Genus: Sinornithosaurus XU, WANG & WU, 1999
Etymology: Sinornithosaurus derived from Sin-Ornitho-Saurus, meaning a bird-like dinosaur form China.

Species: millenii XU, WANG & WU, 1999
Etymology: Millenii derived from Millennium, Latin for one-thousand years, referring to its discovery near the end of the twentieth century.

Holotype: IVPP V12811

Locality: Sihetun, Shangyuan, Beipaio City, Western Liaoning Province, China.

Horizon: Layer 6, Horizon 1, Lower part of the (Chaomidianzi) Yixian Formation, Jehol Group.

Biostratigraphy: Psittacosaurus Fauna, Confuciusornis Avifauna.

Age: Valanginian Stage, Upper Neocomian Subepoch, Early Early Cretaceous Epoch, Early Cretaceous.

Material: Crushed skull and fragmentary skeleton.
Note: With feather impressions, and skin impressions (McNAMARA, ZHANG, KEARNS, ORR, TOULOUSE, FOLEY, HONE, ROGERS, BENTON, JOHNSON, XU & ZHOU, 2018).