Flight Evolved Repeatedly

Flight is so useful that nature invented it more than once. Across all animals, powered flight arose at least four separate times — in insects, pterosaurs, birds, and bats. Each lineage solved the same problem with completely different hardware: insect wings, leathery pterosaur and bat membranes, feathered bird wings. Birds were simply the version that came out of the dinosaurs and is still flying today.

Dinosaurs themselves tried several flight designs before birds won out. Microraptor had four feathered wings — front and back limbs both — and likely glided from tree to tree. Stranger still, Yi qi had bat-like skin membranes stretched over a long wrist bone instead of feathers. Both were dead ends. The theropod body turned out to be wonderfully adaptable, but only the two-winged, feathered design that became birds survived to the present.