In the early Cretaceous, a superb range of coelurosaurian fossils (including avians) are known from the Yixian Formation in Liaoning. All known theropod dinosaurs from the Yixian Formation are coelurosaurs. Many of the coelurosaurian lineages survived to the end of the Cretaceous period (about 65 Ma) and fossils of some lineages, such as the Tyrannosauroidea, are best known from the late Cretaceous. Most coelurosaur groups became extinct in the K/T extinction event. Only the Neornithes (modern birds) survived, and continued to diversify into the numerous forms found today.