The year 2009 in Archosaur paleontology was eventful. Archosaurs include the only living dinosaur group — birds — and the reptile crocodilians, plus all extinct dinosaurs, extinct crocodilian relatives, and pterosaurs. Archosaur paleontology is the scientific study of those animals, especially as they existed before the Holocene Epoch began about 11,700 years ago. The year 2009 in paleontology included various significant developments regarding archosaurs.

Sinotyrannus is a genus of large basal tyrannosauroid dinosaur, known from a single incomplete fossil specimen including a partial skull, from the Early Cretaceous Jiufotang Formation of Liaoning, China. Specifically, it is a member of the Proceratosauridae, a family that originated in the Jurassic whose members are known from Europe and Asia. Though it is not significantly younger than primitive tyrannosauroids such as Dilong, it is similar in size to later forms such as Tyrannosaurus. It was much larger than contemporary tyrannosauroids, reaching a total estimated length of 9–10 m (30–33 ft), and was the largest known theropod from the Jiufotang Formation. The type species, S. kazuoensis, was described by Ji et al. in 2009.