Fossil dinosaur tracks don't often get the same popular attention that skeletons do. The impressions within the rock seem to pale in comparison to the beautiful organic architecture of the bones, but, while they might not be as aesthetically interesting to some, tracks are bits of behavior preserved for millions of years. They were made by living creatures, and by studying them carefully paleontologists can reconstruct the details of how these animals moved.
There are many dinosaur track sites scattered all over the world, but in a paper published in Palaeogeography, Palaeoclimatology, Palaeoecology, scientists Bo Seong Kim and Min Huh focus on just one small set of Cretaceous-age footprints preserved in South Korea. Called "trackway B", this set of impressions was made by a theropod dinosaur while running—the footprints clearly show that it was increasing its stride length between each step as a sprinting creature would do. In order to better appreciate how this dinosaur was moving, though, Kim and Huh made numerous measurements of the tracks to estimate the size of the dinosaur, its speed and how quickly it accelerated as it began to run.
Using the size of the footprints to calculate size, the scientists estimated that the dinosaur would have been about three feet high at the hips—this was a relatively small theropod. It would have been pretty fast, though. The speed estimates obtained for the tracks suggest that the dinosaur was moving at about seven miles per hour and then accelerated to between nine and twenty miles per hour. It appears that the dinosaur was already trotting at the beginning of the trackway, but the latter portion of it shows a quick uptick in speed to full running.
Just what spurred this dinosaur's turn of speed, though, is unknown. The authors state that it was probably running about as fast as it could, so obviously it was moving with some urgency. Perhaps the dinosaur was after a potential meal, or was in danger of becoming a meal itself. We will probably never know for sure, but, regardless of what happened, the footprints represent a snapshot into a dinosaur's life.
Kim, B., & Huh, M. (2010). Analysis of the acceleration phase of a theropod dinosaur based on a Cretaceous trackway from Korea Palaeogeography, Palaeoclimatology, Palaeoecology, 293 (1-2), 1-8 DOI: 10.1016/j.palaeo.2010.04.020