Tyrannosaurus rex is undoubtedly the icon of all carnivorous dinosaurs. It roamed North America and East Asia during the Cretaceous. The heaviest species weighed as much as 6 tons. Scientists are still puzzled by their behavior. The body of the T-rex is huge, but its forelimbs are disproportionately small. Scientists are having trouble figuring out the function of these tiny forelimbs. Some scientists estimated that T-rex could run up to 60 km per hour, but others argue that to achieve such high speeds, the leg muscles of the T-rex would have to account for 90% of the total muscle, something that is very unlikely. Scientists do agree that the T-rex did not move faster than an elephant. Even moving at 25 km per hour, a huge animal like the T-rex would still be a spectacular sight.