ABSTRACT The dinosaur remains from the Upper Cretaceous Lance Formation of Wyoming, USA, have been known since 1870. Most of the fossils that are attributed to theropod dinosaurs are fragmentary skeletons consisting of cranial, axial and appendicular elements, and many isolated teeth are also known. The largest known theropod of the Lance Formation dinosaur fauna is Tyrannosaurus rex. Numerous specimens of this taxon are known from the Maastrichtian strata of the northwestern United States and southwestern Canada. In 1890 and 1892, two pedal phalanges of the left foot and several isolated teeth identified here as belonging to Tyrannosaurus were discovered near Lusk, Wyoming, by John Bell Hatcher and the prospecting party from Yale Univeristy's Peabody Museum of Natural History in New Haven, Connecticut, USA. The discovery of these fossils is significant. One of the first discoveries of Tyrannosaurus from Wyoming, it predates all other discoveries and naming of this taxon in the coeval Hell Creek Formation...