Sinornithosaurus millenii (Ji et al. 2001, NGMC 91, Early Cretaceous, Aptian, 122 mya, 90-120cm) was originally considered a basal droamaeosaurid like Velociraptor . In the large reptile tree it nests with Microraptor in the clade of Tyrannosaurus.

Xu, Wang and Wu (1999) described another specimen and noted similarities to Archaeopteryx.

Sinornithosaurus has fewer and smaller feathers than Microraptor.

The skull of the Sinornithosaurus holotype (Xu et al. 1999, IVPP V12811) and reconstructions by Gong et al. 2010 and using DGS (color). Gong et al. considered grooves in the teeth ideal for venom delivery. Another study (Gianenchini et al 2010) disputed this.

Gianechini FA, Agnolín FL and Ezcurra MD 2010. A reassessment of the purported venom delivery system of the bird-like raptor Sinornithosaurus. Paläontologische Zeitschrift, in press. doi:10.1007/s12542-010-0074-9

Gong E, Martin LD, Burnham DA and Falk AR 2010. The birdlike raptor Sinornithosaurus was venomous. PNAS 107(2):766-768.

Ji Q, Norell MA, Gao KQ, Ji S-A and Ren D 2001. The distribution of integumentary structures in a feathered dinosaurs. Nature, 410(6832): 1084-1087.

Xu X, Wang X-L, Wu X-C. 1999. A dromaeosaurid dinosaur with a filamentous integument from the Yixian Formation of China. Nature 401:262-266 16 September 1999.

wiki/Sinornithosaurus