Basal tyrannosauroids from China and evidence for protofeathers in tyrannosauroids

摘要

Tyrannosauroids are one of the last and the most successful large-bodied predatory dinosaur groups(1-5), but their early history remains poorly understood. Here we report a new basal tyrannosauroid from the Early Cretaceous Yixian Formation of western Liaoning, China, which is small and gracile and has relatively long arms with three-fingered hands. The new taxon is the earliest known unquestionable tyrannosauroid found so far(6-9). It shows a mosaic of characters, including a derived cranial structure resembling that of derived tyrannosauroids(1-5) and a primitive postcranial skeleton similar to basal coelurosaurians. One of the specimens also preserves a filamentous integumentary covering similar to that of other coelurosaurian theropods from western Liaoning. This provides the first direct fossil evidence that tyrannosauroids had protofeathers.