There are several theories on how early feathered animals developed flight. One theory states that gliding creatures increased their surface area from the body outward, but flying animals increased it away from their center of gravity, giving them lift and more maneuverability to escape predators. Another theory states that wing motions evolved from the hunting techniques of the coelurosaurs. The skeletal structure of these dinosaurs allowed them to swing their arms down from above and behind their shoulders, allowing for easier grabbing of prey. Both these theories imply that birds developed flight from the ground up, not from the trees down, which is also known as the cursorial theory.

Other paleontologists believe that flight developed in animals that lived in trees (the arboreal, or tree, theory); jumping out of these trees provided enough acceleration to generate lift. Still others believe that some animals ran and flapped their wings, increasing their angle of attack on the down stroke and generating enough lift to fly, especially if they were running downhill.