 Long filamentous structures have been preserved along with skeletal remains of numerous coelurosaurs from the Early Cretaceous Yixian Formation and other nearby geological formations from Liaoning , China . These filaments have usually been interpreted as " protofeathers , " homologous with the branched feathers found in birds and some non @-@ avian theropods , although other hypotheses have been proposed . A skeleton of Dilong was described in 2004 that included the first example of " protofeathers " in a tyrannosauroid . Similarly to down feathers of modern birds , the " protofeathers " found in Dilong were branched but not pennaceous , and may have been used for insulation . The discovery and description of the 9 meter ( 30 ft ) feathered tyrannosauroid Yutyrannus in 2012 indicates the possibility large tyrannosaurids were also feathered as adults . 
