The tyrannosauroid fossil record is mainly restricted to Cretaceous sediments of Laurasia, although some very fragmentary Jurassic specimens have been referred to this group^{1, 2}. Here we report a new basal tyrannosauroid, Guanlong wucaii gen. et sp. nov., from the lower Upper Jurassic of the Junggar Basin^{3, 4}, northwestern China. G. wucaii is the oldest known tyrannosauroid and shows several unexpectedly primitive pelvic features^{5, 6}. Nevertheless, the limbs of G. wucaii share several features with derived coelurosaurs^{7, 8, 9}, and it possesses features shared by other coelurosaurian clades¹⁰. This unusual combination of character states provides an insight into the poorly known early radiation of the Coelurosauria. Notably, the presumed predatory Guanlong has a large, fragile and highly pneumatic cranial crest that is among the most elaborate known in any non-avian dinosaur and could be comparable to some classical exaggerated ornamental traits among vertebrates.

1. Institute of Vertebrate Paleontology and Paleoanthropology, Beijing 100044, China
2. American Museum of Natural History, New York, New York 10024, USA
3. Department of Biological Sciences, George Washington University, Washington DC 20052, USA
4. Department of Anatomical Sciences, Stony Brook University, Stony Brook, New York 11794, USA
5. Department of Biological Science, Florida State University, Tallahassee, Florida 32306, USA
6. Royal Tyrrell Museum, Drumheller, Alberta T0J 0Y0, Canada

Correspondence to: Xing Xu^1,2 Correspondence and requests for materials should be addressed to X.X. (Email: xingxu@vip.sina.com or Email: xu@amnh.org).

Received 12 October 2005; Accepted 5 December 2005

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