Cheetahs

• The cheetah is the fastest land mammal on Earth. It can reach speeds of 70 miles per hour. It also has a very fast acceleration speed, going from zero to 68 miles per hour in only three seconds. However, the cheetah can go at top speed for only short distances -- the length of two or three football fields. At that point, the cheetah's body overheats and it must rest. The cheetah's lightweight bones, large lungs, rudder-like tail and flexible spine contribute to its speed. Cheetahs are found in Africa and a small part of the Middle East.
  
  

Pronghorn Antelopes

• The pronghorn antelope is the fastest mammal in North America.Jupiterimages/Photos.com/Getty Images
  
  The pronghorn antelope is the second-fastest animal on Earth and the fastest in North America. Pronghorns can reach 60 miles per hour in short bursts, and they can sustain speeds of 25 to 40 miles per hour for miles. Pronghorns can cover up to 24 feet in a single stride. This mammal's strong legs and even gait contribute to its speed and endurance.
  
  

Wildebeest

• Wildebeest rely on their speed to outrun predators.Photos.com/Photos.com/Getty Images
  
  The wildebeest might not look fast, with its boxy head, top-heavy frame and gangly legs, but it can reach 51 miles per hour. Wildebeests live in herds, and stampedes of up to 500 animals at full speed are a common sight on the African Serengeti. Wildebeest are also known as gnus.
  
  

Lions

• Lions must rest after running at high speeds.Photos.com/Photos.com/Getty Images
  
  The African lion, despite its massive size, can reach 50 miles per hour. Lions can't sustain such high speeds for long periods, so they hunt as a group, taking turns chasing down their prey. Female lions do most of the hunting. Unlike most wild cats, lions are highly social and live in prides, which they protect from outsiders.
  
  

Thompson's Gazelles

• Thompson's gazelles run across the plains of Africa.Anup Shah/Photodisc/Getty Images
  
  The Thompson's gazelle, with its light, graceful frame, can reach up to 50 miles per hour. Unlike its chief predator, the cheetah, it can sustain top speed for long distances and make fast turns, allowing it to outrun and outmaneuver the cheetah -- if it isn't caught quickly. The Thompson's gazelle can leap up to 30 feet per stride and can jump as high as 10 feet.
  
  

Other Fast Mammals

• Humans are among the fastest mammals.Photos.com/Photos.com/Getty Images
  
  Other fast mammals, with top speeds of 40 to 45 miles per hour, include quarter horses, elk, Cape hunting dogs, coyotes, gray foxes, and hyenas. Greyhounds can run at 45 miles per hour for short bursts, and 35 miles an hour for up to seven miles. Humans are also faster than many mammals -- Olympic sprinter Usain Bolt has run 100 meters in less than 10 seconds and 200 meters in less than 20 seconds, or about 28 miles per hour. Most average runners sprint at 12 to 15 miles per hour.