T-Rex, The Lizard King

The T-Rex is probably the most popular dinosaur in pop culture from Jurassic Park to even Transformers. If you’ve ever wondered what this giant dinosaur ate, when it roamed the earth, and how fast it was, you’ve come to the right place.

Palais_de_la_Decouverte_Tyrannosaurus_rex_p1050040 (1)

Time Period

The T-Rex lived from around 85 million years ago to 65 million years ago. This was toward the end of the Mesozoic era and before the extinction of dinosaurs.


T-Rex, one of the largest carnivores to roam the earth, weighed up to 10,000 kilograms. Given its huge size, its diet and whether it acted as a predator, scavenger or something else have interested many paleontologists. We all know it ate meat as a carnivore, but did you know that this meat sometimes came from its own kind? Interestingly, one study found that the Tyrannosaurus Rex probably participated in cannibalism, feeding on herbivorous dinosaurs along with its own kind. This may sound surprising, but many other animals do the same, like bears, crocodiles, hyenas, and others.

Age and Growth of T-Rex

One study points to the growth pattern of the T-Rex as similar to the development of the African elephant. ┬áThe study found that T-Rexes grew to their full size within 15 years. This points to a high basal metabolic rate to sustain itself, bringing up questions concerning its eating patterns. Due to the small sample size available to paleontologists, it is difficult to develop any ecological models. One speculation is that contrary to warm-blooded mammals today, the T-Rex grew in spurts. It didn’t grow continuously, but rather went through phases in which it didn’t require a lot of food to sustain itself and phases in which it needed more food to survive.

How Fast Was It?

Some scientists believed that T-rexes could hit speeds of 20 m/s by looking at other vertebrates, while other paleontologists believed that it could be fatal if a Tyrannosaurus tripped and fell so the max speed was actually 10 m/s. Using a biomechanical model, another study determined that T-Rexes at their top speed of 11 m/s could only be modestly fast after the paleontologists looked at the physics and muscle mass compositions of related species with their model. However, this has not closed the door on the discussion and needs to be researched thoroughly. A free body diagram is shown below that was used in the aforementioned study that used a biomechanical model to determine the speed of the T-Rex.


for a running T-Rex, the angles of the leg joints (top) are critical parameters. In addition to the forces and torques produced by leg muscles, external forces (bottom) including the weights of the body ( ), thigh ( ), shank ( ), and metatarsus ( ), as well as the ground reaction force (GRF) that acts a distance from the toe joint must be incorporated.

Citation: Phys. Today 55, 4, 18 (2002); http://dx.doi.org.libproxy.lib.unc.edu/10.1063/1.1480769


Fitzgerald, Richard. “How Fast Could Tyrannosaurus Rex Run?” Phys. Today Physics Today 55.4 (2002): 18-19. Web.
Horner, J. R., and K. Padian. “Age and Growth Dynamics of Tyrannosaurus Rex.” Proceedings of the Royal Society B: Biological Sciences 271.1551 (2004): 1875-880. Web.
Lerner, K. Lee, and Brenda Wilmoth Lerner. “Tyrannosaurus Rex.” Gale Encyclopedia of Science. Detroit: Gale, 2004. Print.
Longrich, Nicholas R., John R. Horner, Gregory M. Erickson, and Philip J. Currie. “Cannibalism in Tyrannosaurus Rex.” PLoS ONE 5.10 (2010): n. pag. Web.

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