Pterosaur Feathers

With the discovery that pterosaur pycnofibers are most likely feathers you knew I could not remain silent about this. The implications have been discussed aplenty, from the fact that branched filaments predate dinosaurs, to the fact that all dinosaurs were not only ancestrally feathered but also had branched feathers and thus we need to rethink how dinosaurs secondarily lost feathers and so forth.

However, I do think we need to notice one peculiar details.

As the diagram above shows, the anurognathid specimens analysed have at least four types of feathers: simply pycnofibers, tufted pycnofibers, vaned pycnofibers and down. The distribution of the first two types is pretty standard on the body, and the third’s prominence on the mouth has already been noted as evidence for the fabled anurognathid whiskers long speculated about.

The fourth type, however, occurs on the wing membranes.

Anurognathids have long been noted as having furry wings, speculated to serve as a means to render their wing beats silent much as the odd structures trailing owl flight feathers (Witton 2013). This follows; down is is anything even better at this than simple fur-like filaments.

However, the more complex feathers seen in ornithischians like Kulindadromeus are also seen on the animal’s limbs (Godefroit 2014), while simpler filaments adorn the body. Likewise, simple feathers adorn Yi‘s body while slightly longer and more complex ones occur on the limbs (Xu 2015). This makes me wonder if complex feathers not only first appeared in archosaur limbs, but may actually have helped the development of powered flight.

If this is the case, complex feathers did in fact evolve as airfoils of some kind, perhaps an indicator of the “sifaka model” hypothesis. Unlike modern sifaka lemurs, these archosaurs were most certainly terrestrial, but a similar hopping and parachuting behaviour could explain the origin of powered flight in pterosaurs and dinosaurs.

As always, can’t wait for newer finds.

References

Benton, Michael J.; Xu, Xing; Orr, Patrick J.; Kaye, Thomas G.; Pittman, Michael; Kearns, Stuart L.; McNamara, Maria E.; Jiang, Baoyu; Yang, Zixiao (2019–01). “Pterosaur integumentary structures with complex feather-like branching”. Nature Ecology & Evolution. 3 (1): 24–30. doi:10.1038/s41559–018–0728–7. ISSN 2397–334X.

Witton, Mark (2013). Pterosaurs: Natural History, Evolution, Anatomy. Princeton University Press. ISBN 978–0691150611.

Godefroit, P., Sinitsa, S.M., Dhouailly, D., Bolotsky, Y.L., Sizov, A.V., McNamara, M.E., Benton, M.J., and Spagna, P. 2014. “A Jurassic ornithischian dinosaur from Siberia with both feathers and scales.” Science, 345(6195): 451–455. Published 25 Jul 2014. doi:10.1126/science.1253351

Xu, X.; Zheng, X.; Sullivan, C.; Wang, X.; Xing, L.; Wang, Y; Zhang; O’Connor, J.K.; Zhang, F.; Pan, Y. (7 May 2015). “A bizarre Jurassic maniraptoran theropod with preserved evidence of membranous wings”. Nature. 521 (7550): 70–73. doi:10.1038/nature14423. PMID 25924069.