1. Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences, Beijing 100044, China
2. American Museum of Natural History, New York 10024, USA
3. Tianjin Museum of Natural History, Tianjin 300074, China
4. Present address: American Museum of Natural History, Central Park West at 79th Street, New York City, New York 10024, USA

Correspondence to: Xing Xu^1,4Mark A. Norell² Email: xu@amnh.org
Email: xingxu@vip.sina.com
Email: norell@amnh.org

Abstract

Tyrannosauroids are one of the last and the most successful large-bodied predatory dinosaur groups^{1, 2, 3, 4, 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, 7, 8, 9}. It shows a mosaic of characters, including a derived cranial structure resembling that of derived tyrannosauroids^{1, 2, 3, 4, 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.

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