Some early birds may have had four wings.

Chinese paleontologists have analyzed the fossil remains of 11 four-winged specimens of early birds. The creatures lived about 130 million years ago, and could offer insight into dinosaurs’ transformation into the birds that we live with today.

The study was published in the journal Science on Thursday and may help explain how dinosaurs grew feathers and learned to fly. The scientists claim that the fossils they discovered belonged to bird-like dinosaurs that had already begun to shed their hind leg feathers and grow scaly legs resembling those of modern birds.

The actual use for the feathered rear legs isn’t clear, but the researchers have theories. They describe the rear wings as “aerodynamic in function, providing lift, creating drag and/or enhancing maneuverability, and thus played a role in flight.”

The research was conducted at the Institute of Vertebrate Paleontology and Paleoanthropology in Beijing, and led by Zheng Xiaoting of the Shandong Tianyu Museum of Nature. The researchers studied fossils from the northeastern China's Liaoning Province. The fossils analyzed include Sapeornis, Yanornis and Confuciusornis species that lived during the early Cretaceous period, reports the New York Times.

Feathered dinosaur birds (or bird dinosaurs?) with feathered back legs were first discovered in China in 2001, when paleontologists found fossils of Microraptor and Sinonithosaurus. These are widely believed to have used their feathered rear legs for aerial locomotion, for flight or for gliding between and parachuting down from trees.

Unfortunately, the way the fossils have been preserved makes it difficult to fully understand how and where the birds’ feathers were located on the legs. The fossilized remains are preserved only in two dimensions, with the legs splayed out to the side of body, or folded underneath.