New information on cretaceous troodontids (Dinosauria, Theropoda) from the People's Republic of China

Troodontid specimens were recovered from three localities in China by the Sino-Canadian expeditions between 1987 and 1990. These include a Lower Cretaceous form (Sinornithoides youngi), which is the most complete troodontid skeleton ever found, isolated bones from the Iren Dabasu Formation (?Turonian), and partial skeletons of Saurornithoides mongoliensis from Djadokhta-equivalent beds (?Campanian). These, and other specimens recently described from North America, allow a better assessment of the phylogenetic position of troodontids than has been possible before. Although troodontids have autapomorphies that eliminate them from consideration as bird ancestors, they are nevertheless one of the closest avian outgroups within the Theropoda.