Arkansaurus is a genus of ornithomimid theropod known for fossils in Arkansas. The name used to be informal until it was official in March 2018. It was a related to Ornithomimus, Velociraptor, Birds and Tyrannosaurus, suggesting a coelurosaur. The leg bones were very elongated, and thin like those of birds. Arkansaurus lived in the Cretaceous time period.