FIGURE 1. Sinornithosaurus millenii, Holotype, IVPP V12811.
The posterior part of the skull is disarticulated from the snout and lower jaws and turned 180° in the opposite direction. The postcranial skeleton is also not articulated, but the bones retain a close association. Integumentary filaments have been displaced, lacking their direct relationships to bony elements.
Drawing of the specimen shown in Fig. 1
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 birds. 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 China. 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 up. The discovery of Sinornithosaurus widens the distribution of integumentary filaments among non-avian theropods. Phylogenetic analysis indicates that, among known theropods with integumentary filaments or feathers, Dromaeosauridae is the most bird-like, and is more closely related to birds than is Troodontidae.
Xu, Xing, Wang, Xiao-Lin, Wu, Xiao-Chun. 1999. A dromaeosaurid dinosaur with a filamentous integument from the Yixian Formation of China. Nature. 401:262-266.