Four-Winged Dinosaurs, Bird Precursors, or Neither?

Abstract

N fossil specimens from the Early Cretaceous lakebeds of Liaoning, in northeastern China, are once again bridging and even overturning what we thought we knew about various aspects of vertebrate evolution. Or are they? The latest finds are of a small carnivorous dinosaur called Microraptor gui, which is very close to the first birds. This discovery, reported by Xu Xing and his colleagues in a recent issue of Nature (2003), is not the first discovery of Microraptor. But it is unusual in several respects. Most notably, the animal seems to have very long feathers attached to the hind limbs, as well as to the arms and tail. The authors infer that these feathers effectively created a “four-winged” gliding planform and that this should be seen as an incipient stage in the origin of bird flight. Moreover, they conclude, it supports the idea that bird flight began in the trees. There are amazing features about this discovery, and if the claims for them pan out, the specimens are potentially as important as Archaeopteryx. The feathering in this nonavian dinosaur is more extensive than we’ve ever seen, and the size of the animal is getting closer to the optimal that is necessary to start evolving flight. It’s an incredible discovery, the kind of thing that we’ve wished for—well, for centuries now. That said, some inferences that the authors make aren’t yet convincing, based on the evidence presented. This is a problem with the required brevity of articles in Nature, not necessarily with the evidence itself, but the case will have Four-Winged Dinosaurs, Bird Precursors, or Neither?