Competing interests statement The authors declare that they have no competing financial interests. Gregory M. Erickson 1,2 , Peter J. Makovicky 3 , Philip J. Currie 4 , Mark A. Norell 2 , Scott A. Yerby 5 & Christopher A. Brochu 6 Correspondence and requests for materials should be addressed to J.M.M. (james.murphy@metoffice.com). NATURE | VOL 430 | 12 AUGUST 2004 | www.nature.com/nature Supplementary Information accompanies the paper on www.nature.com/nature.