Pronghorn are endemic to North America, and are the only living members of the family Antilocapridae. There are five subspecies including the endangered Sonoran Desert (in AZ) and Mexican populations. Instead of hiding from predators, they rely on their large eyes and exceptionally good vision to spot predators from up to 4 miles away. They are the fastest runners in North America, attaining speeds of 40 miles per hour. Pronghorn run with their mouths open in order to gulp extra oxygen to supply their large hearts. Herds prefer open terrain at elevations varying between 3,000 and 6000 ft. They eat a variety of plants, often including those unpalatable or toxic to other grazers.