Aerodynamic Characteristics of a Feathered Dinosaur Measured Using Physical Models. Effects of Form on Static Stability and Control Effectiveness

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.

An integrative approach to understanding bird origins

“…6) are consistent with the gravityassisted hypothesis for the origin of bird flight. Moreover, the concurrent presence of a large and flattened tail, along with potential use of the feathered hind legs in aerodynamic control, suggests substantial capacity for using these as rudders and for maneuvering even during the earliest stages of bird evolution (10,144). Aerial righting reflexes, targeting movement while aloft, and controlled landings all would have been enhanced via bilaterally asymmetric motions of either wing pair.…”

“…The increasing interest in the origins of birds from developmental biology and other disciplines has enriched our understanding of this important evolutionary event (8,10,11), and alternative evolutionary models on various aspects of the origin of birds have sometimes been provided based on neontological data (4,11). However, any evolutionary model must be tested using the fossil record.…”

“…Recent discoveries of spectacular dinosaur fossils from China and elsewhere ( Fig. 1) provide significant new information to address these issues and also prompt numerous studies in disciplines other than paleontology to explain how bird characteristics originated and evolved (4)(5)(6)(7)(8)(9)(10)(11). Whereas these new discoveries and studies have addressed many issues on the origin of birds, they also open new research directions.…”

Ontogeny of aerial righting and wing flapping in juvenile birds

“…Documentation of additional manoeuvering abilities early in development, such as pitching, yawing or aerial displacement towards targets of interest would add further indirect support to this hypothesis. Palaeontological documentation of hind wings in ancestral paravian taxa [16] further suggests a concurrent diversity of aerodynamic function [6]. More generally, manoeuvring is clearly important for any animal exhibiting rudimentary aerial capacity [7], even in the complete absence of wings [1][2][3][4][5].…”

Global dynamics of non-equilibrium gliding in animals

“…Other phase-space structures, such as the terminal velocity manifold and the acceleration along it, likely confer other stability or energetic advantages. Detailed wind tunnel measurements of aerodynamic coefficients of Microraptor gui [44] can be used in the framework presented here to quanti fy how phase-space structures lead to variable glide performance between prehistoric and modern gliders.…”