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. 2021 Jul 22;11(1):13130.
doi: 10.1038/s41598-021-92499-z.

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

Darren Naish  1 , Mark P Witton  2 , Elizabeth Martin-Silverstone  3
Affiliations

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

Darren Naish et al. Sci Rep. .

Erratum in

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.

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Conflict of interest statement

The authors declare no competing interests.

Figures

Figure 1
Figure 1
Skeletal restorations of pterosaur taxa (hatchlings and adults) used in this study. (A) Sinopterus dongi hatchling (based on IVPP V-14377); (B) S. dongi hatchling compared to adult (adult based on Sinopterus benxiensis holotype, BXGM V0011); (C) Pterodaustro guinazui hatchling (based on MHIN-UNSL-GEO-V 241); (D) hatchling compared with adult (adult modified from a skeletal restoration in). White shading indicates well-represented bones requiring no or only minimal reconstruction, grey shading indicates elements which are represented in fossils but are difficult to reconstruct accurately.
Figure 2
Figure 2
Crania of Jiufotang tapejarid taxa arranged by size. Note progressive change in skull shape and exaggeration of cranial crest in larger specimens, a feature consistent with cranial growth in other pterosaur species. Skulls redrawn from literature.
Figure 3
Figure 3
Limb ratios of Jiufotang tapejarid specimens. Limb metrics taken from descriptive papers of listed taxa.
Figure 4
Figure 4
Best glide angles of gliding tetrapods and hatchling pterosaurs. Hatchling pterosaur glide angles represent the range of results obtained for all hatchlings modelled in this study (both minimum sink and best glide values), gliding tetrapod values obtained from,–. See Table 2 for predicted wing parameters of hatchling pterosaurs.
Figure 5
Figure 5
Relative Failure Force (RFF) relative to body weight (N) of adult and hatchling pterosaur humeri. See Table 1 for bone parameters used in calculating humeral RFF.
Figure 6
Figure 6
Humeral R/t (bone radius/cortex thickness) ratios in hatchling and adult pterosaurs.
Figure 7
Figure 7
Hatchling-adult body mass differentiations in precocial flying tetrapods. Pterosaur mass differentials are considerably larger than those of any extant precocial fliers, which we predict as having a significant impact on the flight performance and ecology of their growth stages.
Figure 8
Figure 8
Visual summary of how basic, size-dependent flight parameters (wing loading, wingspan and aspect ratio) could have influenced pterosaur ecology throughout ontogeny. The animals shown here are giant azhdarchids, species which likely had the largest ontogenetic mass differentials of any pterosaurs (see text) and thus potentially the broadest ecological range across their various growth stages. Azhdarchids were primarily terrestrial pterosaurs, which is reflected in this figure, though the environments and points made here are generalised: they do not expressly pertain to any azhdarchid taxon. Ontogenetic niche exploitation may have differed in other environments.
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