Researchers have unveiled a simple yet powerful formula that explains why some animals run, fly and swim faster than all others. Knowing just the animal’s weight and the medium it moves in—water, air or across land, the formula can calculate maximum speed of the animal with 90 percent accuracy – and it even works “retroactively” for dinosaurs, the researchers say.
Myriam Hirt, who is the lead author of the study explains that the top speeds of an animal – including humans – comes down to acceleration. “While the largest animals, in theory, could be the fastest, the energy and time required to accelerate their larger bodies keeps them from ever attaining it,” Hirt tells Wired. She also explains if scaling of size and speed were linear “elephants would reach maximum speeds of about 600 km/h (370 m/h), but instead they max out at about 34 km/h (21 m/h) – in reality.”
According to the “speed rule,” strength does not solely determine maximum speed because “land mammals, birds and fish can only accelerate for as long as they can draw from available energy stored in muscle tissue.” And for big animals, the so called anaerobic energy, supplied by the muscles gets used up before being able to reach their theoretically maximum speed.
Researchers also find that an intermediate body size – like cheetah, falcon or marlin – is optimal for hitting a sweet spot between brawn and energy burst. The model also predicts Tyrannosaurus Rex could only have reached 30 km/h, and therefore they were not a pursuit predator. The formula, by the way, is k=cM^d-1, where k is the acceleration constant, and M is the body mass. The study has been published in the journal Nature Ecology & Evolution.