Bird flight began to evolve some 150 million years ago. This chapter discusses typical structures of the oldest bird-like fossils of Archaeopteryx. Conflicting scenarios — the arborial and cursorial — describe how flight might have evolved. A new hypothesis is offered that explains most of the peculiar anatomical features, and suggests a matching ecological niche. Archaeopteryx is depicted to run like a Basilisk lizard over water. A quantitative biomechanical assessment shows that it could have generated the lifting forces required using spread wings and tail. Abundant water skaters from the same deposits are suggested as a possible food source. The remains of younger Mesozoic bird-like animals reveal the existence of parallel lines of evolution of flight related characters. A few groups of flying birds survived the mass extinction 65 million years ago, and were ancestral to the extant birds rapidly radiating during the beginning of the Tertiary.
Keywords: Archaeopteryx, arborial scenario, cursorial scenario, anatomy, Basilisk lizard, biomechanics, water skaters, Mesozoic birds, modern birds