Evolution of Flight

Abstract

There are two major conflicting hypotheses about the origin of powered flight in vertebrates, the arboreal (``trees-down'') and cursorial (``ground-up'') theories. According to the arboreal theory, powered flight in birds, bats and pterosaurs evolved via gliding in tree-living animals, while the cursorial theory holds that flapping flight in birds evolved in ground-running and jumping animals without a gliding intermediate.