The T. Rex was slower than you might think

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New simulations based on the movement of the T. Rex’s tail have estimated the average walking speed of these animals at just under 5 km / h. To put this in perspective, this is the average walking speed of a human.

The T. Rex, which lived in what is now western United States between 66 million and 68 million years ago, is possibly the most iconic of the carnivorous dinosaurs. According to the American Museum of Natural History, an adult would have measured about twelve meters long, 3.6 meters high for five to seven tons on the average on the scale. A question then arises: how fast could such a large animal move?

Consider the tail of T. Rex

A few years ago, researchers answered this question by examining the mass and height of the predator’s hips, sometimes incorporating the stride length of preserved footprints. These estimates then placed the walking speed of a T. Rex at between 7.2 and 10.8 km / h.

Within the framework of new work, researchers at the Free University of Amsterdam explored the role played by the vertical movement of the tyrannosaur’s tail.

Dinosaur tails naturally influenced the way they moved in multiple ways“, Explains Pacha van Bijlert van Bijlert, who led this study. “Not only did it act as a counterweight, but the tail also produced much of the force needed to move the body forward thanks to two large muscles (the caudofemoral muscles) capable of pulling the legs back with each step.“.

The researchers here calculated the walking speed of T. Rex by modeling the movement of this flexible tail.

According to the simulations, that of the famous Tyrannosaurus would have swung up and down during the walk. These movements stored and released energy by stretch ligaments. When the rhythm of a swinging tail reaches resonance (the greatest movement response with the least effort), that rhythm can then “indicate the frequency of the animal’s steps during an unhurried walk“, Write the authors.

Credits: Rick Stikkelorum, Arthur Ulmann, Pasha van Bijlert

Less than 5 km / h

This work focused on an adult specimen known as “Trix”, the remains of which are held in the collection of the Naturalis Biodiversity Center in Leiden, the Netherlands. The researchers scanned and modeled the bones in his tail by referring to marks on the vertebrae highlighting where his ligaments were attached. From this digital bone and ligament reconstruction, they then created a biomechanical model of the animal’s tail.

The tail pattern gives you a probable step rate / pace for T. Rex, but you also need to determine the distance traveled with each step.“, Note the researchers. To do this, they took the stride length of a tyrannosaurus slightly smaller than Trix, and then scaled it down to its size. Based on these calculations, Trix’s step length was approximately 1.9 m. They finally calculated the walking speed by multiplying the step frequency by the step length.

Result: The average walking speed of a T. Rex was around 4.6 km / h, according to this work, which is significantly slower than previous estimates.

In contrast, this study focuses on the up and down movements of the tail, “but lateral movements are not taken into account“Says John Hutchinson of the Royal Veterinary College in Hertfordshire, UK. This flexible tail model is nonetheless interesting. The next step will be to estimate the maximum running speed of a T. Rex.

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