation (e.g., cranial crest and limb proportions) has likely been over split and their diversity overestimated into nine nominal species 1 , 7 , 13 , 14 . In these varied features (e.g., cranial crest), ontogenetic variation of the cranial structures is well documented in some azhdarchoids (e.g., Caiuajara and Tupuxuara ) 15 , 18 .…”

“…5 ) 1 , 13 , 14 . Therefore, a taxonomic revision has been proposed that most or even all the Jehol tapejarids should be synonymized as Sinopterus , but “ Huaxiapterus ” benxiensis needs to be further confirmed 1 , 7 , 8 , 12 , 14 . Based on the comparable limb proportions (wing metacarpal/humerus length ratio 1.41, wing metacarpal/ulna length ratio 1.01, wing metacarpal/first wing phalanx length ratio 0.77, and wing phalanges first/second 1.37) 7 , 13 , 14 , 35 , we refer SDUST-V1014 to Sinopterus .…”

“…The Jehol tapejarids plot as a distinct ontogenetic series in size, except for “ Huaxiapterus ” benxiensis (Fig. 5 ) 13 , 14 . Their cranial crests, especially the presence of a premaxillary crest, is correlated with size as exemplified by the plot of the humerus and ulna in length (Fig.…”

“…They flourished in the Jehol Biota with a preponderance of immature individuals 1 , 6 , 7 . However, these immature fossils were likely subject to taxonomic misinterpretations, resulting in nine nominal species 1 , 7 – 14 . The putative diagnostic features (e.g., cranial crest and limb proportions) of these species are possibly the result of individual variation, ontogeny, or sexual dimorphism as evident in Caiuajara 15 and other pterosaurs (e.g., Anhanguera , Hamipterus , Pteranodon , Pterodactylus, and Tupuxuara ) 16 – 20 .…”