Gallimimus (Gallimimus bullatus) dinosaur incubating eggs, artwork. This species of dinosaur lived during the late Cretaceous, 70-65 million years ago. It belongs to the ornithomimosauridgroup of extinct animals. These were ostrich-like dinosaurs, which had long necks, small heads and toothless beaks. Gallimimus grew to a length of 4- 6 metres and weighed up to 440 kilograms. Its long legs and short toes suggest that it was a fast runner.