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 8 m (26 ft), 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).