Barb geometry of asymmetrical feathers reveals a transitional morphology in the evolution of avian flight.

Feo, TJ and Field, D. J. and Prum, RO (2015) Barb geometry of asymmetrical feathers reveals a transitional morphology in the evolution of avian flight. Proceedings of the Royal Society B: Biological Sciences, 282 (1803). p. 20142864. ISSN 0962-8452 DOI https://doi.org/10.1098/rspb.2014.2864

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Abstract

The geometry of feather barbs (barb length and barb angle) determines feather vane asymmetry and vane rigidity, which are both critical to a feather's aerodynamic performance. Here, we describe the relationship between barb geometry and aerodynamic function across the evolutionary history of asymmetrical flight feathers, from Mesozoic taxa outside of modern avian diversity (Microraptor, Archaeopteryx, Sapeornis, Confuciusornis and the enantiornithine Eopengornis) to an extensive sample of modern birds. Contrary to previous assumptions, we find that barb angle is not related to vane-width asymmetry; instead barb angle varies with vane function, whereas barb length variation determines vane asymmetry. We demonstrate that barb geometry significantly differs among functionally distinct portions of flight feather vanes, and that cutting-edge leading vanes occupy a distinct region of morphospace characterized by small barb angles. This cutting-edge vane morphology is ubiquitous across a phylogenetically and functionally diverse sample of modern birds and Mesozoic stem birds, revealing a fundamental aerodynamic adaptation that has persisted from the Late Jurassic. However, in Mesozoic taxa stemward of Ornithurae and Enantiornithes, trailing vane barb geometry is distinctly different from that of modern birds. In both modern birds and enantiornithines, trailing vanes have larger barb angles than in comparatively stemward taxa like Archaeopteryx, which exhibit small trailing vane barb angles. This discovery reveals a previously unrecognized evolutionary transition in flight feather morphology, which has important implications for the flight capacity of early feathered theropods such as Archaeopteryx and Microraptor. Our findings suggest that the fully modern avian flight feather, and possibly a modern capacity for powered flight, evolved crownward of Confuciusornis, long after the origin of asymmetrical flight feathers, and much later than previously recognized.

Item Type:	Article
Uncontrolled Keywords:	NILAREP;
Subjects:	04 - Palaeobiology
Divisions:	04 - Palaeobiology
Journal or Publication Title:	Proceedings of the Royal Society B: Biological Sciences
Volume:	282
Page Range:	p. 20142864
Identification Number:	https://doi.org/10.1098/rspb.2014.2864
Depositing User:	Sarah Humbert
Date Deposited:	13 Dec 2019 16:00
Last Modified:	13 Dec 2019 16:00
URI:	http://eprints.esc.cam.ac.uk/id/eprint/4559

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