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New Study Finds T. Rex Walked at a Slow Pace of Three Miles Per Hour

Dutch researchers calculated the surprising speed of the dinosaur based on 3-D reconstructions of its lengthy tail

To calculate how the tail propelled the T. rex, the researchers scanned and modeled an adult T. rex specimen at the Naturalis Biodiversity Center in Leiden known as "Trix," pictured here. (Rique via Wikicommons under CC BY-SA 4.0)
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On the big screen, the Tyrannosaurus rex is often depicted as a predator that could easily catch up to a speeding car with a few swift stomps. That's probably because paleontologists had suggested that the T. rex clocked a top speed of 30 miles per hour and a walking speed between 4.5 and 6.7 miles per hour, reports Jeff Spry for SYFY Wire.

Now, researchers from the Netherlands have used computer reconstructions of a T. rex tail to estimate that the walking speed of the carnivore was much slower. According to the new study published in Royal Society Open Science, the predators walked at just under 3 miles per hour, reports Katie Hunt for CNN.

Previous walking estimates of the T. rex were based on research that centered only on the prehistoric reptile's meaty hips and legs, reports Mindy Weisberger for Live Science. However, to find the walking speed of the T. rex, the researchers of the new study focused on the vertical movement of the tyrant lizard king's tail. While calculations on the hips and legs are essential, estimating walking speed only on some parts of the dinosaur's anatomy may give inaccurate results, CNN reports. Dinosaurs overall had unique tails that are not found in any other animals today and may have played a crucial role in the way they walked.

When walking, the T. rex would have had its tail suspended in the air. In this position known as passive suspension, the dinosaur's tail would have actively bounced vertically with each step. Dinosaur tails were vital to the way they moved around, in multiple ways, Pasha van Bijlert, a graduate student at the Free University of Amsterdam and first author of the study, tells Live Science. Not only does it serve as a counter balance, the tail also produces a lot of the required force to move the body forward. It does this through two large tail muscles—the caudofemoral muscles—that pull the legs backwards during each step.

To calculate how the tail propelled the T. rex, the researchers used an adult T. rex specimen at the Naturalis Biodiversity Center in Leiden known as Trix. They scanned and modeled Trix's tail bones to find where the ligaments would have been attached and then used a computer model to simulate how these ligaments would have moved while the dinosaur walked, reports Live Science. The paleontologists found that the ligaments stretched to create the vertical bounce and held the dinosaur's suspended tail in a way that did not use up extra energy. The T. rex, they concluded, would walk in a way that matched the speed of its swaying tail, reports Bryan Lawver for Inverse.

The tail model gives you a likely step frequency/rhythm for T. rex, but you also need to know how much distance it travels with each step, van Bijlert told Live Science.

Researchers combined the tails swaying rhythm with an estimated step length obtained from another T. rex fossil's footprints, Inverse reports. They estimated that Trix's step length would have been 6.2 feet and then multiplied that by the step frequency and step length to get a walking speed of 2.86 miles per hour, Live Science reports. Per Inverse, this speed is within the walking speed ranges for other animals and humans.

Studying how dinosaurs moved can help paleontologists further understand dinosaur behavior and how they thrived in their prehistoric ecosystems, CNN reports. In future studies, the researchers plan to use this method to calculate the top speed of a T. rex when it's sprinting. Other researchers have surmised that the heavy body of a T. rex, weighing between 11,000 to 15,000 pounds, hindered its running speed. However, van Bijlert suspects that the dinosaur's tail may have absorbed the shock in a way that made it able to run faster without breaking any bones, Live Science reports.

About Elizabeth Gamillo
Elizabeth Gamillo

Elizabeth Gamillo is a science journalist based in Milwaukee, Wisconsin. She has written for Science magazine as their 2018 AAAS Diverse Voices in Science Journalism Intern.

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