Sinornithosaurus

What it was like

Sinornithosaurus was a small, feathered dromaeosaur, part of the same raptor-like family as Velociraptor and Microraptor. Like its relatives, it likely had long, grasping hands and a sickle-shaped claw on the second toe of each foot, tools probably used for gripping prey. Its body was covered in filament-like feathers, among the clearest early evidence that many small theropods were feathered, not scaly, animals. Its incomplete skeleton leaves its full body length uncertain.

Some researchers have argued that grooves on its teeth suggest it delivered venom into prey, though other scientists dispute this idea, and no agreement has been reached.

Its world

Sinornithosaurus lived from about 126 to 120 million years ago, during the Early Cretaceous, in what is now China. Its fossils come from the Yixian Formation, a site famous for extraordinary feathered dinosaur finds. It shared this world with other feathered dinosaurs such as Beipiaosaurus, Caudipteryx, and Sinosauropteryx, the plant eater Psittacosaurus, and the much larger, feathered predator Yutyrannus.

How it was found

Xu and colleagues named Sinornithosaurus in 1999, from fossils found in the Yixian Formation. Three fossil finds are known today. Its excellent preservation helped paleontologists study feather structure in a small, bird-like theropod, adding to the evidence that birds evolved from within this group of dinosaurs.