Size key to top speed in animals, study finds

July 17, 2017 by Marlowe Hood
The African elephant is the largest animal on land, but not the fastest. Credit: Bernd Adam

It's not quite E=mc2, but scientists unveiled Monday a simple, powerful formula that explains why some animals run, fly and swim faster than all others.

Call it the " rule": strength alone does not determine top velocity because land mammals, birds and fish can only accelerate for as long as they can draw from available energy stored in muscle tissue.

An intermediate body size—think cheetah, falcon or marlin—is optimal for hitting that sweet spot between brawn and energy burst, the researchers discovered.

Too small, and there's not enough musculature; too big, and there's too much mass.

Knowing only an animal's weight and the medium it moves in—water, air or across land—is enough to calculate its with 90 percent accuracy, they found.

The axiom even works retroactively for dinosaurs, they reported in the journal Nature Ecology & Evolution.

"Scientists have long struggled with the fact that the largest animals are not the fastest," said lead author Myriam Hirt, a biologist at the German Centre for Integrative Biodiversity Research in Leipzig.

If muscles were all that mattered "elephants would reach maximum speeds of about 600 kph (370 mph)," she told AFP.

Instead, tuskers peak at about 34 kph (21 mph).

A parabola-like relationship between the body mass of animals and the maximum speed they are able to reach. For the first time, researchers are able to describe how this comes about, thanks to a simple mathematical model. Credit: Myriam Hirt

Big beasts, in other words, run out of so-called anaerobic energy, supplied by the muscles, before being able to reach their theoretically maximum speed.

Among birds, falcons and hawks are the fleetest, clocking speeds well in excess of 140 kph (87 mph). Nearly as fast, the rock dove, wandering albatross and Ascension frigate could fly in their slipstream.

Cheetahs hold the land record, comfortably topping 100 kph (62 mph).

Not coincidentally, one of the their preferred prey—the springbok—can run almost as fast, along with other antelope, such as the blackbuck, historically hunted by big cats.

T-rex not fleet of foot

That's evolution at work, explained Hirt.

"Species that gain the most selective advantage—predators and prey with few places to hide, for example—will approach the predicted maximum speeds," she said.

Humans, by contrast, have not evolved over millions of years to outrun fast prey (or predators), even if they fall within the intermediate weight class corresponding to extreme speed.

Homo sapiens, it seems, invested in outsmarting other animals instead.

The new model also provides results for extinct species which agree with the results produced by highly complex biomechanical simulations. Credit: Myriam Hirt

Long-limbed giraffes can hit 60 kph (37 mph) when motivated, and bears—grizzly, brown and polar—can top 45 kph (28 mph) for a few seconds before their fat-laden bodies slow them down.

The black marlin holds the known record in the sea, slicing through water at expressway speeds of 130 kph (80 mph), even faster than its quick cousin the Atlantic sailfish.

Full-grown Yellow fin and bluefin tuna can swim 70 kph (43 mph), only slightly faster than the quickest shark, the shortfin mako.

Killer whales—which, like humans, teach their young hunting techniques—are somewhat slower, but reign unchallenged at the top of the .

Altogether, the researchers tested their new hypothesis against data on 454 species weighing in at one gram to 10 tonnes, from molluscs to blue whales, from gnats to whopper swans.

"Hirt and colleagues provide a unifying explanation for what sets the limits to maximum speed," Christopher Clemente and Peter Bishop, scientists at the University of the Sunshine Coast in Australia, wrote in a comment.

"The exciting part ... is that it applies equally well to animals on land, in the air and in water."

And to dinos, too.

The model matched data on the handful of dinosaurs for which scientists have been able to estimate running speeds.

The study estimates that lithe velociraptors could sprint at 50 kph (31 mph), while the lumbering T-rex could barely move at half that pace.

But that was still quick enough to catch a plant-eating Triceratops or the even slower Brachiosaurus, meals fit for the dino king.

The magic formula, by the way, is k=cMd-1. (where k—acceleration constant, M—body mass)

Explore further: Whale attack simulations reveal prey escape strategies

More information: Myriam R. Hirt et al, A general scaling law reveals why the largest animals are not the fastest, Nature Ecology & Evolution (2017). DOI: 10.1038/s41559-017-0241-4

Related Stories

Whale attack simulations reveal prey escape strategies

July 5, 2017

Humpback whales feed from a range of species that have adapted to escape their fate in a variety of ways. As much as humans track their prey according to the species they are stalking, so whales lunge open-mouthed in different ...

Meals on the go: The physics of whales' eating habits

June 6, 2017

In a recent paper published in PLOS One, Saint Louis University professor of physics Jean Potvin, Ph.D., and biologist Alexander Werth, Ph.D. at Hampden-Sydney College, detail for the first time how baleen whales use crossflow ...

Study reveals new insight into how Cheetahs catch their prey

September 5, 2013

A new research study has revealed that the cheetah, the world's fastest land animal, matches and may even anticipate the escape tactics of different prey when hunting, rather than just relying on its speed and agility, as ...

Recommended for you

Archaeologists discover Incan tomb in Peru

February 16, 2019

Peruvian archaeologists discovered an Incan tomb in the north of the country where an elite member of the pre-Columbian empire was buried, one of the investigators announced Friday.

Where is the universe hiding its missing mass?

February 15, 2019

Astronomers have spent decades looking for something that sounds like it would be hard to miss: about a third of the "normal" matter in the Universe. New results from NASA's Chandra X-ray Observatory may have helped them ...

What rising seas mean for local economies

February 15, 2019

Impacts from climate change are not always easy to see. But for many local businesses in coastal communities across the United States, the evidence is right outside their doors—or in their parking lots.

The friendly extortioner takes it all

February 15, 2019

Cooperating with other people makes many things easier. However, competition is also a characteristic aspect of our society. In their struggle for contracts and positions, people have to be more successful than their competitors ...


Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.