Dale Russell
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.