Analysis of Montana fossils shows the battling predator was a fully grown Nanotyrannus, not a young T rex Analysis of Montana fossils shows the battling predator was a fully grown Nanotyrannus, not a young T rex The fossilised remains of two dinosaurs locked in combat have unleashed a fresh drama, suggesting diminutive specimens thought to be teenagers of Tyrannosaurus rex could instead belong to separate, smaller species. The “duelling dinosaurs” fossil, which reveals a triceratops in battle