Short answers, pulled from the story.
The pronghorn, Antilocapra americana, is an even-toed hoofed mammal native to interior western and central North America. It is not a true antelope, though it is called the American antelope, prong buck, and prairie antelope because parallel evolution made it resemble Old World antelopes. It is the only surviving member of the family Antilocapridae.
The pronghorn is the fastest land mammal in the Americas, reaching 55 miles per hour over half a mile. It can hold 35 miles per hour for 4 miles and 42 miles per hour for 1 mile. It is slower than the African cheetah in a sprint but can sustain top speed far longer.
The pronghorn's closest living relatives are the giraffe and the okapi. The antilocaprids belong to the infraorder Pecora, making the pronghorn a distant relative of deer, bovids, and moschids.
The pronghorn likely evolved its speed to escape now-extinct predators such as the American cheetah, since its speed far exceeds that of every living North American predator. Isotope evidence from Natural Trap Cave shows American cheetahs fed on pronghorns, though American lions and wolves hunted them too.
Pronghorns live west of the Mississippi River, from southern Saskatchewan and Alberta south through the western United States into Mexico. They prefer open terrain between 3000 and 5900 feet and have been wiped out from Iowa, Minnesota, and Manitoba.
By the 1920s hunting had cut the pronghorn population to about 13,000, and the Boone and Crockett Club judged extinction likely. Habitat protection and hunting restrictions, including refuge lands set aside under Presidents Hoover and Franklin Roosevelt, helped numbers recover to an estimated 500,000 to 1,000,000 since the 1930s.