How big were T. Rex's feet?

In our Curiosity Challenge Series...

How big were T. Rex’s feet?

Question submitted by Aidan Barry, Age 5

Great question, Aidan! While not the biggest carnivorous dinosaur (that distinction belongs to the Spinosaurus), Tyrannosaurus Rex (T. Rex) is arguably the most popular. It is estimated that an adult T. Rex was roughly twelve feet tall - more than double the height of the average American male adult - and weighed about seven tons (about the weight of an African elephant). We often think about - and mock! - the puny size of T. Rex’s arms, but its feet were decidedly more impressive. Foot size can be estimated by looking at a T. Rex skeleton and by measuring T. Rex footprints.

No complete T. Rex skeleton has ever been found (the closest we’ve gotten is Sue, the resident T. Rex at the Fields Museum in Chicago, who is about 90% real bone). STAN, the resident T. Rex at the Black Hills Institute of Geological Research, is about 65% real bone. Fully extended, STAN’s feet were each about 4 feet long. In other words, STAN’s feet were the same length as an average sleeping seven year old human! Unlike humans, STAN’s heels would not have touched the ground while walking. Interestingly, there are only two known T. Rex footprints. The more recent one was identified in Montana in 2007 and clocked in at 3 feet wide. Like humans, T. Rex foot size likely varied based on factors such as age, which means that there might be as yet undiscovered T. Rex skeletons with even bigger feet than STAN!     

The Friendly Neighborhood T. Rex at the Boston Museum of Science (image courtesy of the author)

In spite of its gigantic feet, T. Rex was not a particularly fast walker. Paleontologists believe that T. Rex probably walked at a pace of about 2.7 to 5 miles per hour; the average adult human walking pace is about 3 miles per hour.

For more information on dinosaurs, check out the permanent local exhibits at the Boston Museum of Science and the Harvard Museum of Natural History. And if you’re interested in checking out some actual dinosaur footprints, check out the Dinosaur State Park in neighboring Connecticut!

Saheli Sadanand is a post-doctoral fellow at the Ragon Institute of MGH, MIT and Harvard. She’s always loved dinosaurs - her favorite is the Spinosaurus - and still harbors dreams of going on a dino dig someday!