Although the dinosaurian hypothesis of bird origins is widely accepted, debate remains about how the ancestor of birds first learned to fly. Here we provide new evidence suggesting that basal dromaeosaurid dinosaurs were four-winged animals and probably could glide, representing an intermediate stage towards the active, flapping-flight stage. The new discovery conforms to the predictions of early hypotheses that proavians passed through a tetrapteryx stage.
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We thank L. Witmer and A. Milner for their suggestions and comments, M. Norell, X.-J. Ni, J. Liu, J. Clarke and P. Sereno for discussions, Y.-L. Huo, Y.-T. Li and H.-J. Wang for preparing the specimens, R.-S. Li for drawings, and Z.-G. Sun and B. An for help with CT scanning. Thanks also go to members of the Liaoxi expedition team of the IVPP for fieldwork. This work was supported by grants from the National Natural Science Foundation of China, the National Geographic Society, Special Funds for Major State Basic Research Projects of China, and the Chinese Academy of Sciences.
The authors declare that they have no competing financial interests.
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Xu, X., Zhou, Z., Wang, X. et al. Four-winged dinosaurs from China. Nature 421, 335–340 (2003). https://doi.org/10.1038/nature01342
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