How fast was the dinosaur T. Rex? In the movie classic Jurassic Park, T. Rex is shown as being able to catch a car. But studies into the muscle mass needed for a creature that size indicate that such speed might not be possible for a huge animal the size of T. Rex. As the mass of a creature goes up so does the needed amount of muscle to move the body. The calculated minimum amount of muscle mass needed for a chicken to run was figured at 4.7% of it’s body mass in leg muscle in each leg. The actual figure of a chicken’s leg muscle is around 8.8% of it’s body mass. Using the same model, the arrived figure for a dinosaur the size of T. Rex to run, it would need around 43% of it’s total body mass to be leg muscle. It is readily seen that such can not be the case for anyone who has seen a picture of what we believe T. Rex looked like. For the rest of the article: here