It is not easy to assess the speed of an extinct animal and the different estimates may differ according to the calculation method. There are two rules most used. The first is to compare the speed of today's dinosaur-like animals in body size and shape. The second involves the analysis of the fossilized traces: from the calculation of the distance of the footprints it is possible to estimate the speed. For a precise calculation, however, it is also necessary to know the length of the legs and it is not always easy to find fossilized bones next to the footprints.
Record. The fastest were the bipedal carnivorous dinosaurs with slender legs and light bodies. Among these, ornithomimids (dinosaurs with an ostrich-like appearance) probably reached 70 km / h.
The slowest would have been the large herbivorous dinosaurs like the stegosaurus that at most could have kept up with a man who normally walks (about 6 km / h); the great sauropods like the Apatosaurus probably moved like the modern elephants.
Furthermore, according to the most recent studies, the structure of the Tyrannosaurus rex's legs would not have allowed it to exceed 40 km / h. The scene of the movie "Jurassic Park" in which the dinosaur reaches a car traveling at 70 km / h would therefore have to be redone.