Albertosaurus diorama
Albertosaurus diorama, Royal Tyrell Museum, 27 Dec 2008.

Riley Black, writing for Smithsonian magazine, reports on new findings that tyrannosaurs dominated their ecosystems because juveniles and adolescents operated in different ecological niches. “The differences between adult and adolescent tyrannosaurs were so great that the animals almost lived like different species, pushing out mid-sized carnivores in a prehistoric takeover.” So instead of smaller carnivorous dinosaurs hunting smaller prey, you had younger tyrannosaurs.