Microraptor, the four-winged dinosaur

Microraptor carries long asymmetric flight feathers not only on its arms but on its legs, an arrangement with no living parallel and no obvious ancestor. Reconstructions have argued for gliding, for powered flight, and for a biplane-like stacked configuration; none has fully won. Its melanosomes indicate iridescent black plumage, and preserved gut contents include fish, birds and a mammal, showing a generalist predator. It matters because it demonstrates that the invention of aerodynamic feathers was messier and more experimental than a straight line from ground to air.