A fearsome giant with long legs – but they did not bring Tyrannosaurus rex to rapid speeds, as a study once again shows. The biomechanical analysis of the running behavior of various two-legged dinosaurs shows that while the long legs of the smaller species were primarily responsible for speed, they were designed for high energy efficiency at T. rex. The king of the predatory dinosaurs was particularly persistent and economical on his hunting trains.
It is one of the most exciting scenes in the film Jurassic Park: A T. rex races after a car with the escaping protagonists. It takes a lot of throttle to finally escape from the gnashing sprinter. But it is now clear that a bike would have been enough to escape. Because T. rex only reached about 27 kilometers per hour, calculations have shown. They follow the rule: for small to medium-sized animals, more size means more speed, but for very large animals, the speed decreases due to the inertia. That is why the T. rex, which is up to 13 meters long and weighs seven tons, only reached low speeds compared to smaller predatory dinosaurs.
Why the long legs?
However, this raises the question of why T. rex’s physique also seems to be geared towards speed. “It is assumed that particularly long legs are an adaptation to convey high running speeds,” says Thomas Holtz from the University of Maryland. In the context of their study, he and his colleagues have now investigated how body size and leg length could have been linked to speed and energy efficiency when running in bipedal dinosaurs. To this end, they developed biomechanical models of the running behavior of 70 species from the group of theropods. In addition to the huge giants such as T. rex or Allosaurus, the selection also included smaller species such as raptors or even rabbit-sized tiny things.
The analyzes initially confirmed: Even the long hind legs could only provide more speed up to a certain height. From about 1000 kilograms, the gain was over. T. rex with its up to seven tons was significantly above this mark. As can be seen from the calculations, these giants apparently benefited in other ways from their long legs: Compared to shorter limbs, the long hind legs of the tyrant dinosaurs provided biomechanical properties that were associated with significantly lower energy consumption, the scientists report.
A frugal king
“Apparently, T. rex was more about being a long-term marathon runner than a fast sprinter,” summarizes Holtz. The researchers say that this was probably a great advantage. “Predators generally spend a large part of their time looking for prey,” says Holtz. The scientists say that those who consume less “fuel” have a much better chance of survival.
As they explain, T. rex’s way of life suggests that efficiency was particularly important when moving around. The predator is believed to hunt other dinosaurs such as the famous Triceratops. These were rather slow, but very agile and defensive prey animals that lived in herds. Endurance may have been particularly important to kill them, the scientists explain. Exactly how exactly tyrannosaurs went while hunting is so far unclear. “We find that T. rex’s anatomy was efficient and elegant at the same time, but also designed to use incredible force. He is rightly considered the king of the predatory dinosaurs, ”write Holtz and his colleagues at the end of their study.
Source: University of Maryland, professional article: PLOS ONE, doi: 10.1371 / journal.pone.0223698