Gallimimus was a large, fast-running dinosaur that lived during the Late Cretaceous period, around 70 million years ago. It belonged to a group called ornithomimids, which are known for their bird-like features. Gallimimus could reach lengths of up to 20 feet and had long legs, a slender body, and a small head with a beak-like mouth. This dinosaur is believed to have been an omnivore, feeding on plants, insects, and small animals. Fossils of Gallimimus have been found in Mongolia, providing valuable insights into its habitat and behavior. Its speed and agility likely helped it escape predators and find food.