Gallimimus was the largest of the ornithomimids. At 16-20 feet long and 650 pounds, it was a medium sized dinosaur. Gallimimus was also one of the fastest. They could run up to 65 miles per hour. These dinosaurs were probably omnivores. Their diet probably included small reptiles, insects, eggs, and the occasional plant. Gallimimus lived 80 million years ago in Asia.