"The cost of transport for an animal is like the miles-per-gallon rating of a car, she explained."

"If you think of a cheetah as a BMW, this paper shows that if you put that BMW motor on a streamlined boat, it would use the same amount of gas to move a mile in the water as it did on land," Williams said. "The trick is the chassis has to be adapted to the environment, and that means specializing."