The pronghorn is the fastest land mammal in the Americas. At top speed, they can hit 55 mph. But what are they running from?

Running at top speed causes their bodies to quickly overheat and they need lots of rest time between sprints. Zebras, on the other hand, can keep running at their top speed of 40 mph for over a mile!

Here’s how medium-sized animals, like the cheetah, occupy an optimal balance between muscle size and body mechanics. Being the largest or having the longest limbs doesn’t guarantee the title of the ...