This is a clip that illustrates the most probable, according to our current research, ways in which an adult Tyrannosaurus rex would have been able to sit and stand despite its enormous size and tiny arms. The clip was developed based on physical constraints, primarily kinematic but also accounting for dynamics during the high acceleration and velocity phases of the cycle.

As you can see it’s likely that the animal used its mass to propel itself from the sitting position. It was unlikely to "just stand straight up"as an adult given the weight to musculature without significant additional effort.

It is useful to consider the weight distribution of the T. rex and how that contributed to its action. The heavy tail acted as a counterweight to the large forward section of the animal, balancing like a teeter-totter around the pelvic region. Therefore, to sit down it would lean forward to break the weight symmetry while lowering itself to begin reducing the distance to the ground.

This ends up centering a greater amount of the midsection weight near the hips (fulcrum) while the dinosaur continued to lower itself to the ground. With this rocking motion providing a non-linear force vector, this would have allowed the animal to stabilize itself momentarily with its arms without overtaxing them with too much of the animal’s mass.

After the forward section (belly) makes contact with the ground the animal would likely rock backward to prevent the ribs from absorbing too much weight and instead use the pelvis as a solid anchor on which to roll the weight of the animal backward. Ultimately the dinosaur would come to rest with it’s weight spread like a tripod between the two feet and the pelvis, although it’s possible that the pelvis could have supported the animal enough for it to raise its legs for periods of time to say scratch itself.

Getting up from the sitting position is harder and required greater momentum and, therefore, velocity to achieve. The process started with the animal rocking backward and then forward quickly to generate the momentum.

It would then need to step forward with one foot to keep its center of mass dynamically within its balance of support and not fall over. It would also need to simultaneously push upward with its feet to reduce the stress on the ribs and arms while the direction of momentum shifts into an upward direction.

Finally, the dinosaur would push with its legs and use the existing momentum to lift off the ground and return to a standing position. Certainly not a simple task.

This particular clip was developed for the Tokyo Museum of Natural History as part of their permanent exhibit, although it has since been loaned out to tour other museums in Asia.