Hit the Ground (or Water or Air) Running
Let's not slowly build suspense. Every fast list should start with the cheetah. These guys can reach speeds of 59 mph (95 kph) in seconds [source: Yong]. A somewhat surprising second-place contender for fastest? The pronghorn antelope, which can rival cheetahs with a speed of 53 mph (85 kph) [source: National Geographic]. So there you go: the speediest animals on the planet.
Not so fast.
If we're counting water-based animals, the sailfish is our clear winner, reaching 68 mph (110 kph) -- and that's just what they've been clocked at when bursting out of the water [sources: National Geographic, Sagong et al.].
Now look up. The peregrine falcon cackles at the cheetah and sailfish eating its dust. When it's hunting for smaller birds, the falcon can dive -- at 200 mph (320 kph) -- to strike its target [sources: National Geographic, Ponitz et al.]. The peregrine wins the title of fastest animal by a long shot.