The largest known "Tyrannosaurus rex" skulls measure up to in length. Large openings ('fenestrae') in the skull reduced weight and gave places for muscle attachment, as in all carnivorous theropods. But in other respects "Tyrannosaurus"<nowiki>'</nowiki>s skull was significantly different from those of large non-tyrannosaurid theropods. It was extremely wide at the rear but had a narrow snout. This permitted good binocular vision. The skull bones were massive. Some bones were fused, preventing movement between them; but many were pneumatized, with a "honeycomb" of tiny air spaces. This may have made the bones more flexible as well as lighter. These features are part of the tyrannosaurid trend towards an increasingly powerful bite. Its bite easily surpassed that of all non-tyrannosaurids. 