Researchers today announced the discovery of a stunning new dinosaur fossil: a glider with wings similar to both birds and bats. It has been named Yi qi (meaning ‘strange wing’) and is a small feathered dinosaur from the Middle Jurassic age fossil beds of China that have yielded a host of important fossils in recent years. Yi qi, like so many other small dinosaurs, is preserved with a full coating of feathers and was a close relative of the lineage that ultimately gave rise to birds.

However, what sets this animal apart from numerous other dinosaurian gliders and proto-birds is the composition of its wings. In addition to some unusual feathers that are positioned on the long arms and fingers, there is a truly gigantic bone on each wrist that extends backwards, and between this bone and the fingers is preserved a membrane-like soft tissue that would have given the animal something of a wing, like that of bats.

Yi qi is not a direct ancestor of birds, and more particularly has nothing to do with the origins of the mammalian bats, but its wings are an excellent example of convergent evolution. At various times a great many animals have evolved a similar arrangement of a large bone in the wrist or hand and a supporting membrane, most obviously in numerous gliding mammal lineages. In addition to the bats that are capable of active powered flight, various passive gliders like flying squirrels, sugar gliders and the so-called “flying lemurs” have all independently evolved some extension that that helps to support a membranous wing. At some level then, this is a quite common feature, but it is a real shock to see it in such a dinosaur.

Professor Xu Xing, lead author of the study from the Institute of Vertebrate Paleontology and Paleoanthropology, Beijing said “It definitely evolved a wing that is unique in the context of the transition from dinosaurs to birds.”



The long rod-like wrist bone (longest on the photo) of the right hand of Yi qi. Some bits of membrane are present at the tip and numerous feathers are clearly preserved on the animal. Photograph: Zang Hailong

There are a number of feathered dinosaurs close to the origins of birds that are thought to have been some form of glider. All were small and light and had extensive feathers that would have formed the flight surface and allowed them to move effectively through the air. Yi qi is from a very odd group of small dinosaurs called scansoriopterygids, who are known from only two other specimens and little is known about their biology or lifestyle, so there is not much to go on. However, it is clearly remarkable that such an animal that had numerous other relatives with large feathers on their arms and would apparently “experiment” with different forms of flight at various times (not least ultimately producing birds) would take such a dramatically different route towards gliding, even if it was one commonly explored by other mammals.

The evolutionary implications are therefore quite incredible. There have already been suggestions that perhaps powered flight evolved multiple times in the dinosaurs and early birds, with perhaps several different groups making the final jump from gliding to a more active form of movement in the air. Given how few and far between the scansoriopterygids are as fossils, this implies that they never really got going as a group – certainly they are much more restricted in both time and space than their near relatives, so at first approximation the bat-bird combination of Yi qi did not lead to a major new radiation of dinosaurs.

However, quite how the animal may have flown is most unclear. The incomplete preservation of the wings and the uncertain position of the long wrist bone means that it could have had a very broad wing or a narrow one, and the flattened nature of the skeleton makes it hard to tell if this animal might have had the muscles and joints needed for powered flight. Professor Xu notes that “We don’t know if Yi qi was flapping, or gliding, or both”, but it does seem clear that the small size of the animal and large surface area of the wings and feathers would have permitted some form of aerial locomotion.

Dr Mike Habib of the University of Southern California, who was not involved in the study, said “All told, this is an unexpected, exciting specimen that changes our views on the evolution of flight in dinosaurs. It appears that multiple types of wing surfaces evolved within the relatives of birds, making the origins of avian flight potentially more complicated than previously thought.” That alone makes the origins of birds, already an area of intense study, a little more complicated and rather intriguing. The pathway to both birds and powered flight from small feathered dinosaurs, though with a few bumps and oddities on the way shows a relatively consistent progression but Yi qi adds a new twist with one evolutionary branch taking a dramatically different route into the air.

Xu et al., 2015. A bizarre Jurassic maniraptoran theropod with preserved evidence of membranous wings. Nature. DOI: 10.1038

