Every walking animal has a preferred walking speed. Unless you are running late for somewhere, there is a leisurely pace you enjoy. If we wind the clock back 66 million years, T. rex also had a preferred walking speed. According to new models, it is remarkably close to the average human walking speed. Whether that's good to know for escape purposes or disconcerting that you could be strolling along only to look up and find a T. rex keeping pace is up to you.
To find this out, researchers constructed a new detailed biomechanical model based on Trix, the Tyrannosaurs rex on display at the Dutch National Museum of Natural History, Naturalis. Reporting in the journal Royal Society Open Science, they found that Trix's preferred walking speed would be 4.6 kilometers (2.9 miles) per hour, about half of what was previously estimated. The average walking speed for a human is 4.8-6.4 kilometers (3-4 miles) per hour.
"There were already some studies investigating dinosaur walking speed, but they mostly looked at the legs and ignored the tail – which is what makes dinos so unique," Pasha van Bijlert, a graduate researcher at the Free University in Amsterdam, said in a statement. "They usually found much higher walking speeds. The one we calculated is lower, but it's similar to that of other animals."
Preferred walking speed is related to the least possible amount of energy spent while still being productively in motion. To achieve this you need resonance. In simple terms, when you are in the swing of things, at the exact right motion, with the right amount of energy being expounded, your walk will feel effortless – your body will resonate. Faster or slower paces will feel forced.
This works for four-legged and two-legged animals. T. rex had long legs, which previous research has suggested were made for walking not running, efficient for longevity, not speed. To work out that natural walking pace, the researchers argue, you need to look beyond the legs and include their enormous tails.
The bones in tails are held together with ligaments. "You could compare it with a suspension bridge," van Bijlert said. "A suspension bridge with a ton of muscle in it."
The team created a model of how the ligaments and muscles of the tail would behave in motion. For every step computer-generated Trix took, its tail moved up and down at a natural frequency that resonates. This motion affected the overall walk, providing a lot of the force to move the body forward, which would affect its overall resonance to reach an average walking speed using the least amount of energy.
The tail may also affect Tyranosaurs' maximum running speed. Previous studies have put T. rex's top speed at around 27.7 kilometers (17 miles) per hour. This was estimated by the likely maximum stresses that their limbs would experience when running. The new model suggests the tail might help reduce this stress. So you could probably outwalk a T. rex, but perhaps only the fastest humans might outrun one.
Despite being one of the most well-studied dinosaurs, there are still many mysteries left to uncover about this notorious creature. Recent research has estimated that a total of 2.5 billion T. rex roamed Earth throughout their existence and that they may have hunted in packs. And now it's possible they enjoyed relaxed walks.