Trying to estimate the speed of animals dead for more than 65 million years is difficult, but some generalizations are rather clear from the shape and size of dinosaur skeletons. For example, immense sauropods, such as Apatosaurus and Diplodocus with their massive bodies and columnar leg structure, were probably not fast runners other than in short bursts. Conversely, lighter and relatively long-limbed theropods, such as Velociraptor and ornithomimids (or "ostrich-mimic dinosaurs") were probably capable of running at high, sustained speeds.