Which was the fastest dinosaur?

This is an impossible question to answer because the speed of fossil creatures cannot be timed against a stop- watch. The most likely contenders for fastest dinosaur seem to be the ornithomimosaurs (bird-mimic dinosaurs) of the Late Cretaceous. These combine a light body with very long legs and slender toes (features seen in the most fleet-footed of living creatures) which would have enabled these dinosaurs to make long strides and move across the ground extremely quickly. One of the largest and therefore longest striding of these dinosaurs was Gallimimus from Mongolia and this may well have been one of the fastest of all dinosaurs and may well have been able to cruise for sustained periods of time at anywhere between 40 and 60 kph.