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Nature Advance Online publication: WAIR 2008

Dial, K.P., B.E. Jackson  &  P. Segre. 2008. A fundamental avian wing-stroke
provides a new perspective on the evolution of flight. Nature advance online
publication 23 January 2008 | doi:10.1038/nature06517; Received 20 August
2007; Accepted 27 November 2007; Published online 23 January 2008

Abstract: The evolution of avian flight remains one of biology's major
controversies, with a long history of functional interpretations of fossil
forms given as evidence for either an arboreal or cursorial origin of
flight. Despite repeated emphasis on the 'wing-stroke' as a necessary avenue
of investigation for addressing the evolution of flight1, 2, 3, 4, no
empirical data exist on wing-stroke dynamics in an experimental evolutionary
context. Here we present the first comparison of wing-stroke kinematics of
the primary locomotor modes (descending flight and incline flap-running)
that lead to level-flapping flight in juvenile ground birds throughout
development (Fig. 1). We offer results that are contrary both to popular
perception and inferences from other studies5, 6, 7. Starting shortly after
hatching and continuing through adulthood, ground birds use a wing-stroke
confined to a narrow range of less than 20°, when referenced to gravity,
that directs aerodynamic forces about 40° above horizontal, permitting a
180° range in the direction of travel. Based on our results, we put forth an
ontogenetic-transitional wing hypothesis that posits that the incremental
adaptive stages leading to the evolution of avian flight correspond
behaviourally and morphologically to transitional stages observed in
ontogenetic forms.

Note that there are a LOT of supplementary videos to this one.

Thomas R. Holtz, Jr.
Email: tholtz@umd.edu   Phone: 301-405-4084
Office: Centreville 1216                        
Senior Lecturer, Vertebrate Paleontology
Dept. of Geology, University of Maryland
Fax: 301-314-9661               

Faculty Director, Earth, Life & Time Program, College Park Scholars
Fax: 301-405-0796

Mailing Address:        Thomas R. Holtz, Jr.
                        Department of Geology
                        Building 237, Room 1117
                        University of Maryland
                        College Park, MD 20742 USA