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Primary feather stiffness in Mesozoic birds



From: Ben Creisler
bcreisler@gmail.com


A new paper not yet mentioned on the DML:



WANG, X., NUDDS, R. L., PALMER, C. and DYKE, G. J. (2012)
Size scaling and stiffness of avian primary feathers: implications for
the flight of Mesozoic birds.
Journal of Evolutionary Biology (advance online publication)
doi: 10.1111/j.1420-9101.2011.02449.x
http://onlinelibrary.wiley.com/doi/10.1111/j.1420-9101.2011.02449.x/abstract



Abstract
The primary feathers of birds are subject to cyclical forces in flight
causing their shafts (rachises) to bend. The amount the feathers
deflect during flight is dependent upon the flexural stiffness of the
rachises. By quantifying scaling relationships between body mass and
feather linear dimensions in a large data set of living birds, we show
that both feather length and feather diameter scale much closer to
predictions for geometric similarity than they do to elastic
similarity. Scaling allometry also indicates that the primary feathers
of larger birds are relatively shorter and their rachises relatively
narrower, compared to those of smaller birds. Two-point bending tests
indicated that larger birds have more flexible feathers than smaller
species. Discriminant functional analyses (DFA) showed that body mass,
primary feather length and rachis diameter can be used to
differentiate between different magnitudes of feather bending
stiffness, with primary feather length explaining 63% of variance in
rachis stiffness. Adding fossil measurement data to our DFA showed
that Archaeopteryx and Confuciusornis do not overlap with extant
birds. This strongly suggests that the bending stiffness of their
primary feathers was different to extant birds and provides further
evidence for distinctive flight styles and likely limited flight
ability in Archaeopteryx and Confuciusornis.