A reappraisal of tyrannosauroid fossils from the Iren Dabasu Formation (Coniacian-Campanian), Inner Mongolia, People's Republic of China

The hind limb of the lectotype of Alectrosaurus olseni is described in comparison with other tyrannosauroids. In addition to the autapomorphies described for Alectrosaurus by previous workers, the taxon possesses a specialized pes, where the distal condyles of the metatarsals and most phalanges are strongly elevated beyond the dorsal and ventral surfaces of the shaft of each bone, described here as the 'pediculate' condition. In comparison with the lectotype, previously reported Alectrosaurus and Tyrannosaurus bataar material from the Turonian of Uzbekistan, and fossils from the Kyzylkum Desert, are not referable to Alectrosaurus. A partial skull from the Iren Dabasu Formation is not referable to A. olseni because of the lack of shared diagnostic bones between it and the lectotype. Several features are shared between the skull, the holotype of Raptorex, and an isolated juvenile T. rex lacrimal, to the exclusion of other derived tyrannosauroids.