The world's fastest land animal is the cheetah, able to accelerate to freeway speeds in just a step or two.

While best known as a fleet runner able to sprint short distances at up to 60 miles per hour, it was the cheetah's elegant spotted coat that caught the eye of ancient civilizations. Indeed, “cheetah” means “spotted one” in the Hindi language. But while many people think of cheetahs as being close relatives of the other big cats such as lions and tigers, they are actually quite different.

One difference is that cheetahs evolved much earlier than other large cats, arising from a cat-like mammal that lived about four million years ago. As a result, their bodies are different from lions, tigers and other great cats in many ways. Cheetah claws, for instance, don't retract like a house cat's, in part because the cheetah needs the extra traction during high-speed sprints. Similarly, cheetahs don't growl. They hiss or give a bird-like chirp instead, because they lack the vocal anatomy to roar.

Most importantly, cheetah bodies are uniquely built for speed. Their small heads offer little wind resistance, while their exceptionally long legs allow them to take huge strides. During sprints, the cheetah spine acts like a giant spring, storing energy that can be released in explosive surges. And the cheetah's enlarged heart, lungs and liver help deliver bursts of oxygen and energy, while specially ridged foot pads help provide traction, much like a car's tire. Such adaptations “make cheetahs the elite ‘race cars' of the animal world,” says Don Person, a Dutch biologist who has studied cheetahs in East Africa . “They are speed demons.”
– Adapted from www.pbs.org