Gallimimus

Resembling a giant ostrich, Gallimimus bullatus was the largest of the bird-mimic dinosaurs, reaching about 6 meters and near 440 kilograms. Its long, slender legs made it one of the swiftest dinosaurs, with running speeds estimated around 56 kilometers per hour. A toothless beak and lightly built skull point to an omnivorous diet of plants, insects, and small animals. Rinchen Barsbold and colleagues described it in 1972 from the Gobi Desert of Mongolia, where it lived during the Late Cretaceous, roughly 100 to 66 million years ago. It remains the best-known member of the ornithomimosaur group.