Notably, there is nothing of the elephant in the big tyrannosaurs-rex. Walking dinosaur costume The tyrannosaurs do not have the heavily padded, stiffankled, short feet of elephants, nor their short, weakly muscled shanks and columnar knees (Animatronic dinosaur). Traditionalists wishing to keep T-rex slow have tried to find some sort of slow feature in it. Some say that its femur was straight, which it was not. Others point to the “short” lower limb bones, but the shank and foot are as long, relative to the femur, as are a racehorse’s. Theropod limbs are not exact copies of those of birds or of any other tetrapod, but the limbs of the biggest tyrannosaurs are the same as those of the small, swift ostrich-mimcs. This is powerful evidence of their speed, for the engineering principle that tells us that “machines that are built the same, work the same” shows us that the tyrannosaurs with limbs like ostrich-mimics ran as well as ostrich-mimics. After all, why be built like a fast runner if you are not one?
Were the limbs of the big tyrannosaurs strong enough to run fast on? Mechanical dinosaur There is a way to test this. The plot in Figure 6-6 shows that fast-running living bipeds such as jeroboas and kangaroos have stouter, stronger femurs than do slow-running humans. The more robust femora may be necessary to absorb the stresses of longer ballistic suspended phases. Not surprisingly, the ostrichmimics and tyrannosaurs have stout femora designed to absorb the stresses of high speeds like those of fast mammals. This is very good evidence that they ran fast.