Gallimimus (/ˌɡælᵻˈmaɪməs/GAL-i-MY-məs; meaning "chicken or rooster mimic") is a genus of ornithomimid theropod dinosaurs from the late Cretaceous period (Maastrichtian stage) Nemegt Formation of Mongolia. With individuals as long as 8m (26ft), it was one of the largest ornithomimosaurs. Gallimimus is known from multiple individuals, ranging from juvenile (about 0.5 m tall at the hip) to adult (about 2 m tall at the hip).