Body mass, bone “strength indicator,” and cursorial potential ofTyrannosaurus rex

ABSTRACT We describe a new life restoration of Tyrannosaurus rex, based on a fairly complete skeleton (Museum of the Rockies [MOR] 555). From the volume of this model, we estimate the live mass of the full-sized dinosaur as approximately 6,000 kg. Because MOR 555 is a representative of the gracile morph of T. rex, the mass of the robust morph may have been substantially greater. The "indicator of athletic ability" or "strength indicator" of MOR 555 is 7.5–9.0 meter2/giganewton, similar to previously reported results. The implication is that the cursorial potential of Tyrannosaurus was limited, a conclusion consistent with observed declines in sprint speed with increasing body mass in living animals, and also consistent with the tibia/femur length ratio, and the construction of the hip joint, of the dinosaur. Furthermore, mathematical models of the impact forces and decelerations that would affect a Tyrannosaurus, were it to fall while running at a high speed (20 meters/second), suggest that the animal would be killed in such an accident. We speculate that the top speed of adult individuals of this dinosaur species was about 10 meters/second.