'Microraptors' Shed Light on Ancient Origin of Bird Flight
ScienceDaily (Jan. 26, 2010) — A joint team from the University of Kansas and Northeastern University in China says that it has settled the long-standing question of how bird flight began.
Scientists from the University of Kansas have created a model of a microraptor to show its gliding capabilities. (Credit: University of Kansas)
The team is led by David Alexander, KU assistant professor of biology and an expert on modern animal flight. Alexander is joined by KU colleagues Larry Martin, David Burnham and Amanda Falk, along with Enpu Gong from Northeastern University in China, who are engaged in a comprehensive study of the functional morphology and ecology of early birds from China.
"We've done the scientific work and flight tests to show that microraptor was a very successful glider," said Burnham. "In 2003, they found one that was so well-preserved that you could count the feathers on its wings."
A debate involving the KU scientists, recently documented by the PBS program "NOVA," had flared over the question of whether evidence supported the theory that animals developed flight as ground dwellers, as a majority of paleontologists had asserted. But Martin and Burnham argue that flight originated above, in the trees. Such animals would have been gliders. The researchers say that fossils of the hawk-sized microraptor shore up their theory.
"The controversy was that these animals couldn't spread their hind-wings to glide," said Burnham. "But we've been able to articulate the bones in their hip socket to show that they could fly."
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David E. Alexander a,1, Enpu Gong b, Larry D. Martin a,c, David A. Burnham c, and Amanda R. Falk c,d
-Author Affiliations
aDepartment of Ecology & Evolutionary Biology, University of Kansas, Lawrence, KS 66045-7534;
bDepartment of Geology, Northeastern University, Shenyang, Liaoning 110004, China;
cDivision of Paleontology, Biodiversity Institute, University of Kansas, Lawrence, KS 66045-7561; and
dDepartment of Geology, University of Kansas, Lawrence, KS 66045-7613
Edited by Alan Feduccia, University of North Carolina, Chapel Hill, NC, and accepted by the Editorial Board December 20, 2009 (received for review October 14, 2009)
Abstract
Fossils of the remarkable dromaeosaurid Microraptor gui and relatives clearly show well-developed flight feathers on the hind limbs as well as the front limbs. No modern vertebrate has hind limbs functioning as independent, fully developed wings; so, lacking a living example, little agreement exists on the functional morphology or likely flight configuration of the hindwing. Using a detailed reconstruction based on the actual skeleton of one individual, cast in the round, we developed light-weight, three-dimensional physical models and performed glide tests with anatomically reasonable hindwing configurations. Models were tested with hindwings abducted and extended laterally, as well as with a previously described biplane configuration. Although the hip joint requires the hindwing to have at least 20° of negative dihedral (anhedral), all configurations were quite stable gliders. Glide angles ranged from 3° to 21° with a mean estimated equilibrium angle of 13.7°, giving a lift to drag ratio of 4.1:1 and a lift coefficient of 0.64. The abducted hindwing model’s equilibrium glide speed corresponds to a glide speed in the living animal of 10.6 m·s−1. Although the biplane model glided almost as well as the other models, it was structurally deficient and required an unlikely weight distribution (very heavy head) for stable gliding. Our model with laterally abducted hindwings represents a biologically and aerodynamically reasonable configuration for this four-winged gliding animal. M. gui’s feathered hindwings, although effective for gliding, would have seriously hampered terrestrial locomotion.
biomechanics bird flight evolution feathered dinosaurs model tests tetrapteryx
Footnotes
1To whom correspondence should be addressed. E-mail: dalexander@ku.edu.
Author contributions: D.E.A., E.G., L.D.M., D.A.B., and A.R.F. designed research; D.E.A., E.G., L.D.M., D.A.B., and A.R.F. performed research; D.E.A. analyzed data; and D.E.A., L.D.M., and D.A.B. wrote the paper.
The authors declare no conflict of interest.
This article is a PNAS Direct Submission. A.F. is a guest editor invited by the Editorial Board.
This article contains supporting information online at www.pnas.org/cgi/content/full/0911852107/DCSupplemental.
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