The skeleton of Trix at Naturalis Biodiversity Center. Credit: Mike Bink
Humans and animals have the preferred walking speed. This is partly influenced by the amount of energy required: they prefer to run at the speed at which they use the lowest possible amount of energy. One of the ways to achieve this is to use something called resonance.
You already know how it works: when you’re running, you can not just swing at any speed. If you want to do it properly, you need to get the timing right and swing in the rhythm of the swing. In other words: you have to resonate with it. And when you relax, the parts of your body run as well. Walking a little slower does not require less energy: you notice that it is actually more difficult.
An animation of T.rex Trix running according to the simulations in Van Bijlert et al 2021. The tail resonates, allowing a more realistic, slightly slower gait. Credit: Rick Stikkelorum, Arthur Ulmann & Pasha van Bijlert
It works for animals that walk on all fours, and for bipeds such as humans and ostriches. Pasha van Bijlert, a student of Human Movement Sciences at the Vrije Universiteit in Amsterdam (VU), applied the idea to an animal that walks differently from anything currently walking on earth: Tyrannosaurus rex. These carnivorous dinosaurs not only had two legs, they also had an enormous tail that helped them move.
Student Pasha van Bijlert modeled it with a replica of Trix, the Tyrannosaurus rex, as part of his dissertation. Credit: Tom Brown
Like the bones in our necks, the bones in the tails are held together by ligaments. “You can compare it to a suspension bridge,” Van Bijlert explains. A suspension bridge with a ton of muscle in it. ‘Every step swings the tail up and down. This means that like the swing it has a natural frequency at which it resonates.
To determine what the frequency is, Van Bijlert and his professors Anne Schulp (University of Naturalist / Utrecht) and Knoek van Soest (VU) build a 3D model of Trix, the Tyrannosaurus rex that is in the Dutch National Museum of Natural History, Naturalis can be seen. . They added digital muscles to the famous skeleton, and on this muscle model they were able to perform biomechanical analyzes. From this they deduced the natural frequency and the preferred running speed: 4.6 km / h (2.9 mph). So when Trix walks out, she’s running at about the same speed as you. If you had a T. rex for a pet, you would have no problem – at least in terms of speed.
Van Bijlert, Van Soest and Schulp published their findings in the journal Royal Society Open Science today (April 21, 2021). “There have been a few studies that have examined the walking speed of dinosaurs, but they mostly looked at the bones and ignored the tail. This is what makes dinos so unique,” says Van Bijlert. ‘They usually found much higher running speeds. The one we calculated is lower, but it is similar to that of other animals. ”
Reference: “Natural frequency method: the preferred running speed of Tyrannosaurus rex based on the natural frequency of the tail ”by Pasha A. van Bijlert, AJ ‘Knoek’ van Soest and Anne S. Schulp, 21 April 2021, Royal Society Open Science.
DOI: 10.1098 / rsos.201441