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Feather barbs show history of flight

Ben Creisler

A recent paper not yet mentioned:

Teresa J. Feo , Daniel J. Field  & Richard O. Prum (2015)
Barb geometry of asymmetrical feathers reveals a transitional
morphology in the evolution of avian flight.
Proceedings of the Royal Society B  (advance online publication)
DOI: 10.1098/rspb.2014.2864

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


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