The pronghorn (Antilocapra americana) is a primitive halfway station between antelope and deer, unchanged for at least a million years. It is the fastest mammal in North America and can travel at up to 90kph. Quite why it is so fast is a mystery. There might once have been a predator which could match the pronghorn's speed but if so it has disappeared, leaving the little antelope to charge around the prairies unchallenged. It cannot outrun bullets, though, and a population of 50 million was reduced to just 19,000 by the beginning of the twentieth century. Its intense curiosity makes it easy meat. Conservation has brought numbers back to about one million.