Research published in the journal Science has revealed the existence of a tiny tyrannosaur that lived alongside Tyrannosaurus rex at the end of the Cretaceous. The study analyzed 17 tyrannosaurid specimens ranging from juveniles to massive adults, using advanced statistical algorithms and special bone lighting that revealed hidden annual rings. Tyrannosaurus rex did not reach its full size of around 8 tons until it was 40 years old, which is 15 years longer than previous studies based on an age of 25 years predicted. This slower and more stable growth allowed younger tyrannosaurs to occupy different ecological niches in the environment. Some specimens previously thought to be T. rex may belong to other species in the tyrannosaurid complex. The findings come from the most comprehensive histological analysis of the growth of these predators.