Gallimimus was one of the largest of the ornithomimids. At 16-23 feet long and 650 pounds, it was a medium sized dinosaur overall. Gallimimus was also one of the fastest. They could possibly run up to 45 miles per hour. These dinosaurs were probably omnivores. Their diet likely included small reptiles, insects, eggs, and the occasional plant. Gallimimus lived 80 million years ago in Asia.