Yi qi, the new "bat-winged" dinosaur
The image below is a hot off the press illustration of a brand new dinosaur described last week in Nature
. The artwork is by John Conway (check out the rest of his site, it's mighty impressive). The new animal is called Yi qi
(which comes from "strange wing" in Mandarin - "qi" means strange and "Yi" that means wing).
What makes Yi qi
so special is that it appears to have been a small, feathered dinosaur with membranous wings
. Previously, all known dinosaur wing surfaces (including those of birds) were primarily composed of feathers. A membrane wing is a novelty for a dinosaur (though, of course, both bats and pterosaurs had membrane wings, along with a host of unpowered flyers, so membrane wings are well known among vertebrates).
The original paper is located at: http://www.nature.com/nature/journal/vaop/ncurrent/full/nature14423.html
Sadly, the paper is paywalled. However, some excellent popular articles on the new find can be found at: http://phenomena.nationalgeographic.com/2015/04/29/chinese-dinosaur-had-bat-like-wings-and-feathers/http://www.theguardian.com/science/lost-worlds/2015/apr/29/bird-yi-qi-the-dinosaur-evolution-flight-feather-naturehttp://www.smithsonianmag.com/science-nature/fluffy-little-dinosaur-had-bat-wings-180955122/?no-ist
(full disclosure, I supplied all of those authors with feedback on the specimen, and I am quoted in all three articles. I did not receive any pay for my involvement)+Emily Willoughby
has also done a wonderful illustration, with a different wing attachment: https://plus.google.com/+EmilyWilloughby/posts/PigMErV4aTv
Below are some of my more extended thoughts on the new fossil specimen. Some of these comments were supplied to the magazines listed above, so you will find some redundancy with the online magazine quotes:Yi qi
is a scansoriopterygid, and they are strange animals by any measure. That said, this new specimen is fantastically strange compared to other theropod dinosaurs. It has what appears to be traces of a membrane wing preserved, which was not anticipated for a close relative of birds.Yi qi
is not necessarily as weird in an evolutionary sense as it might first seem. Yi qi
was a member of a group of feathered dinosaurs near the origin of birds. Living birds have membranes around their forelimbs, including a well developed membrane in front of the elbow called a propatagium. In birds, feathers cover and imbed in the membranous parts of the wing, obscuring the soft tissues and making up most of the wing surface.
It has been often assumed that in the lineages near (and including) birds, the wings evolved with a more or less continuous enlargement of the feather surfaces, and that the membranes in the wing never became more elaborate than in living birds. In Yi qi
, however, the membranous part of the forelimbs has been expanded and elaborated far beyond the extent of the feathers, by way of a bizarre "extra" bone from the wrist. In a sense, the lineage containing Yi qi
has built a wing using the same basic parts that birds use to build their wings, but this lineage has expanded the membrane, rather than the feathers. The effect is something a bit like an odd bat-like or pterosaur-like wing, with some feathery covering near the leading edge (similar to the fur on the wings of some bats).
While the new specimen is very exciting, there is a lot we don't know. Because the original orientation of the weird long wrist bone (called a styliform element) isn't known, there is no way to tell if Yi qi
had a broad, bat-like wing, or a much slimmer membrane. If the membrane was broad, then Yi qi
probably would have had enough wing surface to fly (at speeds it could plausibly reach - almost any flat surface will fly if it get it going fast enough) and it would have been relatively stable in pitch while in the air. The broad wing orientation would provide a low enough flight speed for Yi qi
to plausibly launch and land safely. But under the more conservative membrane estimates, Yi qi
would have had a serious positive pitching moment (nose up) unless it could sweep the forelimbs backwards quite substantially. It would also need to fly (or flap) very fast to stay airborne with the slimmer wing profile, and that would mean reaching quite high speeds when launching (i.e. it would need to be a surprisingly good leaper). The anatomy of the upper arm and thorax do not appear to be consistent with powered flight (i.e. flapping flight), but the preservation of the material is insufficient to conclude that with certainty (for example, the available pectoral muscle mass was probably small, and reinforcement of the thorax against compressive loads seems to be lacking. The humerus also seems to lack reinforcement against the torsional loads that dominate during powered flight).
The strange styliform element was subjected to chemical analysis, and it seems to have been bone-like, but not identical to the bone material of the fingers. It may have been comprised of lower stiffness bone or cartilage, allowing it to bend slightly when the membrane was tensioned under aerodynamic load or by muscle forces. That may seem like a minor feature, but it's a key component in making a membrane wing work effectively.
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.