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A dromaeosaurid dinosaur with a filamentous integument from the Yixian Formation of China

Abstract

Dromaeosaurids, despite their notoriety, are poorly characterized meat-eating dinosaurs, and were previously known only from disarticulated or fragmentary specimens1. Many studies have denied their close relationship to birds2,3. Here we report the best represented and probably the earliest dromaeosaurid yet discovered, Sinornithosaurus millenii gen. et sp. nov., from Sihetun, the famous Mesozoic fish–dinosaur–bird locality in China4,5. Sinornithosaurus not only greatly increases our knowledge of Dromaeosauridae but also provides evidence for a filamentous integument in this group. It is remarkably similar to early birds postcranially. The shoulder girdle shows that terrestrial dromaeosaurids had attained the prerequisites for powered, flapping flight6, supporting the idea that bird flight originated from the ground up7,8. The discovery of Sinornithosaurus widens the distribution of integumentary filaments among non-avian theropods5,9,10. Phylogenetic analysis indicates that, among known theropods with integumentary filaments or feathers2,5, Dromaeosauridae is the most bird-like, and is more closely related to birds than is Troodontidae.

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Figure 1: S. millenii, Holotype, IVPP V12811.
Figure 2: S. millenii.
Figure 3: S. millenii, skull with lower jaws.
Figure 4: S. millenii, selected elements of the postcranial skeleton.
Figure 5: Cladogram showing phylogenetic relationships of Dromaeosauridae (including Sinornithosaurus) within the derived theropods.

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Acknowledgements

We thank the participants of the Liaoxi Project of the IVPP; P. J. Currie and H. Osmólska for sharing unpublished information and providing references; and L.-H. Hou, Z.-H. Zhou, H. Osmólska, P. J. Currie, D. B. Brinkman, L. M. Witmer, A. P. Russell and P. Sereno for discussions. We also thank the Royal Tyrrell Museum of Palaeontology for allowing X.-C.W. access to facilities. S.-H. Xie prepared the specimen and G.-H. Cui took the photograph. This work was supported by research grants from the Chinese Academy of Sciences and Chinese Natural Science Foundation and an operating grant from the Natural Science and Engineering Research Council of Canada to A.P.R.

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Correspondence to Xiao-Chun Wu.

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Xu, X., Wang, XL. & Wu, XC. A dromaeosaurid dinosaur with a filamentous integument from the Yixian Formation of China. Nature 401, 262–266 (1999). https://doi.org/10.1038/45769

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