The path to flight in modern birds was full of forks, twists and dead ends.
Bird Flight
PDF) How birds fly according to Newtonian physics.
Giant flying murder heads' and other creatures that ruled the ancient sky
Flying Creatures: Created or Evolved?
National Museum of Natural History Blog Smithsonian Magazine
The reason birds are programmed to fly is all in their DNA and neural networks
Pictorial model of Archaeopteryx illustrating the generating of lift
Nature curiosity: How do birds learn to fly?, learn fly
The story of John Herrington, the 1st Native American in space