 Tyrannosaurids walked exclusively on their hindlimbs , so their leg bones were massive . In contrast to the forelimbs , the hindlimbs were longer compared to body size than almost any other theropods . Juveniles and even some smaller adults , like more basal tyrannosauroids , had longer tibiae than femora , a characteristic of fast @-@ running dinosaurs like ornithomimids . Larger adults had leg proportions characteristic of slower @-@ moving animals , but not to the extent seen in other large theropods like abelisaurids or carnosaurs . The third metatarsals of tyrannosaurids were pinched between the second and fourth metatarsals , forming a structure known as the arctometatarsus . 
