Reconstruction of the Hindlimb Locomotion of Confuciusornis (Aves) and Its Implication for the Origin of Avian Flight

As one of the most basal avian clades, the Confuciusornithids are ideal in revealing the early evolution of avian flight. Birds’ hindlimbs are functionally diverse and contain a wealth of information about their behavior. The hindlimb of Confuciusornis, however, has only been studied in detail in terms of functional morphology, and quantitative studies that directly assess locomotor ability are relatively lacking. This has led to certain controversies on the behavior of Confuciusornis. This paper reviews the debates over the life habits and take-off ability of Confuciusornis, which are closely related to their hindlimb function. Several methodologies adopted engineering techniques, including the geometrical analysis of long bones, physiological reconstruction of muscles, kinematic and kinetic characteristics estimating, and appendage locomotor mechanism analysis, are recommended for estimating the hindlimb functions of Confuciusornis. Considering that the fossil bones are fragile, irregular in shape, and usually deformed, it is appropriate to apply computer numerical simulation techniques to such studies. A sufficient functional quantitative study will help clarify early bird locomotor behavior, which will provide clues and evidence for further exploration of the origin of bird flight and early bird movement.