 Tyrannosaurid skull anatomy is well understood as complete skulls are known for all genera but Alioramus , which is known only from partial skull remains . Tyrannosaurus , Tarbosaurus , and Daspletosaurus had skulls which exceeded 1 metre ( 3 ft 3 in ) in length , The largest discovered Tyrannosaurus skull measures up to 1 @.@ 45 metres ( 4 ft 9 in ) long . Adult tyrannosaurids had tall , massive skulls , with many bones fused and reinforced for strength . At the same time , hollow chambers within many skull bones and large openings ( fenestrae ) between those bones helped to reduce skull weight . Many features of tyrannosaurid skulls were also found in their immediate ancestors , including tall premaxillae and fused nasal bones . 
