Size key to top speed in animals: study

– 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.

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 marine food chain.

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=cM^d-1.