Abstract
We report the effects of posture and morphology on the static aerodynamic stability and control effectiveness of physical models based on the feathered dinosaur, Microraptor gui, from the Cretaceous of China. Postures had similar lift and drag coefficients and were broadly similar when simplified metrics of gliding were considered, but they exhibited different stability characteristics depending on the position of the legs and the presence of feathers on the legs and the tail. Both stability and the function of appendages in generating maneuvering forces and torques changed as the glide angle or angle of attack were changed. These are significant because they represent an aerial environment that may have shifted during the evolution of directed aerial descent and other aerial behaviors. Certain movements were particularly effective (symmetric movements of the wings and tail in pitch, asymmetric wing movements, some tail movements). Other appendages altered their function from creating yaws at high angle of attack to rolls at low angle of attack, or reversed their function entirely. While M. gui lived after Archaeopteryx and likely represents a side experiment with feathered morphology, the general patterns of stability and control effectiveness suggested from the manipulations of forelimb, hindlimb and tail morphology here may help understand the evolution of flight control aerodynamics in vertebrates. Though these results rest on a single specimen, as further fossils with different morphologies are tested, the findings here could be applied in a phylogenetic context to reveal biomechanical constraints on extinct flyers arising from the need to maneuver.
Highlights
The evolution of flight in vertebrates, and in birds, is the subject of lively debate and considerable speculation
Flight ability of extinct vertebrates is often inferred from very simple parameters; these alone may not be sufficient measures of aerodynamic performance because animals flying in real environments will experience perturbations and the need to maneuver around obstacles [1]
We cannot observe the behavior of extinct animals, we can measure the aerodynamic forces on dynamically-scaled physical models in a wind tunnel to quantify the broader effects on performance of different postures and morphologies
Summary
The evolution of flight in vertebrates, and in birds, is the subject of lively debate and considerable speculation. Flight ability of extinct vertebrates is often inferred from very simple parameters (such as lift and drag coefficients and glide angles); these alone may not be sufficient measures of aerodynamic performance because animals flying in real environments will experience perturbations and the need to maneuver around obstacles [1]. Discoveries [2,3,4,5,6,7,8] during the last decade of a diversity of feathered dinosaurs and early birds from the Mid-Late Jurassic through the Cretaceous of Liaoning, China have led to considerable speculation about the roles that the feathers played on these extinct animals. Since physical laws apply to all taxa, regardless of history, knowing about the physical implications of shape can suggest suitable prior assumptions (for example, plesiomorphies; starting estimates for aerial performance within a clade; other limits based on performance that can be ruled out) that should apply in comparative studies of physically-constrained, aerially maneuvering animals of similar shape
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