Camoflauge would have been useful for this metre-long raptor as it hunted the forests of the early Cretaceous Period. Sinornithosaurus was recovered from China's fossil-rich Yixian formation. It represents one of the earliest and most primitive of the Dromaeosaurus. It is also one of the most bird-like of the feathered dinosaurs ever found. Whether the grooves along the teeth suggest Sinornithosaurus was venomous is still debated. Sinornithosaurus was closely related to the more famous Microraptor.