CLEVELAND:- An Ohio zoo said that Sarah , a cheetah designated the world's fastest land mammal by National Geographic magazine in 2012, has died at the age of 15. The Cincinnati Zoo & Botanical Garden said in a statement that it had euthanized Sarah on Wednesday due to her "diminishing quality of life." The average life span of a cheetah , the fastest land mammal, is eight to 12 years, the zoo said. Sarah was dubbed the fastest cheetah when she ran 100 meters in 5.95 seconds, during the filming of a National Geographic special.–Reuters