Figure 3. T. rex trotting along beside a T. rex-sized chicken.
Calculations of the muscle mass required to power a fast-running T. rex showed that this was impossible—a 6-tonne chicken would have needed leg muscles making up almost 100% of its body mass. Realistically, T. rex had the muscles to run at about 5 meters per second (18 km/h, 11 mph) [26]. (Painting courtesy of Luis Rey.)