Genuine fossils with exquisitely preserved plumage from the Late Jurassic and Early Cretaceous of north-eastern China have recently revealed that bird-like theropod dinosaurs had long pennaceous feathers along their hindlimbs and may have used their four wings to glide or fly. Thus, it has been postulated that early bird flight might initially have involved four wings.
Link : https://link.springer.com/epdf/10.1007/s00114-017-1496-y?author_access_token=qK5jILmlXqTUfzaXSeOT4fe4RwlQNchNByi7wbcMAY5XtMiIuzLHT0w7pfMEQCqN57cyEs2GIzoqs5Z9sbEt05ydpRV-wedb1KJ5MwJh8Kg2RuubzDV9r0AJl8jBoI_iqK1-9ikzq8p8bOLVXyh_UA%3D%3D