Sinornithosaurus (derived from a combination of Latin and Greek, meaning 'Chinese bird-lizard') is a genus of feathered dromaeosaurid dinosaur from the early Cretaceous Period (late Barremian) of the Yixian Formation in what is now China. It was the fifth non–avian feathered dinosaur genus discovered by 1999. The original specimen was collected from the Sihetun locality of western Liaoning. It was found in the Jianshangou beds of the Yixian Formation, dated to 124.5 million years ago. Additional specimens have been found in the younger Dawangzhangzi bed, dating to around 122 million years ago. Xu Xing described Sinornithosaurus and performed a phylogenetic analysis which demonstrated that it is basal, or primitive, among the dromaeosaurs. He has also demonstrated that features of the skull and shoulder are very similar to Archaeopteryx and other Avialae. Together these two facts demonstrate that the earliest dromaeosaurs were more like birds than the later dromaeosaurs were. Sinornithosaurus was among the smallest dromaeosaurids, with the holotype measuring long and weighing . Description Specimens of Sinornithosaurus have preserved impressions of feathers both covering the entirety of the body and forming the wings. These feathers were indistinguishable in form from those found on birds from the same geological deposits. The body (contour) feathers were generally between 3–4.5 cm long and included two types: the first type are formed of several filaments joined into "tufts", similar to modern down feathers. The second type, including those on the arms, were composed of rows of filaments (barbs) joined along a main shaft (rachis), making them similar in structure to modern bird feathers. However, unlike the wing feathers of flying birds, they did not have the secondary branches with tiny little hooks (barbules) that flight feathers have, which allow the flight feathers to form a continuous vane. Some scientists have suggested that the feathers might have allowed Sinornithosaurus to glide for short distances after leaping from trees. A 2010 study indicated that Sinornithosaurus may have had feathers which varied in color significantly across different regions of the body, based on analysis of microscopic cell structures in preserved fossils. Based on the rod and spherical melanosomes found in some samples, scientists have interpreted that Sinornithosaurus had black and rufous feathers. Paleobiology Possible venomous bite In 2009, a team of scientists led by Empu Gong examined a well-preserved Sinornithosaurus skull, and noted several features suggesting it was the first-identified venomous dinosaur. Gong and colleagues noted that