 In the Dinosaur Park Formation , Gorgosaurus lived alongside a rarer species of the tyrannosaurine Daspletosaurus . This is one of the few examples of two tyrannosaur genera coexisting . Similarly @-@ sized predators in modern predator guilds are separated into different ecological niches by anatomical , behavioral or geographical differences that limit competition . Niche differentiation between the Dinosaur Park tyrannosaurids is not well @-@ understood . In 1970 , Dale Russell hypothesized that the more common Gorgosaurus actively hunted fleet @-@ footed hadrosaurs , while the rarer and more troublesome ceratopsians and ankylosaurians ( horned and heavily armoured dinosaurs ) were left to the more heavily built Daspletosaurus . However , a specimen of Daspletosaurus ( OTM 200 ) from the contemporaneous Two Medicine Formation of Montana preserves the digested remains of a juvenile hadrosaur in its gut region . Unlike some other groups of dinosaurs , neither genus was more common at higher or lower elevations than the other . However , Gorgosaurus appears more common in northern formations like the Dinosaur Park , with species of Daspletosaurus more abundant to the south . The same pattern is seen in other groups of dinosaurs . Chasmosaurine ceratopsians and hadrosaurine hadrosaurs are also more common in the Two Medicine Formation of Montana and in southwestern North America during the Campanian , while centrosaurines and lambeosaurines dominate in northern latitudes . Holtz has suggested that this pattern indicates shared ecological preferences between tyrannosaurines , chasmosaurines and hadrosaurines . At the end of the later Maastrichtian stage , tyrannosaurines like Tyrannosaurus rex , hadrosaurines like Edmontosaurus and chasmosaurines like Triceratops were widespread throughout western North America , while albertosaurines and centrosaurines became extinct , and lambeosaurines were rare . 
