unchiujar writes to mention a BBC article about the design of the first flying dinosaurs. These possible early ancestors of avians apparently resembled biplanes in many ways, with legs hanging down in a fashion similar to WWI fighters. The researchers who made this discovery use this to argue the 'trees down' model of flight evolution, but the article points out this design may possibly be a failed evolutionary experiment. From the article: "Dr Chatterjee, from Texas Tech University in Lubbock, US, explained that two lines of evidence had led the team to this conclusion. Firstly, the researchers argue, dinosaurs and birds move their legs in a vertical plane, not sideways as the tandem flight pattern requires. Secondly, the feathers on Microraptor's hind legs are asymmetrical; one of the two vanes that extend either side of the shaft is narrower than the other. Aerodynamically, the narrow leading edge of these feathers should face forward in flight, against the direction of airflow. This would have given the flying reptiles lift. "