The Pronghorn's Prowess

With an alleged top speed of 60 miles an hour, the pronghorn antelope is second only to the cheetah. But whereas the cheetah is a mere sprinter, the pronghorn is an endurance runner par excellence. Herds of pronghorn galloping across the high prairies of Wyoming can average 40 miles an hour for half an hour or more. If pronghorn ran marathons, they would complete the course in 40 minutes. Human marathoners manage two hours and eight minutes at best. How does the pronghorn do it?